Estimating suspended sediment concentration using turbidity in an irrigation-dominated Southeastern California watershed

This study investigates the feasibility of using turbidity (T) as a surrogate for suspended sediment concentration (C) in an irrigation-dominated watershed in southeastern California. A nonlinear T-C relationship was developed and evaluated using two independent sets of data obtained by physical sampling and laboratory turbidimeter. The relationship was interpreted in terms of the heterogeneous particle size distribution in the samples. The effects of spatial and temporal variation of particle sizes and water colors on the relationship were examined. Further, possible effects of laboratory procedures on the relationship such as time delay of sample measurement and calibration of T for C using lab-prepared samples were analyzed. The study showed that the variation of particle size distribution is the key factor controlling the T-C relationship. Water color and time delay for sample analysis did not significantly affect the turbidity values, whereas laboratory procedures may mislead the T-C relationship. It is concluded that turbidity may be a surrogate for suspended sediment concentration in such irrigation-dominated watersheds in arid regions, though the T-C relationship has to be established with care.