238 ENVIRONMEN'IAL, ENGINEERING
indicates soil with:
65% silt and very fine sand
5% sand (O.lW2.0 mm)
3% organic matter
Fine granular soil (1-2 mm)
Slow to medium permeability (O.W.6 In/hr)~~
Soil structure size (mm). .... .... ..
2. Mod. to rapid 2.0-6.0
3. Moderate 0.W.O
4. Slow to med. 0.2-0.6
5. Slow 0.6-0.2
6. Very slow < 0.06
Figure 11-2. Soil erodibility nomograph for calculating values of K.EXAMPLE 11.1. An 830-acre watershed is located 5 miles south of Indianapolis in
central Indiana. Given the following information, compute the projected sediment
from sheet and rill erosion in.terms of average daily loading: 180 acres of cropland;
corn in conventional tillage; average annual yield of 4045 bdacre; cornstalks remain
in field after harvest; contour strip-cropped planting method; soil is Fayette silt loam;
slope is 6%; slope length is 250 ft.
The factors for cropland in Eq. (1 1.1) are:
R = 200 from Fig. 11-1,
K = 0.37 from Fig. 11-2,
LS = 1.08 from Fig. 11-3,
C = 0.49 from Table 11-3 and USDA Soil Conservation Field Office,
P = 0.25 from Table 11-4, and
& = 0.60 from USDA Soil Conservation Field Office.