Of course, in regions of the United States where ranchers, foresters and others manage large tracts of land, you may be working with a much larger watershed. Another important feature is the geographic boundary of the watershed. The boundary is formed by a ridge or high area from which water drains either toward or away from your watershed. How flat or steep the land is impacts how fast water drains. The faster the drainage, the more potential for flooding and increased soil erosion.
Soil type is also important.
For example, sandy soils allow the ground to soak up water faster. This reduces surface runoff, but can affect ground water. Clay soils, on the other hand, are tighter and do not allow as much water infiltration. This can lead to more runoff and soil erosion. Whether your watershed drains into a stream or lake, the area nearest the water greatly affects water quality.