Development of Technical Data For Long Term Flood Solutions For the Red River Basin

Transcription

1 IDENTIFYING WHAT WE DIDN T KNOW Development of Technical Data For Long Term Flood Solutions For the Red River Basin

2 LTFS Study Area U.S. Portion of Red River Basin (MN, ND & SD) Main Stem Red River Tributaries

3 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

4 Winnipeg Earliest documents of flooding go back to 1798 Largest flood documented was 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

5 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

6 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

7 Maps Uniform Basin Maps for all Watersheds - Streams - Existing Flood Storage - USGS Gages

8 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

9 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

10 Every Flood is Different

11 Antecedent Conditions 1997 & 2009 Floods Winter Snowfall 1997 Water Content 2009

12 Rainfall Events 1975 & 2002 July 1975 June 2002

13 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

14 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

15 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

16 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

17 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

18 Elevation Flow Relationships Red River: Wahpeton to Emerson Elevation - W/B = F/M = Hal = GF = Oslo = Emer = 780 Change in Flow for 1 Ft of Stage Increase at 100 Year Flood Flow Range - W/B = 2,000 cfs - F/M = 5,000 cfs - Hal = 10,000 cfs - GF/EGF= 10,000 cfs - Oslo = 30,000 cfs - Emer = 50,000 cfs

19 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

20 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

21 Summary of Pertinent Information by City Grafton, ND

22 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

23 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

24 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

25 Flood Storage Built 1960 to = 132,000 ac-ft = 132,000 ac-ft = 156,000 ac-ft

26 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

27 Urban Damages 100 Year Flood $6.3 Potential Flood Damages assumes flood fight actions are not successful $2.7 $3.6 Baseline Hydrology thru 1997 Flood 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

28 Potential Urban Damages 100 Year Flood Existing Conditions (2011) $2.7 Billion

29 $11.4 Urban Damages 200 Year Flood $6.2 $5.2 Potential Flood Damages assumes flood fight actions are not successful 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

30 Potential Urban Damages 200 Year Flood Existing Conditions (2011) $6.2 Billion

31 Potential Urban Damages 500 Year Flood Existing Conditions (2011) $10.9 Billion

32 Sensitivity of Flood Damages to Hydrology Baseline (1997) vs. Wet Cycle ( ) 100 yr: $2.7 to $ yr: $6.2 to $ yr: $10.9 to $13.5 $2.7 $3.8 $7.8 $6.2 $10.9 $13.5

33 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

34 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

35 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.

36 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

37 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

38 Potential Flood Damages Preventable by Projects in LTFS Plan $12.8 $10.2 $7.8 $6.3 $2.8 $ Year 200 Year 500 Year

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43 Existing Flood Storage in Red River Basin