1. AT-GRADE, HINGED, & UNDERGROUND GRADE CONTROL

2. AT-GRADE & HINGED GRADE CONTROL STRUCTURE ON HICKAHALLA CREEK NEAR SENATOBIA, MS. Constructed in 1989 to arrest headward migration of existing downstream knickpoints (headcuts) Mini case study: 1 of 12

3. DEFINITIONS OF TERMS

4. “At-Grade Grade Control Structures” are buried stone grade control structures where the top (crest) of the AGGCS is equal to the invert (lowest elevation) of the stream channel cross-section. AGGCS are typically built of well-graded (adjustable, self- healing) launchable stone. Definition of an At-Grade Grade Control Structure (AGGCS)

5. “Hinged Grade Control Structures” are grade control structures designed to adjust & stabilize undercutting foundation failure (due to headcutting) at the downstream end of the structure. Definition of a Hinged Grade Control Structure (HGCS)

6. AT-GRADE GRADE CONTROL, FLAT-SLOPED SAND BED STREAM Crest of stone equal to bottom (invert) of stream Headcut advancing Stone has adjusted Cover over Stone has adjusted & arrested the advancing headcut Sheet pile Mini case study: 2 of 12 Sheet pile Flow

7. Headcut advancing Stone has adjusted Cover over Stone has adjusted & arrested the advancing headcut Sheet pile cutoff wall Mini case study: 3 of 12 AT-GRADE GRADE CONTROL, FLAT-SLOPED SAND BED STREAM Crest of stone equal to bottom (invert) of stream

8. At-Grade structure, Hickahala Creek, MS, {rural, sand bed, slope<1%, pool-riffle-pool, straightened, incised} as-built in 1989, note concrete cap on sheet-pile cutoff wall (red line) Mini case study: 4 of 12

9. At-Grade, Grade Control structure, Hickahala Creek, MS, as-built in 1989, note concrete cap on sheet-pile cutoff wall Mini case study: 5 of 12

10. At-Grade Grade Control, Hickahala Creek, MS. Functioning as designed to arrest headward migration of knickpoints, picture taken April 2004 Mini case study: 6 of 12 Sheet-pile cutoff wall

11. Hickahala Cr. At-Grade GC at high flow, April 6, 2005. Well-behaved flow, but return current is eroding far bank Mini case study: 7 of 12

12. At-Grade GC, Hickahala Creek, MS. April 2007. Compared to the 2004 pictures, some stone has been displaced on the DS side of the sheetpile cap. Mini case study: 8 of 12 Sheet-pile cutoff wall

13. At-Grade GC, Hickahala Creek, MS. April 2007. Close-up of displaced stone on the DS side of sheetpile cap. Stone upstream of sheetpile is doing nothing. Mini case study: 9 of 12 Sheet-pile cutoff wall

14. At-Grade GC, Hickahala Creek, MS. April 2007. Stone on DS face has self-adjusted to form a pool-riffle-pool configuration. Excessive stone movement is troubling Mini case study: 10 of 12 Sheet-pile cutoff wall Original DS edge of stone

15. At-Grade GC, Hickahala Cr.-April 2010. Stone on the DS side of the cutoff wall has moved. Taller drop @ DS end of displaced stone means another headcut has arrived Mini case study: 11 of 12 Sheet-pile cutoff wall

16. At-Grade GC, Hickahala Creek, MS. April 2010. Structure should be closely monitored. Left bank erosion has increased, right bank is stable. Stone is undersized & structure overwhelmed by number & height of headcuts Mini case study: 12 of 12 Sheet-pile cutoff wall

17. CLEAR CREEK, BOVINA, MS. Arresting an active headcut using an At-Grade Grade Control (GC) Structure (Crest of the grade control structure is equal to the bed of the stream)

18. BACKSTORY: Landowner dug a massive cutoff channel through a big hill in 2002, shortening stream length by approximately 710 ft. The At-Grade Grade Control structure was built to halt the expected headcut generated by the channel cutoff activities, which it has to some degree, but is presently in danger of failing!!

19. Cutoff channel is 590 ft in yellow, original stream length is 1,300 ft in red, shortened 710 ft!! At-Grade Grade Control is blue line.

20. Looking US & across at LPSTP (both banks) and an At-Grade, Grade Control structure on Clear Creek, Bovina, MS. As-built photos unavailable. Since installation, degradation has occurred on the DS side of the structure due to knickpoint migration caused by landowner shortening of the stream. GC & LPSTP installed 2002, pix shot March 2003.

21. One year later, note undersized stone displaced downstream by flow. Considered a functional failure, only one section of rock moved, flow now concentrated. Grade control stone appears smaller than LPSTP stone!!

22. HINGED GRADE CONTROL STRUCTURE

23. BACKSTORY: Headcuts had migrated thru the reach exposing two high pressure pipelines. A significant Submar Inc. Articulating Concrete Mattress system was installed over the pipelines (& keyed to top of both banks) to provide direct protection & cover so that the pipelines were again in compliance with applicable law.

24. HICKAHALLA CREEK NEAR SENATOBIA, MS. Arresting an active headcut at the downstream end of an Articulated Concrete Mattress (ACM) system. Located on Hickahalla Creek DS of the At- Grade GC shown previously.

25. April 2004 2004 No evidence of a headcut.

26. LOOKING US, JULY 2004 March 2007 3-years later, large headcut arrested by Submar ACM mat. Mat undercut but self-adjusted.

27. SELF-ADJUSTING, GRADE CONTROL STRUCTURES WORK WELL !!

28. January 2008 Non-uniform undercutting of mat. Still 14 ft until headcut gets back to the pipeline. Pix by Lloyd Falgout

29. March 18, 2009 A more uniform adjustment of the mat to approx. 3 ft of headcut, still 14 ft until the headcut gets back to the pipeline. Closely monitor this one!! Pix by Derrick

30. Arresting an active headcut at the downstream end of another Articulating Concrete Mattress project.

31. Pickens, MS. ACM “tail” was laid on flat bathymetry, headcuts migrated US, mat has adjusted & arrested the headcut “Hinged” ACM grade control, more mats can be added as needed

32. UNDERGROUND GRADE CONTROL (Headcut mitigation)

33. BUILDING A TOTALLY UNDERGROUND ENGINEERED ROCKED RIFFLE TO STOP DOWNSTREAM HEADCUTS FROM MOVING PAST THE ERR!

34. Entire area excavated Basically an underground extension of an ERR which is designed to halt headcut migration. Depth of stone in the underground ERR would be the effective depth for headcut mitigation. STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION

35. Place a granular filter on the bed, or use a self-filtering stone STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION

36. Stones placed on granular filter STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION

37. Riprap stones placed for bank protection STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION DONE

38. Flow Profile view 20 1 10 1 STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION Underground ERR slope could vary, might be economically driven

39. Flow STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION Depth of stone will be designed to halt the upstream movement of that depth of headcut(s)

40. AN UNDERGROUND ENGINEERED ROCKED RIFFLE WAS BUILT ON SAN ANTONIO CREEK, VANDENBERG AIR FORCE BASE, CA. TO MITIGATE 10 FT OF DOWNSTREAM HEADCUTS. I DESIGNED IT BUT DO NOT HAVE ANY PIX!

41. 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.com Enjoy the information!! d_derrick@r2d-eng.com