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THE ENGINEERED FLOODPLAIN BENCH

THE ENGINEERED FLOODPLAIN BENCH. Conceptually, for an incised system you can: raise the stream, lower the floodplain, or a little of both Lower either one or both banks of the floodplain Or, construct bankfull floodplain benches on either one or both banks.

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THE ENGINEERED FLOODPLAIN BENCH

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  1. THE ENGINEERED FLOODPLAIN BENCH

  2. Conceptually, for an incised system you can: raise the stream, lower the floodplain, or a little of both Lower either one or both banks of the floodplainOr, construct bankfull floodplain benches on either one or both banks

  3. Some designs are very complex, here is a three-stage channel Mini floodplain bench Floodplain bench elevation at height of channel forming discharge Wet meadow active channel

  4. NARROW FLOODPLAIN BENCH ON THE OTTAWA RIVER, OTTAWA HILLS, OHIO

  5. Mini floodplain bench

  6. Looking DS on the Ottawa River, OH, (sand-gravel, less than 1% slope, urban, pool-riffle-pool) note slower water within the veg along left bank, Ottawa River, Ottawa Hills, OH River thalweg delineated by bubble trails

  7. Looking DS, close-up shot Ottawa River, note drag from plants vectoring thalweg away from the bank (second black arrow) Dense plants on narrow floodplain bench effectively reducing near- bank flood velocities!!

  8. Looking DS @ narrow Ottawa River floodplain bench @ low flow. Derrick-7/26/2007

  9. HAW CREEK, PIKE COUNTY, MISSOURI-TRIB TO SALT RIVERERODING STREAM THREATENING COUNTY ROAD #107, FOURTEEN FT TALL ERODING BANKWITHIN 4 FT OF THE ROAD, PROJECT CONSTRUCTED IN 1 DAY, MARCH 10, 2009BY PIKE COUNTY PUBLIC WORKS DEPT, LaDON ATKINSON, ROAD SUPERVISOR

  10. HAW CREEKGENERAL INFORMATION • Bank erosion is threatening county road, threatening public safety • Stream wildly meandering in response to historic straightening • Decent riparian areas in places • Bed material: gravel-sand. Channel is incised • Pool-riffle-pool regime, slope less than 1% • Average width 30-40 ft, 14 ft tall banks • Funding, equipment, and manpower provided by Pike County, MO

  11. PRE-PROJECT PHOTOSby JAYNIE DOERR, REGULATORY, ST. LOUIS DISTRICT FEBRUARY 25, 2009

  12. Looking DS @ the lower end of the project bend. The last two trees undercut & fell in water PRE-PROJECT - HAW CREEK-PIKE COUNTY MO. PIX BY JAYNIE DOERR 2-25-09

  13. Looking US @ the project bend. Road is 4 ft from 14 ft tall eroding bank. PRE-PROJECT - HAW CREEK-PIKE COUNTY MO. PIX BY JAYNIE DOERR 2-25-09

  14. QUESTIONABLE STONE Stone used for keys & LPSTP was a sub-standard shot rock of questionable hardness. The amount of fine material was close to 20-30%. This was a self-filtering stone (too many fines), but not well-graded, & not self-adjusting.

  15. Stone is not well-graded & too many fines. The stone is self-filtering, but not self-adjusting, but only $4.70/ton delivered. CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  16. STONE COSTSHowever, the stone was extremely inexpensive. The 432 tons of rock used in the project, at $4.70 per ton (delivered) total cost of stone = $2032. Very cost effective for what was accomplished. Almost like we paid for hauling & they threw in the stone for free!!

  17. HAW CREEKMETHODS EMPLOYED • 110 ft of Longitudinal Peaked Stone Toe Protection (LPSTP), crest built to 4 ft above the base flow water surface elevation • Locked Logs • A vegetated floodplain bench, planted on a grid • Live Siltation • Live Willow Pole Plantings • Living Dikes • Single-Stone & Short Bendway Weirs • Vegetated & curved upstream key, straight DS key • After the fact Joint Planting in DS riprap bank

  18. We will construct from upstream (US) to downstream (DS)

  19. LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP)

  20. Road Top bank ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) Eroding bank Stream channel

  21. Road ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) Two fallen trees were angled downstream 30 degrees from the bank with the root wads upstream against the eroding bank

  22. LONGITUDINAL PEAKED STONE TOE PROTECTION {LPSTP} • Description: A continuous stone dike placed longitudinally at, or slightly streamward of, the toe of the eroding bank. Cross-section is triangular. The LPSTP does not necessarily follow the toe exactly, but can be placed to form a "smoothed" alignment through the bend. Smoothed alignment might not be desirable from the environmental or energy dissipation points of view . Amount of stone used (2 tons/linear ft, 1 ton/ft, or less) depends on depth of scour at the toe, estimated stream forces (impinging flow) on the bank, and flood durations and stages. • Tie-backs are short dikes connecting the LPSTP to the bank at regular intervals. Tie-backs are usually the same height as the LPSTP or elevated slightly toward the bank end, and are keyed into the bank. If tie-backs are long they should be angled upstream to act as Bendway Weirs.

  23. Longitudinal Peaked Stone Toe Protection (LPSTP) As-built After a high flow event stream has scoured at the toe & some LPSTP stone has self-adjusted (armored the scour hole)

  24. Road ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) Locked Logs are then “locked” under the Longitudinal Peaked Stone Toe Protection (LPSTP).

  25. Looking US. LPSTP crest is 4 ft above base flow stage CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  26. Road Live poles laid against eroded bank ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) Tree or shrub poles (called Live Siltation) installed on top of LPSTP Willow, dogwood, river birch poles can then be laid on the stone and up against the bank. Basal ends should be in vadose zone (capillary zone). Willow only used on this project.

  27. Looking US. Class laying willow poles against eroding bank. CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  28. Road ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) Backfill material from point bar forms a floodplain bench at the Q-2 flood elevation

  29. Looking DS. Backfilling between LPSTP & bank to form floodplain bench @ the Q-2 elevation. CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  30. Looking US. Installing Living Dikes perpendicular to high flow, Live Siltation & Live Poles are parallel with the stream. CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  31. ENHANCED LONGITUDINAL PEAKED STONE TOE PROTECTION (LPSTP) At intervals, install willow Living Dikes (densely deep-planted adventitious poles aligned perpendicular to direction of high flow)

  32. A Living Dike (perpendicular to high flow) on the floodplain bench. CONSTRUCTION-HAW CREEK-PIKE COUNTY, MO. PIX BY DERRICK 3-10-09

  33. Floodplain bench planted on a grid pattern AERIAL VIEW OF ENHANCED LPSTP WITH A FLOODPLAIN BENCH WITH VEGETATION PLANTED ON A GRID PATTERN. Single-Stone Bendway Weir Live Poles Live Siltation Flow Living Dikes-plants perpendicular to flow Single-Stone Bendway Weir

  34. PROJECT CONSTRUCTED IN 1 DAY, MARCH 10, 2009

  35. 4 MONTHS AFTER PROJECT COMPLETIONLooking US to DSPhotos by LaDon Atkinson JULY 11, 2009

  36. 4 MONTHS LATER-Looking DS @ the project bend. 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  37. 4 MONTHS LATER-Looking DS @ floodplain bench 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  38. 4 MONTHS LATER-Looking DS @ the thalweg trace, LPSTP, Bendway Weirs & the floodplain bench. Great growth! 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  39. After 4 months, great growth from the 500 willows we planted! LaDon says the floodplain bench has about 6 inches of sediment deposition on it (eroding bank turned into a depositional feature).

  40. 4 MONTHS AFTER PROJECT COMPLETIONLooking DS to USPhotos by LaDon Atkinson JULY 11, 2009

  41. 4 MONTHS LATER-Looking US @ SSBW, LPSTP & Live Siltation 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  42. 4 MONTHS LATER-Looking US @ project & road 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  43. 4 MONTHS LATER-Looking US @ a Living Dike on the floodplain bench 4 MONTHS LATER - HAW CREEK–From LaDon Atkinson-7-11-09

  44. Haw Creek Project(5 inch rain 48 hours prior to photos) September 20, 2010 Two Growing Seasons After Completion Photos By Rob Gramke, Regulatory, St. Louis District, U.S. Army Corps of Engineers

  45. Looking upstream from the downstream end of the project Sep 2010-notice how wide the shoulder appears now March 2009-bank 4 feet from road

  46. Looking downstream March 2009 September 2010

  47. Looking downstream from left descending bank. The vegetation has almost completely grown over the rock – Sept 2010

  48. Rock toe & short Bendway Weirs

  49. Locked log still in place

  50. This PowerPoint presentation was developed & built by Dave Derrick. Any questions or comments, call my personal cell @ 601-218-7717, or email @ d_derrick@r2d-eng.comEnjoy the information!!

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