A coverage showing land use in the watershed of the study watersheds was obtained from U.S. Geological Survey (USGS). The original sixteen classified land-use types in the watershed were reduced to nine primary land-use types for the purposes of this study. The table below indicates the categories that were lumped.

Table 1. Original land-use categories as determined by USGS and the lumped categories used in the Indiana Geological Survey (IGS) study. See figure on the left for a graphical representation.

USGS Land use type

IGS Land use type

Open water

Open water

Low density residential

Low density residential

High density residential

Urban

Commercial/Industrial

Urban

Bare rock/sand/clay

Bare rock/sand/clay

Deciduous forest

Forest

Evergreen forest

Forest

Mixed forest

Forest

Shrubland

Grasslands/herbaceous/shrublands

Grasslands/Herbaceous

Grasslands/herbaceous/shrublands

Pasture/Hay

Crops

Row crops

Crops

Small farms

Crops

Urban/Recreational grasses

Urban

Woody wetlands

Wetlands

Emergent herbaceous wetlands

Wetlands

Runoff coefficients and loading factors were assigned to various land-use types within the Lake Rim GIS. The following table provides the runoff coefficients and bacterial loading factors assigned to the land-use categories of the Lake Rim GIS. Low density residential areas are assumed to be using on-site sewage disposal systems.

Table 2. Land-use types that correspond to land-use codes. Also shown are the corresponding runoff coefficients and bacterial loading factors for each land-use type.

Land use CODE

Land use - Description

Storm Runoff coefficient

Loading Factor Cfu/100 mL

1

Open water

0.00

200

2

Low density residential

0.40

2000

3

Urban

0.70

25

4

Bare rocks/sand/clay

0.80

25

5

Forest

0.15

100

6

Grasslands/herbaceous/shrublands

0.25

100

7

Crops/farmlands

0.40

500

8

Urban/recreational grasses

0.20

25

9

Wetlands

0.05

200

Areally weighted runoff coefficients and bacterial loading factors were determined for each interfluve segment in the watershed drainage network.

The figure to the left shows one stream segment and its associated contributing interfluve within the East Little Calumet drainage network. The contributing interfluve surface contains eight (8) individual land-use subareas within its total area of 4,494,600 m2 (4.5 km2).

Polygon Number 221, representing a contributing interfluve area, shows land-use categories used in weighted runoff coefficient and bacterial loading calculations.

Combining the area totals for each land-use type with the runoff coefficients and bacterial loading factors provided above, the following table illustrates how the areally weighted values for the interfluve segment are calculated. This was done for all 261 individual interfluve segments in the East Little Calumet drainage network. See the figure below.

Table 3. Example runoff-coefficient and bacterial-loading calculations for Polygon Number 221 (contributing interfluve area), shown above. See Table 2 for corresponding runoff coefficients and loading rates for each land-use type.

Land use CODE

Grid cell count

Grid cell area (m2)

Land use area %

Runoff/area

Weighted Runoff coefficient

Weighted Loading Factor

1

59

53,100

1.18

0.000

2

800

720,000

16.05

0.064

3

1312

1,180,800

26.31

0.184

5

1605

1,444,500

32.19

0.048

6

56

50,400

1.12

0.003

7

547

492,300

10.97

0.044

8

364

327,600

7.30

0.015

9

251

225,900

5.03

0.003

0.361

429.9