Soil Loss Calculation Using RUSLE

Evaluating Soil Loss Using RUSLE

• A disturbed area of 15 acres was created due to development near Norwich, Connecticut.
• The soil is Charlton, exposed in the B horizon.
• The average slope is 8% and the slope length is 400 feet.
• The R-value is 150.

Problem 1

• Calculate the estimated soil loss from the site if it remains unprotected for one year.

Use RUSLE Equation

• A = R • K • LS • C • P
• Find the R-value using isoeoroent maps (Figure 9-1)

Reference Isoerodent maps

• Use Figure 9-1 to find the R-value.

• A = R • K • LS • C • P

• Find R-value using isoeoroent maps

Calculating Soil Erodibility Factor (K)

• Use Table 9-1 to find K-value for soil type Charlton
• K=0.43

Calculating Slope Length and Factor (LS)

• Use Table 9-2 to determine LS from slope grade and length
•  Given slope length of 400 ft. and grade of 8%, LS value is 2.7.

Calculating Plant Cover Management Factor (C)

• Use Table 9-3 to determine the C value
• If there is no ground cover, assume C = 1.

Calculating Support Practice Factor (P)

• Use Table 9-4 to determine the P value
• If there is unprotected land, assume P = 1.

Problem 1 - Solution

• A = 150*0.43*2.7*1*1 = 174.15 tons/acre/year
• Total soil loss for 15 acres = 174.15 x 15 = 2,612 tons per year.

Problem 2

• Determine the soil loss from the site for the period of October 1 to June 1 of the following season.
• Use rainfall intensity distribution (Table 9-6).

Problem 2 - Solution

• Sum the percentages (from Table 9-6 for October to June): 8+8+7+3+3+5+4+6=44
• 0.44 x 2612 = 1149 tons

Problem 3

• Determine the annual soil loss from the site with a temporary seeding of annual rye grass.

What Value Changes?

• C-value decreases with ground cover

Problem 3 - Solution

• Using Table 9-3 find the C value for annual ryegrass: C = 0.1
• 0.1 * 2612 = 261 tons

Problem 4

• Calculate the cubic yards of soil lost if the site remains unprotected; the surface is compact and smooth, and bulldozed uphill and downhill.

Now What Will Change?

• P value increases in table 9-4

Problem 4 - Solution

• P=1.3
• 2612 * 1.3 = 3396 tons
• Convert tons to cubic yards using 105 lbs/ft^³ = 2377 cubic yards

Problem 5

• Calculate the expected soil loss from a 22-acre site in Syracuse, NY.

Problem 5 -Solution (a)

• Use Figure 9-8 to find the percent of annual soil loss for the period of construction
• For this site, from the graph (date range of construction), 90% of annual soil loss is relevant

Problem 5 - Solution (b)

• Use Table 9-3 to find the C-value for 2 tons of straw mulch per acre
•  Calculate the soil loss for the given circumstances.

Problem 6

• Find the sediment yield from a 15-acre site with a runoff rate, Qp=1.56 cfs, and a runoff volume of 2.07''.

This quiz focuses on evaluating soil loss using the RUSLE equation based on the provided data from a disturbed area near Norwich, Connecticut. Participants will calculate the estimated soil loss by applying values for rainfall, soil erodibility, slope, and vegetation management factors. Understanding the RUSLE method is crucial for effective soil conservation and management.