Fulfillment of river environmental flow: applying Nash theory for quantitative‐qualitative conflict resolution in reservoir operation

Abstract

AbstractThe construction of reservoirs for water supply alters the riverine ecology and changes water quality. It is, therefore, imperative to estimate and provide the riverine environmental flow requirement to prevent irreversible environmental damage and to maintain suitable water quality. Water releases from reservoirs constitute the means for meeting environmental flow and water quality requirements downstream from reservoirs. These requirements can be realized through the modification of the reservoir operation programmes by reallocating a percentage of the reservoir releases otherwise dedicated to quantitative objectives. This is performed in this study by considering the qualitative (i.e. pertaining to water quality) objectives alongside quantitative objectives of reservoir releases in order to achieve a general coverage for an operating programme that balances in the most rational manner the interests of riverine environmental protection and quantitative functions. The case study area is located in the river reach between the Gotvand reservoir and Shooshtar city in the Gotvand‐Karoon reservoir‐river system in Iran. The range of riverine environmental flow is calculated in the study river reach with hydrologic methods. Water quality is simulated and included reservoir operation with the QUAL‐2K simulation model. The existing quantitative and qualitative objectives for reservoir operation are determined and classified. The best reservoir releases corresponding to three scenarios are determined by the Nash theory considering all possible objectives in the reservoir‐river system. These scenarios allocate relative weights to defined objectives and releases were determined to be equal to 183.8, 141.8 and 206.8 m3/s for three scenarios.