WSP08749

• File Number: 8272.500
• Description: Colorado River Basin Salinity Control - Colo Dept of Public Health - WQCC and WQCD
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 11/14/1983
• Title: Erosion and Sediment Yield - Channel Evaluation Workshop
• Water Supply Pro - Doc Type: Report/Study

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Table 1. Volume-Weights of Soils

Soi 1 Texture

Volume-Weight

Clay
Silt
Sand
Gravel
Loam'
Sandy loam
Gravelly loam

60-70 pcf
75-90
90-110
110-120
80-100
90-110
110-120

SAMPLE CALCULATIONS

1. There are 12 miles of first order streams in the Doodad Watershed. You go
out to sample one mile of a first order stream. One bank is grassed and
noneroding. The other bank is a sandy loam soil and three spots are bare.
Two of the spots are 600 and 800 feet long. The banks are bare with a few
roots exposed and some rills. There is no grass overhang above the two
spots and the bare areas are about 10 feet high. The third spot is on the
outside edge of a curve in the stream. It is 1,200 feet long and the bare
banks are 12 feet high. Two fence posts are lying at the base of the bare
bank and two trees have fallen into the channel. Most of the bank has
rills and a~out 2 inches of grass overhang is at the top of the bank.
Based on your sample, how much streambank erosion is occurring on 1st
order streams in the Doodad Watershed?

Use direct volume method:

(eroding area) (lateral recession rate)(density) i
- eros on
2000 pounds/ton

1400 ft x 10 ft x 0.06 ft/yr x 100 pcf _ 42 tons/yr/sample
2000 pounds/ton

1200 ft x 12 it x 0~4 ft/vr x 100 pcf _ 288 tons/yr erosion
2000 pounds/tDn 330 tons/yr erosion

2600 ft. eroding _ 25% of sample was eroding
2 bank miles sampled

330 tons/yr erosion _ 660 tons/yr/bank mile is erosion rate
~ mile eroding :
12 miles of 1st order streams x 25% - 3 total miles eroding
3 miles x 2 banks/mile - 6 total bank miles eroding
6 bank miles eroding x 660 tons/yr/bank mile - 3960 tons/yr bank erosion

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