EI, L, and S values should be obtained from local offices of the
U.S. Soil Conservation Service. K values may be determined from published
data ona particular locality. In the absence of such data, it may be
roughly estimated from Figure 12 (after Reference 13, Erosion Control on
Highway Construction, by the Highway Research Board).
2. INVESTIGATION. Where erosion can be expected during earthwork
construction, on-site investigations should include: (1) field
identification and classification for both agricultural textures and the
Unified system, (2) sampling for grain size distribution, Atterberg limits
and laboratory classification, and (3) determination of in-place densities
(see Chapter 2).
3. SURFACE EROSION CONTROL. For typical erosion control practices see
Table 3, (modified from Reference 13). General considerations to reduce
erosion include:
a. Construction Scheduling. Schedule construction to avoid seasons of
heavy rains. Winds are also seasonal, but are negligible in impact compared
to water erosion.
b. Soil Type. Avoid or minimize exposure of highly erodible soils.
Sands easily erode but are easy to trap. Clays are more erosion resistant,
but once eroded, are more difficult to trap.
c. Slope Length and Steepness. Reduce slope lengths and steepness to
reduce velocities. Provide benches on slopes at maximum vertical intervals
of 30 feet.
d. Cover. Cover quickly with vegetation, such as grass, shrubs and
trees, or other covers such as mulches. A straw mulch applied at 2
tons/acre may reduce soil losses as much as 98% on gentle slopes. Other
mulches include asphalt emulsion, paper products, jute, cloth, straw, wood
chips, sawdust, netting of various natural and man-made fibers, and, in some
cases, gravel.
e. Soil Surface.
Ridges perpendicular to flow and loose soil provide
greater infiltration.
f. Exposed Area. Minimize the area opened at any one time. Retain as
much natural vegetation as possible. Leave vegetation along perimeters to
control erosion and act as a sediment trap.
g. Diversion. Minimize flow over disturbed areas, such as by placing a
berm at the top of a disturbed slope.
h.
Sprinkling.
Control dust by sprinkling of exposed areas.
i. Sediment Basins. Construct debris basins to trap debris and silt
before it enters streams.
4. CHANNEL LININGS. Table 4 presents guidelines for minimizing erosion of
earth channels and grass covered channels (modified after Reference 14,
Minimizing Erosion in Urbanizing Areas, by the Soil Conservation Service).
7.1-289
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