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PROBLEMS

This project tackles erosion and groundwater piping on the right bank of the Delaware River, threatening an important archaeological site. Soft stabilization methods are used, including slope adjustment, gravel French drain, native grass seeding, and willow planting. Follow the construction photos and learn about the trench planting technique.

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PROBLEMS

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  1. SITE 6 – DELAWARE RIVER RIGHT BANK BLOW-OUT UP THE HILL FROM THE DELAWARE RIVER(SWIRLING RIVER EROSION & GROUNDWATER PIPING)DELAWARE WATER GAP NATIONAL RECREATION AREA NATIONAL PARK SERVICE PROJECT CONSTRUCTED SEPTEMBER 10-15, 2009

  2. PROBLEMS • This bowl-shaped upper bank blow-out appears to have been initially eroded by river flows guided into the area by a jam of large downed trees at the toe of the right bank (see next slide). The swirling water eroded the bank leaving a circular failure with steep banks. • Additional erosion has been caused by flood waters draining back into the eroded area from the surrounding fields during high water events. • A third stressor is groundwater piping exiting the eroding bank at an old stream location. The stream was rerouted decades ago. Water seeps from the active failing bank. • The actively eroding bank is failing in an uphill direction & presently threatening an important archeological site.

  3. Courtesy of Ecological Restoration, Inc. Aerial view of project area with work limits delineated. Note Large Woody debris (LWD) in river that vectored river energy into the bank causing the bank to initially erode.

  4. PRE-PROJECT PHOTOSby Dave Derrick July 23, 2008, Dec. 15, 2008, & Sept. 9, 2009

  5. From top bank, looking downhill at the blow-out area. PRE-PROJECT DELAWARE RIVER-SITE 6 - PIX BY DERRICK 7-23-2008

  6. Looking north, this area has decent native grasses. PRE-PROJECT DELAWARE RIVER-SITE 6 - PIX BY DERRICK 7-23-2008

  7. Vertical eroding scarp is masked by vegetation. PRE-PROJECT DELAWARE RIVER-SITE 6 - PIX BY DERRICK 7-23-2008

  8. Looking uphill (west) at eroding bank, gully & escarpment. PRE-PROJECT DELAWARE RIVER-SITE 6 - PIX BY DERRICK 7-23-2008

  9. Looking uphill (west) @ the eroding escarpment partially caused by groundwater seepage. PRE-PROJECT DELAWARE RIVER-SITE 6 - PIX BY DERRICK 7-23-2008

  10. Escarpment & erosion is easier to see during winter PRE-PROJECT DELAWARE RIVER-SITE 6-PIX BY DERRICK 12-15-2008

  11. Looking uphill (southwest) @ escarpment & eroded bank. PRE-PROJECT DELAWARE RIVER-SITE 6-PIX BY DERRICK 12-15-2008

  12. Looking south @ escarpment & bank erosion. PRE-PROJECT DELAWARE RIVER-SITE 6-PIX BY DERRICK 12-15-2008

  13. THE PLAN

  14. SOLUTIONS (THE PLAN) • This project is designed to stabilize the bank at the present location by using “soft” stabilization methods. Banks will be sloped and a sloping 12 inch thick gravel French drain installed. The drain will be covered with geotextile and a foot thick layer of topsoil. Native grasses will be seeded in all disturbed areas & over the French drain. A 100% coir Erosion Control Blanket will be installed over the soil with many species of rooted stock shrubs installed at the top and bottom of the French drain. At the toe of the slope two rows of coir logs will be installed with two rows of rooted willow & dogwood whips, & unrooted willows planted in between. • On the lower river bank, 3 rows of rooted willow whips will be installed to bridge a gap in the existing riparian corridor & reduce the chance of high river flows from again swirling into the repaired bank area.

  15. Courtesy of Ecological Restoration, Inc.

  16. CONSTRUCTION PHOTOS by Dave Derrick, September 10-14, 2009

  17. A follow-the-river hiking path had just been completed at the project site. We used a portion of the path for access. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  18. PLANTS PLANTED Common Name # Size • Fragrant Sumac 27 3 gallon pots • Silky Dogwood 400 bare root & cuttings • Black Willow 1210 cuttings & tree bands • Ninebark 9 3 gallon pots • Nannyberry 57 1 gallon pots • Arrowwood 56 1 gallon pots • Grey Dogwood 27 3 gallon pots

  19. TRENCH PLANTING ROOTED-STOCK WILLOW WHIPS DOWN BY THE RIVER

  20. Looking downhill @ mini trackhoe digging a trench for the rooted-stock willow whips. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  21. NARROW TRENCH PLANTING TECHNIQUE Spoil Dig the trench.

  22. NARROW TRENCH PLANTING TECHNIQUE Spoil Place the last scoop of dug soil back in the trench so plantings are in loose material.

  23. Looking DS @ the trench closest to the river & two flats of willow whips. Three trenches parallel with the river will be dug & planted with willow to tie into the existing US & DS forested riparian buffer. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  24. NARROW TRENCH PLANTING TECHNIQUE Spoil Place rooted-stock willow whips into loose soil in trench. Lean whips against side of trench away from the spoil pile

  25. Rooted-stock Black Willow whips in tree bands (small pots) CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  26. Willows are 6 months old, cuttings were planted in a 2.75 inch by 2.75 inch by 6 inch pot in March (now 4-6 ft tall, approx.½ diameter) CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  27. Close-up of rooted-stock Black Willow whips in trench. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  28. Close-up of rooted-stock Black Willow whips in trench. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  29. Whips in trench, planted at a rate of three whips per foot. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  30. NARROW TRENCH PLANTING TECHNIQUE Water plants in & backfill.

  31. Mini-excavator backfilling trench, which plants the willows. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  32. Looking DS. The trench closest to the river is keyed up & into the existing riparian forest @ both the US & DS ends. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  33. Looking DS @ the uppermost of the 3 trench plantings. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  34. Looking DS @ the uppermost of the 3 trench plantings. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  35. Close-up of the trench willow plantings. Good sandy soil. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  36. Looking DS @ all 3 parallel willow trenches & silt fence. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  37. TRENCH PLANTING THE ROOTED-STOCK WILLOW WHIPS DOWN BY THE RIVER IS COMPLETE !!

  38. NEXT ARE THREE SETS OF PIX OF THE FRENCH DRAIN AREA LOOKING NORTH, EAST, & SOUTH. PIX ARE PRE-PROJECT, CONSTRUCTION, & POST-PROJECT

  39. THE FRENCH DRAIN, WITH GEOTEXTILE, SOIL, NATIVE GRASS SEED, & COIR MATTING (LOOKING NORTH)

  40. Looking north @ the eroded, unstable bank. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  41. An archeological dig was undertaken at the eroding bank. We understand nothing of significance was found. This was filled with the 3 inch gravel filter material to form a chimney drain. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  42. Looking north. Bank sloped with the mini tracked loader. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  43. SUITABLE STONE

  44. For the “French drain’ sloped filter a 1 ft thick layer of 3 inch poorly sorted gravel was used. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-10-2009

  45. Looking north. Spreading filter gravel with the mini loader. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  46. Gravel staged down over sloped bank. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  47. Gravel spread, ready for the geotextile separator. Mound at top bank will not allow rainwater to gully down new slope. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  48. Geotextile will be tucked in @ sharp edge @ top bank. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

  49. Rolling geotextile over filter. Twelve inches of soil has been placed over the geotextile in the foreground. CONSTRUCTION DELAWARE RIVER-SITE 6-PIX BY DERRICK 9-11-2009

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