denville flood mitigation presentation

7/29/2019 Denville Flood Mitigation Presentation

1/144

Township of DenvilleTownship of Denville

Morris County, New JerseyMorris County, New Jersey

Flood Risk ReductionFlood Risk Reduction

ConsiderationsConsiderationsJanuary 29, 2013


2/144

Presented by:

HATCH MOTT MACDONALD

John Ruschke, PE, CME, CFM

Leo Coakley, PE, PP


3/144

TOPICS

Hurricane Irene in Perspective

Rainfall and flood frequency

Flood Maps and Updates

Prior Mapping and Reports

Denville Center - Concepts


4/144

Rockaway River

Below Den Brook 97 Sq. Mi.


5/144

Hurricane Irene

August 27 - 28, 2011


6/144

Hurricane Irene -

Rainfall before and during

Peak Flows

Com are to Au ust 2000


7/144

Irene - Prior Rainfallat Newark Airport Rain Gage - 2011

Aug 14 6.40

Aug 15 0.16

.Aug 19 0.82

Aug 21 0.48

Aug 25 0.20

Total 8.24


8/144

The Ground Was Saturated!


9/144

Hurricane Irene Rainfall

Rainfall at Newark

Aug 27 3.70

Aug 28 5.22

Total 8.92

For Morris County:100-year 8.3 in 24 hours


10/144

Rainfall and Flood Recurrence

There is a difference between:

Rainfall recurrence and

Flood recurrence

e -year ra n a oes no necessar yproduce the 100-year flood

Other factors are involved


11/144


Other factors are involved

Changes in land use over time

Ground conditions

grass

seasonal variations soft or frozen ground

Antecedent rainfall over several days prior

to main event


12/144


Rain gage

Measures rainfall in inches per hour

Stream gage

easures ow n cu c ee per secon c s

For each type, period of record is usually

different from other gages in watershed.Affects statistical analysis of data.


13/144

Peak Stream Flows

USGS Stream Gages:Rockaway River at NJ Rt. 15 at Berkshire

Valley (NEW - Data since Aug. 2010)

Drainage Area 24.4 sq. mi. http://nwis.waterdata.usgs.gov/nwis/nwisman/?site_no=01379699&age

ncy_cd=USGS

Rockaway River above Reservoir atBoonton (Data Oct. 1937 Sep 30, 2011;moved to West Main Street, Boonton)

Drainage Area 116 sq. mi. http://nwis.waterdata.usgs.gov/nwis/nwisman/?site_no=01380500&age

ncy_cd=USGS


14/144

Hurricane Irene and Tropical Storm LeeIrene - Aug 28 - Peak Flow 1,840 cfs

Lee - Sep 7-9 - Peak Flow 1,100 cfs (60% of Irene)


15/144

2000 cfsFloodStage atBoonton

Hurricane Irene and Tropical Storm LeeIrene Aug 28 - Peak Flow 8,210 cfs

Lee - Sep 7-9 - Peak Flow 2,510 cfs (30% of Irene)


16/144

Peak Stream Flows - Irene

USGS Stream Gages:Rockaway River at NJ Rt. 15 at Berkshire

Valley

Irene Aug 28, 2011 1,840 cfs

Rockaway River above Reservoir atBoonton

Irene Aug 28, 2011 8,210 cfs


17/144

Peak Stream Flows

Compare Irene to Aug 2000USGS Stream Gages:

Rockaway River at NJ Rt. 15 at BerkshireValley

Irene Aug 28, 2011 1,840 cfs

ug , , c s -year

Rockaway River above Reservoir atBoonton

Irene Aug 28, 2011 8,210 cfsAug 13, 2000 2,750 cfs (3-year)


18/144

Annual Peak StreamflowAbove Reservoir at Boonton 1937-2010

Irene8,210

6000


19/144

Comparison of Peak Flows

For Rockaway River above Reservoir atBoonton NJ (stream gage site)

Drainage area = 116 sq. mi.

Peak flow for Irene 8,210 cfs

Estimated 100-Year peak

7,613 cfs (USACE - model)

6,410 cfs (USGS gage analysis 2009)

Estimated 500-Year peak8,550 cfs (USGS gage analysis 2009)


20/144


For Rockaway River above Reservoir atBoonton NJ (stream gage site)

Irene exceeded:

USACE 100-Year peak by about 8%

USGS 100-Year peak by about 28%

Irene was 96% of USGS 500-Year peak

100-Year < Irene < 500-Year


21/144

Flood History

Review of Peak Flows at Boonton

Flood stage above 2,000 cfs

Peak values for 73 years (1937-2010)

For 1937 to 1968

9 peaks >2,000 cfs

9 floods/ 32 years = 28% of years with floods

For 1970 to 2010

31 peaks > 2,000 cfs31 floods/ 41 years = 76% of years with floods


22/144

Review of Peak Flows at Boonton

Flood stage above 2,000 cfs

For 1996 to 2010 (Last 15 years at gage)

13 peaks >2,000 cfs

13 floods/ 15 years = 87% of years with floods

Only 2001 and 2002 peaks > 2,000 cfs

Flood stage more frequently in recent years


23/144

Flood Frequency - Terminology

Recurrence based on probability of floodbeing equaled or exceeded in a givenyear:

500-Year = 0.2% probability

100-Year = 1% probability (the base flood)

50-Year = 2% probability

25-Year = 4% probability

10-Year = 10% probability 2-Year = 50% probability


24/144

Flows at Boonton (including Aug 2011)Estimated 50-year flow at Boonton

Q50 = 6,534 cfs (USACE)

1 peak > 50-year in period 1938-2011

1 flood/ 74years = 1.4% of years withflood>50 yr (the 2% probability flood)

Estimated 25-year flow at Boonton

Q25 = 5,507 cfs (USACE)

3 peaks > 25-year in period 1938-2011

3 floods/ 74 years = 4% of years withflood>25 yr (the 4% probability flood)


25/144


Location 25-Year

Est.*

50-Year

Est.*

100-Year

Est.*

Irene

Aug 28, 2011

Gage

Rockaway RUpstream ofDen Brook

4,504 cfs 5,260 cfs 6,052 cfs

Rockaway RDownstreamof Den Brook

4,951 cfs 5,809 cfs 6,707 cfs

Rockaway Rat Boontongage

5,507 cfs 6,534 cfs 7,613 cfs 8,210 cfs

* Est. Peak Flows based upon USACE hydrology


26/144

Flows at Denville vs. Boonton

At Boonton annual peaks: Irene (8,201 cfs) exceeded the estimated 100-

Year flood peak (7,613 cfs) by about 8%

There has been only 1 annual peak greater

than the 50-Year (6,534 cfs) since 1938 (Irene- Aug 2011)

There have been only 3 annual peaks equalto or greater than the 25-Year (5,507 cfs)

since 1938 (Jan 1979, April 1984 and Aug2011)


27/144

Flows at Denville vs. Boonton

Denville is subject to flooding for veryfrequent floods less than the 10-Year

eak.


28/144

Rainfall Floods - Frequency

Rainfall frequency and flood frequency canbe different from each other.

The rainfall frequency can be different indifferent arts of the same watershed.

Rainfall duration and intensity can varyacross watershed

The flood frequency can be different in

different reaches of the same river orstream and in tributaries.


29/144

FLOOD MAPS AND UPDATES


30/144

For Flood Delineation Maps

NJDEP maps delineate:Floodway

100-year flood limit

NJ Flood Hazard Area = 100-year flow +25%

FEMA maps delineate:

Floodway

100-year (1% probability) flood limit500-year (0.2% probability) flood limit


31/144

Regulatory FloodwayThe corridor need toconvey the 100-yearflood.

Determined by

encroaching (squeezingin on) the natural 100-year flood limit so thatnot more than 0.2 footincrease occurs in thewater surface elevation.


32/144

Flood Plain Mapping

FEMA maps Basis for:

Flood Insurance

Municipal ordinance (in NFIP compliance)

NJDEP maps Basis for:

Regulatory for work in Flood Hazard Area

NJDEP Permits

Municipal approval (e.g. elevating house)


33/144

Flood Plain Mapping

FEMA maps

Current maps dated April 17, 1985

Index and 5 panels

NJDEP maps

Current maps dated February 1986

Topographic maps, 1=200, with 2 contours

River profiles on large sheets


34/144

Flood Plain Mapping

FEMA maps and NJDEP maps

The two should be in substantial

agreemen n env eMay have some differences due to scale

and detail of maps

FEMA street mapsNJDEP topographic maps


35/144

NJDEP Flood Delineation Map

SAMPLE MAP


36/144

Flood Plain Mapping - FEMA

Coming soon:

Modernized FEMA maps for

Morris County will be availablethrough Google Earth -expected mid-2013


37/144

Flood Plain Mapping - FEMA

FEMA maps no inundation changesexpected from 1985 maps for Denville

Will be on 1988 datum (old was 1929

a um; a ou convers on

Aerial photo background

Following sample taken from GoogleEarth web site (not in Denville)


38/144

S

A

M

P

L

E


39/144

When Morris County Digital Maps

Become Available:

Use the National Flood Hazard Layer

Web Map Service (WMS) in Google

Earth

https://hazards.fema.gov/femaportal/wps/portal/NFHLWMSkmzdownload


40/144

Denville Inundation Mapping

HMM For Planning Use

Rockaway River hydraulic model(courtesy of USACE)

Series of flows 10, 25, 50 and 100-year

e erm ne oo e eva onsTopographic data (courtesy of Morris

County)

Plotted inundation limits on aerialphotographs


41/144

Denville Inundation Mapping -

HMM

Slides will progress through areas ofinundation for:

10-year

-50-year

100-year


42/144

Paste 10-yr10-YEAR


43/144

Paste 10-yr10-YEARGARDNER

ROAD

Separatefloodplainfor each

river


44/144

Paste 25-yr25-YEAR

Floodplainsconnectandintermingle


45/144

Paste 50-yr 50-YEAR

Expanded

Connections


46/144

Paste 100-yr100-YEAR

Full Flow

ConnectionOver Rt. 46


47/144

The depth of flooding will vary through

each flood inundation area, from near zeroat the edge to greater depths in low areasand near the Rockaway River and DenBrook.

The following slide shows the estimatedpeak 100-Year event flood depths


48/144

100-Year

FloodDepth MapZones for:

- ,2-4,

4-6,6+


49/144

FLOOD RISK REDUCTION


50/144


Can reduce the depth, frequency, orextent of damage by implementingappropriate flood mitigation measures.

benefits and cost.

Irene level of protection not practical toimplement on local level.


51/144


Review of Prior Investigations

Review Re ional Conce ts

Focus on Denville Center


52/144


Review of Prior InvestigationsMorris County Hazard Mitigation Plan (2010)

Map of Repetitive Loss Properties (2012)

Denville Master Drainage Plan (1980)

USACE Alternative Plan Formulation (2008)


53/144


Review Regional Concepts

Bridges and Powerville Dam

Dredging and maintenance

Regional detention facilities


54/144



Some local alternatives for consideration


55/144

REVIEW OF PRIOR

Flood Risk Reduction


56/144


Flooding in Denville has been studiedbefore:

Corps of Engineers (USACE)

Morris County

env e s consu an s


57/144


No silver bullet

Difficult and costly to address

Environmental constraints have becomemore restrictive (2007 NJ- FHA Rules)


58/144

NJDEP Flood Hazard Rules

2007 rules are stricter

No negative effects

W.S. chan e tolerance0.04 ft. (1/2 inch)


59/144

NJDEP Flood Hazard Rules

NJDEP Rules are currentlunder review for revision willthey be more practical???


60/144


Morris County, New Jersey, Multi-

Jurisdictional Hazard Mitigation Plan,prepared by Morris County Office of Emergency

Management, Third Final Draft July 23, 2010.


61/144

County All Hazard Plan (2010)

Covers multiple hazards (e.g. Flooding,Dam and Levee Failure, Earthquake,Drought, Hazardous Materials Release,High Wind, Wildfire)

Hazard Identification, Profiling, Ranking

Risk and Capability Assessment

Mitigation Action Plan

Plan Monitoring and Maintenance


62/144


Sect 9 Mitigation Action Plan Included 14 Actions

Can be summarized in 9 categories

2 categories pertain to all hazards

Backup power for Municipal Building

Public education and outreach program

5 categories are specific to Flood Hazard


63/144


5 Categories specific to flood issues1. Retention Basins for Den Brook (3)

2. Feasibility study to install check valves onstormwater runoff system

3. Construct Den Brook protection berm

4. Remove silt at 3 areas of Rockaway River

5. Acquisition/elevation of:

9 severe repetitive loss properties

40 repetitive loss properties


64/144


Comments:

Items 2, 3 and 5 are addressed in potentialprojects and Actions discussed below.

2. Storm sewer check valves

.5. Acquisition/ elevation of structures

Item 4. Remove silt at 3 areas ofRockaway River (locations not specified)

Silt removal is addressed as a topic below.


65/144


Comments:

Item1. Retention Basins for Den Brook (3basins)

Location: not s ecified. Generall betweenRt. 46 and I-80


66/144


Comments:

Den Brook detention (between Rt. 46 and I-80)

Lower reach of Den Brook is currently subjectto backwater from Rockaway River

existing flood elevations

Increase in Den Brook flood elevations notacceptable


67/144


Comments:

Den Brook detention (continued - excavation)Excavation to gain storage would be costly,

have environmental restrictions (wetlands)

Deeper storage may be ineffective for peak

flow reduction:Storage elevation is controlled by backwater

from Rockaway River

New volume in low areas would fill at lower

flows.Horizontal expansion limited by highways.


68/144


Comments:

Den Brook detention (continued - hydrology)

Den Brook drainage area (DA) 9.0 sq. mi.

Rockawa River DA above Den Brook 88.3sq. mi. (DA ratio almost 10:1)

Existing contribution of Den Brook duringperiod of Rockaway River peak flow:

100-Year: 655 cfs of RR 6,707 cfs; DB 10%

25-Year: 447 cfs of RR 5,809 cfs; DB 8%


69/144


Comments:

Den Brook detention (continued - summary)

Area already provides some detention benefit

Potential for additional storage volume is

Potential for any significant reduction inRockaway River peak is highly questionable

Existing flood storage areas should be

preserved to maintain existing benefits.


70/144


Comments:

County Plan should be updated to include:Updated NFIP repetitive loss data, including

Hurricane Irene losses.

Additional data for losses that are not

nc u e n a a pr va e nsurance .Updated accounting of location of repetitive

loss properties

Updated mitigation actions - items selected by

Denville for continued Action Plan (prepareupdated Table for Sect 9).


71/144


Map entitled: Severe Repetitive &

Repetitive Properties, CRS Program,

Township of Denville, Morris County,New Jersey, prepared by William Denzlerand Associates, Community PlanningConsultants, dated April 2012


72/144

2012 Map of Repetitive Loss

Properties

Map shows total of 64 affected properties18 Severe Repetitive Loss properties

46 Repetitive Loss properties

Includes 56 between I-80 and RockawaRiver

29 on Riverside Drive East

6 on Hinchman Ave.

5 on Snyder Ave.Thus 40 clustered and 16 at other locations


73/144


Properties (comments)

Township has acquired 11 propertiesalong Riverside Drive (in 2012).

Leaves 53 for evaluation.

5 on Snyder Ave

4 on Hinchman Ave

3 on Third Ave

3 on West Main St. and Main St.


74/144


Properties (comments)

Remaining 53 sites should be evaluatedfor elevation

(see FEMA guidelines)

Inundation Depth Map can be useful forplanning


75/144


Master Drainage Plan, Elson T. Killam

(includes a list of prioritized projects.)


76/144

Master Drainage Plan (1980)

Includes lists of prioritized projects

Recommendations for an emergencywarning procedure

ropose ormwa er anagemenOrdinance

Some discussion of channel conditionsand Powerville Dam

Recommendation to evaluate bridges


77/144


Large Scale Projects

9 projects

Require services of a contractor

ma ca e ro ec s8 projects (mostly small reaches of storm

sewer)

Could be undertaken by municipal forces

(Some have since been completed)


78/144


Rank Large Scale Projects 1980 Estimated

Cost

Priority Points

L1 Peck Meadow Brook $1,500,000 220

L2 Hinchman & Corey Road Area 300,000 205

L3 Woodland Avenue Area 215,000 180

Table 2.6-1A Priority Evaluation of Large Scale Drainage Projects

L4 Sunset Bay Area 230,000 180L5 Franklin Road Area 195,000 180

L6 Morris Ave. at savage Road 140,000 175

L7 Holly Drive area 80,000 160

L8 Burton Lane Area 110,000 150

L9 NJ Foundation for Blind 340,000 125TOTAL LARGE SCALEPROJECTS (1980 est.)

$3,110,000


79/144

Review of Large Scale Projects

Rank Large Scale Projects 1980 EstimatedCost

Priority Points

L1 Peck Meadow Brook $1,500,000 220

L2 Hinchman & Corey Road Area 300,000 205

L3 Woodland Avenue Area 215,000 180

Flood Mitigation Projects related to stream flooding

L4 Sunset Bay Area 230,000 180L5 Franklin Road Area 195,000 180

L6 Morris Ave. at Savage Road 140,000 175

L7 Holly Drive area 80,000 160

L8 Burton Lane Area 110,000 150

L9 NJ Foundation for Blind 340,000 125Local drainage Projects notconsidered part of floodmitigation


80/144

Review of Large Scale Projects

Rank Large Scale Projects Comments

L1 Peck Meadow Brook Modified plan Assess risks, evaluatelimited alternatives

L2 Hinchman & Corey Road Area Modified Plan reconfigure stormsewers

Comments on 5 Large Scale Projects

. Assess risks, evaluate alternatives

L4 Sunset Bay Area Modified plan Identify at riskstructures, consider small PS

L9 NJ Foundation for Blind Berm near Rockaway River Assessrisks, impacts, revise layout

Local flood risk reduction may be practical with modifiedplan at each location.


81/144


Stormwater Management Ordinance

Has been adopted based on NJDEP model.

Other items are reviewed below:

mergency warn ng sys emChannel conditions and Powerville Dam

Bridges


82/144


Upper Rockaway River, New Jersey,Flood Damage Reduction and

Ecosystem Restoration, Alternative

Plan Formulation Report, USACE,

dated June 2008 (documents include MainReport and 2 additional volumes withAppendices.)

USACE Alt ti Pl R t


83/144

USACE Alternative Plan Report

(2008)

Not the first look at the Rockaway River bythe USACE

USACE Alt ti Pl R t


84/144


(2008)

1997 report reviewed prior USACE studies(spanning 8 decades)

Considered Upper Rockaway River

,1990, Morris County

1997 Reconnaissance Study recommended feasibility study be

undertaken

USACE Alt ti Pl R t


85/144


(2008)

May 1997 Congress authorizedfeasibility study

1999 Cost sharing agreement

NJDEP as local sponsor

2003 Public scoping process

Determine the acceptability of plans that are

economically justified

USACE Alt ti Pl R t


86/144


(2008)

Economically justified:

Benefits/Cost >1

Potential USACE Project B/C = 1.3

ur er eve opmen o p an a eSignificant public concern

Costs and impacts, level of protection

Withdrawal of NJDEP support

2008 Report summarizes work completed

USACE Alt ti Pl R t


87/144


(2008)

USACE potential Project

3-mile long diversion culvert Dover to LakeEstling

Rockaway Borough, through Denville toBoonton

Bioengineered channel, 25 cut within banks

Powerville DamReplace dam with crest gate structure

USACE Alt ti Pl R t


88/144


(2008)

In Denville:

Identified 335 structures in 100-Yearfloodplain

.(Aug. 2004 price levels)

Primarily between Den Brook and I-80

Est. annual damage value $1.1 million

USACE Alt ti Pl R t


89/144


(2008)

In Denville: Alternatives considered

Preliminary Screening 9 Plans

Numbered 1-9

Then 5 Alternative Plans evaluated

Identified as A E

USACE Alternati e Plan Report


90/144


(2008)

In Denville: Preliminary Screening

Several flood management measuresevaluated (levees, channels, reservoirs,diversion combinations

Only structural measure selected wasdiversion (thus tunnel from Dover to LakeEstling)



91/144


(2008)

In Denville: Preliminary ScreeningPlan 2 Denville only levee system

Plan 2A NJ Foundation for Blind Levee

Plan 4 Channel Modifications 100-Year

protection (Boonton to Dover)

Plan 5 Channel Modification 25-Yearprotection (Boonton to Denville)

Plans 6 through 9 Reservoir (detention)

(Longwood Valley, Green Pond Brook,Beaver Brook)



92/144


(2008)

In Denville: Preliminary ScreeningAll screened out due to one or more:

Limited protection

Aesthetic im acts

Environmental impacts

Not economically justified

Specific to Reservoirs - Not supported by non-Federal interests



93/144


(2008)

5 Alternative Plans Evaluated forRockaway River - Dover to Boonton

Denville components:

, ,backflow gates, Powerville Dam modifications

Plan B and C Nonstructural

Plans D and E Limited channelimprovements, Powerville dam modifications



94/144


(2008)

For each of the 5 Plans:

USACE evaluated environmental impacts

Selected Alternative Plan D



95/144


(2008)

Alternative Plan D NED PlanDenville Limited channel improvements

25-foot channel cut within banks

Dover Lar e diversion culvert

Level of Protection:

Denville: 2-Year

Dover: 25-Year



96/144


(2008)

Alternative Plan D NED PlanProject Cost Est. $111 million (2010

construction, exclusive of mitigation)

17% associated with channel modifications

88% of channel through Denville anddownstream

Proportional cost through Denville to Boonton,roughly $17 million (2010 construction,

exclusive of mitigation)



97/144


(2008)

Alternative Plan D NED Plan

What do you get for $17 million + ?

Benefits to Denville



98/144


(2008)

Alt. Plan D - Benefits to Denville

For 2-Year and 5-Year up to 0.5 lower

For 25-Year greater than 0.5 lower

For 100-Year 0.2 reduction in flooddepth



99/144


(2008)

Flood Damage reduction benefits toDenville:

Alt. Plan D:

. ,protection

For Non-structural Alternative

$0.4 million if only non-structural upstream

$1.4 million if structural measures (includingdiversion culvert) constructed upstream



100/144


(2008)

B/C ratio for Denville Alt D.Est. annual benefits at $523,300

Est. annual cost $1.1 million (based on

B/C = 0.523/1.1 = 0.48 < 1

Conclusions:



101/144


(2008)

Conclusion for Denville: based upon abovereview

River not cost effective: B/C < 1

Non-structural measures may have some

merit (can be done where justified)



102/144


(2008)

Conclusion for Upper Rockaway River:

USACE Selected Alternative Plan D as the.

Since no non-Federal sponsor

No further work after 2006

Evaluation not completed

No Recommended Plan


103/144




r ges an owerv e amDredging and maintenance

Regional detention facilities



104/144


Bridges and Powerville DamUSACE screened out alternative

HMM review:

H draulic anal sis of Rockawa River

Existing conditions

Remove all bridges and Powerville Dam

No channel modifications


105/144

Bridges and Powerville Dam

HMM review:Flood reduction with no bridges and no

Powerville Dam

Flows: 2, 10, 50, 100-Year

Flood depth reduction:Pocono Rd: 2-Yr -0.35 50-Yr 0.99

Diamond Spr. Rd: 2-Yr -0.15 50-Yr 1.05

Cannot remove all structures, so best

achievable will be less than indicated.


106/144


Dredging and Maintenance

USACE concluded 25-foot channel cut


107/144


Rockaway River is flat low velocity overlong distance

Larger channel cross section with sameflat slo e results in slower velocities

Lower velocities result in more sedimentaccumulation

Channel dredging has temporary

benefits, may be short-lived.


108/144


Benefits of extensive channel dredgingappear to be minimal

Limited improvement of capacity within thechannel banks

Rockaway River capacity depends onoverbanks for major flows


109/144


Good maintenance:Remove sediment at bridges and narrow

locations requires periodic cleaning

Remove trash and debris from river and

overbanks (prevent obstruction at bridges)Regular maintenance program and special

effort before and after storm


110/144


Regional Detention FacilitiesPrior Study by Morris County Looked At:

Longwood Valley

Green Pond Brook not effective er USACE

Dalrymple Pond

Mill Brook

Beaver Brook

Stony Brook

R i R i l C


111/144


Regional Detention FacilitiesUSACE found 5 of the sites potentially

beneficial to lower 100-year water surface byapproximately one-foot.

Screened out due to no interest by non-Federal sponsor.

May merit another look.



112/144




Focus on Denville CenterSome local alternatives

Paste 100-yr

100-YEAR


113/144

Paste 100 yr

F D ill C t


114/144


Structural measures - concepts

Consider elevation of structures wherepractical

oo warn ng sys emNow have 3 active stream gages


115/144

STRUCTURAL CONCEPTS


FORDENVILLE CENTER

F D ill C t


116/144

Focus on Denville CenterAddress natural divides

Low areas along river

Need for barriers gates, tide gates,levees/walls

Storage loss H&H for effect on peak flowand water surface elevation

Floodway constraints

Stormwater pumping

Grant application

Considered Pump Station


117/144

Co s de ed u p Stat o

Locations

Denville has submitted (2012) a grantapplication for 2 pump stations at Rt. 46near Den Brook

Hinchman-Corey drainage area.

PS#2 Would convey the flow from the1st Avenue, Bloomfield Ave. drainage

area.


118/144

PS#1 At Rt. 46 Hinchman-Corey Area


119/144

PS#2 At Rt. 46 - 1stAve. Bloomfield Ave. Area

Storm ater P mp Station


120/144

Stormwater Pump Station

Example: Small station

with one submersiblepump



121/144


Example:Below groundstation with

pump 30 cfs.

Stations maybe designed for

multiple pumps.


122/144

Hinchman Area outfall at Rt. 46


123/144

Thin steel flap gate


124/144

Modern back flow

prevention device


125/144



126/144


Structural measures ConceptsStorm sewer back flow devices

Road regrading

Pump stations



127/144


Structural measures Develop concepts

Evaluate level of protection 50-yr (or 25, or-

H&H for alternatives start w/ 50 yr, thendepending on 50-yr results, look at 25 or 75-yr

Evaluate effects of reduction of floodplainstorage

Road Regrading to Block Overland


128/144

Flow at Gardner Road

10-Yr Flood 25-Yr Flood

FLOODWAY


129/144

504.5 2 Yr

505.6 5 Yr

506.4 10 YrEl. 507.5

FLOODWAY

507.6 25 Yr

508.3 50 Yr

509.0 100 Yr

El. 506.5ABOVE100-YrFLOOD

Street Regrading at Gardner Road

Intersection


130/144

Gardner & Corey

Intersection


131/144

Gardner & Hinchman

FLOODWAY


132/144

504.5 2 Yr

505.6 5 Yr

506.4 10 Yr El. 504CONTOUR

FLOODWAY

507.6 25 Yr

508.3 50 Yr

509.0 100 Yr

El. 507.9ABOVE100-YrFLOOD

Evaluate elevation of houses

BLOOMFIELD AVE NEAR DEN BROOK


133/144

FLOOD WALL WITH

MOVEABLE GATEACROSS ROAD

501.3 2 yr 505.1 25 yr 502.5 5 yr 505.7 50 yr 503.6 10 yr 506.2 100 yr


134/144



135/144


Moveable flood barriers

Example:

Den Brook overflows Rt. 53 bridge and flowsunder Rt. 46 to center of Denville


136/144

Rt. 53 underpass at Rt. 46, near Den Brook

Gate in lowered


137/144

position, allowspassage ofvehicles.

Gate can belifted duringflood event toblock flow of

water.

Concrete piers former Morris Canal


138/144

Concrete piers former Morris Canal

Piers snag debris in river

Picatinny Lake


139/144

Picatinny Lake

13:00 hr 855 cfs (peak)

Gage 200 downstream of Picatinny Lake

Consider Picatinny Lake


140/144

Consider Picatinny Lake

At Denville 100-Yr flow = 6,052 cfs upstreamof Den Brook (Irene would be higher)

Reduce flow by 300 cfs

300/6052 = 5% if full peak on peak (worst

case) 300 cfs over a short period of time would be

attenuated in floodplain from Picatinny toDenville

Small scale modification to control structuresunlikely an effective mitigation plan.

Going Forward


141/144

Going Forward1. Develop and review concepts and alternatives for

downtown area.2. Preliminary modeling to assess impacts.

3. Obtain detailed survey information to better refineconce t lans and im acts anal sis.

4. Public participation on concept plans.

5. Meet with NJDEP to discuss permittingrequirements and State funding.

5. Meet with USACE and solicit Federal funding.

6. Continue to pursue grant opportunities.


142/144

Summary

Resources are available to identify floodareas use with understanding

Flood Control has limitations

Risk ReductionNot practical to eliminate all flooding

Select level of protection


143/144

Questions?

Thank You!


144/144

Thank You!

denville flood mitigation presentation

Documents