saeed sarvari; Ali Naghi Ziaei; Ata Joodavi
Abstract
Introduction: Understanding water budget components is crucial for making decisions regarding water resources planning and management. Surface water–groundwater interactions are commonly investigated at the river reach scale and generally classified as connected or disconnected type systems. Connected ...
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Introduction: Understanding water budget components is crucial for making decisions regarding water resources planning and management. Surface water–groundwater interactions are commonly investigated at the river reach scale and generally classified as connected or disconnected type systems. Connected systems are either gaining surface water system, where groundwater discharges through the streambed to contribute to streamflow, or losing surface water system which loses (or recharges) water to the local groundwater system. Disconnected systems are defined by an unsaturated zone beneath the surface water system which loses water at a rate related to the hydrogeological properties of the streambed and the aquifer. These interactions have significant implications for both water quantity and quality. Seepage of fresh groundwater into a river can be important in maintaining flows during extended dry periods. This can be critical for supplying the needs of surface water users such as irrigators as well as for aquatic ecosystems. Pumping from an aquifer near a river can dramatically change the amount of this base-flow to the river. In contrast, if the groundwater is contaminated, increased groundwater discharge can have a negative effect on river water quality. The Bojnourd catchment is located in North Khorasan province. The catchment covers an area of about 1265.8 km2. The main river in this area, Firouze River, is approximately 10 km in length, and is hydraulically connected to the Bojnourd alluvial aquifer. The alluvial aquifer of Bojnourd plain with 65.2 km2 area is mostly covered by urban area. Hence, effective management of water quantity and quality issues in the Bojnourd catchment requires quantifying flow between surface water and groundwater. Furthermore, conveying water from the outside of basin caused water table to rise which made some problems for urban buildings and infrastructures. Therefore, the river and aquifer interaction needs to be studied more comprehensively.
Materials and Methods: Numerous techniques and methods are available to describe and quantify the flow between surface water and ground water. This study combined two methods, numerical modeling using MODFLOW code and reach measurements, to quantitatively evaluate groundwater/surface water interactions under highly transient conditions. The groundwater flow system of the study area was conceptualized based on borehole logs, pumping tests, and available hydrogeological and geophysical information. Moreover, field work, including measuring streamflow in three seasons, was carried out to conceptualize and quantify the groundwater/surface water interactions. Following the conceptual model, the numerical model was developed to simulate flow through the system. The model grid had 1274 active cells with a uniform cell spacing of 250×250 m. The water exchanges between the main regional river, Firouze river, and Bojnourd aquifer was simulated using the River (RIV) package. Both hydraulic head target and flux target were used to calibrate the model. The head targets were compiled from the monitoring network which contains 11 observation wells. The flux targets were located in three measurement points along the Firouze river. The data obtained from the fieldwork were used as observed values for the groundwater/surface-water exchanges. The transient model was calibrated and validated for 15 hydrological years, i.e. from 1 October 2001 to 1 October 2016
Results and Discussion: Model performance was evaluated using root-mean-square error (RMSE). The model results were in agreement with corresponding observed data, including groundwater heads and measured groundwater/surface-water exchanges. The RMSE values during calibration and validation periods were 0.83 m and 1 m, respectively. Analyzing water balances resulted from transient simulation showed that Firouze river is gaining in some reaches and losing in other reaches. In losing reaches, the total flux into the aquifer is 6.4 MCM per year. In gaining reaches, the volume of groundwater discharges through the streambed is about 4 MCM per year. Furthermore, the effect of several management scenarios, including continuing the existing condition, turning the domestic wells off and implementing a sewage system by 2025, on groundwater heads and groundwater/surface-water exchanges was examined using the numerical model. Results showed that by implementing the sewage system, the volume of water discharged to the river would decrease, but it will prevent aquifer and river contamination caused by sewage water.
Conclusion: In this study, groundwater budget components in Bojnourd aquifer including groundwater/surface-water exchanges were calculated. The results showed that understanding of these surface water-groundwater interactions, which has been ignored in previous studies, is important for effective management of water quantity and quality issues in Bojnourd plain. Moreover, the methodology used in this study including numerical modeling and measuring flow at multiple points along the stream is effective and easy to apply to estimate the direction and magnitude of seepage on a stream reach basis.
fatemeh sadat Mortazavi Zadeh; Masoud Godarzi
Abstract
Introduction: After the industrialization period, when humankind was able to multiply the speed and quantity of its production, the planet faced a new crisis, although this crisis was less known until the late 20th century. From the last years of the 20th century, the term of change has been added to ...
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Introduction: After the industrialization period, when humankind was able to multiply the speed and quantity of its production, the planet faced a new crisis, although this crisis was less known until the late 20th century. From the last years of the 20th century, the term of change has been added to the scientific literature of the world. The main reasons are the change in the phenomenon of blockage of greenhouse gases, especially carbon dioxide in the atmosphere of the planet. In this research, while introducing CMIP models under RCP scenarios, modeling of groundwater fluctuations using the MODFLOW numerical code is dominated by GMS software. The LarsWG software was used for statistical exponential measurements. Groundwater changes in the study area (Hashtgerd) are of great importance to the people of this region due to the proximity of the area to Tehran and the availability of horticultural products. The main objective of this research is to investigate the future fluctuations of groundwater in Hashtgerd plain over the next period from 2015 to 2040 using the HADGEM2 model under two scenarios RCP2.6 and RCP8.5. Innovations of this scheme include the use of the HadGEM2 climatic model to investigate the variation of underground water fluctuations. Materials and Methods: In order to study and model the aquifer using the finite difference method and the Modflow model, the first step in the spatial division of the study area into a square or rectangular cell or network. Therefore, using topographic maps 1: 25000 of the Army Mapping Organization, the topographic layer was extracted and digitally extracted. Based on the 14 piezometers in the aquifer area, the potential lines were plotted and entered into the model as the initial staging level. In order to determine the thickness of the saturation layer, based on the geophysics in the aquifer, the bedrock was also introduced into the model network. In addition, to accurately evaluate the design of the network and its cells in the aquifer area, the hydrodynamic, feeding and evacuation characteristics of the aquifer within a cell are assumed the same. It is necessary to select smaller dimensions in areas where hydrological and hydrodynamic characteristics of the aquifer are significant at low distances, or that parts of the aquifer are studied for specific cases. Otherwise, it is not necessary to reduce the size of the cells. According to aquifer conditions, cells with 500 * 500 square meters area were selected. Calibration and verification were used in two steady state (one year data) and non-residual (full statistical period), each used for estimation of hydraulic conduction values and storage factor. Results and Discussion: After calibration of the groundwater model in steady state, the hydraulic conductivity of the aquifer in different locations is in the range of 0.5 to 19 meters. In order to run the model in an unstable state, time intervals must be defined for the model. The time interval in modeling is defined in terms of both the stress period and the time step which must be defined before the definition of other parameters such as power and discharge conditions in unstable conditions. In the Hashtgerd plain, the length of the one-month stress period and the monthly measurements of the water level in piezometers, the time step were also selected for a month. Therefore, in order to simulate the groundwater flow, the study area for the unstable state was defined from October 2007 to late December 2013 for six years and three months for the model and the conceptual model was changed from unstable to unstable state. Therefore, data on surface water in rivers, the feeding of rainfall and return water from wells, pumping rates from wells, hydraulic load of boundary conditions, and groundwater surface data in piezometers were introduced monthly into a conceptual model. In addition, in an unstable state, the specific discharge parameter must be defined for the model. After implementation of the model in unstable conditions, special discharge rates were optimized. The amount of specially tailored discharge in the study area varies from 0.001 to 0.27. It should be noted that at this stage, the resource and expenditure statistics of 2008 were used. After constructing groundwater and surface water models for the base period, maintaining the existing coefficients and parameters, changing the rainfall and temperature values for the future period, first, the amount of surface water flow changes for the future period and then using the amount of nutrition The groundwater entered the model. Future modeling showed that surface runoff variations would be about 7 percent lower for RCP 2.5 and 19 percent for the RCP scenario of 8.5. Nutrition also includes nutrition from the rainfall. For the upcoming period, changes in land use and land use counts are considered constant. With rainfall changes under the two scenarios, the aquifer is projected to drop by about 12 m by 2040 for the RCP scenario of 2.6 and for the RCP scenario of 8.5 by 18 m. Conclusions: After simulating the meteorological component by the HadGEM2 model introduced in AR5 using LarsWG software and applying future changes in rainfall and temperature on the IHACRES model and ModFlow model under GMS software for the two scenarios RCP2.6 and RCP 8.5, respectively. Due to the temperature rise of 1.8 ° C in the worst case and different rainfall variations in different months, it was found that runoff would be about 15% for the first scenario and 20% for the second scenario. The same factors are because the level of penetration into groundwater through snow melting as well as precipitation along with surface runoff is one of the important factors in feeding to the aquifer. Given the constant maintenance of groundwater withdrawals in the coming years, it was found that the aquifer will drop by about 12 m for the scenario RCP 2.6 by 2040, and for the RCP 8.5 scenario, it will drop by 18 m.
