at-grade, hinged, & underground grade control. at-grade & hinged grade control structure on...
TRANSCRIPT
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
Mini case study: 2 of 12
Sheet pile
Flow
Headcut advancing
Stone has adjustedCover overStone 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
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
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
Mini case study: 7 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.
Mini case study: 8 of 12Sheet-pile cutoff wall
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 12Sheet-pile cutoff wall
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 12Sheet-pile cutoff wall
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
Mini case study: 11 of 12Sheet-pile cutoff wall
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 12Sheet-pile cutoff wall
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
STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION
Stones placed on granular filter
STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION
Riprap stones placed for bank protection
STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION
DONE
Flow
Profile view
201
10
1
STONE UNDERGROUND ERR TO STOP HEADCUT MIGRATION
Underground ERR slope could vary, might be economically driven
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)
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!!