Sediment Control Practices

John MathewsOhio Dept. of Natural Resources,

Division of Soil and Water Resources

Practices Treat the Largest Soil Particles

SandSilt Clay

Treated Untreated

Settleable Non-settleable0.01

1 m

m

Sand

Energy to Dislodge & Suspend

Removing Sediment

Settling Soils is dependent upon:• Size of the particle• Energy keeping it in

suspension

Stokes’ Law: denser particles sink faster than less dense particles when suspended in a liquid.

Understand Runoff on the Site in order to Properly Site Controls

• How does water flow across and off the site?– What is the flow path and length?– What is the drainage area to the capture point?– Is the practice capturing sheet flow or concentrated flow?

Most Sediment Controls Slow Flow

Proper Placement of Silt Fence and Other Sheet Flow Practices

Filter Berm & Compost Filter Logs

Filter Socks – Same Slope Guidance as Silt Fences in RLD

Don’t Allow Sheet Flow Controls in Concentrated Flow Locations

Sediment Trap• Simple Rock Outlet• Typically smaller drainage areas

Sediment Trap• Drainage Area of 5 acres or less

Sediment Trap

Sediment Basins and Skimmers

Most Effective Sediment Control

Effective Pool Shape• Utilize entire shape of pond

• Optimum depth is ~ 3 feet

• Length to width especially for non-dewatering (optimum 4:1 or greater)

Prevent Short Circuiting:Direct Flow w/ Baffles

Dewatering Risers in Basins:• Single orifice• Perforated and wrapped riser.• And now skimmers

Ohio EPA CGP Requires Skimmers• Part II. G. d.ii “…sediment settling ponds shall

be dewatered at the pond surface using a skimmer or equivalent device.”

• Skimmers draw water from the water surface (the least turbid water) of the sediment basin.

Sediment Settling Process

vs

vw

Pond Inflow

Pond Discharge

Permanent Pool/Sediment Storage

Sediment Settling Process

vs

vw

Pond Inflow

Pond Discharge

Permanent Pool/Sediment Storage

Sediment Settling Process

vs

vw

Pond Inflow

Pond Discharge

Permanent Pool/Sediment Storage

vsand vsilt vclay

Sediment Settling Process

vs

vw

Pond Inflow Pond

Discharge

Permanent Pool/Sediment Storage

National Trends• Doubling of pond capacity

– From 67 to 134 yd3/ac (wtrshd)• Sometimes without detention time specified.

(Both Ohio EPA and the Rainwater and Land Development manual require 48 hours.)

Variety of Skimmers• 2 Commercial (constant head) skimmers:

– JW Faircloth and – Innovation Applied Systems.

• Delaware DOT skimmer (Variable head)• Or an alternative someone might design & build.

JW Faircloth Skimmer• Developed by Warren Faircloth who was a

former county Erosion Control Supervisor in NC.

(See www.fairclothskimmer.com)

IAS Water Quality Skimmer• Also developed in North Carolina.

IAS is Innovative Applied Solutions, LLC. See www.iasllcusa.com

Delaware DOT Skimmer

See Rainwater and Land Development Manual Ch. 6 and www.deldot.gov/stormwater/pdfs/EandS_fieldguide/V+SedimentTrapsAndBasins.pdf

Design Issues with Basins(Attaching a skimmers doesn’t undo poor basin design)

This outlet was sized (perforationsand spacing) for 100’s of acresversus the actual 10’s of acres going to it. It provided only a few hoursof detention instead of the required 48 hours.

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

Sediment Storage

Dewatering Zone

(often planned wet, but may be dewatered as well)

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

Drain time is a function of the orifice size and/or the pipe size of the skimmer.

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

3. Area and shape of the basin– L:W = 4:1 or plan baffles to increase flow length or slow flow– Basin depth and surface area

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

3. Area and shape of the basin– L:W = 4:1 or plan baffles to increase flow length or slow flow– Basin depth and surface area

4. Principal Spillway- Barrel/riser pass 10-yr 24-hr discharge

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

3. Area and shape of the basin– L:W = 4:1 or plan baffles to increase flow length or slow flow– Basin depth and surface area

4. Principal Spillway- Barrel/riser pass 10-yr 24-hr discharge5. Emergency Spillway - 25 yr 24hr discharge capacity

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

3. Area and shape of the basin– L:W = 4:1 or plan baffles to increase flow length or slow flow– Basin depth and surface area

4. Principal Spillway- Barrel/riser pass 10-yr 24-hr discharge5. Emergency Spillway - 25 yr 24hr discharge capacity6. Other requirements: embankment height, width and side

slopes; anti-seep collars, outlet and inlet protection, non-floating riser…

Sediment Basin Requirements1. Basin capacity

– Dewatering volume, 67 yd3/ac of drainage area– Sediment storage volume, 37 yd3/ac of disturbed area

2. Drain time: min. 48 hours for the dewatering volume. – Recommend that the drain time be extended up to 72 hours if the

sediment storage volume is also dewatered.

3. Area and shape of the basin– L:W = 4:1 or plan baffles to increase flow length or slow flow– Basin depth and surface area

4. Principal Spillway- Barrel/riser pass 10-yr 24-hr discharge5. Emergency Spillway - 25 yr 24hr discharge capacity6. Other requirements: anti-seep collars, outlet and inlet

protection, non-floating riser…7. Seed and mulch within 7 days of constructing the basin

Stabilize Inlets

Sediment vs. Perm SW Pond

Plan Review and Field Inspectors

1 1⁄2" Red

2" Yellow

2 1/2" Green

3" Blue

4" Orange

5" Silver

6" White and unique shape of vent

8" None; distinguished by it size

Color Codes For Faircloth Skimmers

IAS colors generally correspond but add black for 1.75” (http://www.iasllcusa.com/downloads.html)

• Plans: show specific skimmer to be used including pipe size, connections, and orifice size.

• Use Colors to field check against plans.

Maintenance of Skimmers• Pull the skimmer to the side and inspect.• This is primarily cleaning debris from the intake.• Insure the orifice is fixed as planned (size).• Insure the flexible pipe is whole without cracks.

Request Summary Design Info

14 Acre Site (12 acres Disturbed)• Total Drainage Area x 67 yd3= 938 yd3

• Disturbed Area x 37 yd3 = 444 yd3

• Total Pond Capacity = 1382 yd3

444 cubic yards

938 cubic yards

Temp Modifications to SW Ponds• Permanent pond used for temporary sediment• Follows sediment basin and trap specifications

Ponding Volumes for Different LUsePonding Volumes for Sediment & WQv-Commercial

0.0

1.0

2.0

0.0 20.0 40.0 60.0 80.0

Basin Bottom

Dep

th

Pond Site Sed PoolWQv-Dry ED WQv-Wet

Ponding Volumes for Sediment & WQv-Med. Residential

80.0 100.0 120.0 140.0

Basin Bottom

Sed Pool + DwtrngWQv-Wet P WQv-Wet P+ED

Storm Drain Inlet Protection• Promotes settling by ponding muddy runoff outside a

storm drain inlet• For storm systems where diverting storm system outfall

to sediment basin isn’t possible, short time periods or extra level of treatment

Inlet Protection

• 2 x 4 frame;• Wire mesh;• Geotextile;• 2”stone placed on geotextile and wire mesh or

trenched (18”), backfilled and compacted similar to silt fence.

Inlet Protection• Inlets on a slope will route runoff downstream. In other

words, they block the inlet rather than pond runoff.

Inlet Protection Fails• Where construction personnel are inconvenienced by ponding

and mud on the streets

How Do You Know If an Inlet Protection Device Has Been Working?

Ponded water Mud Stain marks

Inlet Protection• Must be maintained after every significant rainfall or• Sediments will be re-suspended and nuisance complaints will

abound

Direct Storm Sewers to Sed Basin

Sed Ponds Stay Until Stabilization

Small Lot Building Sites

All Best Management Practices Are Not Equally Good

Poor Good Just (OK) Better Best