NRCS Mohawk Watershed Symposium

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NRCS Mohawk Watershed Symposium

  1. 1. Natural Channel Restoration afterIrene and Leea Schoharie County OpportunityWill VanDeValk, Area EngineerUSDA/NRCS2013 Mohawk Watershed Symposium 1
  2. 2. NRCS Emergency WatershedProtection Program Several towns approached NRCS in late 2011 seekingtechnical and financial assistance State Office staff evaluated sites for EWP eligibility 10 sites (reaches) on 6 Streams were determined eligible Significant Threat to Public Health and Safety 75% NRCS Funding for construction(25% Local Match req’d) NRCS determined that a holistic approach to streamrestoration is critical to long-term success2
  3. 3. Platter Kill/Flat Creek Road (5,500 LF reach) Approx. 40-ft high raw bank near upstream end of5,500 LF reach3
  4. 4. Platter Kill/Flat Creek Road (5,500 LF reach) Loose, saturated, highly-erodible bank Bed & bank armoring washed away by flood4
  5. 5. Platter Kill/Flat Creek Road (5,500 LF reach) Approx. 50-ft high near vertical bank Bed & lower bank armoring washed away by flood5
  6. 6. Platter Kill/Flat Creek Road (5,500 LF reach) Home site destroyed by channel relocation6
  7. 7. Platter Kill/Flat Creek Road (5,500 LF reach) 15-ft wide x 7-ft high box culvert beneath roadway7
  8. 8. Little Schoharie Reach A (9,600 LF reach) Overwidened channel w/ loose berms8
  9. 9. Little Schoharie Reach B (8,200 LF reach) 40-ft high raw bank below laboratory facility9
  10. 10. Little Schoharie Reach B (8,200 LF reach) Downcutting of exposed clay/silt material10
  11. 11. Little Schoharie Reach C (6,000 LF reach) Original meandering channel, abandoned by flood11
  12. 12. Little Schoharie Reach C (6,000 LF reach) Approx. 20-ft high eroding bank near Brooky Hollow Evidence of considerable downcutting12
  13. 13. Little Schoharie Reach D (6,700 LF reach) Sharp bend @ Huntersland Rd., 10’ – 15’ downcutting13
  14. 14. Little Schoharie Reach D (6,700 LF reach) Conditions on 1/24/12 (~ 5 mos. after Irene)14
  15. 15. Little Schoharie Reach D (6,700 LF reach)15 Conditions on 3/06/13 (~ 18 mos. after Irene)
  16. 16. Little Schoharie Reach D (6,700 LF reach) Sloughing of bank near residence as stream downcutsg16
  17. 17. 17
  18. 18. Line Creek/Mill Valley Rd. (10,400 LF reach) Home site destroyed by channel relocation18
  19. 19. Line Creek/Mill ValleyRd. (10,400 LF reach) Stream adjacent to road& residences Some hard-armoring orstructural solutions maybe required19
  20. 20. Damage Survey Report (DSR) Process Field Procedures (began in Jan. 2012) GPS-locate features & estimate lengths & heights Office Procedures (Conceptual – Level) Enter field data into GIS system Preliminary Hydrologic & Hydraulic analyses Conceptual solution (reconnect stream w/ floodplain,remove berms, restore meander pattern, size channelfor 1 to 2 year flows, provide grade-control, revegetatebanks, hard-armoring only where necessary) Quantity estimates Cost Estimating (completed 3/27/12)20
  21. 21.  Loss of stream meander Raw Bank Height & Areaestimates ~ 885,000 sq. ft. of rawbank along 5.6 miles(Reaches A – D)21
  22. 22. Project Finances (NRCS estimates) 10 Project sites on 6 streams covering approximately47,300 LF (9 miles) of stream Construction Cost estimated at $21.2M NRCS share (75%) = $15.9M NYS has agreed to fund Local share (25%) = $5.3M NRCS will fund up to $1.59M for allowable non-construction costs (administration, engineering, etc.)22
  23. 23. Project Plan – Schoharie County EWP County under contract with AECOM to “ProvideAssessment, Design and Construction Administrationfor Support of Natural Stream Restoration Projects” Assessment & Design in 1st half of 2013 Construction to begin this summer, with completion bymid-January, 2014 (EWP condition)23
  24. 24. Fluvial Geomorphology The study of how landforms change with time underthe influence of rivers and streams Frequently takes a “watershed scale approach” Attempts to work with a river’s natural processesvs. Conventional Channelization Tends to make the river conform to a preconceivedregular shape Often used in short reaches, to meet very specificcriteria (e.g. 100-year flood)24
  25. 25. Conventional Channelization Wide, trapezoidalchannel Often straight25• Contain Floods
  26. 26. Conventional Channelization Wide, trapezoidalchannel Often straight26• Contain Floods• Levees sometimesused
  27. 27. Conventional Channelization Wide, trapezoidalchannel Often straight27• Contain Floods• Levees sometimesused• Low flows wide &shallow
  28. 28. Natural Channel Design28• Irregular shape w/low-flow channel• Meandering• Channel contains~ 1.5 year flood(Bankfull Flow)
  29. 29. Natural Channel Design29• Irregular shape w/low-flow channel• Meandering• Channel contains~ 1.5 year flood(Bankfull Flow)• Higher flows usefloodplain
  30. 30. Natural Channel Design30• Irregular shape w/low-flow channel• Meandering• Channel contains~ 1.5 year flood(Bankfull Flow)• Higher flows usefloodplain• Low flows confined
  31. 31. Side-by-side Comparison31• Natural Channel Design •Conventional ChannelizationLow FlowsLow Flows
  32. 32. Side-by-side Comparison32• Natural Channel Design •Conventional ChannelizationBankfull(~ 1.5 yr Flood)Design Flood(>>1.5 yr flood)
  33. 33. Side-by-side Comparison33• Natural Channel Design •Conventional ChannelizationLarge FloodsLarge Floods(if berms are used)
  34. 34. Energy Balance of Streams (Lane, 1955)34
  35. 35. Regional Curves – Flow35
  36. 36. Energy Dissipation in Stable Streams Bed Roughness Form Resistance- Step Pools (steeper streams)- Riffle/Pool sequences (moderate slope streams)- Meander Pattern (flatter streams) Floodplain acts like an “Energy Relief Valve”36
  37. 37.  Rock cross-vanes forenergy redirection,grade control &sediment transport37Man-madeapproaches
  38. 38. Bed Material is Important!38
  39. 39. Summary – Natural Channel Design puts the ~ 1.5 year flood in the channel and larger floodsout onto a floodplain Low-Flow conditions, Water Quality, Habitat, EcosystemFunction, and Resilience are all important In areas w/out an adequate floodplain, other methods (ora combination of methods) may be necessary Requires extensive data collection & analysis should provide Schoharie County with many streamcorridor benefits39
  40. 40. Slide 40"The U.S. Department of Agriculture (USDA) prohibitsdiscrimination in all of its programs and activities on the basisof race, color, national origin, age, disability, and whereapplicable, sex, marital status, familial status, parental status,religion, sexual orientation, political beliefs, geneticinformation, reprisal, or because all or part of an individualsincome is derived from any public assistance program. (Notall prohibited bases apply to all programs.) Persons withdisabilities who require alternative means for communicationof program information (Braille, large print, audiotape, etc.)should contact USDAs TARGET Center at (202) 720-2600(voice and TDD).“To file a complaint of discrimination, write to USDA, AssistantSecretary for Civil Rights, Office of the Assistant Secretary forCivil Rights, 1400 Independence Avenue, S.W., Stop 9410,Washington, DC 20250-9410, or call toll-free at (866) 632-9992 (English) or (800) 877-8339 (TDD) or (866) 377-8642(English Federal-relay) or (800) 845-6136 (Spanish Federal-relay). USDA is an equal opportunity provider and employer.

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