A SUBMERGED FLEXIBLE CURTAIN IN THE RESERVOIR TO REDUCE THE NUTRIENT

Abstract

Pre-dams of optimum size normally located upstream of reservoirs have proven effective in phosphorus load reduction due to sedimentation of allochthonous and autochthonous seston. In order to achieve similar effects, model and in-situ experiments were carried out with an overstreamed submerged flexible curtain (SFC, 160m long, 6m deep) installed perpendicular to the flow direction in the mouth region of the main tributary of the Saidenbach Reservoir (Saxony, Germany). Before the installation of the SFC, the inlet normally formed a hydraulic short circuit between mouth and main basin of the reservoir along the upper metalimnetic layers during summer stratification. Therefore, the retention time of the inflowing water was too short (1.7 days on an average) to allow soluble reactive phosphorus (SRP) elimination higher than approximately 20% in the mouth region. The flow through regime changed after the SFC was built-in. The average retention time increased to about five days and sedimentation was favoured in the volume separated. The SRP elimination varied between 40% and 60% in the summer months. It is conclusive from the results of a research project that flexible curtains of sufficient depth may be cost-effective substitutes for conventional pre-dams of eutrophic lakes or reservoirs.