December 2010 Final Indian Creek, Dago Slough, and Prairie Creek LRS/TMDL
151 | P a g e
Pollutant Load Models
Formulas and selected variables were derived from STEPL (Spreadsheet Tool for
Estimation of Pollutant Load) Version 3, Tetra Tech, 2004. Unique values were utilized
where data was available or where adjustments were needed. Total Nitrogen and Total
Phosphorous were modeled. TSS was also modeled in urban areas.
Runoff and Soil Nutrient Model Values:
Model Rain days Correction
Factor
(precipitation)
Curve Number
(by soil
hydrologic
group)
Runoff
(by soil
hydrologic group
in inches)
N
concentration
P
Concentration
Total
Suspended
Solids
Agriculture Hancock
Co. = 96.3
Knox Co. =
96.6
Warren Co.
= 97.2
0.424 A = 64
B = 75
C = 82
D = 85
Hancock Co.
A = 0.079
B = 0.122
C = 0.169
D = 0.197
Knox Co.
A = 0.078
B = 0.122
C = 0.168
D = 0.196
Warren Co.
A = 0.077
B = 0.12
C = 0.166
D = 0.194
In Runoff = 1.9
mg/l
In Sediment =
0.0016 %
In Runoff =
0.3 mg/l
In Sediment =
0.00062 %
N/A
Pasture Hancock
Co. = 96.3
Knox Co. =
96.6
Warren Co.
= 97.2
0.424 By Cattle Rank:
Rank 1-3
A = 39
B = 61
C = 74
D = 80
Rank 4-5
A = 68
B = 79
C = 86
D = 89
By Cattle Rank:
Rank 1-3
A = 0.031
B = 0.070
C = 0.117
D = 0.152
Rank 4-5
A = 0.091
B = 0.145
C = 0.207
D = 0.247
In Runoff
By Cattle
Rank:
1 = 2 mg/l
2 = 3 mg/l
3 = 4 mg/l
4 – 6 mg/l
5 – 8 mg/l
In Sediment =
0.0016 %
In Runoff =
By Cattle
Rank:
1 = 0.15 mg/l
2 = 0.225
mg/l
3 = 0.3 mg/l
4 – 0.8 mg/l
5 – 1.25 mg/l
In Sediment =
0.00062 %
N/A
Urban
Hancock
Co. = 96.3
Knox Co. =
96.6
Warren Co.
= 97.2
0.424 Assumes 65%
impervious
A = 77
B = 85
C = 90
D = 92
Prairie Creek
A = 0.134
B = 0.197
C = 0.265
D = 0.304
Indian/Dago
A = 0.133
B = 0.196
C = 0.264
D = 0.302
In Runoff =
2.01 mg/l
In Runoff =
0.31 mg/l
100.2
mg/L
Vegetation
(non-pasture;
timber, CRP
and other
Hancock
Co. = 96.3
Knox Co. =
96.6
Warren Co.
0.424 Average curve
number between
a meadow, fair
forest, and fair
timber/grass
Prairie Creek
A = 0.027
B = 0.068
C = 0.112
D = 0.146
In Runoff =
0.15 mg/l
In Sediment =
0.0016 %
In Runoff =
0.08 mg/l
In Sediment =
0.00062 %
N/A
