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A study to determine the base flow components in drainage channels was undertaken in two watersheds namely Big Ditch (Site A) and Embarras (Site B) in Champaign County, Illinois. Two channel sections were selected in the two watersheds and rectangular cutthroat flumes were installed at upstream and downstream ends in the channel sections. The stream segment (194 m long) in Site A had two tile outlets draining into it. The stream segment (183 m long) in Site B did not have any tile drain. Flow rates were measured at each of the flumes and tile outlets at 15 minute intervals. Twelve piezometers were installed on both sides of each of the channel sections to monitor the water table elevations in order to estimate the base flow to the channels.

Hydrographs were developed for storm events of different intensities for the flumes and tile outlets starting from March04 to December04. In total, twenty four hydrographs were studied. A mass balance approach was used to estimate the base flow volume per unit length of the channels. Dupuit equation was also applied to determine the base flow in three transects in the stream sections during base flow periods.

It was observed that the base flow rate was predominantly dependent on the antecedent moisture conditions, rainfall distribution, the types of soil in the watersheds and plant water uptake.