AT-GRADE, HINGED, & UNDERGROUND GRADE CONTROL. AT-GRADE & HINGED GRADE CONTROL STRUCTURE ON...

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

“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)

“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)

AT-GRADE GRADE CONTROL, FLAT-SLOPED SAND BED STREAM

Crest of stone equal to bottom (invert) of stream

Headcut advancing

Stone has adjustedCover overStone has adjusted & arrested

the advancing headcut

Sheet pile


Sheet pile

Flow

Headcut advancing

Stone has adjustedCover overStone has adjusted & arrested

the advancing headcut

Sheet pile cutoff wall


AT-GRADE GRADE CONTROL, FLAT-SLOPED SAND BED STREAM

Crest of stone equal to bottom (invert) of stream

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)


At-Grade, Grade Control structure, Hickahala Creek, MS, as-built in 1989, note

concrete cap on sheet-pile cutoff wall


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 12Sheet-pile cutoff wall

Hickahala Cr. At-Grade GC at high flow, April 6, 2005. Well-behaved flow, but return current is eroding far bank


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.


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.


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


Original DS edge of stone

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


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 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 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 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.

April 2004

2004 No evidence of a headcut.

LOOKING US, JULY 2004

March 2007

3-years later, large headcut arrested by Submar ACM mat. Mat undercut but self-adjusted.

SELF-ADJUSTING, GRADE CONTROL

STRUCTURES WORK WELL !!

January 2008

Non-uniform undercutting of mat. Still 14 ft until headcut gets back to the pipeline.

Pix by Lloyd Falgout

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

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!

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

Place a granular filter on the bed, or use a self-filtering stone


Stones placed on granular filter


Riprap stones placed for bank protection


DONE

Flow

Profile view

201

10

1


Underground ERR slope could vary, might be economically driven

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 PowerPoint presentation was developed & built by Dave Derrick.

Any questions or comments, call my personal cell @ 601-218-7717, or email @ [email protected]

Enjoy the information!!

mailto:[email protected]

AT-GRADE, HINGED, & UNDERGROUND GRADE CONTROL. AT-GRADE & HINGED GRADE CONTROL STRUCTURE ON...

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