Slide 4 of 7
The relationships between land and water resources can be characterized by indicator numbers or coefficients, called here transform coefficients because they describe the way a land system transforms the quantity and quality of water as it flows through a landscape. Some examples include:
(1) A runoff coefficient, C, specifies the proportion of precipitation that becomes runoff. It can be applied to mean annual or monthly precipitation to determine the corresponding runoff or water yield of a watershed.
(2) The Soil Conservation Service Curve Number, CN, (0-100), is a function of land use and soil type that characterizes the amount of flood runoff occuring for a given storm precipitation.
(3) Effects of land management on groundwater can be described by the net recharge rate, which is the rate of natural recharge from the land surface to an aquifer, minus the pumping rate of groundwater from the aquifer.
(4) Water quality is characterized by the Expected Mean Concentration, (EMC), which is the ratio of pollution load to flow during a runoff period. Pollutant loads are found by taking the product of the EMC and the streamflow rate.
(5) The sediment yield of a watershed is measured by the Erosion Rate, or sediment load in a river divided by the upstream drainage area.