مجله سامانه های سطوح آبگیر باران
سال هفتم شماره 4 (پیاپی 23، زمستان 1398)

The Khash alluvial aquifer, in Sistan and Baluchestan Province, supplies the water needed for agriculture, drinking, and industry in the Khash area. In order to predict the future status of groundwater level and water quality, and to find aquifer management solutions, groundwater flow and solute transport models were developed using MODFLOW and MT3DMS. GMS 10.3 was used to develop the model. Calibration and validation of the model were performed using a seven-year period and a three-year period, respectively. The results showed that the flow model has a good performance in simulating groundwater levels when compared to observational data. The RMSE values ​​for calibration and validation periods were 0.67 m and 0.96 m, respectively. The solute transport model was established based on the groundwater flow model and was calibrated based on observational data of Cl- concentration in eight wells over a 10-year period from October 2007 to September 2016. The calibrated models were used to evaluate two scenarios in the forecast period (2016-2026). In the first prediction scenario, assuming the aquifer recharge and discharge rates are similar to the current condition, it was found that a significant drawdown in water levels will occur in most parts of the aquifer, especially south and southeast of the aquifer. As a result, the average water level will drop by more than 1.5 meters over 10 years, and consequently, Cl- concentration and groundwater salinity will increase. In the other scenario, which was defined to determine the safe yield of groundwater, it was found that to reach equilibrium and prevent increases in salinity, groundwater withdrawals from wells should be reduced by 50%.

In recent decades, due to the importance of watershed management programs and the need for adequate information and correct estimation of rainfall and runoff, many conceptual models have been proposed. These models have parameters that must be estimated according to observational data. However, finding the optimal values for the parameters of simulation models has always faced uncertainty. One of the main methods for evaluating and predicting floods is the soil conservation methods provided by the Soil Conservation Service (SCS). This study aims to calibrate model parameters for three modified SCS models, i.e. 1- the Mishra and Singh model, 2- curve number model, and 3- modified curve number (MCN) model, in a basin in southern Chile using the evolutionary PSO algorithm. Comparison of the results was carried out using performance criteria such as Kling Gupta Efficiency (KGE), Nash-Sutcliff coefficient (NS), and mean square error (RMSE). Results revealed that simulated runoff is more efficient in MCN and Mishra and Singh models with KGE = 0.91 in rainfall-runoff simulations.

In the last decade, various aspects of groundwater resource depletion have gained a special place among water sector experts and decision makers. Research in this area is relatively new in most parts of the world. Groundwater depletion, which has been in a concerning state for most plains in Iran in recent years, has various consequences which impede sustainable development. One of the most important consequences of the dropping groundwater table is its impact on the economy of the agricultural sector. A problem that, despite its obviousness and bi-directionality, has rarely been quantified. In this research, it is attempted to simulate the status of groundwater resources under the influence of continued groundwater overdraft until 1420 (2041), on the basis quantitative (harvestable water) and qualitative (electrical conductivity) effects on the economic status of agricultural sector using cultivation area indices. We examine agricultural products, their performance, farmers’ income, and labor force. Questionnaires were used to estimate costs and incomes and the results of combined modeling of surface and groundwater in Neishaboor plain were used to estimate the amount available water. The model predicted a decrease of up to 24 m in water table and an average increase in salinity of 5500 mmhos/cm for the Neishaboor plain. The effects of the occurrence of these events was then modeled. Based on models for cropping patterns, water-yield equations, and salinity patterns, we estimated a 30% reduction in area under cultivation, a 65% decrease in crop yields, and a 28% decrease in labor force by 2041. Over the next 20 years, these impacts will significantly reduce revenues in the agricultural sector in Neishaboor plain, which will pose important secondary problems and consequences.

Excessive use of groundwater, especially in agriculture, has led to a drop in aquifer water levels, and along with droughts, has dealt irreparable losses such as drying of karizes, springs, wells and land subsidence. One of the traditional ways of protecting these resources is the use of rainwater catchment systems as an Iranian technique for storage of precipitation. Among water extraction systems, turkey nest dams can be introduced to recharge groundwater aquifers, enable permanent utilization, and prevent drying of springs and karizes. The benefits of using turkey nest dams are the large volume of these reservoirs and reduction of water costs. Turkey nest dams reduce drilling depth and increase capacity. In this research, we consider the application, dimensions, and location of this system. Turkey nest dams can be built near a river. In the Meshnagh sub-basin of Lake Urmia, about 40 deep wells and 4 active karizes discharge nearly 5 Mm3 of water from groundwater aquifers. In order to construct two turkey nest dams with the aim of recharging the wells of the Katkahriz kariz, excavation and earthwork operations were carried out along the Meshnag River in the north of Lake Urmia. The dams had a large diameter of 60 m, a small diameter of 50m, and a height of 3m with a 1:3 slope. The effective capacity of the dams was estimated at 27,000 m3. If technical principles are observed, a dam of this size on soil with coarse grains and alluvial sediments with a minimum porosity of 35% will supply more than 10,000 m3 of water into the main well of the kariz.

Not only have recent global challenges including drought, climate change, land degradation and land use change impacted the quantity of available surface water and groundwater, but also water quality has been affected as well. To study this impact, Landsat 5 satellite images and water quality data were obtained to compare the effects of land use changes on surface water quality between July of 1992 and 2011. The maximum likelihood algorithm was used for preparing and processing land use maps in ENVI 4.8 and Arc GIS9.3. For land use classification, the Jeffreys–Matusita, Kappa coefficient, and overall accuracy indexes were used. The results showed that the values ​​of Kappa coefficients and overall accuracy were 84.23 and 87.72% for 1992 and 93.84% and 95.55% for 2011, respectively. Most land use changes were related to dryland agriculture and residential land use, which increased 1.46 and 2.45 times, respectively. The results for water quality parameters showed that electrical conductivity (EC) and total dissolved solids (TDS) increased during the study period and that their values ​​at Gardeh Yaghub station (basin outlet) were higher relative to the Cotter station (upstream). This observation can be explained by the fact that the Mahabad River flows through agricultural lands between Cotter and Gardeh Yaghub stations. It can be concluded that land use changes have played a major role in changing surface water quality parameters in the region and have reduced water quality of the Mahabad River during the period from 1992 to 2011.

The aim of this research was to study how water use management can increases vegetation cover inrainwater catchment systems. The study was conducted through comparison of two methods of irrigation, i.e. traditional sub-surface drip irrigation and drip irrigation. Three soil samples were taken and analyzed from three locations in north of Sistan from a depth of 50 cm. A furrow was dug with a base depth of 60 cm, width of 50 cm, and  length of 48 m. 12 holds were dug 4 m long, 70 cm deep and 50 cm in diameter. For subsurface irrigation, a 3-inch pipe with a length of 48 m was placed horizontally in the furrow. At 8-m intervals, 2-mm holes were made in the pipe. In the drip irrigation method, a ½-inch pipe with a length of 48 m was placed on the furrow and drippers were connected every 8 m. In each pit, a mulberry tree was planted. Soil moisture was measured every month and growth was measured each season. Data shows that the amount moisture, increase in plant height, and trunk diameter in subsurface irrigation were 53.1, 91.6, and 52.8 percent more than drip irrigation, respectively. Statistical analyses show that soil moisture, plant height, and trunk diameter were significantly higher in subsurface irrigation (P<0.05). In subsurface irrigation, water directly flows to the root zone. Because in this method transpiration is less than drip method, subsurface irrigation has good potential to establish suitable moisture levels for plant growth.