Seep And Runoff Detector Design And Performance To Determine Extent And Duration Of Seep/Runoff Zone From Precipitation On Hillsides

Abstract

ABSTRACT A field cross-section instrumented with transducer water potential sensors and with seep and runoff detectors was used to evaluate the size of the area contributing surface runoff to a stream. Runoff and seep detectors were designed as water-activated, printed-circuit switches connected to a programmable data logging system to indicate and distinguish when seepage and runoff had occurred at the soil surface. The results from the runoff and seep detectors predicted the seep area indicated by measured water potential well. Seepage and overland flow following storms on the 21.3-m (70-ft) cross-section expanded the variable source area up to 15.2-m (50-ft) from the stream which decreased to within 6.7-m (22-ft) of the stream within two days after the end of the storm. Localized precipitation, applied only to the cross-section via sprinkler irrigation under a similar water potential distribution, caused equivalent source area expansion which decreased to the 6.7-m (22-ft) area in only 16 h. This 6.7-m (22-ft) source area exhibited seepage and seepage overland flow in both cases for five to seven days after the precipitation event. The extent of the variable source area was shown to be dependent on the antecedent moisture of the entire hillslope as well as the amount and areal extent of precipitation.