IDENTIFYING WHAT WE DIDN’T KNOW Development of Technical Data For Long Term Flood Solutions For the Red River Basin resourceful. naturally. LTFS Study Area • U.S. Portion of Red River Basin (MN, ND & SD) • Main Stem Red River • Tributaries resourceful. naturally. Items Needed for Development of Plan • Level of Protection Goals • Consistent mapping and data • Understanding Floods Along Red River • Existing Projects • Potential Flood Damages • Effectiveness of Alternatives resourceful. naturally. Winnipeg • Earliest documents of flooding go back to 1798 •Largest flood documented was 1826. Peak flow was estimated about 225,000 cfs, about 40% greater than in 1997 • Winnipeg Floodway was expanded in 2010 to handle 140,000 cfs and safely pass about 700 year flood through Winnipeg resourceful. naturally. Level of Protection Goals • Establish “Level of Flood Protection” goals to use as “Guideline” to achieve Flood Resiliency • Major Urban areas and critical infrastructure – 500 year flood or greater • Cities – 200 flood year or greater • Rural residences/farmsteads – 100 year flood or greater • Use “flood of record” as goal if it is larger than the “guideline frequency” event resourceful. naturally. Consistent Mapping & Data Compilation • Develop maps for basin that shown similar data and information for all watersheds • Economic and other data should be compiled to be comparable between states and watersheds • Evaluation of alternatives will focus on Red River main stem, but consider effects along tributaries wherever possible resourceful. naturally. Maps Uniform Basin Maps for all Watersheds - Streams - Existing Flood Storage - USGS Gages resourceful. naturally. Runoff Models • HEC-HMS Runoff Models for subbasins • Same criteria for all subbasins • Use LiDAR data • Travel times • Non-contributing areas • Can be used to estimate effectiveness of retention sites resourceful. naturally. Understanding Red River Floods • Basic factors related to a spring or summer event (water content, etc.) • Timing of Flows from tributary subbasins • Characteristics of each subbasin • Effects of existing flood storage resourceful. naturally. Every Flood is Different resourceful. naturally. Antecedent Conditions 1997 & 2009 Floods Winter Snowfall Water Content 1997 2009 resourceful. naturally. Rainfall Events – 1975 & 2002 July 1975 June 2002 resourceful. naturally. 2009 Flood - Fargo • White Rock Dam – no flow contributed to Fargo peak • Ottertail River/Orwell had small effect at Fargo • Drainage area upstream of Wahpeton/Breckenridge had major contribution to Fargo peak • Wild Rice River upstream of Abercrombie had major contribution to Fargo peak resourceful. naturally. 2009 Flood - Fargo •White Rock Dam – no flow contributed to Fargo peak • Drainage area upstream of Wahpeton/Breckenridge had major contribution to Fargo peak •Drainage area along Red River between Wahpeton/Breckenridge and Fargo had major contribution to Fargo peak • Wild Rice River upstream of Abercrombie had major contribution to Fargo peak resourceful. naturally. 1997 Flood - Fargo • Releases from White Rock Dam did affect Fargo peak; This was only flood where this has occurred • Drainage area upstream of Wahpeton/Breckenridge contributed to Fargo peak • Drainage area along Red River between Wahpeton/Breckenridge and Fargo was not a major contributor to Fargo peak •Wild Rice River upstream of Abercrombie was major contributor to Fargo peak resourceful. naturally. 2009 Flood - Halstad • Peak flows from the Sheyenne River occurred several weeks after peak at Halstad; not major contributor to Halstad peak. • Maple River had 2 peaks; first peak contributed to Halstad peak • Maple River Dam reduced the Maple River’s contribution to the Halstad peak • First peak from Maple River that contributed to Halstad peak was mainly from the drainage area downstream of Maple River Dam resourceful. naturally. 2009 Flood - Emerson • The flood peak from Fargo/Moorhead continued downstream to Emerson • This was generally consistent with other large floods for which data is available resourceful. naturally. Elevation – Flow Relationships Red River: Wahpeton to Emerson Elevation Change in Flow for 1 Ft - W/B = 960 of Stage Increase at 100 - F/M = 900 Year Flood Flow Range - Hal = 860 - W/B = 2,000 cfs - GF = 825 - F/M = 5,000 cfs - Oslo = 810 - Hal = 10,000 cfs - Emer = 780 - GF/EGF= 10,000 cfs - Oslo = 30,000 cfs - Emer = 50,000 cfs resourceful. naturally. Analysis of Different Periods of Flow Records •Baseline through 1997 flood is currently in use • Shorter wet period increases flows at Fargo, by most agencies (Red) but decreases flows for large events at Grand • Updating through 2009 flood increases flows Forks (Green) for various frequency events (Blue) • Changes larger at Fargo; smaller at Grand Forks resourceful. naturally. Existing Flood Risk Reduction Projects • Compile data on existing projects from Federal and state agencies and cities and watershed districts • Local protection: Permanent projects; levels of protection • Flood storage projects resourceful. naturally. Summary of Pertinent Information by City Grafton, ND resourceful. naturally. Flood Insurance Policies Issued • Policies increased in 1997 due to forecast flooding • Policies in Moorhead increased in 2009, 2010 & 2011 due to forecast flooding • Policies at Warren dropped off after levee & diversion project completed • Policies at EGF in “required zone” dropped off after levee project completed resourceful. naturally. Existing Permanent Flood Risk Reduction Projects • Red River Main Stem – 9 of 22 Cities w/ 100 yr or greater protection – Only 2 meet “Level of Protection” goals • MN Tributaries – 5 of 40 Cities w/ 100 yr or greater protection • ND Tributaries – 7 of 37 Cities w/ 100 yr or greater protection – Only 1 meets “Level of Protection” goals resourceful. naturally. Flood Storage Built in Basin 1909 to 2010 • Total Existing Flood Storage = 1.9 Million Ac-Ft • About 75% by Federal Agencies with non-Federal partners • Much of early storage was dual-use, with flood storage obtained by winter/spring drawdown of pool resourceful. naturally. Flood Storage Built – 1960 to 2010 1960-79 = 132,000 ac-ft 1980-99 = 132,000 ac-ft 2000-10 = 156,000 ac-ft resourceful. naturally. Potential Flood Damages • Urban – Corps Data indexed to 2010/2011 Price Levels • Agricultural – Agency Data for 1975, 1979, 2002 & other floods • Rural Farmsteads & Residences – Corps 2011 inventory plus other agency data • Transportation – Agency information resourceful. naturally. Urban Damages 100 Year Flood • Potential Flood Damages $6.3 – assumes flood fight actions are not successful •Baseline Hydrology – thru $3.6 1997 Flood $2.7 • Damages Prevented by Existing Flood Storage Projects = $2.2 Billion • Damages Prevented by Existing Local Protection Projects = $1.4 Billion • Potential Remaining Flood Damages = $2.7 Billion resourceful. naturally. Potential Urban Damages – 100 Year Flood Existing Conditions (2011) $2.7 Billion resourceful. naturally. $11.4 Urban Damages 200 Year Flood •Potential Flood Damages – assumes flood fight actions are not $6.2 successful $5.2 •Baseline Hydrology – thru 1997 Flood • Damages Prevented by Existing Flood Storage Projects = $3.2 Billion • Damages Prevented by Existing Local Protection Projects = $2.0 Billion • Potential Remaining Flood Damages = $6.2 Billion resourceful. naturally. Potential Urban Damages – 200 Year Flood Existing Conditions (2011) $6.2 Billion resourceful. naturally. Potential Urban Damages – 500 Year Flood Existing Conditions (2011) $10.9 Billion resourceful. naturally. Sensitivity of Flood Damages to Hydrology Baseline (1997) vs. Wet Cycle (1942-2009) 100 yr: $2.7 to $3.8 200 yr: $6.2 to $7.8 500 yr: $10.9 to $13.5 $13.5 $10.9 $7.8 $6.2 $3.8 $2.7 resourceful. naturally. Agricultural Flood Damages • Acres Flooded – 10 year flood = 550,000 acres – 50 year flood = 1.1 million acres – 100 year flood = 1.4 million acres • Damages Greatest due to Summer Flood – 1975 summer flood about $1 Billion • Summer Floods affect Tributaries more than Red River main stem resourceful. naturally. 1997 Flooded Area • Red River main stem - Grand Forks to International Border • Very wide floodplain • Widest part of Red River floodplain in the U.S. part of basin • Generally from 6 to 10 miles wide resourceful. naturally. Rural Residences & Farmsteads • Detailed inventory along Red River from Abercrombie to Drayton – 2,400 Residential Structures – 6, 200 Farm Building • Includes barns, grain bins,machine sheds, etc. resourceful. naturally. Components of LTFS Plan • Projects to be Implemented by Cities, Watershed Districts, and States & Federal Agencies • Non-structural Measures – Continued floodplain regulation and buyouts • Local Protection Measures – Levees, floodwalls and diversions at about 40 communities • Upstream Flood Storage – 1.5 Million acre-feet of storage at “appropriate/effective” locations – Distributed throughout subbasins resourceful. naturally. Effectiveness of Alternatives • Red River Main Stem ( MN & ND) (Effectiveness on tributaries difficult to measure at this stage as it is very dependent on amount & location of flood storage) • Combination of LTFS Local Measures & Upstream Flood Retention Storage – 18 of 22 Cities w/ 100 year or greater protection – 9 Cities meet “Level of Protection” goals resourceful. naturally. Potential Flood Damages Preventable by Projects in LTFS Plan $12.8 $10.2 $7.8 $6.3 $4.0 $2.8 100 Year 200 Year 500 Year resourceful. naturally. resourceful. naturally. resourceful. naturally. resourceful. naturally. resourceful. naturally. Existing Flood Storage in Red River Basin resourceful. naturally.
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