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 Attenuation of animal waste pollutant load from the feedlot edge to the watercourse is a function
of infiltration, filtration, settling, and adsorption. Reduction of pollutant concentration depends on
vegetative cover effects and time of contact (Tc).
Tc = L/V
(1.1.35)
Where:
Tc = time of contact (sec)
L = distance from feedlot edge to discharge point (ft)
V = flow velocity (ft/sec)
Where:
log V = 0.5 log S-C
S = slope (percent)
C = surface condition constant (Table 1.1.1)
An additional process for the reduction of feedlot pollution concentration may take place by
dilution from the runoff of adjacent areas (Areas 3a-3f):
CT VT = CRVF + C3V3
(1.1.36)
Where:
CT
= final pollutant concentration at discharge point (mg/1)
VT
= total runoff volume at discharge point (ac-in)
CR
= reduced pollutant concentration after filtration (mg/1)
C3
= pollutant concentration of runoff from Area 3 (mg/1)
V3
= runoff volume from Area 3 (ac-in)
A more detailed, process-based model for erosion and sedimentation estimation is the Water
Erosion Prediction Project (WEPP). A large team of researchers have been collaborating with field and
watershed erosion experiments and model testing (Flanagan et al., 1995). Numerous papers on WEPP
have been published in Transactions of the American Society of Agricultural Engineers.
1.1.3 NONPOINT SOURCES
Land use practices that result in nonpoint sources of pollution are difficult to manage. Land use
changes may affect infiltration, runoff volumes, peak flows, and stream morphometry. Such changes are
termed hydromodification. Habitat for fish and wildlife can be adversely affected by hydromodification.
1.1-28
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