flood control plan feasibility...

BYU STORMWATER ENGINEERS PAGE 1

Flood Control Plan Feasibility Study

Project ID: CEEn-2016CPST-007

3/31/2017 BYU Stormwater Engineers

Mentor: Christian Kesler

Team leader Matt Johnson

Donald Anderson

Fabian Zamorano

A Capstone Project Final Report

Submitted to

Travis Jockumsen, P.E. Payson City Development Services Director,

Public Works Director, & City Engineer

Department of Civil and Environmental Engineering

Brigham Young University


Executive Summary

PROJECT TITLE: Flood Control Plan Feasibility Study

PROJECT ID: CEEn-2016CPST-007

PROJECT SPONSOR: Travis Jockumsen, Payson City Engineer

TEAM NAME: BYU Stormwater Engineers

A detention basin needs to be designed to handle the Payson City 100-year storm requirements for the Ridge Lane Area. The contributing area of 11 acres and a new stormwater conveyance system will be designed and stormwater will be routed to a detention basin to prevent flooding issues that have existed in this area for 30 to 40 years.

This area currently has no stormwater system, which ends up causing some of the houses to occasionally flood in the area. The City of Payson bought a property where they would like to put a detention basin to prevent flooding in this area. We studied the feasibilty of this option.

To fix this problem, we propose to install an underground stormwater pipe. One major sag point was identified during the analysis which makes for an excellent inlet basin location. An inlet basin will be expanded and connected to an existing storm water system which will pipe stormwater to a pretreatment manhole, and ultimately to a detention basin. In addition, one major sag point will be eliminated to completely fix the issue of flooding in the area.

This design is attractive as it utilizes preexisting stormwater conveyance systems which will allow for greater effectiveness at reduced cost. This new system will be capable of handling the rainfall for a 25-year worst case event. The detention basin will be capable of holding water from a 100-year 24-hour rainfall event. Ultimately, the problem of flooding in the area will not occur under design rainfalls.

We recommend a slope stability analysis be performed on the detention basin lot to determine the impact of water percolation on stability and on houses down the hill. If the impact is deemed acceptable, then this flood control plan is safe and feasible.


Table of Contents

Introduction ........................................................................................................................................................ 4

Project Timeline ................................................................................................................................................. 6

Experimentation Summary ............................................................................................................................... 6

Design Specifications ........................................................................................................................................ 7

Conclusion ........................................................................................................................................................ 10

References ......................................................................................................................................................... 10

Appendix ........................................................................................................................................................... 12

Table of Figures Figure 1. Contributing rainfall area, general area of the stormwater system is circled. Flood prone areas are highlighted in orange. ........................................................................................................................ 4

Figure 2. Satellite imagery of the Ridge Lane area ........................................................................................ 5

Figure 3. First site visit in January 1. ............................................................................................................... 6

Figure 4. Major flood point due to asphalt failure and sag, picture taken with permission of owner. 495 Ridge Lane. .................................................................................................................................................. 7

Figure 5. Current stormwater system. ............................................................................................................. 7

Figure 6. Current flood mitigation systems with previous attempt at open channel. .............................. 8

Figure 7. Current flood mitigation system: previous concrete open channel into city lot. ..................... 8

Figure 8. Combination Inlet ............................................................................................................................. 8

Figure 9. Stormwater system area. Various locations given in picture are labeled below. ...................... 9

Figure 10. Top view of the pipe system and detention basin .................................................................... 11


Introduction The Ridge Lane area of Payson City, UT

currently experiences flooding problems that are due to lack of infrastructure in the stormwater system. These issues cause flooding in several locations in the backyards and garages of homeowners (figure 1). As a result, the main goal for this project was to determine the feasibility of a stormwater system that will eliminate flooding in the area. This system will have the capacity of handling a 25-year storm event. A detention basin will also be constructed that will have the capability of storing water for a 100-year storm event.

A contributing rainfall area of 11 acres was provided by Payson City. Flow rates were calculated to determine the dimensions of the

pipes, inlets, and detention basin. The system was designed to handle the flow and velocity of the water from the contributing area while also maintaining proper surface cover of pipes. The rainfall and time of concentration was calculated to determine the feasibility of several options.

Design limitations of this new stormwater system include the location of existing pipes, utilities, and manholes. Sediment and debris related clogging was also a primary concern.

Due to these limitations, several design solutions were envisioned. One: a pre-treatment manhole that will mitigate issues with clogging. Two: the design of a system which avoids underground obstacles to the extent possible. Due to unforeseen factors and conditions that

Figure 1. Contributing rainfall area, general area of the stormwater system is circled. Flood prone areas are highlighted in orange.


occur during a major storm event, the system was designed to be conservative.

This report shows the important aspects of the design including a summary of how we decided with this particular system. The report will also display the design and calculations used to determine the most viable design.

This project will help provide much needed improvements in the stormwater system for the

Ridge Lane area of Payson City, UT. The software program results obtained and methods used during the design of this new stormwater system will also be provided to show how certain issues and obstacles were solved during the design of the project.

Figure 2. Satellite imagery of the Ridge Lane area


Project Timeline We spent the month of January visiting the

site and doing research to better understand stormwater design. After we had a better understanding of the current infrastructure in place and the scope of the project, we started the design process.

The month of February was initially spent designing an underground piping system. This time was also used to gain experience using AutoCAD Civil 3D and Storm and Sanitary Analysis (SSA). After the initial design we again visited the site and talked to other neighbors. With this additional visit, we considered the option of an open channel system and prepared a design plan.

The month of March was spent in communicating our initial design with our

sponsor. We decided that an underground system would be a better option, as an open channel system had more design limitations than we had previously anticipated. The rest of the month was spent in finalizing the pipe design, estimating the financial cost, and preparing the final report for our sponsor.

Experimentation Summary The site visits affected our design more than

any other component in this project as it completely altered our understanding of the location. Aerial and google map images showed a much flatter slope, rather than the steep and sag ridden area we actually saw.

Initially, we encountered several challenges such as determining the hydrology of the area, the rainfall intensity, time of concentration, and pipe design. We initially used AutoCAD Civil 3D to get a feel of the hydrology of the area but that did not yield useful results. Then we used the Watershed Modeling System (WMS) which did not yield useful results.

Our initial pipe design was performed with SSA. This program simultaneously solved our challenges of hydrology, rainfall intensity, time of concentration, and stormwater pipe design. This

program expedited our stormwater design. With the program, we were able to get the worst case 25-year storm scenario and design the system around that.

We also used a spreadsheet provided by Payson City to calculate water flow, detention basin area, and coefficient of discharge (see figures 10a, 11a in the Appendix). These values were confirmed by the SSA program.

We quickly realized several limitations to a pipe system. For one, there were existing pipes that were in the way for the optimal piping location. In addition, the problem of flooding, which was our chief concern, was not able to be solved without unreasonably sized inlets. This was due to our initial inexperience with SSA. The sag point at 475 Ridge Lane (which floods) quickly ponded. The majority of the water would

Figure 3. First site visit in January 1.


run past the inlet basin and into the driveway of 495 Ridge Lane. This problem was exasperated by leaf and sediment clogging.

We decided on another site visit and were fortunate enough to speak with the owner of the house that flooded most consistently. It became apparent that the nature of the flooding for his house would only be solved by fixing the sag point at that location.

After the second site visit, we considered an open channel design. We considered channeling the water directly into the pretreatment manhole. This would indirectly amerliorate the sag point problem. We were not alone in our thinking, we observed a previous attempt at an open channel design, though on the other side of the street (figure 5,6).

We consulted with our sponsor and learned that the city required open channels to be covered which made the design more expensive and

difficult to implement. In addition, open channels were discouraged due to difficulty in cleaning and maintenance. Ultimately, we abandoned the open channel concept.

For our final design, we decided to take advantage of the existing stormwater system. One major sag location was determined, which we felt confident contributed to the vast majority of flooding. Repairing the road, curb, and gutter at 495 Ridge Lane would eliminate flooding at that house. A large inlet basin at the main flood sag point combined with a curb and gutter was sufficient to eliminate flood recurrance.

Design Specifications Three major causes of flooding were

identified: 1) A major sag point, 2) an inadequate curb and gutter, and 3) a pipe that transported water in the reverse direction of its intended design.

Figure 4. Major flood point due to asphalt fail-ure and sag, picture taken with permission of

owner. 495 Ridge Lane.

Figure 5. Current stormwater system.


First, water pooled at the major sag point. The reverse direction pipe contributed to this effect. Then, the water would overfill and rush down to the downhill neighbor’s house. The curb and gutter had a gap that prevent water from bypassing properly.

The solutions for these issues are to add an inlet basin and stormpipe at the major sag point and to repair the inadequate curb and gutter.

The existing inlet basin must be removed and refitted with a larger inlet basin such as the combination inlet show in figure 8. An alternative would be to place a new inlet basin directly next to the existing one. The in-place storm water pipes will still be utilized to pipe water to the sag point. The modified or adjacent inlet basin will collect this pooling water. At the bottom of this basin will be a 15” concrete pipe which will transfer stormwater to a pretreatment manhole. We anticipate at least one sewer, two water, and two gas lines which will be crossed.

This first concrete pipe will have two bends in it. The first bend will be 150 degrees and the second bend will be 139.3 degrees as shown in figure 10. This 15” pipe will have an average of 1’ of cover, which will be sufficient to have it fit over the existing sewer and water lines.

Figure 6. Current flood mitigation systems with previous attempt at open channel.

Figure 7. Current flood mitigation system: pre-vious concrete open channel into city lot.

Figure 8. Combination Inlet


The pretreatment manhole will be about 8’ deep. This manhole will utilize a 15” pipe to transfer the water to the sump, which will be located in a detention basin. The dimensions of the sump and detention basin are given in figure 4 of the appendix.

We will use a prefabricated concrete sump. There will be 3’ drain rock around the sump to help the stormwater drain into the ground. A soil percolation rate of 2 in/min designed for. Around the drain rock, there will be a filter fabric that will prevent the surrounding soil from filling the void spaces in the drain rock.

In the event of overflow, there is a grate at the top of the sump that will allow the detention

basin to fill. This detention basin is designed for a 100-year, 24-hour storm.

The detention basin will have side slopes of 5:1 (horizontal to vertical) which is in accordance to the specifications given in the Payson City manual. The storage required for a 100-year rainfall event was around 8300 ft3 according to the spreadsheets provided by Payson City and utilizing parameters that were concluded during analysis. The detention basin will be 5 ft deep and the top area would be about 75 ft by 60 ft. The storage volume of the detention basin would resemble a truncated pyramid with rectangular bases, so the volume was calculated to be about 9800 ft3 as shown in figure 2a in the appendix.

Figure 4. Current Stormwater grate

Figure 6,7. Open channel attempt

Figure 4. Sag point driveway

Detention Basin

Figure 9. Stormwater system area. Various locations given in picture are labeled below.


The storage volume of the detention basin is well above the 8300 ft3 required for a 100-year rainfall event.

To resolve the inadequate curb and gutter at the driveway, a new curb and gutter will be installed. The new curb and gutter will start at the end of the existing curb and gutter. The curb and gutter will be 34’ feet long and connect with the curb and gutter on the other side of the resident’s property.

The gutter will be 8” wide and will be sloped at a 5 degree angle from the asphalt road. To allow the home owner to park in their driveway, a 10 degree concrete ramp will be used. This ramp will start at the edge of the gutter and meet the owner’s driveway. The top of the ramp will be rounded off to provide a smooth transition from the concrete ramp to the residents existing driveway. The curb and gutter will also have contraction joints every 10 feet to allow for thermal expansion and retraction of the concrete. This new curb and gutter will allow stormwater to countiue down the street. See appendix 13a for reference.

All the design results were obtained using AutoCAD Civil 3D, Storm and Sanitary Analysis, and Payson City provided spreadsheets.

Conclusion This report gives our recommendation for a

viable stormwater system for the Ridge Lane area in Payson City, UT. In particular, as per sponsor request, we investigated the feasibility of a detention basin design.

The greatest challenges we faced designing this project was obtaining new software skills and making progress amid the ambiguity of general stormwater design.

We learned that software knowledge primarily comes from taking time to read product manuals and tutorials. Stormwater ambuigity comes mostly from a lack of coursework in school regarding the subject. The best solution we found was to just jump into the project and learn bit by bit. Researching stormwater design without imbibing too much of the theoretical calucations was key to a good design. Using the right resources and software was crucial to the timely success of this capture project.

In conclusion, this stormwater design is viable for the Ridge Lane area. However, we recommend having a slope stability analysis be done on the hill with the detention basin. This is expedient because there are homes both above and below this hill. Diverting the stormwater and draining it in the hill could increase the risk of slope instability and/or water seepage.

References Storm Water Project Cost Estimates & Location

Maps, Appendix F. Report. January 2009. Accessed April 5, 2017. http://www.riverdalecity.com/depart-ments/public_works/CFP/CFP_Appendix_F.pdf

"Stormwater Management Fact Sheet: Dry Extended Detention Pond." Dry Extended Detention Pond. Accessed April 05, 2017. http://www.stormwater-center.net/As-sorted%20Fact%20Sheets/Tool6_Stormwater_Prac-tices/Pond/Dry%20ED%20Pond.htm

Garver, Brian M. "Price List Page 3." Price List Page 3. Accessed April 05, 2017. http://www.ncp-inc.com/price3.html.

"Precise Calculator Geometric Figures." Precise Cal-culator Geometric Figures. Accessed April 05, 2017. http://preccalc.sourceforge.net/geome-try.shtml.

http://www.ncp-inc.com/price3.html

http://www.ncp-inc.com/price3.html

http://preccalc.sourceforge.net/geometry.shtml

http://preccalc.sourceforge.net/geometry.shtml


Figure 10. Top view of the pipe system and detention basin


Appendix

Figure 1a. Detention basin specifications. .................................................................................................. 13

Figure 2a. Detention basin calculations. ..................................................................................................... 14

Figure 3a. Inlet basin calculations. .............................................................................................................. 15

Figure 4a. Junction calculations. ................................................................................................................. 15

Figure 5a. Inlet to junction 15" pipe ........................................................................................................... 16

Figure 6a. Junction to basin 15" pipe. ......................................................................................................... 17

Figure 7a. General street profile for Ridge Lane ......................................................................................... 18

Figure 8a. Pre-treatment and sump specifications. .................................................................................... 19

Figure 9a. Estimated project costs. ............................................................................................................. 20

Figure 10a. 25 year, 10 minute time of concentration calculations. .......................................................... 21

Figure 11a . 100 year, 24 hour time of concentration calculations. ........................................................... 22

Figure 12a. Concrete pipe cost quote. ........................................................................................................ 23

Figure 13a. New curb and gutter with driveway. ....................................................................................... 24

Figure 14a. Profile View .............................................................................................................................. 25


Figure 1a. Detention basin specifications.

Detention Basin.

5:1 incline, sump is placed in the middle.


Figure 2a. Detention basin calculations.


Figure 3a. Inlet basin calculations.

Figure 4a. Junction calculations.


Figure 5a. Inlet to junction 15" pipe


Figure 6a. Junction to basin 15" pipe.


Figure 7a. General street profile for Ridge Lane


Figure 8a. Pre-treatment and sump specifications.


ITEM DESCRIPTION UNIT PRICE ITEM COST

1 ASTM C76 15" Diameter Concrete Pipe 350 ft 12.50$ 4,375.00$ 2 Concrete for Curb and Gutter 120 ft 20.00$ 2,400.00$ 3 Pretreatment 4' Diameter Manhole 1 2,550.00$ 2,550.00$ 4 Sump 5' Diameter Manhole 1 2,950.00$ 2,950.00$ 5 Sump 1 300.00$ 300.00$ 6 Single Grate Inlet Catch Basin 1 2,725.00$ 2,725.00$ 7 Remove Surface Materials (Asphalt, Curb & Gutter) 250 ft 8.75$ 2,187.50$ 8 Remove Existing Storm Drainage Piping 0 ft 16.00$ -$ 9 Furnish Trench Backfill Materials 136 tons 4.50$ 610.42$ 10 Furnish Bedding Materials 152 tons 10.50$ 1,590.88$ 11 Roadway Patching 310 yd³ 20.00$ 6,202.79$ 12 Traffic Control & Flagging 19 days 150.00$ 2,775.76$ 13 Landscaping & Surface Restoration 1 3,365.04$ 3,365.04$ 14 Connection To Existing System 1 2,800.00$ 2,800.00$ 15 Mobilization 1 5,212.91$ 5,212.91$ 16 Constructing Detention Pond 1 13,390.00$ 13,390.00$

53,435.30$ 10,687.06$

8,015.29$ 72,137.65$ 72,100.00$

QUANTITY UNIT

Construction Cost:Construction Contingencies (20%):

Engineering Design and Construction Management (15%):Total Cost:

Total Cost (Rounded):

Figure 9a. Estimated project costs.


Figure 10a. 25 year, 10 minute time of concentration calculations.


Figure 11a . 100 year, 24 hour time of concentration calculations.


Figure 12a. Concrete pipe cost quote.


Figure 13a. New curb and gutter with driveway.


Figure 14a. Profile View

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