The effect of upstream river hydrograph characteristics on zinc deposition, dissolved oxygen depletion and phytoplankton growth in a flood detention basin system

Abstract

In flood modelling, the characteristics of the upstream flood hydrographs may have a large influence on simulation results. Hence, the focus of this paper is to investigate the influence of shape and magnitude of hydrographs on detention basins; especially on suspended sediment and micro-pollutant transport and on dynamics of nutrients, oxygen and organic carbon. Five flood events with different filling and emptying curves were created by normalising the flood hydrographs and performing a cluster analysis. The resulting clusters describe typical, realistic hydrographs, whose discharges were used as boundary conditions for the simulations. The models DYNHYD, TOXI and EUTRO from the WASP5 modelling package were used as a basis for the simulations. Monte-Carlo simulations were carried out to investigate the differences and analogies in sediment deposition, depletion of oxygen or growth of phytoplankton for each cluster. The results show that the shape of the upstream hydrograph and the severity of the flood do not have a significant influence on the amount of deposited sediment and particulate zinc. However, the hydrograph characteristics have an impact on the severity of oxygen depletion and phytoplankton growth, which is a consequence of the control strategy of flood water diversion by the opening and closing times of the flood gates and the retention times of flood water in the detention basins.