Dimensionless Light Attenuation Number for Modeling Suspended Sediment Concentration in Open Channels

Abstract

The present work focuses on estimating suspended sediment concentration in rivers using sediment transport modeling coupled with wireless sensors. The vertical attenuation of light intensity within the water column of open channels with suspended sediment closely fallows the exponential Beer-Lambert Law but varies considerably due to sediment physical characteristics. Dimensional analysis is performed using principles of optical physics in a liquid and dimensionless arrangement of controlling variables to formulate a light attenuation number that includes sediment density, particle size, concentration and attributes of the incident light. The light attenuation number is used to predict a dimensionless light attenuation coefficient that parameterizes the Beer-Lambert Law. Dimensional analysis results are tested for a range of laboratory and field data of light attenuation by sediment in rivers and lakes reported in the literature and laboratory data collected in this study. We used our recently developed light attenuation sediment sensors for stream sediments in the lab to collect data results for natural and engineered sediments. Results show that the light attenuation number predicts well data across a range of sediment characteristics. And, implications are that knowledge of sediment properties allows the light attenuation number combined with sensor measurements and transport models to predict suspended sediment concentration in rivers. We also highlight that the low cost wireless light attenuation sediment sensors are well suited for sediment measurements within watershed sensor networks that can be coupled to more traditional sediment transport modeling approaches.