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 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 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 Sediment quantity Sediment quality Dam size Dam condition 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? Urban setting (how might this affect project?) Potential infrastructure conflicts Flooding conditions Other barriers Stream gradient/basic character How do we use the information? 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.