Investigating Changes of Water Quality in Reservoirs based on Flood and Inflow Fluctuations

Abstract

Water temperature and dissolved oxygen are essential indicators of water quality and ecosystem sustainability. Lately, heavy rainfalls are happening frequently and forcefully affecting the thermal structure and mixing layers in depth by sharply increasing the volume of inflow entitled flash flood. It can occur by sudden intense precipitation and develop within minutes or hours. Because of heavy debris load and speedy water, this phenomenon has remarkable effects on water quality. A higher flow during floods may worsens water quality at lakes and reservoirs that are thermally stratified (with separate density layers) and decrease dissolved oxygen content. However, it is unclear how well these parameters represent the response of lakes to changes in volume discharge. To address this question, researchers simulate the thermal structure in two stratified reservoirs, considering the Rajae reservoir as a representative reservoir in the north of Iran and Minab reservoir in the south. In this study, the model realistically represented variations of dissolved oxygen and temperature of dams Lake response to flash floods. The model performance was evaluated using observed data from stations on the dams lake. In this case, the inflow charge considered in a 10-day flash flood from April 6th to April 16th during the yearly normal flow. The complete mixture in a part of the thermal structure has been proved in Rajaee reservoir. The nonpermanent impact of the massive inflow of storm runoff caused an increase in oxygen-consuming, leading to a severe decrease in dissolved oxygen on epilimnion and metalimnion. The situation in Minab reservoir was relatively different from Rajae reservoir. The inflow changes not only cause mixture but also help expanding stratification.