Toward Nonintrusive Flood Discharge Measurement

The current discharge measurement methods in rivers are known to be accurate for low and mean discharges, but large debris and high velocities prevent the use of these conventional methods during flood season. Therefore, a nonintrusive method to measure discharge during floods has been developed. The method elaborated in a laboratory channel proceeds in two steps. In a first step the water surface was recorded with three calibrated charge coupled device (CCD) cameras using identical frequency. To determine the geometry and the velocity field of the free surface, floating tracer particles were added to the flow. In a second step a finite element program was employed to compute the discharge based on recorded surface information. An iterative procedure using the commercial finite element program CFX allows one to determine discharge. This approach considers river portions with a locally strong variable bed geometry such as drop structures whose bed profile is measured conventionally prior to or after the flood event. Laboratory experimentation demonstrated an average error in discharge measurement of 2-3%.