Session4: Hydrology and water resources

4-4

Title: TEMPORAL VARIABILITY OF DISCHARGE RATING CURVE INVESTIGATED USING SHALLOW-WATER ACOUSTIC TOMOGRAPHY

Kiyoshi Kawanishi, Mohamad Basel Al Sawaf

Acquiring continuous streamflow estimates is paramount in hydrological studies, extreme event analyses, and water resources management. The discharge uncertainty caused by temporal variability of stage–discharge relationships is significant. The short-term changes of the discharge rating curve (HQRC) caused by flood events are undetectable by traditional rating techniques. This paper investigates the temporal variability in HQRC from unique high-frequency (every 10 minutes) streamflow time series. The time series data have been obtained using a novel acoustic method: fluvial acoustic tomography (FAT). In contrast to the traditional point/transect measurements of discharge, the FAT system enables us to continuously measure the depth- and range-averaged flow velocity along the ray path. A 115-m wide straight reach of the Gono River, Miyoshi City, Japan was selected as the survey site. The riverbed consisted of gravel (d50=27 mm). The bed slope around the observation site was approximately 0.11%, and the Manning roughness was approximately 0.03. For falling limbs of 16 hydrological events, the discharge rating curves were analyzed. Temporal variations in hydraulic parameters of the rating curve were examined in addition to the variability of HQRC. The rapid changes of HQRC occurred owing to flood events.