cove stormwater pump station and collection …€¦ · hydrology and hydraulic study flood control...

COVE STORMWATER PUMP STATION AND COLLECTION SYSTEM

HYDROLOGY AND HYDRAULIC STUDY

FLOOD CONTROL & WATER CONSERVATION DISTRICT

FINAL

July 2016

Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

FLOOD CONTROL & WATER

CONSERVATION DISTRICT

Cove Pump Station and Collection System Hydrology & Hydraulic Study

Table of Contents

7/28/2016 i Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

Table of Contents

Table of Contents .............................................................................................................................. i

Table of Tables ................................................................................................................................. ii

Table of Figures .............................................................................................................................. iii

List of Appendices ........................................................................................................................... iv

Executive Summary ................................................................................................................... ES-1

ES.1 Study Objectives ............................................................................................................................... ES-1

ES.2 Sources of Flooding .......................................................................................................................... ES-1

ES.3 Work Products .................................................................................................................................. ES-1

ES.4 Current Operations and Performance............................................................................................... ES-2

ES.5 Potential Projects .............................................................................................................................. ES-2

Chapter 1. Introduction ............................................................................................................... 1-1

1.1 Overview ................................................................................................................................................. 1-1

1.2 Setting ..................................................................................................................................................... 1-1

1.3 Climate .................................................................................................................................................... 1-1

1.4 Drainage and Flood Protection Facilities ................................................................................................ 1-2

1.5 References ............................................................................................................................................. 1-2

Chapter 2. Data ............................................................................................................................ 2-1

2.1 Overview ................................................................................................................................................. 2-1

2.2 Data Sources .......................................................................................................................................... 2-1

2.3 Storm Drain Data .................................................................................................................................... 2-6

2.4 Modeled Data Assumptions .................................................................................................................... 2-6

Chapter 3. Methodologies ............................................................................................................ 3-1

3.1 Overview ................................................................................................................................................. 3-1

3.2 Evaluation Criteria .................................................................................................................................. 3-1

3.3 GIS Based Modeling ............................................................................................................................... 3-1

3.4 Hydrologic Model .................................................................................................................................... 3-3

3.5 Hydraulic Model .................................................................................................................................... 3-10

3.6 Creek Models ........................................................................................................................................ 3-14

3.7 Comparison to Previous Reports .......................................................................................................... 3-14

Chapter 4. System Assessment .................................................................................................... 4-1

4.1 Overview ................................................................................................................................................. 4-1

4.2 Assessment Procedures and Standards ................................................................................................ 4-3

Chapter 5. Potential Projects ....................................................................................................... 5-1

5.1 Overview ................................................................................................................................................. 5-1

5.2 Results .................................................................................................................................................... 5-1




Table of Contents

7/28/2016 ii Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

5.3.1 Short Term ........................................................................................................................................... 5-5

5.3.2 Long Term ........................................................................................................................................... 5-6

5.2.3 Climate Change ................................................................................................................................. 5-11

Chapter 6. Cost Estimate ............................................................................................................. 6-1

6.1 Overview ................................................................................................................................................. 6-1

6.2 Tools for Prioritizing Potential Projects ................................................................................................... 6-1

6.3 Condition ................................................................................................................................................. 6-3

6.4 Conveyance Projects .............................................................................................................................. 6-3

6.5 Pump Station .......................................................................................................................................... 6-4

6.5 Floodwall ................................................................................................................................................. 6-7

Table of Tables

Table ES-1: Project Cost Summary Table............................................................................................... ES-3

Table 1-1: Watershed Areas and Length of Modeled Storm Drain Pipe ...................................................... 1-2

Table 2-1: Land Use Descriptions and Percentages in Cove Watershed ..................................................... 2-4

Table 3-1: Model Drainage Areas based on Existing Conditions ................................................................. 3-2

Table 3-2: Constant Loss Rate for Hydrologic Soil Group C and D ............................................................. 3-7

Table 3-3: Calibrated CLRs for Cove Drainage Area .................................................................................. 3-8

Table 3-4: Percent Impervious for Cove Watershed ................................................................................. 3-8

Table 3-5: Basin Roughness Values ......................................................................................................... 3-9

Table 3-6: MU Manning’s ‘n’ Values ....................................................................................................... 3-10

Table 3-7: Pump #1 Flow versus Total Differential Head ........................................................................ 3-13

Table 4-1: Trash Rack Head Loss Summary Table .................................................................................... 4-6

Table 4-2: Trash Rack Alternatives .......................................................................................................... 4-9

Table 4-3: Mechanical Screen/Rake Product Options ................................................................................. 49

Table 4-4: Pump Drawdown Test Results .............................................................................................. 4-10

Table 4-5: Pump Capacity at Design Head ............................................................................................. 4-11

Table 4-6: Pump Station Inflow Rates ................................................................................................... 4-11

Table 4-7: Pump Bay and Wetwell Dimensions ...................................................................................... 4-12

Table 4-8: Existing and Recommended Pump On/Off Levels ................................................................... 4-15

Table 4-9: Pump Cycling ...................................................................................................................... 4-15

Table 4-10: Communication Options ..................................................................................................... 4-17

Table 4-11: Arc Flash Analysis Summary ............................................................................................... 4-19

Table 4-12: Generator Dimensions ........................................................................................................ 4-20

Table 5-1: Short Term Upgrades ............................................................................................................. 5-6

Table 5-2: 10-Year Project Summary Table ............................................................................................. 5-7




Table of Contents

7/28/2016 iii Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

Table 5-3: 25-Year Project Summary Table ............................................................................................. 5-7

Table 5-4: Pump Station Long Term Upgrade Recommendations ............................................................ 5-10

Table 6-1: Storm Drain Unit Costs Based on RCP ...................................................................................... 62

Table 6-2: Project Cost Summary Table .................................................................................................. 6-2

Table 6-3: CMP Replacement Cost Summary ........................................................................................... 6-3

Table 6-4: Summary of 10-year Pipe Project Costs ................................................................................... 6-3

Table 6-5: Summary f 25-year Pipe Project Costs .................................................................................... 6-4

Table 6-6: Automatic Trash Rack Cost Estimate ....................................................................................... 6-5

Table 6-7: Pump Station Short Term Upgrades Cost Estimate ................................................................... 6-5

Table 6-8: Pump Station Long Term Upgrades Cost Estimate, Existing Storm Drain System, Existing LOS ... 6-6

Table 6-9: Pump Station Long Term Upgrades, 100-Year Inflow, 25-Year Pipe Projects, & Modified Wetwell6-6

Table 6-10: Floodwall Cost Summary ...................................................................................................... 6-7

Table of Figures

Figure ES-1: Drainage Areas ................................................................................................................. ES-4

Figure 1-1: Location of Cove Stormwater Pump Station and Hydraulic Study Area ..................................... 1-1

Figure 1-2: Study Drainage Areas ........................................................................................................... 1-3

Figure 2-1: Gauge Locations for Cove Watershed ..................................................................................... 2-2

Figure 2-2: Cove Drainage Area Land Use ............................................................................................... 2-5

Figure 3-1: 24-hour, 100-year Design Storm ............................................................................................ 3-4

Figure 3-2: Catchments Modeled in MIKE URBAN ..................................................................................... 3-5

Figure 3-3: Catchments Specific to Cove Pump Station ............................................................................ 3-6

Figure 4-1: Study Location ..................................................................................................................... 4-1

Figure 4-2: Study Storm Drain System .................................................................................................... 4-2

Figure 4-3: Responsible Parties for Cove Drainage System ....................................................................... 4-4

Figure 4-4: Mechanical Trash Rack Site Layout with Existing Wetwell Configuration ................................... 4-8

Figure 4-5: Cove Pump Station System Curve ........................................................................................ 4-10

Figure 4-6: Existing Wetwell and Pump Bay Layout ................................................................................ 4-13

Figure 4-7: Existing Pump Set Levels and Interconnectivity between Pump Bays #1 and #2 .................... 4-14

Figure 4-8: Possible ATS Location ......................................................................................................... 4-20

Figure 5-1: 10-Year Storm Event with Existing Drainage System ............................................................... 5-2

Figure 5-2: 25-Year Storm Event with Existing Drainage System ............................................................... 5-3

Figure 5-3: 100-Year Storm Event Floodplain ........................................................................................... 5-4

Figure 5-4: Corrugated Metal Pipes Replacements ................................................................................... 5-5

Figure 5-5: 10-Year Conveyance Pipe Upgrades ....................................................................................... 5-8

Figure 5-6: 25-Year Conveyance Pipe Upgrades ....................................................................................... 5-9




Table of Contents

7/28/2016 iv Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

List of Appendices

Appendix A – Data Sources

Appendix B – LiDAR Metadata

Appendix C – Rainfall Design Patterns

Appendix D – Hydrology Methodology Memorandum

Appendix E – Percent Impervious Values for the Town of Tiburon

Appendix F – CCTV Inspections

Appendix G – Pump Station Structural Assessment Memorandum

Appendix H – Pump Curves

Appendix I – Potential Project Cost Breakdown

Appendix J – Gauge Data

Appendix K – GIS and MU Models




Executive Summary

7/28/2016 ES-1 Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

Executive Summary

ES.1 Study Objectives

Schaaf & Wheeler analyzed Marin County Flood Control and Water Conservation District’s Cove Stormwater Pump Station and the contributing drainage network to

determine the current operations and capacity of the system. This document provides a

detailed summary of the analyses, results and recommendations for the pump station and drainage system. The analyses performed under this study gauge the performance

of the existing system and identify upgrades necessary to increase the level of service. Hydraulic and hydrologic models were used to size upgrades to achieve either a 10-year

or 25-year level of service. Planning level cost estimates were developed for each identified system upgrade. The following list presents a summary of tasks completed to

analyze the pump station and drainage network:

1. Developed hydraulic models of the Town of Tiburon’s existing storm drain system and the Cove Pump Station from GIS information provided by the

District. Storm drainage analysis methodologies and criterion were established in coordination with District staff.

2. Inspected and documented existing condition of drainage system leading to the

pump station.

3. Installed three (3) water level gauges and one (1) rain gauge within the

drainage system to document winter 2015-2016 storm events and compare with modeling results.

4. Established upgrades that will enhance drainage system and pump station

capacity and operations.

5. Developed a list of recommended projects.

6. Project costs.

ES.2 Sources of

Flooding

The watershed that flows into Cove Pump Station is the main focus of this study. Runoff

generated within this watershed is conveyed through the storm drain network and through the pump station which outfalls to East Creek and ultimately to San Francisco

Bay. Capacity limitations within the storm drainage network can contribute to ponding

of water. For the purposes of this report, flooding is defined as the surcharge of water above the ground surface and may or may not affect or damage structures. The

primary objective of this report is to determine the potential causes of flooding and to identify potential system upgrades. Because this watershed is located near the Bay, the

capacity of these drainage systems and creeks may be hydraulically linked to the tides.

Tidal influences on East Creek and the pump station were analyzed.

ES.3 Work

Products

This report is intended to function at several levels. The drainage system discharging

into the pump station is comprised of four (4) responsible party groups; private property owners, Caltrans, Town of Tiburon, and the Marin County Flood Control and

Water Conservation District (District). The planners and engineers responsible for the respective projects should find this document contains sufficient background

information and data to serve as a basis for future project design and analysis. For

those parties interested in a more in-depth examination of the Cove watershed and adjacent systems, the companion GIS-based Mike Urban (MU) hydraulic model is

included as an electronic attachment. The model inputs and summarized results can also be viewed in standalone ArcGIS. The following information is contained in the GIS

data:




Executive Summary


1. Inventory of Drainage Facilities. Drainage pipes 6-inches in diameter and

larger in the study area have been imported into the storm drain model.

Information pertaining to each system component may be accessed graphically or through database spreadsheets which have been provided electronically in

Appendix K.

2. Tributary Drainage Areas. Land areas used to generate local runoff to each

major drainage inlet are available graphically in the storm drain model. Attributes include tributary area, factors related to land use, soil conditions,

slope and shape.

3. Storm Drain Capacity Evaluation. The capacity of the storm drain system is documented in the model. For each drainage system component, peak

discharge, and maximum hydraulic grade line (HGL) are computed. Based on hydraulic grade calculations, the degree of surcharge and depth (based on

theoretical HGL) of water above ground are also determined. This

determination can be used to assess potential severity of flooding which could be used to assign priorities for system upgrades.

ES.4 Current Operations and

Performance

The existing Cove Pump Station has capacity to handle the directly connected 100-year inflows with the existing storm drain system and all three pumps running; however, like

most drainage systems, the storm drain pipes within the Town of Tiburon are not designed to convey the 100-year storm flows. Upsizing the Tiburon pipes would

increase the peak flows at the Cove Pump Station and potentially exceed the capacity of

the pump station during storm events larger than the 25-year. Changes to the pipe network will need to be coordinated with pump station upgrades. The existing District-

owned drainage network (Figure 4-3) is adequately sized to convey flows from the Town drainage system as well as runoff from the private shopping center system. The

system can also convey additional flows if the Tiburon system is upsized to a 10-year or

25-year level. There are a few aging corrugated metal pipes (CMP) within the District-owned system that are corroding and should be replaced in the near future.

The pump station has sufficient capacity to convey inflows from large storm events; however, some of the mechanical equipment within the pump station is approaching

the end of its useful life and replacement should be scheduled as funding allows.

ES.5 Potential

Projects

The results from this study were used to determine potential projects for the Cove

watershed to upgrade system capacity, operations, and ultimately reduce flooding

during large storm events. The projects have suggested timelines: short, medium, and long. Short term projects include select conveyance pipe replacements and pump

station upgrades. Medium term projects include the implementation of an automatic trash rack screen at Cove Pump Station. Long term projects conveyance pipe upgrades

and major pump station projects and a floodwall to prevent East Creek from spilling

onto the low lying developments. The recommended projects are discussed in detail in Chapter 5. Table ES-1 summarizes the cost and priority of the projects. These cost

estimates are discussed in further detail in Chapter 6.




Executive Summary


Table ES-1: Project Cost Summary Table

Potential Project Urgency Estimated

Cost

CMP Replacement Short $ 100,000

Short Term Pump Station Upgrades Short $ 430,000

East Creek Survey and Hydraulic Study Short $ 15,000

10-Year Projects or 25-Year Projects Long $ 1,010,000 / $ 1,180,000

Long Term Pump Station Upgrades, Existing LOS or 100-Year LOS w/ 25-Year Projects

Long $ 1,800,000 to $ 2,400,000

Floodwall Long $ 150,000

Trash Rack Medium $ 440,000




Executive Summary


Figure ES-1: Drainage Areas




Chapter 1: Introduction

7/28/2016 1-1 Schaaf & Wheeler CONSULTING CIVIL ENGINEERS

Chapter 1. Introduction

1.1 Overview The Cove Stormwater Pump Station and Collection System Hydrology and Hydraulic

Study (Study) provides a capacity analysis, condition assessment, recommended projects with estimated costs, and a discussion of drainage design standards for both

the drainage network and pump station located in the Cove Shopping Center in Tiburon, CA. This chapter provides a general discussion of the Study area setting, storm drain

network, and history of drainage issues and flooding.

1.2 Setting The entire watershed on the northwest side of Tiburon was reviewed as part of the Study. The Study area is bounded by West Creek on the west, East Creek on the east,

Tiburon Boulevard on the south, and Marin County Open Space on the north as shown in Figure 1-1. The majority of the study area gently inclines with some steep slopes

north of Karen Way. Elevations range from 6 feet North American Vertical Datum (NAVD), to about 600 feet NAVD.

Figure 1-1: Location of Cove Stormwater Pump Station and Hydraulic Study Area

1.3 Climate Tiburon’s climate is marine-influenced with an average annual high temperature of 71°F and average annual low temperature of 48°F. Average summertime temperatures range

from 85°F to 53°F. Average winter temperatures range from 56°F to 41°F. Mean annual precipitation is 25 inches (https://rainfall.weatherdb.com/l/2198/Belvedere-Tiburon-






California), with the majority of precipitation falling from November through March.

Precipitation occurs entirely as rainfall. Snowmelt is not a hydrologic process that

significantly affects runoff in the Town.

1.4 Drainage

and Flood Protection

Facilities

Precipitation that falls within Tiburon generates storm runoff. This runoff is conveyed

through storm drain networks that discharge to creeks or San Francisco Bay through a combination of pump stations and gravity outfalls. The entire Study watershed area is

roughly 435 acres and has been divided up into 3 drainage areas which are shown in

Figure 1-2 and detailed in Table 1-1.

For the purposes of this study, the analysis focuses on the Cove watershed which

contains the drainage network and pump station of interest. Most of the streets in this drainage area have traditional curb and gutter lined streets which directs runoff to inlets

and catch basins. East Creek also provides storm runoff conveyance and flood

protection for the Cove watershed.

Table 1-1: Watershed Areas and Length of Modeled Storm Drain Pipe

Drainage Watershed Area

(acres) Modeled Pipe Length

(miles)

Cove 31 0.9

East Creek 221 2.3

West Creek 183 3.1

TOTAL 435 6.3

1.5 References

Various documents were referenced during the preparation of this Study as listed below:

Bala & Strandgaard, Tiburon Drainage Master Plan 1974 (Revised Editions May 1975) for Watersheds Belveron, Miraflores, Rock Hill, 1975.)

Harris & Associates, Town of Tiburon Storm Drain System Map, February 2004

Caltrans right-of-way map (1966)

Marin County Department of Public Works, Master Drainage Plan for the Bel Aire Flood Control Zone, early 1970s.

U.S. Department of Agriculture Natural Resources Conservation Service, Soil Survey of Marin County, California 1985 (GIS map data downloaded from http://marinmapims.marinmap.org).

Roy’s Sewer Services, Closed Circuit Television (CCTV) of Cove Pump Station

and Shopping Center, September 2015.

Bob Pascaretta from County of Marin, Cove Pump Station Pump Curves

CSW/Stuber-Stroeh Engineering Group, Inc., Town of Tiburon Storm Drainage Master Plan, May 2008.

U.S. Department of the Interior Geological Survey, Guidelines for Determining Flood Flow Frequency Bulletin #17B of the Hydrology Subcommittee, Revised September 1981 and Editorial Corrections March 1982.

Nute Engineering, Scope of Work for an Assessment of the Cove Stormwater Pump Station and Collection System, July 21, 2015.

http://marinmapims.marinmap.org/






Figure 1-2: Study Drainage Areas




Chapter 2: Data


Chapter 2. Data

2.1 Overview

Schaaf & Wheeler reviewed and utilized readily available land use, topographic,

geographical, and storm drain system data within the Study area. This chapter summarizes data acquired as part of the Study. Data limitations, assumptions, and

impacts are also summarized.

2.2 Data

Sources

Several data sources were used and referenced to develop this study. A complete listing

of all collected data and its source is included in Appendix A.

Topography and Aerial

Imagery

All project data and results were standardize to NAVD88 (feet) vertical datum and State Plane (California Zone III) coordinate system. Marin County’s 2010 LiDAR topography

data (NAVD) with roughly half-foot accuracy (plus or minus 0.6 feet) was utilized for ground surface information throughout this study. See Appendix B for LiDAR metadata

specifying complete list of sources. High resolution digital aerial imagery provided by ESRI was also used.

GIS Data

The District provided GIS files to Schaaf & Wheeler for use on this project. The District

GIS attribute information includes: storm drain pipes and laterals, storm drain manholes and inlets, outfalls, pump stations, topography, and land use. GIS files for zoning,

roads, and parcel data within Tiburon were obtained from MarinMap. MarinMap is a group of local governments, special districts, and other public agencies that have

combined knowledge and resources to create a comprehensive GIS source for anyone

to use. In addition, Schaaf & Wheeler obtained National Resources Conservation Service (NRCS) soils data, National Land Cover data, FEMA floodplains, and aerial imagery. The

County’s GIS data completeness and accuracy varies and some information critical to accurately model the storm drain system was absent.

CCTV Data A CCTV video inspection of the District-owned system between Cove Pump Station and Cecilia Way was performed. This inspection video confirmed pipe shapes and materials,

and exposed corrosion and sedimentation within the pipes in this region. Sediment was

removed. CCTV inspection of the shopping center system was also performed. Videos and photos from the inspections are included in Appendix F. The District system

showed significant corrosion in the corrugated metal pipes (CMP). There was very little sedimentation or debris within the public pipes north of the pump station; the public

pipes south of the wetwell had significant debris.

Gauge Data Three (3) water level gauges and a rain gauge were installed along the drainage system to provide useful data for calibrating and validating the storm drainage model and

hydrology method used in this study. The data was also useful in determining how the pump station operates during storm events. The gauge locations are shown in Figure 2-

1. See Appendix J for gauge data.




Chapter 2: Data


Figure 2-1: Gauge Locations for Cove Watershed




Chapter 2: Data


As-Builts The District provided the following as-built plans:

Bel-Air Tiburon Culvert Replacement between Claire Way and Cecilia Way dated

07/1972

East Ditch Pump Station and Improvements As Builts dated 11/13/76

Pump Station Control Panel Improvements dated 03/2006

Culvert Replacement between Cecilia Way and Cove Shopping Center dated

08/1977

Greenwood Cove Drainage Improvements dated 06/1972

Karen Way Drainage Project dated 02/1976

Modification to East Ditch Pump Station dated 05/1983 (Trash Rack

Improvmeents)

Additional Data The District also provided other data to Schaaf & Wheeler including pump station plan drawings, pump station equipment information, easement mapping, and engineering

reports.

Report on Drainage Improvements for Lower Cecilia Way dated 09/1988

Scope of Work for an Assessment of the Cove Stormwater Pump Station and

Drainage System dated 07/2015

Cove Pump Station equipment logs dated 11/2002 to 11/2015

Cove Pump Station O&M logs dated 12/2013 to 11/2015

Tiburon Highlands Drainage Report for the East Ditch dated 08/1988

Preliminary Design Bel Aire Flood Control Zone No. 4 East Ditch and Pump

Station dated 07/1974

Soil Investigation for the Proposed Bel Aire Drainage Pumping Station and

Improvements dated 08/1974

Various maintenance reports, maintenance records, and equipment data

Pump Stations

There are a total of two pump stations located in the study area. Cove Pump Station,

the main focus of this report, and Pamela Court Pump Station.

The Cove Pump Station was visited by Schaaf & Wheeler staff to visually inspect the

condition of the station and to document the equipment and operation. Pump curves

were provided by the District for all three pumps within the Cove Pump Station. Flow tests were performed in November 2015 to determine the current pump capacity of

each pump.

Field

Measurements

Schaaf & Wheeler conducted selective field research to verify pipe sizes, layouts, and to

measure invert depths. Unlike sanitary sewer modeling, storm water systems are

designed to surcharge (pressure flow). Invert elevations become less critical than pipe diameter because the system’s hydraulic grade lines (HGLs) are not governed by open

channel flow dynamics. Interpolation was used to determine missing information not available from GIS, as-builts or field measurements. Schaaf & Wheeler also documented

channel vegetation and sedimentation in East Creek and West Creek.

FEMA Data 2016 FEMA maps and GIS data were referenced to obtain FEMA flood risk information.

The pump station is not currently in a FEMA 100-year special flood hazard area.




Chapter 2: Data


Regulatory This study applies several different sets of guidelines and standards to evaluate the reliability, function, and worker safety of the Cove Stormwater Pump Station. A list of

guidelines, codes, and standards that were used to evaluate the pump station is included below.

Existing structure, electrical equipment, and equipment layout evaluated based

on: National Fire Protection Association (NFPA), California Electrical Code (CEC), National Electrical Code (NEC), and California Building Code (CBC)

Pump station reliability, redundancy, and capacity evaluated based on standards

for interior drainage

Pump station hydraulics and wetwell configuration evaluated based on Hydraulic

Institute Standards and pump manufacturer recommendations

Land Use Data

and Runoff Characteristics

The land use conditions used in this study reflect the existing conditions within the Cove

drainage area. The land use data is based on the Town of Tiburon’s current zoning, which was obtained as a GIS shapefile from MarinMap. The zoning map became

effective on March 31, 2006 by the Community Development Department. In general,

the land use is primarily single family residential, interspersed with educational facilities, office parks, commercial, and open space. The various land use descriptions within the

GIS database are summarized in Table 2-1. The land use within the Cove watershed is shown in Figure 2-2.

Table 2-1: Land Use Descriptions and Percentages in Cove Watershed

Description

Existing

Area (acres)

Percent of area

Single Family Residential 0.03 0.1%

Bel Aire Single Family Residential 19.6 63.9%

Residential Open 0.4 1.4%

Neighborhood Commercial 3.2 10.3%

Public/Quasi-public 0.3 1.1%

Open Space 1.0 3.3%

Road 6.1 19.8%

Neighborhood Commercial/ Affordable Housing Overlay

0.04 0.1%




Chapter 2: Data


Figure 2-2: Cove Drainage Area Land Use




Chapter 2: Data


Hydrologic Soil Group

The Hydrologic Soils Group (HSG) data for the study area was taken from the National Cooperative Soil Survey Geographic database (SSURGO) downloaded from the following

link:http://www.arcgis.com/apps/OnePane/basicviewer/index.html?appid=a23eb436f6ec4ad6982000dbaddea5ea.

The Natural Resources Conservation Service (NRCS) has classified soils into four hydrologic soil groups (A, B, C, and D) according to their infiltration rates. Group A soils

have low runoff potential when thoroughly wet and typically consist of sand or gravel

type soils. Group B soils are moderately well draining when thoroughly wet and consist of loamy sand or sandy loam textures. Group C soils have moderately high runoff

potential when thoroughly wet and consist of loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures. Group D soils have high runoff potential when

thoroughly wet and consist of clayey textures. All soils with a water table within 24-

inches of the surface are in Group D. The larger extents of the watershed examined in this Study is comprised of 80% Hydrologic Group C soils and 20% Hydrologic Group D

soils. However, the Cove watershed is 100% Hydrology Group C.

2.3 Storm Drain

Data

The completeness of the data readily available for the study varied. The County’s GIS

appeared to be spatially accurate and contains detailed attributes. There were 276 pipes

and 227 manholes and inlets within the study area. The County’s pipe shapefile provided shape, size, and material, however about 2% of the pipe diameters were missing and

3% of the pipe materials and sizes were missing. The County’s manhole shapefile provided depth, material, and size information, however it did not include the rim and

invert elevations and was missing about 5% of invert depths. The County’s inlet shapefile provided depth, inlet size and type, however it did not include rim and invert

elevations and was missing about 5% of invert depths.

In addition, the District provided the GIS files for Cove Shopping Center (Shopping Center), a privately owned storm drain system; this included GIS files for manholes,

inlets, and pipes from April 2015. There were 22 pipes within the shopping center and only 1 was missing. There were 2 manholes, 16 inlets, and 4 structures identified in the

GIS files. The Shopping Center’s manhole shapefile included depth, size, and material.

The Shopping Center’s inlet shapefile included depth, size, type, and descriptions about each inlet. The Shopping Center’s pipe shapefile included size, shape, and material. The

Shopping Center’s structures shapefile also had a description of each structure and provided the depth and size for one of the four structures. In addition, each shapefile

specified the ownership information about each inlet, manhole, and pipe.

Rim and invert elevations were added to these shapefiles based on LiDAR provided by

Marin County. The LiDAR accuracy is discussed in the previous section of this report.

2.4 Modeled Data

Assumptions

Schaaf & Wheeler completed field research to verify the accuracy of the GIS data provided by the District. From there, corrections or additions were manually entered into

GIS with their data source noted.

As described previously, one of the significant shortcomings of the existing GIS database

was that the majority of rim and invert data did not exist. To create a uniform ground

surface for hydraulic modeling, rim elevations were globally assigned based on the LiDAR from Marin County. The remaining inverts were assigned from interpolating between

upstream and downstream nodes. The method of assigning elevation data is preserved in the “Description” field of the final GIS database.

Groundwater flows do not significantly reduce the capacity of the Cove system. Based on 2015 and 2016 pump run times, the base flow in the system ranges from 1 to 5 gpm

which is less than 0.05% of the pump station capacity.

http://www.arcgis.com/apps/OnePane/basicviewer/index.html?appid=a23eb436f6ec4ad6982000dbaddea5ea

http://www.arcgis.com/apps/OnePane/basicviewer/index.html?appid=a23eb436f6ec4ad6982000dbaddea5ea




Chapter 3: Methodologies


Chapter 3. Methodologies

3.1 Overview Neither the Town of Tiburon nor District have published hydrology standards that are

adequate for this study; therefore, Schaaf & Wheeler developed a hydrology method to analyze the Cove watershed drainage system and pump station performance.

Methodologies used to evaluate the storm drain system performance must be technically

sound yet simple to understand and apply. The hydrology method developed for this study is primarily based on the Alameda County Public Works Agency (ACPWA) procedure.

However, the hydrologic procedure was modified to match the hydrologic conditions of Marin County. This study applies both the Clark and SCS Unit Hydrographs instead of the

Snyder Method that is used in the ACPWA procedure. In addition, the constant losses

used in this procedure were calibrated based on four long duration gauges in the Bay area. This hydrologic method can be used for future hydrologic studies within Marin

County.

This method was used along with Mike Urban (MU) storm drain modeling software to

determine drainage system performance and necessary upgrades. Physical parameters

used in the model were based on the County’s GIS data and other information detailed in Chapter 2 - Data. Storm drain evaluation criteria described in the following section was

discussed with and agreed upon by the District.

3.2 Evaluation

Criteria

The methodology described in the Alameda County Hydrology and Hydraulics Manual

(Manual) was the basis for estimating storm runoff in the Cove watershed. The Manual, developed in 2003, provides easy-to-follow procedures with generally accepted hydrology

and hydraulic design practices. The manual was used to establish basin roughness and

constant loss rates for the drainage area.

In addition, a design storm hydrologic model was used to estimate peak discharge during

different frequency storm events (e.g. the 100-year design storm or the 10-year design storm). It should be noted that a design storm is a hypothetical storm and is not an actual

rainfall event. Therefore, this type of model cannot be used to replicate a specific event in

time. Once calibrated, a design storm hydrologic model can be used to study the effect of changing land use or ground cover on peak discharge, and analyze any effects from

storage on downstream discharges.

Specifically, this study models the hydrology for the 10-year, 25-year, 50-year, and 100-

year storm events. The 10-year and 25-year storm events where used as the design events for the drainage network. The 10-year and 25-year level-of-service are consistent

with the neighboring municipalities and the Town’s drainage master plan. For the

purposes of this report, upgrades are recommended that reduce the hydraulic grade to no higher than 0.5 feet above the gutter elevation at any node such that the maximum

hydraulic grade is the top of curb elevation. This will minimize the risk to property and public safety.

3.3 GIS Based

Modeling

The MIKE-Urban (MU) software by DHI with MOUSE hydraulic solver was selected for this

study because it is tested and reliable software with a GIS interface. MIKE is a package of software programs designed by the Danish Hydraulic Institute (DHI) for the analysis,

design, and management of urban drainage systems, including storm drain and sanitary sewers. The MU model works within ArcMap GIS and can simulate runoff, open channel

flow, pipe flow, water quality, and sediment transport. MU has the ability to combine 1D

and 2D overland flow models to simulate a more comprehensive model as well. The program was chosen to model the Cove watershed because of its capabilities with

overland flow, and ability to connect to a drainage system consisting of pipes, pumps and channels.






The study area was divided into three independent sub-areas based on outlet points and major drainage channels. These sub-areas are: East Creek, Cove, and West Creek as

described in Table 3-1. Each drainage system model is composed of a conveyance

network (pipes, nodes, pump stations, etc.) and the urban catchments contributing runoff to the pipe network. The main focus of this study is the Cove watershed; however, the

East Creek and West Creek watersheds were modeled to determine their interconnectivity.

Table 3-1: Model Drainage Areas based on Existing Conditions

Watershed Description Percent of

area

Miles

of pipe

Modeled Pump

Stations

Part 1: East Creek

This drainage area is bounded by the fire roads to the North, East Creek to the West, and Tiburon Blvd to the South. Flow drains south into East Creek.

50.9% 2.3 0

Part 2: Cove

This drainage area is generally bounded by Bel Aire Elementary School to the North, East Creek to the East, and Tiburon Boulevard to the South. The Cove Pump Station pumps the flow into East Creek.

7.1% 0.9 1

Part 3: West Creek

This drainage area is generally bounded by fire roads to the North and Tiburon Boulevard to the South. Pamela Court Pump Station pumps the flow into the West Creek.

42.0% 3.1 1

Operation

For the 1D model, two separate calculations are performed by MU: a rainfall-runoff calculation estimating the amount of water entering the storm drain system during a

design rainfall event; and the network flow calculation which replicates how the drainage system will convey flows to outlet locations. Flows resulting from the runoff calculation

are used as inflows for the subsequent network flow calculation. The MU offers a choice

of infiltration and transform methods; this study used constant loss and the SCS dimensionless unit hydrograph. A simulation can be started at any point during the

chosen design storm to assess surface runoff for any period of the design storm, with computations made based on a user-specified time step. The runoff time steps were

chosen to be at one minute which is sufficient for the small-sized urban catchments used in this study.

The MU network flow model offers a choice of three flow description approximations:

Steady, Dynamic Wave, and Kinematic Wave; distinguished by the set of forces each takes into account. This study uses the most comprehensive flow description, Dynamic

Wave, which incorporates the effects of gravitational, friction, pressure gradient and inertial forces. Because it accounts for all major forces affecting flow conditions, this

equation allows the model to accurately simulate fast transients and backwater profiles.

The simulation of flooding at a node is accommodated by the insertion of an artificial “basin” above the node which will store water when the water level rises above the






ground level. The surface area of the “basin” gradually increases (up to a maximum of 1000 times the node surface area) with rising water levels at the node, replicating the

effects of flooding.

2D Overland Flow

2D overland flow allows for simulation of surface flooding through the MIKE 21 2D overland flow model. For this study, the 2D overland flow model and 1D model were used

together in a combined model, MIKE FLOOD. Essentially the model works by using a working pipe flow model, with a digital elevation model (DEM), and specified couplings

between the 1D and 2D model. The DEM allows the model to simulate overland flow

paths and velocities. The specified couplings, typically manholes or inlets, act as the connection between the 1D and 2D model to allow for transfer of water between the two

models.

Input and

Output

MU surface runoff calculations require two types of input data: the hydrologic model and

the hydraulic model. The hydrologic model consists of an input rainfall time series representing the design storm event for the model, watershed delineation, and hydrologic

parameters such as constant loss and basin lag among others. The hydraulic model

includes the pipe network, inlets, manholes and pump stations.

Output from the pipe flow computation includes the calculated water level at each node,

pump discharges, weir discharges, water level in network branches, discharge in network branches, velocity in network branches, water volume in the system, and time step data.

Output is viewed using MOUSE or in GIS. Results may be displayed in plan view or as a

profile for a selected network section, and may be viewed as a temporal animation or paused at a specific time step. Additional outputs which can be derived from MOUSE pipe

flow results using GIS include: water depth, flooding level, pressure in closed conduits, percentage pipe filling, and the flow calculated for each link.

3.4 Hydrologic Model

As described above, the first step of the MU model is to complete a storm runoff calculation that determines the amount of water entering the storm drain system from a

specific rainfall event. This hydrology model is formed by developing rainfall and

catchment data.

Boundary Data Methods used in this study to estimate peak storm water flow rates and volumes require

the input of precipitation data. Since it is impossible to anticipate the impact of every conceivable storm, precipitation frequency analyses are often used to design facilities that

control storm runoff. A common practice is to construct a design storm, which is a rainfall

pattern used in hydrologic models to estimate surface runoff. A design storm is used in lieu of a single historic storm event to ensure that local rainfall statistics (i.e. depth,

duration and frequency) are preserved. When combined with regional specific data for land use and loss rates, the model should produce runoff estimates that are consistent

with frequency analyses of gauged stream-flow in the Marin County area. In other words,

the ten-year design storm pattern used for MU modeling creates results consistent with a ten-year storm runoff event.

Precipitation-frequency analyses are based on concepts of probability and statistics. Engineers generally assume that frequency (probability) of a rainfall event is coincident

with frequency of direct storm water runoff, although runoff is determined by a number of factors (particularly land use conditions in the catchment) in addition to the precipitation

event. Because the study’s storm pattern has been adjusted to preserve local statistics,

there is increased confidence in this correspondence between the frequency of the rainfall and the frequency of the runoff.

Rainfall The rainfall distribution pattern for this study is based on the 48-hour New Year’s 2006

storm. However, for the purposes of this study, the 48-hour storm was shortened to a 24-hour design storm and balanced with NOAA Atlas 14 statistics. The design storm is






balanced to the following durations: 15-minute, 30-minute, 1-hour, 2-hour, 3-hour, 6-hour, 12-hour, and 24-hour.

The final 24-hour design storm pattern was developed using a 10-minute time-step and

the precipitation frequency estimates were applied to the design storm pattern to develop design storms for the 10-year, 25-year, 50-year, and 100-year storm events and prorated

based on statistical data provided by NOAA Atlas 14 for those storm events. See Appendix C for the design pattern, as well as prorated design storm events. Figure 3-1 shows this

data for a 24-hour, 100-year storm event.

Figure 3-1: 24-hour, 100-year Design Storm

Catchment Data

Catchment data is important for determining the amount of runoff in a drainage area, or “watershed”. There are several accepted hydrology methods for calculating runoff;

however this report uses a loss method of initial and constant loss and a transform method of SCS Dimensionless Hydrograph to determine the runoff hydrograph for each

catchment. Catchment data includes the boundaries of each drainage catchment, along with relevant physical and hydrologic parameters including surface area, land use

characteristics, basin lag, and basin roughness, etc.

Watershed

Delineation

A watershed typically encapsulates all points that contribute runoff to an identified location or outfall during a storm event. Initially, one large watershed area was delineated

for each outfall location; one for East Creek, one for Cove watershed, and one for West Creek. From there, the watershed was broken down into smaller drainage areas called

“catchments” that range from less than an acre to about ten acres in size. These

delineations rely heavily on engineering judgment, field verification and on experience in using contours, lot lines, storm drainage system layout, and aerial imagery. Figure 3-2

below shows the catchments used in this study. However, the Cove watershed is the main focus of this study as shown in Figure 3-3.






Figure 3-2: Catchments Modeled in MIKE URBAN






Figure 3-3: Catchments Specific to Cove Pump Station






The Cove watershed is mainly single family residential, campus education facility, and commercial spaces. There are some undeveloped areas that are open space, parks or

conservation land. The majority of the developed parcels have high concentrations of

impervious surfaces that include buildings, roads, parking lots and sidewalks. Schaaf & Wheeler used imperviousness tables from the Santa Clara Valley Hydrology Manual

(Schaaf & Wheeler, 2006) and adjusted them based on aerial imagery. There is a degree of uncertainty in applying standard values to all similar land uses; however, this is

adequate for a master planning level study.

Unit

Hydrograph

A unit hydrograph is a numerical representation of the time response of catchment runoff caused by one inch of excess rainfall applied uniformly over a unit of time. Many different

techniques are available to estimate unit hydrographs. The SCS Dimensionless unit hydrograph was used for this study. Direct runoff is calculated by subtracting losses, such

as soil infiltration, from the rate of rainfall. Runoff is the combination of excess runoff on pervious portions of the watershed plus precipitation on directly connected impervious

areas. The Initial and Constant Rate Loss method reflects these potential losses for a

given soil type and land use.

Percent

Impervious

and Constant

Loss Rate

The initial and constant rate model was chosen as the loss method for this study. These

losses represent the physical properties of the watershed which include soils, land cover, and the antecedent moisture condition. In general, the Constant Loss Rate (CLR) is used

to separate rainfall into loss and excess. It is viewed as the ultimate infiltration capacity of

the soil. Initial loss represents the initial interception and depression storage of water, with these losses occurring prior to the onset of any runoff. Since the watershed is already

in a saturated condition, initial loss is essentially zero. Since Initial Loss does not have an impact on the peak runoff flow, a value of zero was chosen.

Constant Loss Rate (CLR) values are based on land cover and soil group within the watershed. Since the constant loss rate is not a measured parameter, it is best determined

by calibration. The CLR (in/hr) for this study was calibrated using the statistics from the

flow frequency analysis of four (4) local gauged watersheds which included: Sonoma Agua Caliente, Arroyo Corte Madera Del Presidio, Corte Madera Ross, and San Ramon.

These watersheds were selected because they met the following Bulletin 17B guidelines: 30 years or more of record, unaffected by upstream reservoirs, and similar urbanization

factors. See Appendix D for the Bulletin 17B report. However, Arroyo Corte Madera del

Presidio did not meet the 30 years or more of record criteria; it was included for its proximity. Please see Appendix D for further explanation of calibration methodology.

The CLR values created for this study are included in Table 3-2. The CLR values were calibrated based on the results of the four watersheds. Using the peak flow rates

developed from the flow frequency analyses for each gauge, the constant loss rate was

varied so that the peak runoff approximately matched the peak discharge from the gauged statistics. The calibrated loss rates, in inches per hour, used for each watershed

are presented in Table 3-3.

Table 3-2: Constant Loss Rate for Hydrologic Soil Group C and D

Land Use HSG-C

(in/hr)

HSG-D

(in/hr) Forest 0.34 0.22

Urban 0.36 0.30

Rural 0.30 0.18






Table 3-3: Calibrated CLRs for Cove Drainage Area

Description

Constant Loss

Group

A Soil (in/hr)

Group

B Soil (in/hr)

Group

C Soil (in/hr)

Group

D Soil (in/hr)

Single Family Residential 0.300 0.250 0.150 0.125

Bel Aire Single Family Residential 0.300 0.250 0.150 0.125

Residential Open 0.300 0.250 0.150 0.125

Neighborhood Commercial 0.300 0.250 0.150 0.125

Public/Quasi-public 0.275 0.225 0.125 0.075

Open Space 0.275 0.225 0.125 0.075

Road 0.300 0.250 0.150 0.125


0.300 0.250 0.150 0.125

Percent

Impervious

Each type of land use has a related percent impervious value. Percent impervious represents the portion of ground that will not allow infiltration to occur and therefore all

flow is attributed to runoff. Table 3-4 below specifies the percent impervious values used

for the Cove watershed.

Table 3-4: Percent Impervious for Cove Watershed

Description Percent Impervious

Single Family Residential 40%

Bel Aire Single Family Residential 63%

Residential Open 41%

Neighborhood Commercial 98%

Public/Quasi-public 52%

Open Space 20%

Road 98%


98%

For a complete list of percent impervious values for several land uses categorized by the Town of Tiburon, see Appendix E. The percent impervious value was estimated by taking

two to three sample parcels in each type of land use and estimating the portion of impervious surface to total surface area using aerial imagery.

Basin

Roughness

Factor (N-

factor)

The basin roughness factor, also known as the basin friction factor, is used to describe the condition, vegetation level, and overall clearness of a representative watercourse

throughout a catchment. This is typically determined through site visits and/or a

combination of aerial photography. The N-factor value is based on the 2011 National Land Cover Dataset (NLCD). For this study, the N values are summarized in Table 3-5 below.






Table 3-5: Basin Roughness Values

Classification Basin

Roughness

Water 0.01

Developed, Open Space 0.06

Developed, Low Intensity 0.06

Developed, Medium Intensity 0.05

Developed High Intensity 0.04

Bare Rock/Sand/Clay 0.04

Deciduous Forest 0.10

Evergreen Forest 0.10

Mixed Forest 0.10

Shrub/Scrub 0.09

Grasslands/Herbaceous 0.04

Pasture/Hay 0.05

Cultivated Crops 0.05

Woody Wetlands 0.08

Emergent Herbaceous Wetlands 0.08

Basin Lag Time This study uses the Soil Conservation Service (SCS) Dimensionless Transform method to

derive a Synthetic Unit Hydrograph (UH). This method was chosen because it is a commonly accepted hydrology method and it works well with the MU model. Two

parameters are required for this methodology; the area, as discussed previously, and a timing parameter. The timing parameter, called basin lag (hour), is a function of basin

geometry, as mentioned in the watershed delineation section, and basin roughness, or

basin N-value shown in the following equation.

Lag=KN (L*LC

√S)

0.38

Where:

K: for L> 1.7 miles K = 24, for rest K = 15.22 + 2.1464*L + 8.6981/L

L: length of the longest flow path (miles)

Lc: length of the longest water course measured from the outlet to a point

perpendicular to the watershed area centroid (miles)

S: average stream slope (feet/mile)

N: Basin roughness factor

1 The channel slope was calculated in GIS by using LiDAR data to determine the highest and lowest elevation along the channel. The equation for determining slope is:

S=Zh-Zl

L

Where:

Zh: highest elevation point (feet)

Zl: lowest elevation point (feet)

L: length of flow path (mile)

The basin lag for this study ranged from 4 to 28 minutes, showing the wide range of

catchment geometry this model incorporated.






3.5 Hydraulic Model

The second step of the MU model is to input the hydraulic portion of the model which consists of network data, structural system elements, operational data, and boundary

data. Ultimately, the model will take the results generated from the hydrologic model and

use that as an input through the hydraulic model.

Network Data Network data consists of the pipe network elements including nodes (manholes, outlets,

and storage nodes) and links (pipes, culverts, and open channels).

Nodes The node ground levels are based on LiDAR and consequently, the invert level was based

on the ground level minus the depth provided either in field measurements or County GIS

data.

Junction

Losses

Hydraulic losses at junctions (manholes, inlets, intersections) can be significant in drainage

systems. Losses can vary due to construction methods, condition, and shape. Schaaf & Wheeler performed a sensitivity analysis of the loss coefficients used in MU to determine

the most realistic model parameters. The MU Weighted Inlet Energy Method is used for this study.

Links Pipes are modeled as one-dimensional closed conduit links which connect two nodes in the

model. The conduit link is described by a constant cross-section along its length, constant bottom slope, and straight alignment. Unsteady flow in closed conduits is calculated using

conservation of continuity and momentum equations, distinguishing between pipes flowing partially full (free surface flow), and those flowing full (pressurized flow). Based on field

observations all modeled pipes are assumed to be free of debris and sediment. A

Manning’s ‘n’ coefficient is assigned to account for surface roughness of the links.

Table 3-6: MU Manning’s ‘n’ Values

Material Manning’s ‘n’

Corrugated Metal Pipe (CMP) 0.025

Gravel Channel 0.023

Light Vegetated Channel 0.025

Vegetated Channel 0.030

Heavy Vegetated Channel 0.040

Iron (cast) 0.014

Plastic 0.012

Reinforced Concrete Pipe (RCP) 0.013

Culverts and channels are also modeled in this study; however, they are not intended to

meet FEMA level accuracy. They are utilized to route flows through the system and provide continuity. Culverts are defined as pipes that allow water to flow under a road.

Channels are defined as any open conduit which connects two nodes in the model. Location specific cross-sections can be input into the MU model. For this study, channel

cross-sections were created using LiDAR. In addition, the Manning’s ‘n’ value for these

channels range from 0.023 to 0.040 based on observed field visits and aerial imagery.

Parameters required to describe links include the name of upstream and downstream

nodes, shape and dimensions, material or roughness, and upstream and downstream inverts. Structural system elements including gates and weirs are all modeled as functional

relationships connecting two nodes in the system, or associated with one node in the case of free flow out of the system. Operational data consists of parameters which describe

how these elements function in the network. Boundary data for the pipe flow computation

can include any external loading, inflow discharges, water levels at interaction points with receiving waters, as well as the results of a run-off calculation.






Structural System

Elements

Structural system elements including gates, weirs, and pumps are all modeled as functional relationships connecting two nodes in the system, or associated with one node

in the case of free flow out of the system.

Pump Stations A portion of the West Creek watershed and the entire Cove watershed drain to pump stations that discharge to channels and ultimately San Francisco Bay. Pumps are modeled

in MU as a functional relation between the water level of the inlet and outlet nodes. Pumps are characterized by starting and stopping water levels and a capacity curve of

differential head vs. flow data for the pump.

Pump curves, as provided by manufacturers, represent the flow through the pump itself based on various flow and head conditions. Over time, the pumps become worn down

and are less efficient at pumping than the data provided in the original pump curves. For older pumps, it is sometimes necessary to de-rate the pump to account for lower

production based on field tests of the pump (see page 4-10 for specifics on de-rating of the pumps in this study).

The pump curves are used in conjunction with a system curve in order to come up with an

operating point, where the two curves cross. The operating point is how much flow can be expected from the pump at that particular pump station. The system curve is

calculated based on the pump discharge piping and the elevation change between the wet well and discharge location to come up with the total dynamic head for various flow

conditions. Since the elevation of the wetwell is constantly changing during pumping

cycle, there will be a maximum head condition where the pumps are running with the wet well at its lowest level (typically at the pump off elevation) and a maximum flow condition

where the wetwell is at its highest level.

The system curve is calculated based on various flow conditions using the following

equations.

Velocity Equation

V=Q

A,

Where: A = area of the discharge pipe (ft2) = π(D/2)

Q = pump discharge from the manufacturer’s curve (cfs)

D = diameter of the discharge pipe (ft) V = velocity of discharge (ft/s)

Friction Loss Equation

The friction loss equation is derived from the Hazen Williams equation.

V=k*C*R0.63

*S0.54

,

Where: K = US customary units conversion factor (1.318 ft/s)

C = roughness coefficient R = hydraulic radius (ft)

S = slope of the energy line

For circular pipes flowing full, the hydraulic radius is

R=A

P=

D

4,






Where: A = area of pipe (ft2)

P = perimeter of pipe (ft)

D = diameter of pipe (ft)

The following conversion is used to convert the pipe diameter to inches, while the remaining units of length are in feet.

R=D

(4*12)=

D

48,

Where:

D = diameter of pipe (in)

By definition, the slope of the energy line represents the head loss per length of

pipe.

S=Hf

L,

Where: 𝐻𝑓 = loss in head due to friction in pipe

𝐿 = length of pipe (ft)

By substitution and simplification, the Hazen Williams Equation for finding

frictional losses is

Hf=L* (V

2

0.115*C*D*0.63)

1.85

,

Where:

C = Hazen-Williams Discharge Coefficient =120

D = pump discharge pipe diameter (in) L = length of pump discharge pipe (ft)

V2 = velocity of discharge (ft/s) Hf = loss in head due to friction in pipe

Minor Loss Equation

HL=K* (V

2

2g)’

Where:

K = Loss Coefficient V = velocity of discharge (ft/s)

g = gravitation constant = 32.2 ft/s^2 HL = minor losses

Total Dynamic Head TDH= HE+Hf+HL

Where: TDH = Total Dynamic Head (ft)

HE = Height difference between discharge and wetwell elevations (ft)

Hf = loss in head due to friction in pipe






Information used to calculate the total dynamic head was based on field measurements and record drawings. Loss coefficients were based on generally accepted standards for

the pipe material/devices.

The system curves developed for the Cove Pump Station, the original pump curves, and the adjusted pump curves are included within Chapter 4 of this report.

Operational Data

Operational data consists of details which describe how these elements function in the network. This report focuses on the Cove Pump Station, which uses various control

functions to generate a range of operational situations of both existing situations and

future simulations. Specific to this study, there are three main control functions that operate the Cove Pump Station (Pump Station) in the MU model: pump on/off levels,

pump capacity curve, and pump on/off controls. The first control function is the user-defined START/STOP levels for the Pump Station.

The second control function is the capacity curve for each pump. A capacity curve representing the relationship between discharge and differential head is specified for each

pump. Table 3-7 shows an example of the capacity curve used for Pump 1. Additional

information about how the capacity curve was derived is included in Chapter 4 of this report.

Table 3-7: Pump #1 Flow versus Total Differential Head

Q (gpm) TDH (ft)

1280 22.8

1360 21.9

1440 20.9

1520 19.8

1600 18.6

1680 17.1

1760 15.3

1840 13.2

1920 11

2000 8.8

2080 6.3

2128 4.6

The third control function is pump on/off status. All three, aforementioned control

functions can be manipulated to analyze various operational scenarios at Cove Pump Station; these results are discussed in Chapter 5.

Boundary Data Boundary data for the pipe flow computation can include any external loading, inflow discharges, water levels at interaction points with receiving waters, pump performance

curves, as well as the results of a runoff calculation. Specifically, pipe network outlets can

be modeled with either a free outfall or a water surface elevation (fixed or variable with time) which captures backwater effects due to receiving water levels.

Cove Pump Station has a close proximity to the San Francisco Bay; however, the pump station’s outfalls are not currently tidally influenced. The current elevations of the

discharge pipes are approximately equal to the 100-year tide level. Future sea-level-rise

could inundate the pump discharge piping and impact pump performance.






3.6 Creek Models

The hydraulic models developed for this project are not intended for the evaluation of the East Creek and West Creek channels. The channels are included in the models to convey

flows through the system and to the bay. Channel survey data and a more detailed model

would be required to determine the capacity and hydraulics of East Creek and West Creek.

The capacity of the existing East Creek culverts under Tiburon Boulevard where estimated

using the Federal Highway Admiration’s HY-8 computer software. This program estimates the hydraulic head required to convey various runoff through culverts. The 10-year, 25-

year and 100-year peak flows from the MU network model along with various tide

conditions were modeled in HY-8 to estimate the water level in East Creek near the Cove Pump Station.

3.7 Comparison to

Previous Reports

This study is similar to the 2008 Town of Tiburon Storm Drainage Master Plan (Master Plan). The methodology used in the Master Plan analysis differs from the methodology

used in this study; however, the results are similar within the Cove watershed. The Master Plan used XPSWMM hydrologic and hydraulic modeling software, whereas this study uses

MU. In addition, the Master Plan sized improvements and replacements to at least the 25-

year storm event, whereas this study sized upgrades and replacements to the both the 10-year storm and 25-year events. The Master Plan used the Rational Method, while this

study uses a more complex methodology based on Alameda County’s Hydrology Manual and SCS Unit Hydrograph Model.




Chapter 4: System Assessment


Chapter 4. System Assessment

4.1 Overview

The Marin County Flood Control and Water Conservation District (District) engaged

Schaaf & Wheeler, Consulting Civil Engineers to assess the Cove Stormwater Pump Station (historically known as the East Ditch Pump Station) and drainage system.

The Cove Pump Station is located at the southeastern corner of the Cove Shopping

Center parking lot in the incorporated Town of Tiburon in Marin County as shown in Figure 4-1. The station is located on the bank of East Creek and also discharges to East

Creek on the North side of Tiburon Boulevard. The drainage system consists of 4,000 linear feet of pipe, 40 inlets, 7 manholes, and has a 30.6-acre watershed located

between West Creek and East Creek as shown in Figure 4-2. East Creek discharges to

Richardson Bay approximately 350 feet downstream of the pump station; therefore, the creek is tidally influenced.

Figure 4-1: Study Location






Figure 4-2: Study Storm Drain System

Schaaf & Wheeler and electrical and structural subconsultant TJC and Associates, Inc.

visited and evaluated the pump station and drainage system. This report documents the assessment procedures, standards, and summarizes the results of the assessment. The

assessment is categorized into the following items:

Drainage System Inspections (District Owned)

Drainage System Inspection (Privately Owned Shopping Center)

Pump Station Structural Inspection

Automatic Trash Rack Screen Feasibility Review

Hydraulic Performance

Inspect Electrical Controls and Alarms

Inspect Existing Electrical Systems Regarding Power

Review SCADA Capability






Recommended upgrades were developed for short term and long term implementation. This report summarizes the Cove Stormwater Pump Station and System Assessment and

results.

4.2 Assessment

Procedures and Standards

The following sections describe the pump station and drainage system assessments. Analysis of the current condition was limited to visual inspection, previous reports, and

information provided by the District. The pump station assessment was performed on November 9, 2015 and the drainage system assessment was performed over several

days from September 2015 to March 2016. Information regarding the existing pumping

logic, operating conditions, and specific requests were obtained from District staff during the site visits and follow-up correspondence.

The assessments were based on the current standards and codes which include:

National Fire Protection Association (NFPA)

California Electrical Code (CEC)

National Electrical Code (NEC)

California Building Code (CBC)

Occupational Safety and Health Administration (OSHA)

ASTM E2026 – Standard Guide for Seismic Risk Assessment of Buildings

ASCE/SEI 41 - Seismic Evaluation and Retrofit of Existing Buildings

FEMA P-154 - Rapid Visual Screening of Buildings for Potential Seismic Hazards

FEMA standards for interior drainage behind accredited levees for pump station

capacity and backup power supply

Hydraulic Institute Standards for wetwell and pump hydraulics

Bay Area Air Quality Management District (BAAQMD)

The upgrades recommended herein are based on typical service life of pump station equipment, structures, and drainage infrastructure. Anticipated service life of pump

station equipment varies greatly based on several factors. It may be necessary to

replace some equipment earlier than noted, and some may last longer than expected.

Drainage

System Inspections

Schaaf & Wheeler conducted an inspection of the drainage systems that feed into the

Cove Pump Station. The drainage system is comprised of four responsible parties: Caltrans, Town of Tiburon, County of Marin, and private property owners. Based on our

research, the ownership of the pipes is shown in Figure 4-3.

Drainage

System

Inspections

(District

Owned)

The District currently owns a portion of the storm drainage system that feeds into the

Cove Pump Station. Schaaf & Wheeler performed a visual inspection of storm drain

pipes, inlets, manholes, and outfalls as well as measured several pipes, inlets, and manholes to verify the accuracy of the GIS data provided by the District. In addition,

CCTV inspections were performed on the main trunk-line that feeds into the Pump Station. CCTV inspection videos and reports are included in Appendix F.

In this drainage system, the District owns two (2) corrugated metal pipes (CMP), three

(3) reinforced concrete pipes (RCP), three (3) inlets, and one (1) manhole. The CMP’s were found to be poor condition and are in need of immediate replacement. The most

important pipe of note is the 36” CMP that drains directly into the Cove Pump Station wetwell. The invert of the pipe is completely corroded and missing which poses a risk of

pipe failure and collapse.






Figure 4-3: Responsible Parties for Cove Drainage System

Drainage

System

Inspections

(Privately

Owned

Shopping

Center)

The privately owned shopping center has a drainage system that feeds into the Cove

Pump Station. Schaaf & Wheeler performed a visual inspection of the storm drain pipes and inlets, as well as measured several pipes, inlets, and manholes to verify the

accuracy of the GIS data provided by the County of Cove Shopping Center. The

ownership of the CMP along Tiburon Boulevard has not been confirmed. Caltrans right-of-way maps show a temporary easement granted to Caltrans in 1963 by a private land

owner. We assume this pipe is not owned by the District.

In the privately owned shopping center drainage system there are four (4) corrugated

metal pipes (CMP), three (3) reinforced concrete pipes (RCP), two (2) polyvinyl chloride

pipes (PVC), two (2) other material types, nine (9) inlets, and zero (0) manholes. The results of the CCTV inspection are shown in Appendix F. In summary, several pipes had

debris, sedimentation or corrosion issues.






Pump Station

Structural

Inspection

Schaaf & Wheeler’s subconsultant, TJC and Associates, Inc. (TJCAA) conducted a condition assessment of the Cove Stormwater Pump Station. TJCAA conducted a

seismic risk assessment in accordance with the Standard Guide for Seismic Risk

Assessment of Buildings (ASTM E2026), Seismic Evaluation and Retrofit of Existing Buildings (ASCE/SEI 41), and Rapid Visual Screening of Buildings for Potential Seismic

Hazards (FEMA P-154).

The Cove Storm Water Pump Station, a cast-in-place concrete wetwell with light wood

framed pump house, was constructed in 1976, which predates the codifying of seismic

design and construction techniques specific to this type of construction by 3 years. Of the 32 applicable “checks” from the ASCE/SEI 41 Tier 1 screening, 16 were found to be

potentially “Non-Compliant” and two were “Unknown.” The noncompliant elements are presented within the structural assessment memorandum included as Appendix G to this

report.

The following recommended upgrades have been implemented by the District since the

pump station inspections occurred:

Install missing nuts and washers on the removable roof per the original design

(this was completed by District staff in March 2016)

Install anchorage for pump #2 (this was completed by District staff in March

2016)

As indicated in the structural assessment memorandum, it is recommended to perform a Tier 3 Systematic Evaluation prior to future pump station upgrades.

The Cove Storm Water Pump Station is in a seismically active area of Northern

California. Based on a review of the 2010 Fault Activity Map of California (State of California Department of Conservation), the known significant active faults and seismic

sources within 50 miles of the site include the Hayward, San Andreas, San Gregorio, Greenville, Point Reyes, and Mission Faults. Specific faults that occur within 10 miles of

the Cove Storm Water Pump Station are the San Andreas Fault at 7.5 miles, San Gregorio Fault at 8.75 miles, and the Hayward Fault at 10 miles.

Based on the Tier 1 Screening of ASCE/SEI 41 and on applying FEMA P-154’s Rapid

Screening Method, the final seismic hazard score “S” for the pump house is 1.1, which implies that there is a 1 in 12 chance that the pump house would collapse if the

maximum considered earthquake were to occur. This is considered acceptable for the age and use of the building; however, building upgrades should be considered during

the next pump station upgrade. The maximum considered earthquake corresponds to a

ground motion with a 2% probability of exceedance in 50 years, equating to a recurrence interval of 2,475 years.

The potential for the Cove Storm Water Pump Station to be founded on liquefiable soils is considered high according to the USGS Liquefaction Susceptibility Map of the San

Francisco Bay Area. Consequently, seismic settlement as a result of liquefied soil is credible. Furthermore, the Pump Station is also within the tsunami inundation zone as

defined by the Tsunami Inundation Map for Emergency Planning, San Rafael/San

Quentin Quadrangle.

Automatic

Trash Rack Screen

Feasibility

The Cove Pump Station has a trash rack that prevents large debris from entering the

wetwell. The trash rack is located in the northwest corner of the wetwell, just downstream of the two influent storm drain pipes. The trash rack was significantly

altered in 1983. The trash rack requires regular cleaning during the wet season. The

trash rack is cleaned manually, typically using rakes to pull debris up the 9-foot long sloped trash rack to the surface where it can be disposed of. More significant cleaning






requires maintenance workers to descend into the wetwell to dislodge debris that can’t be reached from the ground level. If the trash rack is not manually maintained on a

regular basis during the wet season, the flows entering the pump station would be

restricted.

Existing Trash

Rack

The existing trash rack extends from the invert of the wetwell to the top slab and spans

the 5-foot wide inlet channel. The trash rack consists of 3/8” steel bars spaced at 2” on center. The trash rack has severe corrosion near the invert of the wetwell and minor

corrosion throughout. A few trash rack bars have completely corroded away, leaving a

small hole in the trash rack. The severely corroded bars should be replaced by welding new bars of equivalent size in place. Cathodic protection consisting of galvanic anodes

should also be installed on the trash rack to control additional corrosion. Full replacement of the trash rack is recommended during the next major pump station

upgrade.

The existing manual trash rack functions as intended; however, it requires extensive

manual maintenance during the wet season. Benefits of the existing trash rack include:

relatively inexpensive, less complicated operations and maintenance, and it is not susceptible to mechanical breakdown. Some of the disadvantages include: regular

cleaning during the wet season and it can be difficult without entering the wetwell which is considered a confined space, which District/County employees are generally not

permitted to enter

The head loss through the trash rack with various percent blockages are shown Table 4-1 below. The head loss was calculated assuming the wetwell water level is equal to the

current pump #3 on level, which is approximately 4 inches below the invert of the influent 36” pipe. The head loss does not significantly impact the upstream water

surface elevation until the trash rack becomes approximately 50% blocked.

Table 4-1: Trash Rack Head Loss Summary Table

Flow Rate Resulting Head Loss With 25%

Blockage (feet)

Resulting

Head Loss With 50%

Blockage

(feet)

Resulting

Head Loss With 75%

Blockage

(feet)

10-Year Storm 0.3 0.8 4.0

100-Year Storm 0.4 1.3 6.2

The current pump on/off levels are set below the invert elevations of the influent pipes; therefore, the trash rack does not currently affect pump cycling. As discussed in the

following sections it is recommended to adjust the pump on/off levels to achieve better pump cycle times. If the levels are adjusted it will become more critical to maintain a

clean trash rack to achieve favorable pump cycling. With enough blockage, an individual

pump-off setting can be reached well before the requisite run time is achieved and the pump could start and stop in rapid succession. The trash rack will need to be cleaned on

a regular basis depending upon the amount of debris in the system. To reduce the cleaning requirements and improve worker safety it may be necessary to install a trash

rack with an automatic rake system as discussed below.

Trash Rack

with

Automatic

Rake

To reduce the maintenance requirements and improve the ability to keep a clean trash rack, the District may want to consider installing a trash rack system with an automatic

rake or screen system. There are several products available to the District as described below:






Automatic trash rake/screen systems require electrical power, programmable logic controller (PLC), transducer(s), and a specifically positioned trash bin. Additionally it is

recommended to connect the unit to a SCADA system and to provide a backup power

system, such as a permanent backup generator at the pump station. The mechanical screen can use the existing pump station transducer to control the operation. It is

recommended that the mechanical screen turn on at the lowest pump level on setting (currently pump #1) and turn off at the pump off setting. It is also recommended to

connect the mechanical screens operation to a backup transducer or float switches in

case of a transducer failure.

The trash rack size, location, and layout should be coordinated with future pump station

upgrades. If the wetwell is reconfigured in the future; as recommended in the following sections, the size and location of the trash rack will be different than what would be

required to accommodate the existing pump station layout.

It is typically recommended to install the mechanical rake/screens at an inclined angle.

Depending on the manufacturer and product used, the recommended angle is typically

between 10 to 30 degrees and has a dumpster directly behind the unit or has a chute system to deliver debris to a close-by dumpster. If the District plans to install a

mechanical rake/screen to accommodate the existing wetwell layout, the site layout restricts the potential screen angle to approximately 20 degrees maximum (depending

on the product used). Marin Sanitary Services’ standard 2 cubic yard dumpster is too

large to be placed directly behind the trash rack so a chute system would be necessary to deliver the trash to the dumpster.

The existing wetwell opening would need to be slightly modified to accommodate the new mechanical rake/screen system, and it is recommended to add a fence around the

site as the trash rack will have moving parts and debris. A potential site layout for the addition of a mechanical trash rack and fence with the current wetwell configuration is

shown in Figure 4-4. This layout may interfere with the current trash collection

operations for the adjacent shopping center waste bins and dumpsters. Additional concrete pads may also be necessary depending on the desired layout and operations.






Figure 4-4: Mechanical Trash Rack Site Layout with Existing Wetwell Configuration






If the District does not have room to install a chute and trash bin system on the site (within the current easements), the top slab of the wetwell could be modified to provide

additional room for the trash receptacle, or the District could consider installing a steeper

mechanical screen to minimize the footprint. With a new trash bin on site, the higher profile of the mechanical screens, and any chutes, the area should be enclosed with a

security fence. Mechanical screens have moving parts that will also require routine maintenance and can fail to operate.

The trash rack alternatives are summarized in Table 4-2 below.

Table 4-2: Trash Rack Alternatives

Description Advantages Disadvantages

Recommended

Site Modifications

Installation

Cost Estimate

Existing Trash Rack

Inexpensive, simple to maintain,

won’t break down

Regular maintenance is required during the wet season and physically

difficult to perform

Consider purchasing

alternative rakes to clear debris

$0

Mechanical Screen

Self-Cleaning with little

maintenance needed

Modifications to the site needed,

specialized trained personnel needed

when maintenance is

required, aesthetic issues, potential

odor issues

Electrical conduits,

SCADA, Trash Receptacle and chute, back-up power, fence

$440,000 including

installation and soft

costs

There are several different mechanical screens and options that can be utilized. It is recommended that the mechanical screen be stainless steel and have a maximum clear

space between bars of less than 1.5 inches. The various types of mechanical screen/rake products are summarized in Table 4-3. Based on our review, we recommend installing a

mechanical screen system (option 3) to adequately remove the leaves and debris that

enter the wetwell.

Table 4-3: Mechanical Screen/Rake Product Options

Option Description Products Advantages Disadvantages

1 Self-Cleaning Trash Rack

Duperon SCT, Aqua Systems 2000 In

Line Trash Cleaner

Self-Cleaning, more reliable, handles long

periods of being shut down

Higher friction losses

2 Mechanical Bar Screens

Duperon Flexrake FRHD, Huber Pro Trash Max, Headworks Mahr

Bar Screen

Easy to install and operate

3 Mechanical

Screens Duperon Flexrake FP,

Huber Rakemax Captures more difficult debris

Difficult to install, higher profile, more expensive






As discussed within this report, the District may want to consider revising the layout of the pump station during the next pump station rehabilitation. The revised layout may affect

the size and location of the trash rack; therefore, the District should consider future

rehabilitations prior to proceeding with the installation of a mechanical trash screen/rake.

Hydraulic

Performance

Drawdown tests of the pumps (Pump #1-3) were performed by Schaaf & Wheeler on

November 9, 2015. All three pumps were run twice for approximately one minute. Pump #4 (a sump pump) had been decommissioned and was not tested. The pump discharge

velocities were measured at the outlets using a piezometer. The water levels were

measured in the wetwell before and after each drawdown test to determine the corresponding static head for each pump test. Results from this test are shown in Table

4-4.

Table 4-4: Pump Drawdown Test Results

Pump

# Test #

Average Static Lift

(ft)

Calculated Flow

(gpm)

1 Test #1 7.5’ 2,166

1 Test #2 9.5 1,875

2 Test #1 7.8’ 6,180

2 Test #2 9.3’ 5,744

3 Test #1 7.6’ 9,635

3 Test #2 8.2’ 9,141

The existing pump curves were provided by District staff and are included in Appendix H. A system curve was developed for each pump which takes into account friction and minor

losses. The pump curves and tested flow rates were plotted on the same table as shown in Figure 4-5.

Figure 4-5: Cove Pump Station System Curve






The tested pump capacity of Pump #1 is approximately 20% less than the original pump curve which is typical for a pump that has been in use for a long period of time. The

tested pump flows of Pump #2 and Pump #3 are larger than the pump curve flow rate at

similar head conditions. This could be due to impeller or motor modifications over time. For analysis purposes the pump curve for Pump #1 was derated to match the measured

flow rates as indicated in Figure 4-5 and the original pump curves for Pumps #2 and #3 were used. The estimated total pump station capacity with all three pumps operating is

indicated in Table 4-5. These flow rates are based on the design head condition where the

wetwell water level is approximately 7.5’ above the wetwell invert.

Table 4-5: Pump Capacity at Design Head

Pump # Capacity

(gpm)

1 2,000

2 5,200

3 8,800

TOTAL 16,000

The pump station inflow rates for various design storm events with the existing storm

drain system, 10-year storm drain system upgrades, and 25-year storm drain system

upgrades are shown in Table 4-6. The pump station has sufficient capacity to convey the modeled 100-year inflow rates with the existing storm drain system and all 3 pumps

running. If the upstream storm drain system is upgraded, the inflow rates to the pump station increase.

Table 4-6: Pump Station Inflow Rates

Scenario

Pump Station Inflow (gpm)

10-Year Storm

25-Year Storm

50-Year Storm

100-Year Storm

Existing Storm Drain System

10,400 12,600 13,900 14,900

10-Year Storm Drain System Upgrades,

Existing Pumps 14,300 16,300 17,100 18,100


Larger Pumps 14,400 17,000 18,300 19,300


Existing Pumps

Not Modeled

17,300 18,700 19,600


Larger Pumps

Not Modeled

17,900 19,700 21,100

Wetwell and

Pump Bay

Hydraulics

The existing Cove Pump Station wetwell and pump bay hydraulics were analyzed and compared to Hydraulic Institute (HI) standards. Ideally, a wetwell is designed to condition

flows to achieve favorable velocity, straight and uniform flow into each pump, low levels of

turbulence, sufficient depth at the pumps (submergence), and minimal risk of harmful vortices and cavitation. Non-uniform velocity profiles into a pump can result in uneven and

fluctuating load on the impeller and bearings, resulting in noise, vibration, and shaft failure in extreme cases. Surface and submerged vortices due to low submergence and






pre-swirl due to insufficient flow straightening at the intake can cause cavitation, which leads to inefficient operation and damage to the pump.

The HI publishes Pump Intake Design Standards (ANSI HI 9.8), intended to provide

guidelines for proper design of pump stations and the modification of existing designs. The standard has been developed to provide straight, uniform approach flows and

minimize the risk of adverse flow conditions that could cause damage to the pumps. Pump station approach and wetwell dimensions promulgated by the HI and axial flow pump

manufacturers are shown in Table 4-7.

Table 4-7: Pump Bay and Wetwell Dimensions

Parameter / Dimension

Existing

Pump #1

Pump #1 HI

Existing

Pump #2

Pump #2 HI

Existing

Pump #3

Pump

#3 HI

Maximum Discharge (gpm)

2,500 - 6,000 - 9,600 -

Suction Bell Diameter (feet)

1.00 - 1.25 - 1.50 -

Suction Bell to Wetwell Floor

(feet) UNK 0.50* UNK 0.60* UNK 0.75*

Minimum Submergence

(feet) 4.5 4.0 4.5 5.5** 4 4**

Pump Bay Width (feet)

10.0 2.0* 10.0 2.5* 10.0 3*

Pump Bay Length (feet)

15 > 6* 16 > 7* 20 > 9*

Pump Bay Velocity (ft/s)

0.2 < 1.5* 0.4 < 1.5* 0.8 < 1.5*

Max. Cross Flow Velocity (ft/s)

3.8 < 0.1* 2.3 < 0.2* - < 0.4*

Maximum Floor Approach Angle

(°) 5 10 5 10 5 10

Maximum Wall Approach Angle

(°) 0 10 0 10 0 10

*Suggested by Hydraulic Institute Pump Intake Design standard **Suggested by pump manufacturer Red Bold values Indicate that Hydraulic Institute Design Standards at not met

The pump bay and wetwell dimensions do not conform to current HI standards;

specifically the following issues were noted as indicated in Table 4-6.

1. The minimum submergence for Pump #2 is not currently being met. Therefore

the pump off level for Pump #2 should be adjusted to be at least 5.5 feet above the suction bell.

2. The pump bays are not narrow enough to channel flow uniformly towards the pumps. Reconfiguring the pump station wetwell should be considered during the

next pump station rehabilitation.

3. The HI recommends the maximum cross flow velocity be smaller than 50% of the pump bay velocity. The maximum cross flow velocity is significantly larger than






the recommended values. Reconfiguring the pump station wetwell should be considered during the next pump station rehabilitation.

The Cove Pump Station wetwell configuration was designed prior to the development of

an intake design standard. The wetwell and pump bays have been modified from the original design to accommodate the existing trash rack, to connect the existing pump

bays, and the two small sump pumps have been decommissioned. The pump station wetwell consists of an intake channel and trash rack that approaches pump bay #1.

Pump #1 is designed to be the primary operating pump until the wetwell levels increase,

calling for pump #2, then pump #3.

There is an undocumented connection between pump bays 1 and 2. As the water level

increases and decreases below the weir connection elevation the water level remains nearly the same in all three pump bays. The wetwells were drained and inspected by a

CCTV contractor hired by the District and they were not able to find a clear connection between the bays. The water level at the time of inspection was a couple of feet above

the sump invert; therefore, there is likely a small knockout near the invert of the sump

between pump bays 1 and 2. Pump bays 2 and 3 are connected with a 12”x12” knockout in the pump sumps and through a 4-foot wide opening in the joining wall. The existing

wetwell layout is shown in Figure 4-6.

The 12”x12” connection between the pump bays is located at the invert of the sump and

is close to the pump intake. This connection may cause unwanted vortices and potential

cavitation; however, it is necessary to convey flows to pump bays #2 and #3 with the current pump station layout and operation. Removal of the interconnectivity within the

wetwell sump should be considered when the wetwell is modified in the future.

Figure 4-6: Existing Wetwell and Pump Bay Layout






Pump Cycling,

Set Levels and

Control Logic

Pump cycling affects the service life of the pumps. Less cycling leads to less wear on the pumps and longer lifetimes. Most motor manufacturers give a minimum cycling time,

which can be related to the maximum number of starts per hour per pump. The

manufacturers of the existing pumps at the Cove Pump Station were not able to provide minimum cycle times. Generally it is desirable to maintain 6 starts per hour per pump or

less for electric motor driven pumps. The pump station is not currently designed to alternate lead and lag status of the three pumps. Due to the varied pump sizes it is not

recommended to revise the pump control logic to rotate lead-lag status. Additionally, the

lack of sufficient interconnectivity within the pump operating elevations between pump bays #1 and #2 prevents the possibility of modifying the pump control logic at this time.

The pump set levels for Pump #2 and #3 are lower than the weir elevation between pump bays #1 and #2 as shown in Figure 4-7. During lower wetwell levels pumps #2 and #3

are only fed through the unknown lower connection between pump bays #1 and #2. This connection is believed to be relatively small; therefore, the total operating wetwell volume

for the pumps is less than the entire wetwell. Additionally, pump on and off levels are

below the influent storm drain lines; therefore, there is limited operating volume for the pumps regardless of the wetwell interconnectivity.

Figure 4-7: Existing Pump Set Levels and Interconnectivity between Pump Bays #1 and #2

The existing pump station on and off levels and the recommended modified levels are

shown in Table 4-8. The recommended modified on levels are intended to decrease the number of starts per hour as discussed below. Off level for Pump #2 should be adjusted

to be at least 5.5 feet above the suction bell as previously discussed. The recommended






on levels were modeled with various design storms to determine the potential impacts to the resulting upstream water surface elevations. The modified on levels do not have a

significant impact on the hydraulics of the upstream system.

Table 4-8: Existing and Recommended Pump On/Off Levels

Pump #

Existing Set Levels Recommended Revised Set Levels

On Level, Distance

from

Wetwell Invert

(feet)

Off Level,

Distance from

Wetwell

Invert (feet)

On Level,

Distance from

Wetwell

Invert (feet)

Off Level, Distance from Wetwell

Invert (feet)

Pump #1 5.83 5.00 same, 5.83 same, 5.00

Pump #2 6.00 5.17 9.18 6.17

Pump #3 6.25 4.67 9.68 same, 4.67

The maximum pump cycling for existing and modified conditions are included in Table 4-9.

Maximum pump cycling occurs when the inflow is equal to one-half of the pump capacity.

Three conditions are presented; existing conditions with minimal wetwell interconnectivity and existing set levels, modified wetwell interconnectivity, and modified wetwell

interconnectivity with modified pump on levels as recommended in Table 4-8.

Table 4-9: Pump Cycling

Pump # Condition

Maximum

Starts Per Hour,

Existing Conditions

Maximum

Starts Per Hour, Entire

Wetwell Interconnected

Maximum Starts

Per Hour, Wetwell Interconnected,

Modified On/Off Levels

Pump #1 Pump #1 Cycling

22 7 7

Pump #2 Pump #1 On,

Pump #2 Cycling

26 17 5

Pump #3 Pump #1 &

#2 On, Pump #3 Cycling

22 15 5

During the next major pump station upgrade it is recommended to modify the pump bays

to be completely interconnected within the pump operating range, replace the pumps with three similar sized pumps, rotate the lead-lag status of the pumps, and to modify the

pump on and off levels. Additionally, modifying the pump on/off levels as discussed herein

should be considered in the short term.

Electric Controls

and Alarms

The Cove Pump Station is controlled locally by a Rockwell Automation CompactLogix 1769-

L32E programmable logic controller (PLC) that was installed in the motor control center’s (MCC) control section as part of the 2006 upgrade project. The PLC includes Series 1769

Compact I/O modules that consist of one four-channel analog input, one 16-point 24VDC digital input, and two 16-point relay output modules. A Rockwell PanelView Plus 600

operator interface terminal (OIT) provides the user interface to the PLC system and

communicates with the PLC via a Hirschman model RS2-5TX 5-port Ethernet switch. The OIT provides the user interface that allows operators to monitor status and to adjust the

PLC based alarm and pump control set points.






A Panalarm Series 90 annunciator is mounted in the door of the MCC’s control section and provides local indication and alarming. Status indication is displayed for Pump 1, Pump 2,

Pump 3 (the engine driven pump, which is controlled separately), and Pump 4 (which is

not currently being used). Annunciator alarms include Pump 1 Failure, Pump 2 Failure, Pump 3 Failure, Pump 4 Failure, Utility Power Failure, Wetwell High Level, Wetwell Level

Detector Failure, and Station Intrusion.

The station wetwell level is monitored by a Siemens HydroRanger 200 ultrasonic level

transmitter that is also mounted in the door of the MCC’s control section. The level

transmitter is connected to an analog input channel of the PLC and provides a 4-20mA signal proportional to the level in the wetwell that is used as the primary control signal for

the two electric pumps.

A telephone line based automatic alarm dialer is installed in the control panel. The alarm

dialer provides the only external monitoring of the pump station. There are three alarm conditions that produce a call out from the pump station; Utility Power Failure, Station

Intrusion, and High Wetwell Alarm. The alarm dialer is currently managed by a 3rd party

security company (Redwood Security). Additionally, the alarm conditions are received and relayed by Redwood Security.

The control system includes an APC Back-UPS ES 650 VA uninterruptible power supply that maintains power to the control panel components in the event of a short term (~20

minute) power outage.

Instrumentation

and Control

Condition

Assessment

The existing Rockwell 1769-L32E PLC is in good condition but it is no longer a marketed product; therefore, it will become increasingly difficult to support and maintain in the

coming years. This product line is still currently fully supported by Rockwell Automation but the CompactLogix 5370 is now the latest hardware version available. The estimated time to

hardware obsolescence for the installed controller is four to five years. The PLC programming software, RSLogix5000, that is used to program the 1769-L32E PLC is now at

least five full versions old, and is no longer compatible with the latest Microsoft operating

systems.

Since the County has an existing Flygt Aquaview SCADA system, and at least one other

pump station that is controlled by a Flygt MultiSmart pump station controller, we recommend replacement of the existing PLC and OIT with a MultiSmart controller. This

new controller can be installed either in the existing MCC control panel, or incorporated

into a new control panel if the MCC is to be replaced. The MultiSmart controller includes standard pump station control programs so no additional custom programming is required.

The MultiSmart controller functions can be seamlessly integrated into the District’s existing Aquaview SCADA system (which is currently being piloted at the Strawberry Pump Station).

There is currently no backup control for the electric pumps. Failure of the ultrasonic level

transmitter will result in loss of control for the electric pumps from the PLC system. The engine driven pump is controlled from a separate float switch system. In the event of a

power failure, ultrasonic transmitter failure, or a PLC failure, the engine driven pump is called to run based on the floats in the north end of the wetwell.

We recommend adding a hardwired relay based float backup control system. The hardwired float backup provides an additional level of control redundancy in the event of

either the wetwell level transmitter, or the pump station controller failing. If the wetwell

level transmitter fails, new high and low float signals can be added to the automatic controls to start and stop the pumps. If the primary pump station controller fails, the float

switches activate a hardwired circuit that turns the pumps on and off.






SCADA Capability

The existing PLC system is capable of integration into most SCADA systems. The processor module includes both an Ethernet port and an EIA-232 serial communications port. The

Ethernet port supports Ethernet/IP protocol and the serial port supports DF1 protocol.

Either of these protocols are available for both third party SCADA packages (such as Wonderware and iFIX), or as an optional protocol on the District’s existing Aquaview

SCADA software.

While the existing controller can be integrated into the Aquaview software, many of the

beneficial features of the software that are inherently available when used with the Flygt

controller products would not be available when used with a third party controller such as the Rockwell PLC. Integration of the existing PLC into the existing Aquaview SCADA

software would require significant custom programming of the Aquaview package, and potentially require additional communications driver licenses.

Communications

Options

There are four primary media that are typically used for communicating control data between remote facilities and a central SCADA system:

Radios

Leased Telephone Lines

Wireless (Cellular) Modems

Fiber Optic Cables

Table 4-10 provides a brief summary of pros and cons for each of these communication

mediums, as well as a subjective suitability for the Cove Pump Station.

Table 4-10: Communication Options

Medium Pros and Cons Suitability

Radio

Medium installation cost

Significant design effort required (path survey, licenses, etc.)

Low maintenance cost

High reliability

High speed/bandwidth available (higher cost)

Marin County typically has very poor radio paths and require one or more repeater locations that can be seen from all remote sites

Fair/Poor

Leased Line

Low installation cost

High maintenance cost (monthly bill)

Low reliability

Low speed/bandwidth

Dependent on phone company and tends to go down when most needed

Poor

Wireless (Cellular) Modem

Low installation cost

Low maintenance cost (monthly bill)

Medium reliability

Medium speed/bandwidth

Dependent on wireless service provider signal strength in the area

Good

Fiber Optic

Extremely high installation cost

Low maintenance cost

High reliability

Very high speed/bandwidth (including video)

Poor






We recommend that the controls for the pump station be integrated into the District’s existing Aquaview SCADA software package.

If the existing Rockwell PLC is replaced with a new Flygt MultiSmart pump station

controller, as recommended above, only a new wireless modem would be required to integrate the Cove Pump Station controls into the District’s SCADA software. The labor

required to add this site to the Aquaview software would be relatively trivial and there are significant benefits in safety and reliability with a continuously monitored site.

Even if the existing Rockwell PLC remains in place, the cost of integration of the pump

station controls into the existing Aquaview software would be well worth the benefits achieved.

Existing Power Systems

The existing electrical service is a 240-VAC, 3-phase, 4-wire, 200-Amp Pacific Gas and Electric Company (PG&E) service that is fed from a set of pole mounted transformers

(three 15 kVA transformers connected in a 3 phase bank) adjacent to the north end of the existing building. The power system consists of a wall mounted 200-Amp meter main

mounted to the north end of the building, and a three section Eaton Freedom 2100 Series

motor control center. The MCC consists of two 20”-wide bussed electrical sections, and one 28”-wide control panel section. In addition to the pump starters, the MCC includes a single-

phase 240/120VAC lighting panel, a surge protective device (SPD), and an electronic power meter.

The pump station currently includes two full voltage electric pumps, Pump 1 and Pump 2,

and one natural gas engine driven pump, Pump 3. Pump 1 is a 15-HP pump and Pump 2 is a 20-HP pump. There are provisions for a small, 1-1/2 HP Pump 4, but the fourth pump is

not currently being used and the starter bucket is locked and tagged out.

Each of the electric pump’s starters include an MCC mounted Hand-Off-Auto selector

switch. In Hand, the pump turns on immediately. In Auto, the pump is controlled by the PLC based on the level in the wetwell.

Electrical

Equipment Condition

Assessment

The existing MCC is in good condition. There are no indications of enclosure corrosion,

excessive heating, excessive dust, or failing components. All of the installed MCC components are still commercially available and fully supported by Eaton.

The MCC is not installed per NEC working clearance requirements. NEC 110.26 requires a minimum of 42” of working space between the front of the MCC and any grounded parts.

Pump 1 is only 31” away from the front of the MCC. The Pump 4 mounting location is only

33” away from the front of the MCC. Since Pump 4 is non-operational, it is recommended to remove the pump and piping to create more working space.

There is no potential equipment arrangement within the existing building that can meet the working space requirements of the NEC. In order to meet working space requirements, the

MCC would have to be replaced with a new NEMA 3R MCC located outside of the building

and all existing conduits and conductors would need to be re-routed to the new MCC location. If the existing building is to remain in the current configuration, we would

recommend this course of action in the short term. If the existing pump station building will be replaced within the next few years, we recommend that the building size be

increased to include an electrical equipment room, and the entire electrical system be upgraded at that time. An indoor MCC would provide higher reliability, a lower equipment

cost, and a pump station that is easier to operate and maintain. Regardless of how or

when the MCC is replaced, the control system components recommended above can easily be relocated in a new control section of a replacement MCC.

There are currently no arc flash hazard stickers on the electrical equipment, as required by the NFPA 70 (National Electrical Code - NEC) 110.16 and per NFPA 70E (Electrical Safety in






the Workplace). The NEC requires arc flash labels on any equipment that are “likely to require examination, adjustment, servicing, or maintenance while energized”. NFPA 70E

calls for suitable Personal Protection Equipment (PPE) to be used when personnel are

exposed to live parts.

An arc flash hazard analysis, using SKM software, has been performed based on the

observed installed conditions and short circuit and protection information that was provided by PG&E. The results of the arc flash analysis are summarized in Table 4-11.

Table 4-11: Arc Flash Analysis Summary

Location Incident Energy

Arc Flash Boundary

PPE Level

Meter/Main CB 83.0 J/cm2 100” Level 4

MCC 74.0 J/cm2 93” Level 4

Pump 1 0.36 J/cm2 < 6” Level 0



Based on the current installation and available short circuit current, both the meter/main

and the MCC require Level 4 PPE within the Arc Flash Boundary. Level 4 PPE includes arc-rated shirt and pants, arc-rated coveralls, and an arc rated flash suit. Both the meter/main

circuit breaker and the MCC main circuit breaker are non-adjustable molded case type. The available short circuit current from PG&E is relatively low; therefore, the potential trip time

for these two breakers is up to 2 seconds. The long trip delay results in higher incident

energy and the resulting arc flash hazard.

Arc flash hazard labels should be affixed to the front of the motor control center to alert

County operations and maintenance staff of the potential hazard. While the appropriate PPE is required when personnel are exposed to live parts, NFPA 70E does not require this

protection level for “normal” operation of the equipment (e.g., switching a pump on or off). Prior to opening any of the energized MCC cubicles, electricians must have the

recommended Level 4 PPE. We recommend that work inside of the MCC be performed only

with the full MCC de-energized at the pump station’s meter main.

The arc flash hazard at the MCC can be mitigated by replacing the existing meter/main

circuit breaker with a molded case breaker that includes an electronic trip unit. By installing a breaker with an electronic trip unit, the breaker settings can be adjusted to reduce the

arc flash energy to less than 5 J/cm2 and the required PPE to Level 0 at the MCC. It should

be noted that under NFPA 70E, staff must also be trained regarding the nature of the arc flash hazard, use of appropriate PPE, and other safety features. This safety training is

considered a fundamental part of complying with requirements of NFPA 70E.

As noted NFPA 70E is the recognized standard addressing workplace electrical safety. The

standard has been adopted by the Occupational Safety and Health Administration (OSHA)

as an extension of the NEC. OSHA has also ruled that enforcement of NFPA 70E falls under OSHA’s General Duty Clause. Therefore requirements for equipment labeling and ensuring

proper training and application of PPE for both employees and third party contractors are defined in NFPA and interpreted by OSHA as being the responsibility of the Owner.

We recommend replacement of the meter/main breaker to reduce the arc flash hazard within the building at the MCC. Because electronic trip units are only available on larger

frame breakers (typically 600A frame and larger), the complete meter box assembly would

need to be replaced with a new meter/main.






Backup Power The pump station is not currently equipped with backup power. In the event of electrical power failure, the station is dependent on the natural gas driven pump #3. Upgrading the

station to have a diesel standby generator and an automatic transfer switch (ATS) would

increase the pumping capacity during power outage.

Based on the current motor load and required starting currents for full voltage starters, a

200kW/200kVA generator is required to power the existing electric motors. Due to the proximity to the shopping center, a Level 2 sound attenuating enclosure is recommended.

Bay Area Air Quality Management District (BAAQMD) requires that standby generators

meet Tier 3 emissions requirements. The physical space required for the generator will depend on the size of the fuel tank selected. Table 4-12 shows the physical size required

for the two available fuel tank sizes. Note that the run times shown are based on the generator running at full capacity, not at the full load of the pump station. Actual run time

based on normal pump operation may be significantly longer, depending on inflow rates.

Table 4-12: Generator Dimensions

Fuel Tank Size Run Time at Full Load Dimensions

150 Gallons 9.7 Hours 134”L x 63”W x 86”H

400 Gallons 26.0 Hours 134”L x 63”W x 101”H

An ATS in a free standing NEMA 3R enclosure can be installed on the outside west wall at the northwest end of the building as shown in Figure 4-8. The existing conduit and

conductors between the meter main and the MCC can be intercepted above the new ATS location and routed to the ATS.

Figure 4-8: Possible ATS Location

Possible ATS Location

Existing MCC Conduit

Existing Meter/Main




Chapter 5: Potential Projects


Chapter 5. Potential Projects

5.1 Overview

This chapter discusses the results of the hydraulic models along with upgrades to improve

system capacity. Upgrades to the pump station based on the findings in Chapter 4, Pump Station and Drainage System Assessment, are also discussed. Upgrades to the privately

owned drainage system are not covered under this study. The identified projects provide

an overall guideline for the District and partners to use in preparing for future upgrades to the Cove Pump Station and the public drainage system.

5.2 Results The performance analysis of Cove Pump Station and its drainage system forms the essential core of this study and the results from the MU models are the basis for the drainage

network projects. Several models were run to determine the existing capacity of the

drainage system, as well as determine system upgrades necessary to meet the requirements of either a 10-year or 25-year storm. All pipes were assumed to be free of

debris and sediment.

Existing The existing drainage network and pump station configuration for the models are based on

data specified in Chapter 2 and methodologies discussed in Chapter 3. Four storm events

were analyzed in MU with the existing system; 10-year, 25-year, 50-year, and 100-year. The focus of this study is the how existing drainage system and pump station handle 10-

year and 25-year storm events. The 100-year storm is modeled to compare interior drainage system capacity to standards for facilities behind FEMA accredited levees.

10-Year Storm

Event

Figure 5-1 shows the node flooding results form a 10-year storm event on the existing drainage system and Cove Pump Station. The colored nodes denote location where the

peak hydraulic grade is above the existing ground level. Portions of the system upstream of

Claire Way do not have 10-year capacity and may need upsizing.

25-Year Storm

Event

Figure 5-2 shows the node flooding results from a 25-year storm event on the existing

drainage system and Cove Pump Station. The colored nodes denote location where the peak hydraulic grade is above the existing ground level. Portions of the system upstream of

Claire Way do not have 25-year capacity.

100-Year

Storm Event

The MU 2D Overland model was used to simulate the floodplain generated by a 100-year

storm event on the existing drainage system and Cove Pump Station. Figure 5-3 shows these results. The colored areas indicate the maximum potential depth of ponding on the

ground surface. The majority of the ponding occurs within the street right-of-way; however, there does appear to be some deeper ponding near Karen Way and Claire Way.






Figure 5-1: 10-Year Storm Event with Existing Drainage System






Figure 5-2: 25-Year Storm Event with Existing Drainage System






Figure 5-3: 100-Year Storm Event Floodplain






5.3 Potential Projects

There are several potential projects identified by this study that would increase system capacity, upgrade operations, add flood protection and plan for climate change. The

following sections discuss the various projects.

This study and proposed projects are merely the starting point. It is anticipated that District staff and/or their consultants will evaluate the proposed upgrades once additional

information is gathered as part of the preliminary design process (detailed topography, utility conflicts, easements, etc.) to determine if there are more affordable or effective

upgrades.

5.3.1 Short Term

The short term drainage system upgrades address corrosion in the corrugated metal pipes (CMP) and reduce the risk of pipe failure. The short term pump station upgrades address

observed conditions and include minor upgrades to the pump station operation.

Pipe Conditions As noted in Chapter 4, several pipes located in the Cove Pump Station drainage system are in poor condition and are at risk of failing. Schaaf & Wheeler recommends the replacement

of the three (3) CMPs that directly drain into the wetwell be replaced in the short term. Two

(2) of the CMPs are owned by the District and one (1) of the CMPs is in a Caltrans easement or privately owned. The three CMPs are shown in Figure 5-4 below.

Figure 5-4: Corrugated Metal Pipes Replacements






The CMP that poses the most risk of failing, and could lead to a complete system failure, is PIPE_390. This is a 36” CMP that flows directly into the pump station wetwell. This pipe has

been in place since 1976 when the pump station was built. The invert of the pipe has

completely corroded and missing which poses a significant risk of collapse and therefore failure. This pipe is critical to the entire drainage system flowing into Cove Pump Station

because it carries flow from the entire drainage system north of the Cove Pump Station. PIPE_106 and PIPE_389 are both 18” CMPs that are recommended to be replaced as 18”

RCPs. PIPE_390 is recommended to be upsized to a 48” RCP or equivalent.

Pump Station Recommended upgrades for the pump station were developed for short term implementation. The recommended short term upgrades that have been discussed

throughout this report are summarized in Table 5-1.

Table 5-1: Short Term Upgrades

Recommended Upgrade Comments

Replace PLC Replace controller. Flygt MultiSmart controller is recommended as it will easily integrate with the District’s Aquaview SCADA system.

Backup Controls Add hardwired relay based float backup control system relays to operate the pumps in the event of a primary controller failure

Integrate SCADA Integrate with District’s existing Aquaview SCADA system

Install Arc Flash Labels Per NEC and NFPA codes

Replace Meter/Main Breaker Replace the meter/main breaker to reduce the arc flash hazard within the building at the MCC

Replace MCC Located Outside of Building, unless building expansion or long term upgrades are planned within the next few years

Replace MCC with a new NEMA 3R MCC located outside of the building to meet working space requirements. Re-route existing conduits and conductors to new MCC.

Remove Pump 4 above ground Motor and Piping

To create more working space within the building

Replace Corroded Bars on Trash Rack

Weld new bars on trash rack to replace corroded and missing bars.

Modify Wetwell Modify wall between Pump bay #1 and #2 to provide interconnectivity within the entire operating range of the pumps

Modify Pump Set Levels Modify set levels to achieve favorable pump cycle times and to accommodate minimum submergence requirements

5.3.2 Long Term

The long term upgrades address issues to replacing aging components and to increase the capacity and redundancy of the Cove Pump Station and its drainage system going into the

future.

Pipe Size The existing conditions 10-year and 25-year models indicate that flows are attenuated in the streets because not all the pipes have capacity for these events. The hydraulic models

were utilized to determine what size pipes would reduce flooding from occurring in the during a 10-year storm or 25-year storm. For the 10-year project summary, four project

areas have been identified for upsizing the current storm drains. Table 5-2 summarizes the recommend 10-year projects for Cove watershed.






Table 5-2: 10-Year Project Summary Table

Potential Project

Pipe ID Length (ft) Recommended Diameter (in)

Claire 1

impPIPE_149 80 15

impPIPE_150 30 15

impPIPE_151 150 15

Claire 2

impPIPE_333 30 24

impPIPE_145 50 24

Harriet impPIPE_28 225 12

Field 1

impPIPE_138 120 24

impPIPE_139 60 24

impPIPE_191 340 15

Field 2

impPIPE_140 160 18

impPIPE_141 40 12

Figure 5-summarizes pipe upgrades to provide capacity for a 10-year storm.

For the 25-year project summary, four project areas have been identified for upsizing the current storm drains. Table 5-3 summarizes the recommended* 25-year projects for Cove

watershed.

Table 5-3: 25-Year Project Summary Table

Potential

Project Pipe ID Length (ft)

Recommended

Diameter (in)

Claire 1

impPIPE_149 80 18

impPIPE_150 30 18

impPIPE_151 150 15

Claire 2

impPIPE_333 30 27

impPIPE_145 50 27

impPIPE_141 70 12

impPIPE_146 115 15

Harriet impPIPE_28 225 12

Field 1

impPIPE_138 120 27

impPIPE_139 60 27

impPIPE_191 340 18

Field 2

impPIPE_140 160 18

impPIPE_141 40 12

*Project implementation would require upgrades to the pump station capacity.

Figure 5-6 below summarizes pipe upgrades to provide capacity for a 25-year storm.






Figure 5-5: 10-Year Conveyance Pipe Upgrades






Figure 5-6: 25-Year Conveyance Pipe Upgrades






While the 10-year projects and 25-year projects offer a different level-of-service (LOS), they involve almost identical upgrades to the current storm drain system with the exception of

three (3) pipes. The 25-year projects include the upsizing of pipes impPIP_138 and impPIPE_139 to 27 inches, whereas the 10-year projects only require those pipes to be

upsized to 24 inches. In addition, the 25-year projects require the upsizing of impPIPE_146

to 15” which is not included in the 10-year projects. It is up to the District and Town of Tiburon to select the desired LOS and implement the associated upgrades to the drainage

system and pump station according to this selection.

Pump Station The long term upgrades for the pump station are recommended to replace equipment that

will eventually fail and ensure long term operational reliability for the pump station. It is

recommended to implement the long term upgrades before the pumps and electrical equipment reach the end of their useful life. The pumps and associated equipment should

be sized to accommodate the desired level of service. The recommended long term upgrades, as described in greater detail throughout the report, are summarized in Table 5-

4.

Table 5-4: Pump Station Long Term Upgrade Recommendations

Recommended Upgrade Comments

New MCC Locate outside of building, or expand building to include sufficient clearance to equipment

Backup Generator and ATS Provide permanent backup power

Replace Pumps Replace all three pumps, sized to accommodate desired level of service

New Electrical Service If required with pump station modifications and new pumps

Miscellaneous Electrical Replace aging electrical equipment, level sensors, etc.

Modify Pump Bays To be in conformance with the Hydraulic Institute’s pump intake design standards and to provide interconnectivity

Add wetwell access hatches Provide easier access to all pump bays for maintenance and cleaning purposes

Automatic Trash Rack Screen Reduces maintenance requirements

Flood Wall The Cove Pump Station discharges to East Creek, which is tidally influenced. Schaaf &

Wheeler recommends constructing a floodwall along the western side of East Creek to prevent the possibility of water overtopping the western bank and flowing into Cove

Shopping Center during an extreme tide and/or flood event. The floodwall should be sized for the 100-year coincident tide/creek level with sea level rise of 18 inches incorporated. An

additional 3 feet of freeboard should be added to the floodwall. Using a tide of 8.5 feet (MHHW plus 18”) and a 100-year flow in East Creek of 350 cfs the HY-8 model calculates a

water level of 11.5 feet NAVD on the upstream side of the Tiburon Boulevard culverts;

therefore, the estimated elevation of the top of the floodwall is 14.5 feet NAVD. This would result in a floodwall approximately 6 feet high, sufficiently deep, and 120 feet long.

East Creek Hydraulic Study

Based on the drainage system hydraulic models developed for this study and field observations, a more detailed hydraulic model of East Creek should be developed. The

model should utilize FEMA guidelines and will help determine if current channel conditions

pose a flood risk to the region. Channel cross section should be surveyed to accurately define the existing channel geometry and hydrology from the 10-year, 25-year, 50-year and

100-year storm drain model should be utilized.






5.2.3 Climate Change

Common climate stressors that may pose a potential hazard to coastal regions are identified as precipitation, sea level rise, and coastal storm surges, all which are projected to increase

in frequency or severity in the future. This study focused on sea level rise as a potential

hazard to Cove watershed due to its proximity to Richardson Bay.

Sea Level Rise Sea level is predicted to rise 18 inches along the California coastline by 20501, leading to

increased coastal flooding and shoreline (cliff) erosion. The floodwall discussed previously, accounts for this sea level rise. The pump station building may require additional

protections. The recommended future East Creek hydraulic modeling effort should

incorporate sea level rise.

1. http://documents.coastal.ca.gov/assets/slr/guidance/August2015/AppA_Adopted_Sea_Level_Rise_Policy_Guidance.pdf




Chapter 6: Cost Estimate


Chapter 6. Cost Estimate

6.1 Overview Chapter 5 evaluates Cove Pump Station and the watershed’s drainage system and recommends short term and long potential upgrades. This chapter provides rough cost

estimates to implement the identified upgrades. Exigent circumstances and future in-field

experiences may necessitate deviations or reprioritization of projects.

6.2 Tools for

Prioritizing Potential

Projects

The proposed projects are is broken into three urgency levels for implementation. These

levels are based on both the criteria of the District, as well as Schaaf & Wheeler’s hydraulic

analysis.

Urgency

Definitions

The District defines the project urgency levels based on five main criteria; life safety risk,

regulatory compliance, property damage risk, arterial and collector street flooding risk, and

high maintenance needs. In addition, Schaaf & Wheeler considered the hydraulic properties of the entire storm drain system to pin-point specific areas that are more urgent in nature

Short Term Projects to provide increased protection against more frequent or severe storm events.

Medium Term Local drainage projects to reduce less significant flood risks during more extreme runoff events.

Long Term Projects that would mitigate future increase flood risk or

maintenance burdens.

Cost of Projects Costs have been estimated using information from other projects, cost estimating guides

(2016 Current Construction Costs, Saylor Publications, Inc.), and engineering judgment and

are in June 2015 dollars. Cost estimates can be updated for work to be performed in the future by adjusting the costs given here by the change in the Engineering News Record

(ENR) construction cost index. The costs correspond to an ENR Index of 11155.07. Future costs can be calculated by multiplying the costs given here by ratio “Future ENR Index /

11155.07).

The cost per linear foot of pipe are shown in Table 6-1. These unit costs were used to develop potential project costs for pipe upgrades. The unit costs are based RCP installed

using open trench in the roadway of up to 10 feet in depth. Connection (manhole or inlet) replacement cost estimates ranged from $13,145 to $15,180 depending on connecting pipe

diameters or box culvert dimensions.






Table 6-1: Storm Drain Unit Costs Based on RCP

Diameter (inches)

2016 Dollar per Linear foot of Pipe

2016 Dollar per Connection

12 $ 255 $ 13,145

15 $ 280 $ 13,260

18 $ 300 $ 13,345

21 $ 335 $ 13,435

24 $ 365 $ 13,515

27 $ 390 $ 13,600

30 $ 420 $ 13,680

33 $ 450 $ 13,765

36 $ 475 $ 13,850

42 $ 530 $ 14,020

48 $ 590 $ 14,185

54 $ 645 $ 14,355

60 $ 700 $ 14,510

66 $ 755 $ 14,680

72 $ 810 $ 14,845

78 $ 875 $ 14,945

84 $ 930 $ 15,180

Note, all costs referred to in Tables 6-2 through 6-10 include an additional 70% for

construction contingency and soft costs.

Summary of

Costs

The cost estimates for each of the proposed project presented in this chapter is shown in

Table 6-2 below. This table summarizes the priority and total cost with contingency for each project.

Table 6-2: Project Cost Summary Table

Potential Project Urgency Estimated

Cost

CMP Replacement Short $ 100,000

Short Term Pump Station Upgrades Short $ 430,000

East Creek Survey and Hydraulic Study

Short $ 15,000

10-Year Projects or 25-Year Projects Long $ 1,010,000 / $ 1,030,000

Long Term Pump Station Upgrades, Existing LOS or 100-Year LOS w/ 25-Year Projects

Long $ 1,800,000 to $ 2,400,000

Floodwall Long $ 140,000

Trash Rack Medium $ 440,000






6.3 Condition The short term projects recommend that two (2) CMPs that directly drain to Cove Pump

Station be replaced with RCPs. The CMPs that are currently in place are in poor condition

and pose the largest vulnerabilities and susceptibility for the system failing. Table 6-3 below summarizes the cost of replacing these pipes.

Table 6-3: CMP Replacement Cost Summary

Potential Project

Pipe Length (ft)

Pipe Diameter (in)

Connections Urgency Estimated

Cost

PIPE_389 36 18 1 Short-term $20,000

PIPE_390 36 48 1 Short-term $40,000

Total w/o Contingency: $60,000

Total w/ Contingency and Soft Costs: $100,000

6.4 Conveyance

Projects

Pipeline conveyance upgrades are recommended for areas where the storm water pipe does

not have sufficient capacity to meet system flows for an identified level of service. There are several locations in the Cove watershed that won’t pass the 10-year and 25-year storm

event flows. The existing pipe size does not support the amount of water at the upstream

end of the drainage system. Two sets of conveyance scenarios were evaluated in this study; one that handles the 10-year storm event’s flows and another that conveys 25-year

storm event flows. Both the 10-year PROJECTs and 25-year projects are marked as long-term projects. The District and Town of Tiburon will need to determine which level of

service to upgrade the system to.

10-year Pipe

Projects

Several pipes within the Cove watershed would need to be upsized in order to convey the

10-year flows without causing ponding in the streets. In particular, pipe upsizing projects

are recommended in two places along Claire Way and two places in the field between Claire Way and Karen Way. The total estimated cost of these upgrades is $870,000 with an

additional 70% for construction contingency and soft costs. See Table 6-4 below for the 10-year PROJECT cost breakdown and reference Appendix I for the itemized breakdown in

each project location.

Table 6-4: Summary of 10-year Pipe Project Costs

Potential

Project

Pipe Length

(ft)

Pipe Diameter

(in) Urgency Estimated Cost

Claire 1 260 15 Long-term $ 125,000


Harriet 225 12 Long-term $ 85,000

Field 1 340 18

Long-term $ 215,000 190 24

Field 2 40 12

Long-term $ 100,000 160 18


Total w/ Contingency and Soft Costs: $1,010,000

25-year Pipe

Projects

Several pipes within the Cove watershed would need to be upsized in order to convey the

25-year flows without causing flooding in the streets. In particular, pipe upsizing projects are recommended in two places along Claire Way, two places in the field between Claire

Way and Karen Way, one place on Cecilia Way, and one of the pumps at Cove Pump

Station. The total cost of these upgrades is $895,000 with an additional 70% for construction contingency and soft costs. See Table 6-5 below for the 25-year project cost

breakdown and reference Appendix I for the itemized breakdown in each project location.






Table 6-5: Summary of 25-year Pipe Project Costs

Potential

Project

Pipe Length

(ft)

Pipe Diameter

(in) Urgency Estimated Cost


Claire 2

80 27

Long-term $ 150,000 75 12

115 15

Harriet 225 12 Long-term $ 85,000

Field 1 340 18

Long-term $ 230,000 190 27

Field 2 40 15

Long-term $ 105,000 160 21



6.5 Pump Station

As discussed in Chapter 5, several upgrades for the Cove Pump Station have been evaluated in this study including the adoption of an automatic trash rack screen, short term

upgrades, long term upgrades with existing level-of-service (LOS), and long term upgrades for 100-year storm event and 25-year PROJECT pipe upgrades.

The upgrade cost estimates have been created to provide expected costs to be used for long term budgetary analysis, and to assist in the development of an on-going pump station

upgrade program.

Pumping facilities rely heavily on mechanical and electrical equipment that wear out. On average, pumping equipment can be expected to last anywhere from 20 to 30 years with

proper maintenance. Structural facilities should last much longer, at least 50 years, although metal, wood, and even concrete surfaces all require regular care. Therefore, a

25-year replacement schedule for all equipment within the pump station is recommended.

Rehabilitation of other items such as pump station roofs and concrete structures can be deferred and rehabilitated as deemed necessary. The existing pump station structures are

in good condition and the identified upgrades assumed that the structures do not have to be replaced during the next pump station upgrade. The major mechanical equipment

within the pump station is approaching the end of its useful life and replacement should be scheduled as funding allows. Replacement of all major mechanical equipment is listed as a

long term upgrade within this report to allow the District with sufficient time to plan, design,

and implement these upgrades.

It is important to keep in mind that numerous uncertainties could alter the future costs and

replacement methods. This study projects costs into the future, when available technology and relevant regulations are unknown at this time. The costs may increase if electrical

service needs to be upgraded or if additional easements are needed.

The estimated cost to install a trash rack with an automatic rake as a standalone project is included in Table 6-6. Table 6-7 identifies the estimated cost to implement the short term

upgrades.






Table 6-6: Automatic Trash Rack Cost Estimate

Item No. Description Unit Quantity Unit Cost Total 1 Mob/Demob LS 1 $25,000 $ 25,000

2 Remove Existing Trash Rack LS 1 $2,000 $ 2,000

3 Install Automatic Trash Rack LS 1 $210,000 $ 210,000

4 Install trash chute LS 1 $5,000 $ 5,000

5 Install electrical controls LS 1 $10,000 $ 10,000

6 Install new fencing & gates LF 90 $100 $ 9,000



Table 6-7: Pump Station Short Term Upgrades Cost Estimate

Item No. Description Unit Quantity Unit Cost Total

1 Replace PLC LS 1 $25,000 $ 25,000

2 Install Backup Control System LS 1 $15,000 $ 15,000

3 Integrate SCADA LS 1 $15,000 $ 15,000

4 Install Arc Flash Labels LS 1 $2,000 $ 2,000

5

Replace Meter/Main Breaker LS 1 $15,000 $ 15,000

6 Replace MCC LS 1 $150,000 $ 150,000

7 Remove Pump 4 and Piping LS 1 $4,000 $ 4,000

8 Replace Corroded Trash Rack Bars LS 1 $5,000 $ 5,000

9 Modify Wetwell LS 1 $20,000 $ 20,000

10 Modify Pump Set Levels LS 1 $1,000 $ 1,000



Table 6-8 identifies the estimated cost to implement the recommended long term pump

station upgrades while maintaining the existing level of service (total pump station capacity)

with the existing storm drain system. This scenario assumes that minimal upgrades to the existing wetwell will be made. Table 6-9 identifies the estimated cost to implement the

long term upgrades to convey the flows for the 25-year pipe PROJECTs and the 100-year storm event. This scenario assumes that existing wetwell and building will remain but

major rearrangement of the wetwell will be performed to improve the hydraulic

performance of the inflows and pumps.

These two long term upgrade scenarios were selected to provide a range of possible costs

depending on the desired level of service and degree of pump station modifications. If funding allows, additional upgrades and expansion to the building and wetwell should be

considered. These additional costs are not included in the cost estimates herein.






Table 6-8: Pump Station Long Term Upgrades Cost Estimate, Existing Storm Drain System, Existing Level of Service

Item No. Description Unit Quantity Unit Cost Total 1 Mob/Demob LS 1 $ 90,000 $ 90,000

2 New MCC LS 1 $ 150,000 $ 150,000

3 Backup Generator and ATS LS 1 $ 110,000 $ 110,000

4 New Pumps, tubes, discharge EA 3 $ 70,000 $ 210,000

5 New Electrical Service (if required) LS 1 $ 30,000 $ 30,000

6 Misc. Electrical Imp. LS 1 $ 50,000 $ 50,000

7 Modify Pump Bays LS 1 $ 40,000 $ 40,000

8 Add Wetwell Access Hatches EA 3 $ 30,000 $ 90,000

9 Automatic Trash Rack, Fence, Etc. LS 1 $ 260,000 $ 260,000

10 Misc. Site Items LS 1 $ 30,000 $ 30,000

Total w/o Contingency: $1,060,000


This cost estimate includes the following assumptions:

Includes minor modifications to the existing wetwell, existing wetwell layout to

remain.

Pumps to be replaced to match existing level of service.

New MCC placed outside of building, does not include building expansion or

upgrades.

Table 6-9: Pump Station Long Term Upgrades, 100-Year Inflow, 25-Year Pipe Projects*, and Modified Wetwell

Item No. Description Unit Quantity Unit Cost Total 1 Mob/Demob LS 1 $ 130,000 $ 130,000

2 New MCC LS 1 $ 160,000 $ 160,000

3 Backup Generator and ATS LS 1 $ 130,000 $ 130,000

4 New Pumps, tubes, discharge EA 3 $ 80,000 $ 240,000

5 New Electrical Service (if required) LS 1 $ 30,000 $ 30,000

6 Misc. Electrical Imp. LS 1 $ 60,000 $ 60,000

7 Modify Wetwell LS 1 $ 200,000 $ 200,000

8 Add wetwell access hatches EA 3 $ 30,000 $ 90,000

9 Automatic Trash Rack, Fence, Etc. LS 1 $ 280,000 $ 280,000

10 Misc. Site Items LS 1 $ 50,000 $ 50,000

Total w/o Contingency: $1,400,000


*Costs for pipe projects not included in this table. See Table 6-5.






This cost estimate includes the following assumptions:

Includes modifying the wetwell layout to meet HI requirements.

New pump to convey 100-year inflow with 25-year pipe network projects.

New MCC placed outside of building, does not include building expansion.

Larger automatic trash rack; therefore, larger cost than what is shown in previous

estimates.

6.5 Floodwall A floodwall is recommended for the western bank of East Creek. Based on the available

topography, the required dimensions to protect against 18 inches of sea level rise and to

provide 3 feet of freeboard would be approximately 6 feet tall and 120 feet long. The recommended floodwall would prevent overtopping of flow into Cove Shopping Center

during a 100-year tidal event with 18 inches of sea level rise. This project is considered a long-term project. The costs associated with floodwall vary depending on the type of

floodwall used and the required depth for seepage protection. This study assumes that the

wall would need to extend 12 feet below the existing grade and a cost of $40/square-foot was used. The total estimated cost included in Table 6-10 includes an additional 70% for

construction contingency and soft costs.

Table 6-10: Floodwall Cost Summary

Length (ft) Height (ft) Depth (ft)

Estimated

Cost w/o Contingency

Estimated

Cost w/ Contingency

120 6 ~12 $90,000 $150,000

Further research will have to be done to determine the exact for this floodwall such as soil

type and physical constraints due to the close proximity to the pump station, channel, trees,

and parking lot. These constraints may greatly impact the total project cost.

cove stormwater pump station and collection …€¦ · hydrology and hydraulic study flood control...

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