Storm size's effect on constant slope hydrograph separation method

The two main components that make up stream flow are baseflow and runoff. Baseflow is important as it maintains flows during times of low precipitation and dryness. Its abundance is also an indicator of habitat. Hydrograph separation techniques are one of the methods used to determine the amount of baseflow in a gauged stream. One widely used and relatively simple hydrograph separation technique is the constant slope method. A limitation of this method is the problem associated with finding the inflection point which is determined by the equation N=A0.2 where N is the number of days past the peak of the hydrograph and A is the watershed area. The equation does not perform equally well in all watersheds and for all storm sizes. The objective of this project is to determine how sensitive the equation is to storm size. To determine this sensitivity, twenty storms ranging in size from (0.01 to 1 cm) were identified in two similarly sized gauged watersheds: the Kickapoo at La Farge (266 sq mi) and Pecatonica (273 sq mi). Hydrograph separation was done manually using the constant slope method and compared to inflection point determination using curve fitting software and USGS HYSEP minimum flow hydrograph separation.