Flood Storage, Damage Reduction & Dam Removal

Report
Combining Conservation
& Hazard Mitigation: The
case for dam removal
and stream restoration in
flood damage reduction
Sara Strassman
American Rivers
Director, River Restoration,
Upper Midwest
Thank You, Contributors!
 Tom
MacDonald, Rita Weaver, Nathan
Campeau: Barr Engineering
 Jake Helminiak & Geoff Goll: Princeton
Hydro
 Bob Watson: WI DNR
 Andy Selle: Inter-Fluve
 Amy Singler, Lisa Hollingsworth-Segedy,
and Brian Graber: American Rivers
Who is American Rivers?
 Founded
in 1973
 National, non-profit, river conservation
organization
 We protect and restore America’s rivers
and the clean water that sustains people,
wildlife, and nature.
 River Restoration Program works on dam
removal and floodplain management
projects and policies
Talk Outline
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How dam removal & FPM align
Snapshot of Texas dams
Traditional motivations for dam removal
Cases of dam removals with flood benefits
Characteristics of dam removals with flood
benefits
Opportunities for collaboration
How dam removal & FPM align
 Many
dams have two primary mechanisms
for affecting flooding:


Reduced instream storage upstream
Dam failure resulting in downstream flooding
 Dams
impact floodplain connectivity and
frequency of out-of-bank flooding
 Some removal projects can incorporate
floodplain or wetland restoration
 Both arenas form a bridge between
conservation and hazard mitigation
practices
Texas Snapshot
 7173
dams in the NID
 Everything is bigger in Texas:
More than 450 dams greater than 50’ in
Primary Purpose
height
Flood control
 Ownership is similar to many other Recreation
states
with majority of dams privately owned
Water supply
(61%), local gov’t (35%)
Fire/livestock
 We’ve got a lot of dirt sitting around…97%
are earthen dams
Hydropower
Other purposes
Traditional motivations for dam
removal
 In







average order of prominence:
Liability of structure
Poor condition/problems caused by structure
Obsolescence
Economics of repair vs. removal
Ecological benefits
Water quality
Recreational improvements
Flood Damage Reduction Projects

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Opportunities for increased floodplain roughness
Low valley slope & low-moderate channel slope
Dams with high aspect ratio
Dams currently contributing to localized
flooding/proximity to flood prone areas
Dams within leveed river reaches
Multiple removals
Dams with full hydraulic height still in place
Measurements:



Trying to affect change at 5-10km scale
Target 2 to 100-yr recurrence interval
Watershed should have good hydrology data (ideally,
USGS gages)
Dunkard Creek, PA
Motivation for dam removal:
Lower Dam: Ecological Restoration
Upper Dam: Liability
Flood benefits: Reduced frequency of
egress road flooding
Dunkard Site
Dunkard Creek Dam Removals
Hydrology Summary -- Within Brave Station Dam Impoundment
100,000
Dunkard Creek Flood Benefits
USGS SteamStats
Existing Threshold Discharge
Estimated Peak Discharge (cfs)
Proposed Threshold Discharge
10,000
1,000
1000
100
~13-yr 10
Average Recurrence Interval (yr)
~3.3-yr
1
Baraboo River, WI
Dams removed in 1972, 1973,
1996, 1997, 1999, 2001
© Louis J. Maher, Jr.
Motivation for dam removal:
Liability, poor condition,
ecological benefits
Flood benefits: Reduced
flooding of structures and
farmland
Baraboo River, WI
•
Tributary to Wisconsin River
•
120 miles long
•
650 mi2 watershed
•
150 ft drop in elevation
•
•
•
•
45 ft drop through City of
Baraboo
4 dams removed in City of
Baraboo
3 dams removed in upstream
communities
History of past flooding,
including 2008
Photo: UW-Extension
Data & Analysis

Data-rich system
Recurrence Interval
(HEC-HMS,
flood height
Rainfall Depth (inches)
ground-truthing,
HEC-RAS)
10-yr
4.8
50-yr
6.3
 Dam break analysis was conducted with
100-yr
7.0
HEC-RAS
500-yrusing a model with all
8.4 7 dams
 ‘With dam’ and ‘Without dam’ scenarios
looked at multiple flows ranging from 10-yr
through 2008 floods (estimated at ~200-yr)
Sauk County Hazard Mitigation
Total Losses
Losses Open Losses Unpaid
Losses
Totaltop
Payments
Flooding
andClosed
thunderstorms
were
the
5
4
0
1
119,974.05
2 natural hazards
for
when
35
31 the county
2
2
1,840,180.40
2
2 probability,
0
0
1,755.90
scored by frequency,
1
1
0
0
140,742.08
magnitude of
29 impacts
21 and damages.
0
8
900,800.98
1
1
0
0
1,121.67
Flooding received
the
highest
estimate
of7,402.72
1
1
0
0
39
29
0
10
363,299.01
damages of113all natural
disasters,
at21 3,375,276.81
90
2
$312.7M from 1950-2009 ($69.6M
property, $243.1M crops)
 Since 2000, they have had 3 Presidential
disaster declarations for flooding
Municipality

Baraboo
Reedsburg
La Valle
North Freedom
Rock Springs
Sauk City
Baraboo
West
Unincorporated
Total
Opportunities for Hazard
Mitigation
 There
are 2 repetitive loss properties in a
neighborhood where flooding was reduced
as a result of dam removal (exact location
of properties is protected)
 Threat of dam failure was removed
 Median dam removal costs
(design+construction) are around $80K,
with a range from $2K to $7.9M (average
dam size 9’)
Noah Hofrichter; http://www.fuzzyworld3.com/3um/viewtopic.php?f=14&t=2456page
Why should floodplain managers
care about dam removal?
 Can
directly mitigate a flood hazard
 Is a cheap alternative to repairs when
structures are damaged during floods
 Provides quick results
 Decommissions obsolete infrastructure
 Addresses safety liability (of particular
concern for river rescue and evacuation)
 Springboard to other beneficial projects
 Healthy rivers are more resilient to climate
change impacts
Related restoration
opportunities
 Culverts
 Wetland
restoration
 Levee
modification/removal
Comparison of Funding
Dams, culverts, river
restoration
 Ecological restoration
(fish passage, aquatic
habitat, wetlands)
 Dam & Public Safety
 Water quality
 Mitigation
 Recreation/parks
Hazard mitigation/FPM
 Dam & Public Safety
 HMA grants
 PA
 Community Block Grants
 HUD programs
 Economic Development
grants
Combining these pots of funding will leverage
more dollars for both sets of practices
Thank You!
Questions?
Sara Strassman
516 23rd St N
La Crosse, WI 54601
608-782-1537 (office)
608-799-2454 (cell)
[email protected]
State Hazard Mitigation Plans
 Iowa
called out 330 high & significant
hazard dams, but the total number is more
than 3,700
 Wisconsin
Dam removal is nifty!
How do I get stated?
Determine the challenges specific to your
project
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Sediment quantity
Sediment quality
Dam size
Dam condition
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Impoundment size
Impoundment shape
Surrounding infrastructure
Surrounding environment
Scale your analysis to the level of complexity!
Initial
Reconnaissance
Bushkill
Initial Reconnaissance
Initial Reconnaissance

What did we learn?
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Urban setting (how might this affect project?)
Potential infrastructure conflicts
Flooding conditions
Other barriers
Stream gradient/basic character
How do we use the information?
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Consider possible funding sources
Begin evaluating scale of complexity
Identify potential stakeholders
Refine search for additional information
Large impoundment with small restored river
Typical run of river dam
Wapsipinicon River, IA
Motivation for dam removal:
Liability, poor condition,
ecological benefits
Flood benefits: Reduce flood
extent & risk of dam failure
No Dam
With Dam
Wapsipinicon River, IA
 Flooding
reduced on smaller events 5-yr
or less, as overbank flow is initiated on a
4-yr instead of 2-yr event
 Homes are located pretty close to the
water
 Flood reduction benefits are important to
the community
 Still undecided on whether to remove the
dam
Connoquennessing Creek, PA
Motivation for dam removal:
Ecological Restoration, Recreation
Flood benefits: Reduced frequency of
property flooding
Connoquennessing Creek,
Harmony, PA

Dam was purchased by local watershed group
for purpose of removal for ecological and
recreational purposes
 On June 16-17, 2009 while the dam was
partially removed (WSEL reduced by about 4
feet) a storm caused the discharge to jump from
80cfs to 1200cfs. An adjacent property owner
called to report that he normally would have
flooded at that discharge, but the water stayed in
the channel.

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