A watershed is any area of land that drains water to common point. The
physical, chemical and biological makeup of a waterbody is created by
its surrrounding physical features and geologic origins. Analysis of
these features aids understanding of stream-watershed relationships.
The shape and slope of a watershed and its drainage pattern influence
surface runoff and seepage in streams draining the watershed. One
factor that greatly influences surface runoff and seepage in streams is
climate. Climate is the type of weather a region has over a long period
of time. It affects water loss from a watershed as well as providing
water. Precipitation and temperature strongly affect soil formation.
Soil is the basic watershed resource which, except over long periods of
time, is a non-renewable resource. Soil supports plant growth which in
turn slows surface runoff and protects the soil surface from the
rainfall's beating and puddling effects (Watersheds, Oregon 's Fish and
Wildlife Department). Tree canopies also protect the soil surface by
intercepting rain and reducing the force with which it strikes the
ground. Grasses, trees, and shrub stems along riverbanks trap sediments
and floating debris during high waterflows. Overall, soil and plant
cover are the elements of a watershed that prevent erosion and thereby
determine water quality.