Determination of the optimal water release of dam with considering quantitative and qualitative demands

2. Materials & Methods
2.1. Environmental flow calculation
To calculate the Environmental flow of rivers, many different methods have been proposed. These methods can be classified into four main categories (hydraulic, hydrologic, simulation settlement and comprehensive methods). In this study due to lack of sufficient data, hydrological methods used to determine the environmental flow, because the hydrological methods are simpler than other methods.
2.2. Purposes
In this study, five purposes in determining the optimal release are intended. As mentioned earlier, one of the main purposes of this study is supply environmental flows. Therefore the first target is the environmental flows supplement. Gotvand dam has been constructed to meet the water requirements of hydropower generation purposes, flood control, agricultural water management and create tourist attractions. Therefore, one of the aspects that needs to be considered in determining the optimal release is to meet these purposes. It is necessary to define the second objective as reliability to determine the optimal release streams while dams purposes also be considered. Taking account the purpose of reliability among the other purposes of the dam, causes the supply of water needs for all purposes (hydropower generation purposes, flood control, agricultural water management and create tourist attractions) in determining the optimal release, be considered.
Another important target related to this issue is supply of high-quality water for downstream regions. Given that the drinking water in the downstream regions including the Ahwaz city, is supplied from the Karun river and given the importance of providing high-quality drinking water, it is necessary to put a purpose to supply a high-quality water. Therefore, another purpose as supply downstream water demands has defined to provide high-quality water for downstream regions.
Surface water pollution is an important phenomenon that is threatened humans health, animals and the environment. Thus, in addition to the environmental flow, it is also necessary to consider a purpose to manage and control river pollution constantration.
There are two river pollution targets due to behavior of the release flow. The two conflicting targets are “average concentration” and “length polluted”. To calculate the average concentration of greater than one ppm, concentrations are averaged and the average value is considered as the concentration of BOD indicator for release flow. Concentrations less than one milligram/liter are not accounted because the water in which concentrations of BOD indicator is smaller than one milligram/liter, is considered pure. The mathematical definition of the average concentration is illustrated:


1.1. Conflict resolution model
If there is more than one stakeholder in the decision-making process, due to the different aims and different priorities of the views of stakeholders, decision-making process will have not made such as lack of agreement. In such matters, it is the decision in such a way that all views of all stakeholders are taken into account, and the rights of all stakeholders be met. One way to solve this kind of problem is using models of conflict resolution. One of the common conflict resolution methods is Nash.
1.2. Case study
One of the main aims of this study was to determine the environmental flow in the Gotvand dam location to downstream of shoshtar city. Karun is the most important river of Iran and it has the largest discharge of water among the Iran's rivers. The length of this river is 800 km and long-term average annual flow of the river is 453 m3/s and average. For the purposes of this study, all data were collected from the study area. This data includes the release of dam, river hydraulic details and characteristics are sources of pollutants.
2. Discussion of Results & Conclusions
In this part, the results will be discussed. At the first, by using the QUAL-2K model, water quality simulations is done and then the simulation results to calculate purposes and average concentrations and length polluted are used. Finally, by using the theory of Nash conflict resolution, the optimal release under three scenarios relative weights is determined.
2.1. Environmental flow calculation
Environmenta flow of Karun River in the study area was calculated by using flow-based Tennant (1976) and Aquatic Base Flow methods. The range environmental flow was 45 to 272 (m3/s).
2.2. Simulation BOD in the range of dam release
Qualitative simulations for releases from the dam flows of the range of 13 to 458 have been done by using the QUAL-2K.
2.3. Calculation of average concentrations and length polluted
Once the river's qualitative simulation is finished, BOD indicator concentrations along the river are obtained for each discharge flow releases from the dam. Using the obtained concentrations, the average concentration and length of contact with the river can be calculated. Therefore, the mean concentrations were calculated for different values of release flow from the dam.
By increasing the release rate, due to increased volume of water and dilution of contamination concentrations, the average concentration decreases and vice versa. But as the flow rate increases, due to increased flow velocities, unallowable concentrations run longer in the river and increase the length of the contact, and vice versa. This issue is of great importance in determining the proper locations for the water extraction from the river. This is especially important in downstream areas that are used to supply drinking water to riverside water. Downstream of the study area, contains many cities and villages such as Ahwaz. Therefore, it is necessary to determine the release rate in such a way that the concentration of water pollution of the river before reaching the water extraction points, has fallen to the standard limits.
2.4. Determining the optimal release
One scenario has been defined to evaluate impact of relative weights that was determined according to the different qualitative and changes various conditions. Normalization of data to assess the importance of purposes is necessary in conflict resolutions methods. According to Nash conflict resolution model, before running the optimization model of conflict resolution, it is necessary set out the minimum acceptable level for each of the purposes. The minimum acceptable level for each of the five purposes listed in the previous section, were defined
After normalization of the data of the purposes and determining their minimum acceptable level, for each of these purposes, relative weights should be determined according to their importance. But relative weights depend on many conditions including economic, social, climate (wet or drought), and so on. Therefore, these conditions may always change at any time, and the relative weights of purposes should be changed. Relative weights are used to indicate the importance of each purpose on determining the release rate of the dam. In the present study, the relative weight of purposes has been determined based on the authors' experiences. Therefore, in order to apply the results of this research, it is necessary to determine the relative weights of each purpose according to the time conditions and existing expectations. In this study, one scenario of relative weights is defined. In this scenario, relative weights for all purposes are equal to and equal to one.
At last, by using Nash conflict solution method, optimal flow releases from the dam under one relative weights for purposes, was determined. The amount of released flow from the dam to the scenario was184 m3/s.
Keywords: flow release, Environmental flow, Water quality, Conflict resolution, Karun river and Gotvand dam.