The effects of river flow on water quality in estuarine impoundments

Several impoundment schemes have been built or are proposed in the UK and worldwide. Impounding fundamentally alters the dynamics of estuaries with consequences in terms of sedimentation patterns and rates as well as water quality. This paper presents some initial findings on the relationships of water quality to river flow based on work done on the Tees impoundment in Northeast England (a total exclusion system) in the summer of 1999 and the winter of 2000. Eleven water quality surveys were undertaken to measure a range of water quality parameters (BOD, alkalinity, pH, Eh, conductivity, dissolved oxygen, temperature, suspended solids, nitrate plus nitrite, ammonium and orthophosphate, and a range of metals) over a variety of states of river flow. Statistical analysis was used to determine whether the major water quality parameters were controlled by processes internal to the impoundment, i.e. with water depth and distance downstream, or external inputs to the impoundment. Those reported as controlled by external inputs include nitrate and nitrite, phosphate, dissolved oxygen, dissolved metals, conductivity, alkalinity, and temperature. pH, and to a minor extent dissolved oxygen and nutrients, show internal control. Understanding the controls on water quality parameters will allow more sustainable management such schemes.