Water Quality Effects of Excavation and Diversion

Abstract

Water quality data collected from Yellow Creek in northeast Mississippi before and during construction of the Divide Cut of the Tennessee‐Tombigbee Waterway provide information regarding the water quality effects of stream channelization and large‐scale construction projects. Simple graphical and statistical procedures for detecting changes in stream water quality are demonstrated. Data analysis was hindered by missing data, inconsistencies in the list of variables monitored, and changes in sampling frequency. Observed water quality changes were evidently due to increased inputs of sediment and reduced shade. Statistically significant changes in variances and means were observed for most grab‐sample variables. Mean values of specific conductance, turbidity, color, COD, and total alkalinity, hardness, ammonia, phosphorus, sulfate, iron, lead, and manganese were 50–100% greater during construction than before construction. Estimated average daily loadings of total metals, nutrients, and dissolved solids were greater during construction. Average daily suspended sediment load was slightly less during construction, probably because the preconstruction suspended sediment record was brief and influenced by high flow events. Average daily maximum stream temperature was 4 °C greater, and coliform densities and phenol concentrations decreased. Total organic nitrogen, phosphorus, iron, manganese, and zinc were significantly correlated with turbidity during construction, but only total phosphorus was correlated with turbidity before construction.