ATGRADE HINGED UNDERGROUND GRADE CONTROL ATGRADE HINGED GRADE

AT-GRADE, HINGED, & UNDERGROUND GRADE CONTROL

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

DEFINITIONS OF TERMS

Definition of an At-Grade Control Structure (AGGCS) “At-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, selfhealing) launchable stone.

Definition of a Hinged Grade Control Structure (HGCS) “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.

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

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

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

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

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

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

Sheet-pile cutoff wall Mini case study: 8 of 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.

Sheet-pile cutoff wall Mini case study: 9 of 12 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.

Sheet-pile cutoff wall Mini case study: 10 of 12 Original DS edge of stone 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

Sheet-pile cutoff wall Mini case study: 11 of 12 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

Sheet-pile cutoff wall Mini case study: 12 of 12 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

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

BACKSTORY: Landowner dug a massive cutoff channel through a big hill in 2002, shortening stream length by approximately 710 ft. The At-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!!

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

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.

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!!

HINGED GRADE CONTROL STRUCTURE

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.

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.

2004 No evidence of a headcut. April 2004

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

SELF-ADJUSTING, GRADE CONTROL STRUCTURES WORK WELL !!

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

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 March 18, 2009

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

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

UNDERGROUND GRADE CONTROL (Headcut mitigation)

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

STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION 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. Entire area excavated

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

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

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

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

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

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!

This Power. Point presentation was developed & built by Dave Derrick. Any questions or comments, call my personal cell @ 601 -218 -7717, or email @ d_derrick@r 2 d-eng. com Enjoy the information!!