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CONSTRUCTION SPECIFICATIONS
(SEDIMENT BASIN WITH RISER BARREL PIPE)
1. Site preparations- Clear, grub, and strip topsoil from areas under the embankment to remove trees, w �getation, roots, and other
objectionable material. Delay clearing the pool area until the dam is complete and then remove brush, trees, and other
objectionable materials to facilitate sediment cleanout. Stockpile all topsoil or soil containing organic matter for use on the outer
shell of the embankment to facilitate vegetative establishment. Place temporary sediment control me,r,ures below the basin as
needed.
2. Cut-off trench- Excavate a cut-off trench along the center line of the earth fill embankment. Cut the trench to stable soil material,
but in no case make it less than 2 feet deep. The cut-off trench must extend into both abutments to at least the elevation of the
riser crest. Make the minimum bottom width wide enough to permit operation of excavation and compaction equipment, but in no
case less than 2 feet. Make side slopes of the trench no steeper than 1:1. Compaction requirements are the same as those for
the embankment. Keep the trench dry during backfilling and compaction operations.
3. Embankment- Take fill material from the approved areas shown on the plans. It should be clean mineral soil, free of roots, woody
vegetation, rocks, and other objectionable material. Scarify areas on which fill is to be placed before placing fill. The fill material
must contain sufficient moisture so it can be formed by hand into a ball without crumbling. if water can be squeezed out of the
ball, it is too wet for proper compaction. Place fill material in 6 to 8 inch continuous layers over the entire length of the fill area and
compact it. Compaction may be obtained by routing the construction hauling equipment over the fill so that the entire surface of
each layer is traversed by at least one wheel or tread track of heavy equipment, or a compactor may be used. Construct the
embankment to an elevation 10 percent higher than the design height to allow for settling.
4. Conduit spillways- Securely attach the riser to the barrel or barrel stub to make a watertight structural connection. Secure all
connections between barrel sections by approved watertight assemblies. Place the barrel and riser on a firm, smooth foundation
of impervious soil. Do not use pervious material such as sand, gravel, or crushed stone as backfill around the pipe or anti -seep
collars. Place the fill material around the pipe spillway in 4-inch layers, and compact it under and aroufrd the pipe to at least the
same density as the adjacent embankment. Care must be taken not to raise the pipe from firm contact with
its foundation
when compacting under the pipe haunches. Place a minimum depth of 2 feet of compacted backfill over the pipe spillway
before crossing it with construction equipment. Anchor the riser in place by concrete or other satisfactory means to prevent
flotation. In no case should the pipe conduit be installed by cutting a trench through the dam after the embankment is complete.
5. Emergency spillway- Install the emergency spillway in undisturbed soil. The achievement of planned elevations, grade, design
width, and entrance and exit channel slopes are critical to the successful operation of the emergency spillway.
6. Inlets- Discharge water into the basin in a manner to prevent erosion. Use diversions with outlet protection to divert
sediment -laden water to the upper end of the pool area to improve basin trap efficiency (References_ Runoff Control Measures
and Outlet Protection).
7. Erosion control- Construct the structure so that the disturbed area is minimized. Divert surface water away from bare areas.
Complete the embankment before the area is cleared. Stabilize the emergency spillway embankment and all other disturbed
areas above the crest of the principal spillway immediately after construction (References: Surface Stabilization).
8. Install porous baffles as specified in Practice 6.65, Porous Baffles.
9. Safety- Sediment basins may attract children and can be dangerous. Avoid steep side slopes, and fence and mark basins with
warning signs if trespassing is likely. Follow all state and local requirements
MAINTENANCE SPECIFICATIONS
(SEDIMENT BASIN WITH RISER BARREL PIPE)
1. inspect temporary sediment basins at least weekly and after each significant (1/2 inch or greater) rainfall event and repair
immediately. Remove sediment and restore the basin to its original dimensions when it accumulates to one-half the design depth.
Place removed sediment in an area with sediment controls.
2. Check the embankment, spillways, and outlet for erosion damage, and inspect the embankment for piping and settlement. Make
all necessary repairs immediately. Remove all trash and other debris from the riser and pool area.
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INSTALLATION SPECIFICATIONS
(SKIMMER)
1. Prevent the skimming device from settling into the mud by excavating a shallow pit under the skimmer or providing a low
support under the skimmer of stone or timber.
2. Assemble the skimmer following the manufacturers instructions, or as designed.
the assembled skimmer on the bottom of the basin with the flexible joint at the inlet of the barrel pipe. Attach the flexible
3. Lay J P P
joint to the barrel pipe and position the skimmer over the excavated pit or support. Be sure to attach a rope to the skimmer and
anchor it to the side of tPie basin. This will be used to pull the skimmer to the side for maintenance.
MAINTENANCE SPECIFICATIONS
( SKIMMER)
I Inspect skimmer sediment basins at least weekly and after each significant (one-half inch or greater) rainfall event and repair
immediately. Remove sediment and restore the basin to its original dimensions when sediment accumulates to one-half the height
of the first baffle. Pull the skimmer to one side so that the sediment underneath it can. be excavated. Excavate the sediment from
the entire basin, not just around the skimmer or the first cell. Make sure vegetation growing in the bottom of the basin does not
hold down the skimmer.
2. If the skimmer is clogged with trash and there is water in the basin, usually jerking on the rope will. make the skimmer bob up and
down and dislodge the debris and restore flow. If this does not work, pull the skimmer over to the side of the basin and remove the
debris. Also check the orifice inside the skimmer to see if it is clogged; if so remove the debris.
3. If the skimmer arm is clogged, the orifice can be removed and the obstruction cleared with a plumber's snake or by flushing with
water. Be sure and replace the orifice before repositioning the skimmer.
4. Freezing weather can result in ice forming in the basin. Some special precautions should be taken in the winter to prevent the
skimmer from plugging with ice.
SKIMMER DETAIL,
FABRIC
SECTION 'A -A'
NOTES:
1. L = THE LENGTH OF THE RIPRAP APRON.
2 d = 1.5 TIMES THE MAXIMUM STONE DIAMETER BUT NOT LESS THAN 6" (INCHES).
3. A FILTER BLANKET OR FILTER FABRIC SHOULD BE INSTALLED BETWEEN THE RIPRAP
AND SOIL FOUNDATION.
MAINTENANCE
RIP RAP SHOULD BE INSPECTED PERIODICALLY FOR SCOUR OR DISLODGED STONES.
CONTROL OF WEED AND BRUSH GROWTH MAY BE NEEDED IN SOME LOCATIONS.
OUTLET PROTECTION ENERGY DISSIPATER
N.T.S.
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CONSTRUCTION SPECIFICATIONS
(SKIMMER SEDIMENT BASIN)
1. Clear, grub and strip the area under the embankment of all vegetation and root mat. Remove all surfa, a soil containing high
amounts of organic matter and stockpile or dispose of it properly. Haul all objectionable material to the designated disposal area.
place temporary sediment control measures below basin as needed.
2. Ensure that fill material for the embankment is free of roots, woody vegetation, organic matter, and othor objectionable material.
place the file in lifts not to exceed 9 inches, and machine compact it. Over fill the embankment 6 inches to allow for settlement.
3. Shape the basin to the specified dimensions. Prevent the skimming device from settling into the mud by excavating a shallow pit
under the skimmer or providing a low support under the skimmer of stone or timber.
4. Place the barrel (typically 4-inch schedule 40 pvc pipe) on a firm, smooth foundation of impervious soil Do not use pervious
material such as sand, gravel, or crushed stone as backfill around the pipe. Place the fill material around the pipe spillway in
4-inch layers and compact it sunder and around the pipe to at least the same density as the adjacent embankment. Care must
be taken not to raise the pipe from the firm contact with its foundation when compacting under the pipe haunches.
5. Assemble the skimmer following the manufacturers instructions, or as designed.
6. Lay the assembled skimmer on the bottom of the basin with the flexible joint at the inlet of the barrel pipe. Attach the fiexibie joint
to the barrel pipe and position the skimmer over the excavated pit or support. Be sure to attach a rope to the skimmer and
anchor it to the side of the basin, this will be used to pull the skimmer to the side for maintenance.
T Earthen spillways - install the spillway in undisturbed soil to the greatest extent possible. The achievement of planned elevations,
grade, design width, and entrance and exit channel slopes are critical to the successful operation of tho spillway. The spillway
should be lined with laminated plastic or impermeable geotextile fabric. the fabric must be wide and lot ig enough to cover the
bottom and sides and extend onto the top of the dam for anchoring in a trench. The edges may be set tired with 8-inch staples or
pines. The fabric must be fang enough to extend down the slope and exit onto stable ground. The wlci lh of the fabric must be
one piece, not joined or spliced; otherwise water can get under the fabric. If the length of the fabric is insufficient for the entire
length of the spillway, multiple sections, spanning the complete width, may be used. The upper section(s) should overlap the
lower section(s) so that water cannot flow under the fabric. Secure the upper edge and sides of the fabric in a trench with staples
or pines. (Adapted from "A Manual for Designing, Installing and Maintaining Skimmer Sediment Basins." February, 1999.J.
Faircloth & Son.).
8. Inlets - discharge water into the basin in a manner to prevent erosion. Use temporary slope drains or diversions with outlet
protection to divert sediment ladon water to the upper end of the pool area to improve basin trap efficiency (References: Runoff
Control Measures and Outlet Protection).
9. Erosion control - construct the structure so that the disturbed area is minimized. Divert surface water away from bare spots.
Compete the embankment before the area is cleared. Stabilize the emergency spillway embankment and all other disturbed
areas above the crest of the principal spillway immediately after construction (References: Surface Stabilization).
10. install porous baffles as specified in practice 6.65, porous baffles.
11. After all the sediment-produing areas have been permanently stabilized, remove the structure and all the unstable sediment.
smooth the area to blend with the adjoining areas and stabilized properly. (References: Surface Stabilization).
MAINTENANCE SPECIFICATIONS
(SKIMMER SEDIMENT BASIN)
I . Inspect skimmer sediment basins at least weekly and after each significant (one-half inch or greater) rainfall event and repair
immediately. Remove sediment and restore the basin to its original dimensions when sediment accumulates to one-half the height
of the first baffle. Pull the skimmer to one side so that the sediment underneath it can be excavated. Excavate the sediment from
the entire basin, not just around the skimmer or the first cell. Make sure vegetation growing in the bottom of the basin does not
hold down the skimmer.
2. Repair the baffles if they are damaged. Re -anchor the baffles if water is flowing underneath or around them.
3. If the skimmer is clogged with trash and there is water in the basin, usually jerking on the rope will make the skimmer bob up and
down and dislodge the debris and restore flow. If this does not work, pull the skimmer over to the side of the basin and remove the
debris. Also check the orifice inside the skimmer to see if it is clogged; if so remove the debris.
4. If the skimmer arm or barrel pipe is clogged, the orifice can be removed and the obstruction cleared with a plumber's snake or by
flushing with water. Be sure and replace the orifice before repositioning the skimmer.
5. Check the fabric lined spillway for damage and make any required repairs with fabric that spaces the Rill width of the spillway.
Check the embankment, spillways, and outlet for erosion damage, and inspect the embankment for piping and settlement. Make
all necessary repairs immediately. Remove all trash and other debris from the skimmer and pool areas,
6. Freezing weather can result in ice forming in the basin. Some special precautions should be taken in the winter to prevent the
skimmer from plugging with ice.
SKIMMER SEDIMENT BASIN
N.T.S
SEDIMENT BASIN
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MATERIALS
(POROUS BAFFLES)
1. Use matting made of 100% coconut fiber (coir) twine woven into high strength matrix with the properties shown in table 6.6.5a.
2. Staples should be made of 0.125 inch diameter new steel wire formed into a "U" shape not less than 12 inches in length with a
throat of I inch in width. The staples anchor the porous baffles into the sides and bottom of the basin.
3. Ensure that steel post form porous baffles area of a sufficient height to support baffles at desired height. Post should be
approximately 1-3/8" wide measured parallel to the fence, and have a minimum weight of 1.25 ib/linear ft. The posts must be
equipped with an anchor plate having a minimum area of 14.0 square inches and be of the self-fastnener angle steel type to have a
means of retaining wire and coir fiber mat in the desired position without displacement.
4. Use 9-gauge high tension wire for support wire.
1 Coir Fiber Material Property Requirements
Thickness
0.30 in. minimum
Tensile Strength (Wet)
900 x 680 lb/ft minimum
Elongation (Wet)
69% x 34% maximum
Flow Velocity
10-12 ft/sec
Weight
20 oz/SY (680 g/m2 ) minimum
Minimum Width
6.5 feet
Open Area
501% maximum
11 Table 6.65a Specifications for Porous Baffle Material
CONSTRUCTION SPECIFICATIONS
(POROUS BAFFLES)
1. Grade the basin so that the bottom is level front to back and side to side.
2. Install the coir fiber baffles immediately upon excavation of the basins.
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3. Install posts across the width of the sediment trap (Practice 6.b , Sediment Fence).
4. Steel posts should be driven to a depth of 24 inches and spaced a maximum of 4 feet apart. The top of the fabric should be a
minimum of 2 inches lower than the top of the earthen embankment.
5. Install at least three .rows of baffles between the inlet and outlet discharge point. Basins less than 20 feet in length may use 2
baffles.
6. Attach a 9 gauge high tension wire stand to the steel post at a height of 6 inches above the spillway elevation with plastic ties or
wire fasteners to prevent sagging. If the temporary sediment basin will be converted to a permanent stornwater basin of a greater
depth, the baffle height should be based on the pool depth during use as a temporary sediment basin.
7. Extend 9 gauge minimum high tension wire strand to side of basin or install steel T-post to anchor baffle to side of basin and
secure to vertical end posts as shown in Figure 6.65b.
8. Drape the coir fiber mat over the wire stand mounted at a height of 6 inches above the spillway elevation. Secure the coir fiber
mat to the wire strand with plastic ties or wire fasteners. Anchor the matting to the sides and floor of the basin with 12 inch wire
staples, approximately 1 ft apart, along the bottom and side slopes of the basin.
9. Do not splice the fabric, but use a continuous piece across the basin.
10. Adjustments may be required in the stapling requirements to fit individual site conditions.
MAINTENANCE SPECIFICATIONS
(POROUS BAFFLES)
I . Inspect baffles at least once a week and after each rainfall. Make any required repairs immediately.
2. Be slue to maintain access to the baffles. Should the fabric of a baffle collapse, tear, decompose, or become ineffective, replace it
promptly.
3. Remove sediment deposits when it reaches half full to provide adequate storage volume for the next rain and to reduce pressure on
the baffles. Take care to avoid damaging the baffles during cleanout, and replace if damaged during cleanout operations.
Sediment depth should never exceed half the designed storage depth.
4. After the contributing drainage area has been properly stabilized, remove all baffle materials and unstable sediment deposits, bring
the area to grade, and stabilize it.
NOTES:
1, L = THE LENGTH OF THE RIPRAP APRON.
2. d = DEPTH OF STONE
3. THE WID rH OF THE RIPRAP APRON IS NOTED ON PLAN
SHEETS
4. A FILTER BLANKET OR FILTER FABRIC SHOULD BE
INSTALLED BETWEEN THE RIPRAP AND SOIL FOUNDATION,
MAINTENANCE
RIP RAP SHOULD BE INSPECTED PERIODICALLY FOR SCOUR
OR DISLODGED STONES, CONTROL OF WEED AND BRUSH
GROWTH MAY BE NEEDED IN SOME LOCATIONS.
POROUSBAFFLES
N.T.S
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DATE
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DRAWN BY
A, BLYE
DESIGNED BY
S. MDORE
CHECKED BY
R. BAKER
SCALE
®
AS SHOWN
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