Laboratory investigation on the effect of particle size, water flow and bottom surface roughness upon the response of an upward-pointing optical backscatter sensor to sediment accumulation

Upward-pointing optical backscatter sensors (OBS) have been recently introduced to measure sediment accumulation in situ. Here, the effect of two potentially important parameters on an upward-pointing OBS response to sediment accumulation measurements is investigated in a laboratory flume: (a) grain-size distribution and (b) bottom surface roughness in relation to water speed. Independent measurements of sediment accumulation were done with a specially built suction chamber. This chamber collects accumulated particles directly with a resolution of the order of 0.01 mg cm−2 and with an accuracy of 70%. The upward-pointing OBS response to sediment accumulation was found to vary (a) with grain size by less than 30% for a range of 15–1000 μm and (b) with water speed on a flat surface by less than 35% for a range of 0–7 cm s−1. Speed had no effect on the OBS response when a rough bottom surface was tested for a range of 0–3.5 cm s−1. This study contributes to the understanding of upward-pointing OBS to sediment accumulation, the only field technique to date able to provide high-resolution measurements of sediment accumulation, with a high temporal resolution but still over extended periods of time.