The mixing of the waters of the Salt and Verde Rivers

Abstract

The mixing of the waters of the Salt and Verde Rivers was studied and modeled. The river waters mix for three and one-third miles between their confluence and Granite Reef Dam, where they are diverted into canals. Mixing is frequently incomplete, and as the natural water chemistries differ, the canal water chemistries frequently differ. The mixing of the river waters was modeled mathematically with the use of a two-dimensional form of the convection- dispersion equation. A finite-difference solution of the equation was used in the development of a computer program. The model was calibrated using flow and tracer data collected at a discharge of 1050 c.f.s. from the onethird mile reach immediately below the confluence. The model adequately simulated mixing at the discharge at which data were obtained. Mixing was found to be relatively rapid, requiring an average value of k, the ratio of the dispersion coefficient to the shear velocity and depth, equal to 3.2. Simulation of a higher discharge of 5340 c.f.s., however, required a much lower value of k, 0.6. This difference is assumed to be due to the effects of channel geometry on the rate of dispersion.