JWSS - Journal of Water and Soil Science

Considering water scarcity in Iran, application of deficit irrigation or water stress on some crops is inevitable. We need to provide appropriate design for deficit irrigation. Furrow irrigation management to obtain high efficiency and uniformity is difficult. Therefore, to investigate the variation of the input discharge, the cut-off time and furrow length that are effective on the efficiency and uniformity are very important. The purpose of this research is to provide a method for determining the optimum water use depth and optimizing furrow irrigation design in deficit irrigation conditions and finally comparing design characteristics under full irrigation conditions and deficit irrigation and comparison in different soil tissues. In order to achieve the objectives of this research, an experiment was conducted on forage corn in Shahrekord in a completely randomized block design with 7 treatments of different levels of irrigation in 3 replications. The costs and benefits functions were determined based on design variable and depth of applied water. The software Lingo was used to optimize the design variables (length of the furrow, the input discharge and cut-off time) and depth of applied water in deficit irrigation condition. The results showed that the highest net profit was obtained using 535 mm (equivalent to 79% of full irrigation) and 85 meters, 0.39 liter per second and 188 minutes, respectively, for the length of furrow, input discharge and cut-off time. The results of this design were compared to full irrigation of deferent soil textures. The results showed that an increase in the permeability of the soil caused length of furrow and the cut-off time to decrease, while the flow rate increases and depth of applied water or percent of deficit irrigation were constant.

Water allocation needs to adhere to the principles of efficiency, equity, and sustainability, but, equity usually is less considered. Foumanat irrigation area with five command areas is one of the three areas of Sefidroud irrigation and drainage network that more than 90% of it is covered by paddy fields. Since water plays a key role in paddy fields, the lack of uniform distribution of water resources throughout the irrigation area during the rice cultivation period causes irrigation water scarcity and severe damage to some irrigation areas. In this study, the equity of groundwater withdrawal and the received surface water from Sefidroud irrigation and drainage canals according to the shared water resources among Foumanat’s command areas were evaluated using the Gini coefficient. Therefore, a water allocation optimization model was developed to maximize the equity in the allocation of groundwater and surface water of canals according to the minimum current economic benefit in the command areas. The results showed that in optimum conditions, the equity of groundwater and surface water resources allocation was increased by 46.3% and 43.7%, respectively. The evaluation of the optimal allocation of available water resources also showed that the amounts of groundwater withdrawal and the received surface water from canals are distributed equally among command areas.

Managed Aquifer Recharge (MAR) using treated wastewater is a viable strategy for water-resource sustainability in arid regions; however, the simultaneous assessment of its hydrogeological and economic aspects remains challenging. The objective of this study was to hydro-economically evaluate the implementation of an MAR project in the Qotb-Abad Plain by integrating numerical modeling and cost-benefit analysis (CBA). The quantitative and qualitative responses of the aquifer were simulated using the MODFLOW and MT3DMS models to estimate changes in groundwater levels, nitrate concentrations, and total dissolved solids (TDS). Economic benefits, including pumping energy savings, the value of stored water, and improvements in water quality, were evaluated alongside capital and operational costs under lower- and upper-bound scenarios. Subsequently, economic indicators, including net present value (NPV), benefit-cost ratio (BCR), internal rate of return (IRR), and payback period, were calculated. The results indicated that implementing MAR with an annual treated wastewater volume of 1.898 million m³ resulted in an approximately 4.5 m rise in groundwater level, accompanied by reductions in TDS from 1859 to 1752 mg/L and in nitrate concentration from 22.2 to 15.4 mg/L by the end of the five-year simulation period. Under the upper-bound scenario, the NPV, BCR, and payback period were 43.7 billion Rials, 1.36, and 3.23 years, respectively. In contrast, the lower-bound scenario was not economically justified, as its BCR was less than 1. Overall, integrating numerical modeling with cost-benefit analysis provides a comprehensive framework for supporting groundwater-management decision-making.