Denville Flood Mitigation Presentation
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Transcript of Denville Flood Mitigation Presentation
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Township of DenvilleTownship of Denville
Morris County, New JerseyMorris County, New Jersey
Flood Risk ReductionFlood Risk Reduction
ConsiderationsConsiderationsJanuary 29, 2013
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Presented by:
HATCH MOTT MACDONALD
John Ruschke, PE, CME, CFM
Leo Coakley, PE, PP
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TOPICS
Hurricane Irene in Perspective
Rainfall and flood frequency
Flood Maps and Updates
Prior Mapping and Reports
Denville Center - Concepts
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Rockaway River
Below Den Brook 97 Sq. Mi.
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Hurricane Irene
August 27 - 28, 2011
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Hurricane Irene -
Rainfall before and during
Peak Flows
Com are to Au ust 2000
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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
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The Ground Was Saturated!
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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
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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
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Rainfall and Flood Recurrence
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
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Rainfall and Flood Recurrence
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.
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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
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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)
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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)
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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
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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)
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Annual Peak StreamflowAbove Reservoir at Boonton 1937-2010
Irene8,210
6000
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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)
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Comparison of Peak Flows
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
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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
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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
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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
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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)
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Comparison of Peak Flows
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
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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)
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Flows at Denville vs. Boonton
Denville is subject to flooding for veryfrequent floods less than the 10-Year
eak.
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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.
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FLOOD MAPS AND UPDATES
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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
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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.
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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)
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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
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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
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NJDEP Flood Delineation Map
SAMPLE MAP
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Flood Plain Mapping - FEMA
Coming soon:
Modernized FEMA maps for
Morris County will be availablethrough Google Earth -expected mid-2013
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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)
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S
A
M
P
L
E
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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
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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
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Denville Inundation Mapping -
HMM
Slides will progress through areas ofinundation for:
10-year
-50-year
100-year
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Paste 10-yr10-YEAR
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Paste 10-yr10-YEARGARDNER
ROAD
Separatefloodplainfor each
river
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Paste 25-yr25-YEAR
Floodplainsconnectandintermingle
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Paste 50-yr 50-YEAR
Expanded
Connections
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Paste 100-yr100-YEAR
Full Flow
ConnectionOver Rt. 46
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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
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100-Year
FloodDepth MapZones for:
- ,2-4,
4-6,6+
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FLOOD RISK REDUCTION
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FLOOD RISK REDUCTION
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.
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FLOOD RISK REDUCTION
Review of Prior Investigations
Review Re ional Conce ts
Focus on Denville Center
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FLOOD RISK REDUCTION
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)
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FLOOD RISK REDUCTION
Review Regional Concepts
Bridges and Powerville Dam
Dredging and maintenance
Regional detention facilities
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FLOOD RISK REDUCTION
Focus on Denville Center
Some local alternatives for consideration
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REVIEW OF PRIOR
Flood Risk Reduction
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Review of Prior Investigations
Flooding in Denville has been studiedbefore:
Corps of Engineers (USACE)
Morris County
env e s consu an s
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Review of Prior Investigations
No silver bullet
Difficult and costly to address
Environmental constraints have becomemore restrictive (2007 NJ- FHA Rules)
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NJDEP Flood Hazard Rules
2007 rules are stricter
No negative effects
W.S. chan e tolerance0.04 ft. (1/2 inch)
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NJDEP Flood Hazard Rules
NJDEP Rules are currentlunder review for revision willthey be more practical???
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Review of Prior Investigations
Morris County, New Jersey, Multi-
Jurisdictional Hazard Mitigation Plan,prepared by Morris County Office of Emergency
Management, Third Final Draft July 23, 2010.
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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
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County All Hazard Plan (2010)
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
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County All Hazard Plan (2010)
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
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County All Hazard Plan (2010)
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.
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County All Hazard Plan (2010)
Comments:
Item1. Retention Basins for Den Brook (3basins)
Location: not s ecified. Generall betweenRt. 46 and I-80
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County All Hazard Plan (2010)
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
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County All Hazard Plan (2010)
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.
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County All Hazard Plan (2010)
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%
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County All Hazard Plan (2010)
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.
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County All Hazard Plan (2010)
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).
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Review of Prior Investigations
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
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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
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2012 Map of Repetitive Loss
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.
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2012 Map of Repetitive Loss
Properties (comments)
Remaining 53 sites should be evaluatedfor elevation
(see FEMA guidelines)
Inundation Depth Map can be useful forplanning
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Review of Prior Investigations
Master Drainage Plan, Elson T. Killam
(includes a list of prioritized projects.)
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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
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Master Drainage Plan (1980)
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)
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Master Drainage Plan (1980)
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
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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
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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.
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Master Drainage Plan (1980)
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
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Review of Prior Investigations
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
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USACE Alternative Plan Report
(2008)
Not the first look at the Rockaway River bythe USACE
USACE Alt ti Pl R t
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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)
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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)
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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
USACE Alternative Plan Report
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USACE Alternative Plan Report
(2008)
For each of the 5 Plans:
USACE evaluated environmental impacts
Selected Alternative Plan D
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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)
USACE Alternative Plan Report
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USACE Alternative Plan Report
(2008)
Alternative Plan D NED Plan
What do you get for $17 million + ?
Benefits to Denville
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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
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USACE Alternative Plan Report
(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:
USACE Alternative Plan Report
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USACE Alternative Plan Report
(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)
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USACE Alternative Plan Report
(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
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FLOOD RISK REDUCTION
Review of Prior Investigations
Review Regional Concepts
r ges an owerv e amDredging and maintenance
Regional detention facilities
Focus on Denville Center
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Review Regional Concepts
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
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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.
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Review Regional Concepts
Dredging and Maintenance
USACE concluded 25-foot channel cut
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Dredging and Maintenance
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.
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Dredging and Maintenance
Benefits of extensive channel dredgingappear to be minimal
Limited improvement of capacity within thechannel banks
Rockaway River capacity depends onoverbanks for major flows
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Dredging and Maintenance
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
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Review Regional Concepts
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
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Review Regional Concepts
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.
FLOOD RISK REDUCTION
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FLOOD RISK REDUCTION
Review of Prior Investigations
Review Regional Concepts
Focus on Denville CenterSome local alternatives
Paste 100-yr
100-YEAR
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Paste 100 yr
F D ill C t
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Focus on Denville Center
Structural measures - concepts
Consider elevation of structures wherepractical
oo warn ng sys emNow have 3 active stream gages
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STRUCTURAL CONCEPTS
FLOOD RISK REDUCTION
FORDENVILLE CENTER
F D ill C t
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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
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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.
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PS#1 At Rt. 46 Hinchman-Corey Area
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PS#2 At Rt. 46 - 1stAve. Bloomfield Ave. Area
Storm ater P mp Station
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Stormwater Pump Station
Example: Small station
with one submersiblepump
Stormwater Pump Station
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Stormwater Pump Station
Example:Below groundstation with
pump 30 cfs.
Stations maybe designed for
multiple pumps.
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Hinchman Area outfall at Rt. 46
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Thin steel flap gate
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Modern back flow
prevention device
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Focus on Denville Center
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Focus on Denville Center
Structural measures ConceptsStorm sewer back flow devices
Road regrading
Pump stations
Focus on Denville Center
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Focus on Denville Center
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
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Flow at Gardner Road
10-Yr Flood 25-Yr Flood
FLOODWAY
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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
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Gardner & Corey
Intersection
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Gardner & Hinchman
FLOODWAY
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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
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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
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Focus on Denville Center
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Focus on Denville Center
Moveable flood barriers
Example:
Den Brook overflows Rt. 53 bridge and flowsunder Rt. 46 to center of Denville
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Rt. 53 underpass at Rt. 46, near Den Brook
Gate in lowered
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position, allowspassage ofvehicles.
Gate can belifted duringflood event toblock flow of
water.
Concrete piers former Morris Canal
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Concrete piers former Morris Canal
Piers snag debris in river
Picatinny Lake
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Picatinny Lake
13:00 hr 855 cfs (peak)
Gage 200 downstream of Picatinny Lake
Consider Picatinny Lake
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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
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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.
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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
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Questions?
Thank You!
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Thank You!