2.5 Soils

Factors related to soil are of extreme importance in determining the quantity of soil eroded and its associated NPS pollutants during given conditions. Different soil types and textures erode at different rates under the same conditions. Clay particles, for example, require more energy to be detached than do particles of silt. However, once clay particles are suspended in the water column they remain in suspension much longer than do particles of silt or sand. In addition, the adhesion of pollutants to different sized soil particles varies.

A list of soil types and the amounts of each type within the watershed is given in Table 2, and the location of different soil textures are shown in Figure 8. Another important soil parameter is the hydrologic soil group, which among other things relates the ability of a particular soil to allow infiltration of water. The locations of hydrologic soil groups are displayed in Figure 9.

Each of these soil constituents is important to the accurate modeling of surface runoff conducted by AWRI and can also determine the suitability of a particular soil group for various uses. For example, sandy soils allow for more infiltration of rain water than do heavier clay soils. Infiltration tendencies of the soil on a particular property could be a starting point for local officials to use when they assess the variety of possible uses for that property. For example, this information can be used by local officials during site plan review of proposed development to require responsible stormwater and erosion control practices during and after land disturbing activities. In order to better promote the use of this information, AWRI used existing soils data to map those areas within the watershed which the county soil survey determined to have limitations for uses such as the construction of dwellings with basements or septic fields (Figures 10-11). The information and classifications were taken from the Soil Survey of Kent County, Michigan. (United States Department of Agriculture, Soil Conservation Service. 1986.) The information presented in map form is often less intimidating and more easily understood, and therefore more likely to be regularly used than tabular data.