Lare Section 4: Erosion Control

Front 1

Methods to protect Ditches from erosion

Back 1

Slope <6%: Bale ditch check, silt fence ditch check, TSD ditch check

Slope>6% or high flows expected: Rock ditch check, erosion control blankets

Front 2

Erosion & silt control on slopes

Back 2

For erosion control: temporary seeding and erosion-control blankets

For silt control: Bale slope barriers and silt fence slope barriers

Front 3

Drop inlet barrier erosion protection

Back 3

Bale drop-inlet barrier, silt fence drop-inlet barrier, TSD drop-inlet barrier

Front 4

Bale Ditch Check

Back 4

Do not place a bale ditch check in areas with concentrated flow:

- directly in front of a culvert outlet.

-in ditches that likely will experience high flows.

Follow prescribed ditch-check spacing guidelines or erosion will occur between the ditch checks.

Do not allow water to flow around the ditch check. The ground level at the ends of the check is higher than the top of the lowest center bale.

Do not place in channels with shallow soils underlain by rock, could wash out. Must be dug into the ground. Bales at ground level do not work because they allow water to flow under the check.

Front 5

Silt fence ditch check

Back 5

Water should flow through a silt fence ditch check, not over it. Place in ditches where it is unlikely to be overtopped.

Do not place posts on the upstream side of the silt fence fabric (puts force on staples not posts if on upstream side).

Do not place:

- in front of a culvert outlet.

-in ditches that likely will experience high flows.

Follow prescribed ditch-check spacing guidelines or erosion will occur between the ditch checks.

Do not allow water to flow around the ditch check. Ground level at the ends of the fence is higher than the low point on the top of the fence.

Do not place in channels with shallow soils underlain by rock.

Front 6

TSD ditch check

Back 6

Triangular silt dike ditch check.

Each TSD has two aprons: one upstream and one downstream. The upstream apron is the shorter of the two. Place one TSD on the downstream side of the trench. Conform the flexible TSD to the geometry ofthe ditch so that no space exists between the dike and the ditch bottom.

Each TSD has an open sleeve at either end. Connect adjoining dikes with these sleeves and then repeat the anchoring procedure in the previous step.· Once all the TSDs have been joined and anchored, fill in the upstream trench with soil and compact it.

Front 7

Rock ditch check

Back 7

For high flows or steep channels. 18-24" high, 1:1 max side slopes.

Front 8

Bale slope barriers

Back 8

Bale slope barriers operate by intercepting and ponding sediment-laden runoff. Water exits the baleslope barrier by flowing over the bales.

Place 5-10 ft away from toe of slope

Front 9

Silt fence slope barriers

Back 9

Operate by ponding water, should exit by filtering through fabric. Fabric attached to wooden posts with staples, wire, zip ties or nails.

Placement should follow contour where practical. May be used at property boundary to keep silt on-site, in which case it may not be able to follow contour.

Max post spacing 4' o.c.

Front 10

Bale drop inlet barriers

Back 10

Surround all 4 sides of drop inlet, trenched into ground 6". Wood stakes, bales tied together with twine. Same principles for other bale barrier-type installations apply: tightly butted, compact soil on upstream side, shallow slopes to hold more water, etc.

Front 11

What are the dimensions of silt fence stakes?

Back 11

-4' long by 2" square.

Front 12

Silt fence drop inlet barriers

Back 12

Same principles as bale barriers, but using silt fencing. May reinforce fabric with chicken wire.

Front 13

Safety concern with silt fence drop inlet barriers

Back 13

A sagging silt fence should be repaired immediately because it has the potential to create a biggerproblem: flooding. If a silt fence falls over onto a drop inlet during a storm, the inlet can becomeblocked, causing flooding of the roadway.

Front 14

TSD drain inlet barrier: section

Back 14

Triangular silt dike.

TSDs should be placed directly against the perimeter of the drop inlet. This allows overtopping water toflow directly into the inlet instead of onto nearby soil, causing a scour hole.· Make sure to orient the TSD properly. The side in contact with the drop inlet should be vertical, and theshorter apron should lie beneath the longer one.· If the receiving apron of a TSD is not dug into the ground, water will flow underneath.

Front 15

TSD drain inlet barrier: plan

Back 15

Triangular silt dike. Only cut two sides to fit, other sides full (7') length

Front 16

Block and gravel inlet barrier

Back 16

Good for moderate flows. Water flows through, not over it. Wire mesh between gravel and block, should not be bigger than the diameter of the gravel. Block should be 2' high but not higher than the elevation of surrounding roads (if applicable) or they could flood.

Front 17

Drop inlet gravel and wire mesh filter

Back 17

1.5" max diameter gravel, 0.5" max diameter mesh placed over inlet.

Front 18

Drop inlet sediment trap

Back 18

Lower grade around inlet so water ponds and sediment falls out. Good for low flows and shallowly sloped sites.

Front 19

Temporary erosion control blanket

Back 19

Use on steep slopes where erosion will occur before vegetation can be established. Overlap edges of blankets and secure with staples to make sure water can't flow beneath blankets. Biodegradable blankets can't be held in place.

Front 20

Seeding for erosion control

Back 20

Should initiate within 7 days of grading activities. Most efficient and cost effective method assuming proper and timely establishment.

Front 21

Universal Soil Loss Equation (USLE)

Back 21

A=RKLSCP, where

A=average annual soil loss (Tons/acre/year)

R= rainfall and runoff factor

K=soil erodability factor

LS=topographic factors (length and steepness, combined into one factor)

C=Crop and cover management factor

P=Conservation practice factor

Developed by the NRCS