Topography

D. Topography

The terrain of the watershed is generally flat with slopes between zero and two percent for approximately two thirds of the watershed. The remaining area varies from gently rolling with slopes between two and six percent and occasional slopes above six percent. Greater differences in elevations are a result of glacial features such as moraines, eskers, and kames. One such area with steep slopes relative to the surrounding area is in the headwater region in Logan and Champaign Counties of the watershed in which slopes greater than 12 percent exist. The following map displays the gradient and topography of the watershed (See Map 5).

In order to examine slope in more detail, four maps were created based on subwatersheds in the Darby Creek Watershed which are displayed in Appendix B. For more information on the creation of the maps see Detailed Soil Mapping in the previous section. Figure 7 summarizes slope for the entire Darby Creek Watershed.

Figure 7: Darby Creek Watershed Slope Summary
Erodibility	All Land (Percent)	Only Agricultural Land (Percent)

0 - 2%	59.49%	63.05%
2% - 6%	31.33%	30.61%
6% - 12%	7.68%	4.91%
12% - 18%	0.03%	0.97%
18% - 25%	0.40%	0.14%
25% - 50%	0.90%	0.12%
Water and Other Soils	0.18%	0.20%
Totals	100%	100%

The slope of soils in each Little Darby, Upper Big Darby, and Lower Big Darby Creek subwatersheds shared similar slopes. The Middle Big Darby Creek subwatershed had the most level topography with approximately 78 percent of agricultural land sloping between 0 and 2 percent as seen in Figure 8 below. For more detail on the slope of soils in each watershed below, see Appendix B.

Figure 8: Percent Slope by Major Subwatershed
Watershed	0 -2%	2-6%	6 -12%	12 -18%	18 -25%	25 -50%	Water and Other Soils
Upper Big Darby	56.45%	33.00%	7.95%	1.78%	0.22%	0.14%	0.46%
Middle Big Darby	78.07%	18.79%	1.26%	0.62%	0.75%	0.52%	0.00%
Lower Big Darby	56.41%	33.48%	7.43%	1.98%	0.38%	0.22%	0.11%
Little Darby Creek	56.66%	33.69%	4.57%	1.44%	0.45%	3.18%	0.00%

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Last updated: June 09, 2008.