Introduction
Flood discharge at a high river stage is important in determining the design of flood-alleviating schemes. Discharge, however, is difficult to measure because high floods usually occur under extreme weather conditions. During flooding, the flow velocity is typically high, for example, above 4 m/sec, and the conventional contact measuring methods can be dangerous for both the persons and the equipment performing the measurements. Therefore,a non-contact method of flood measurement has been important to hydrologists and hydraulic engineers.
Measurement of streamflow at flood stage is normally prohibitive and is therefore not a standard task performed by hydrographic offices. Streamflow estimation at high stages is commonly achieved through transformation of gauged water levels to discharge through rating curves. These stage-discharge relationships often suffer from large errors especially above the highest gauged discharge values corresponding to morphologically formative conditions. Non-contact methods based on radar Doppler technology have recently emerged as promising options because they can remotely measure the surface water velocity without requiring contact of instruments with the stream. They have been used for more than a decade, notably in Japan, but they were expensive and are fixed with the radar beam directed to a small portion of the free surface width.
Wherever a bridge is available and cross-sectional topography can be measured before and/or after a flood, high accuracy for discharge data can be achieved in a very short time and with few gauging points across one single section; therefore measurements can be made at several rivers often ungauged during floods. The Surface Velocity Radar is easily used also in flash floods, where change of stage is very rapid .
Radar intallation sites
Benefits and advantages
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