چكيده به لاتين
Helleh basin is one of the sub-basins of the Persian Gulf and Oman Sea Basin, in which irrigation is the dominant consumer and cultivation of major agricultural crops such as palm wheat and barley is common there. The Helleh basin is located mainly in the two provinces, Fars (upstream) and Bushehr (downstream). Hence, there are challenges in water resources allocation of the basin between these two provinces. These challenges raised because of the effects of water withdrawals due to the developmental needs upstream, which conducive to decreasing in the quantity and quality of water downstream. The main qualitative problem of the basin is salinity. Due to the arid and semi-arid climate of this basin, natural effective factors on salinity (tectonic conditions such as rocks and salt domes) are available in this basin. Besides, with the development of irrigation, which is referred to as secondary salinity, there are some concerns about the salinity of the river and crop yield loss in downstream. At present, various plans for water resources development and agricultural development and improvement in the basin are under consideration. According to the aforementioned arguments, an integrated quantity-quality simulation of water resources in the scale of basin have been developed in this study in order to predict the long-term effects of the decisions and the development of water resources and agriculture on the quantity and quality of water and also the economic benefits of projects. For this purpose, the economic-hydrologic model of Helleh river basin was developed. The main components of the hydrological module include water and salt balance in the different parts of the hydrological catchment system such as the root zone, reservoirs, and rivers and the economic modules include the calculation of gross economic benefits derived from agriculture, which is the output of an agronomic model. WEAP model has been used for water resources modeling. Water salinity modeling based on salt balance and agronomic and economic modeling have been done in MATLAB. In the first step of this research, according to the observations, the current situation of the basin was calibrated and uncertainty analysis was done. SUFI2 algorithm used for calibration. In the next step, developing situation was modeled in WEAP. The results of modeling of the five management options showed that despite the more and better providing of irrigation due to the increasing efficiency from 50% to 70% and 85%, the return flows of lands under modern irrigation networks decreases from about 20% to 10% and 5% respectively. This leads reducing in deep percolation and increasing the salts in the soil and ultimately reducing performance of the plants. In such a way that the yield of products is reduced by at least 40 and 70 percent for irrigation efficiency of 70% and 85%, respectively. In general, it can be concluded that the effect of dams' construction on the salinity of the downstream is almost negligible and in the worst case, leads to increase of about 6.5% of the salt content entrancing to the RaisAli Delvari dam for an increase of efficiency of up to 70% for the Khesht lands (fourth option). In the case of the Dalaki Dam, the construction and operation of this dam in addition to supplying the shortage of Dalaki irrigation network and reducing the dependence of supplying irrigation system on Shapour River, decreases the salinity of the downstream of the Dalaki River in months with more irrigation requirements.
