نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی آب، دانشکده علوم کشاورزی، دانشگاه گیلان، رشت، ایران.
2 گروه مهندسی آب، دانشکده علوم کشاورزی، دانشگاه گیلان، رشت، گیلان.
3 عضو هیات علمی گروه مهندسی آب پردیس ابوریحان دانشگاه تهران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
In this study, the accuracy of estimating shallow aquifer recharge values in Astane-Kouchsefahan using two models: SWAT (a surface water hydrological model) and MODFLOW (a groundwater flow model) was evaluated. Then the need for using SWAT in the modeling of groundwater flow, which is typically done by MODFLOW, was evaluated. For this purpose, the simulation of the Astane-Kouchsefahan aquifer was done by MODFLOW using GMS graphical user interface. Then the SWAT model was built for the Astane-Kochsefahan watershed and calibrated by the SUFI2 algorithm in SWAT-CUP software. In the following, after determining the two models' common spatial and temporal range, the aquifer recharge amounts were compared according to the outputs of the two models. MODFLOW results showed that the total aquifer recharges including recharge from the river in 1391-1392 were equal to 102.71 and 23.71 million m3, respectively. The highest and the lowest amounts of aquifer recharge occurred in December and April, respectively. The results of SWAT showed that the amounts of aquifer recharges including recharge from the river are estimated to be 138.34 and 35.09 million m3, respectively. So, the highest and the lowest recharge amount occurred in December and September, respectively. Based on the regional circumstances, SWAT offers more dependable estimates of the groundwater recharge parameters by considering surface water parameters and factors like the influence of dams and water transfer channels, soil characteristics, land use, climatic and meteorological data, and information regarding agriculture and irrigation management. Consequently, integrating the precise recharge results from SWAT into groundwater models such as MODFLOW leads to enhance and more reliable evaluations of the aquifer's state.
کلیدواژهها [English]
Accuracy assessment of groundwater recharge estimation using SWAT and MODFLOW models in paddy fields
EXTENDED ABSTRACT
Groundwater recharge values depend on surface hydrological processes temporally and spatially and change with changes in weather conditions, land use, soil, vegetation, etc. It is impossible to include these factors in the models used to simulate groundwater flow, and in most cases, only the effect of precipitation is considered. Aquifer recharge is entered into the model as a percentage of rainfall, and the recharge values are calibrated during the calibration of the model. Recently, advanced models have been developed to model groundwater recharge and determine potential recharge areas, and the SWAT model is one of these models. The SWAT model is designed to predict the effect of different land management methods on the amount of water, sediment, and agricultural chemicals in the level of complex and large watersheds with soil, land use, and different management conditions in the long term.
In this study, because the SWAT model takes into account the factors affecting the groundwater recharge and in the groundwater balance equation of this model, the recharge parameter includes any surface recharge, including agricultural return water, rainfall, infiltration of rivers and surface runoff, estimation of Astane-Kochsefahan aquifer recharge was estimated by two models; SWAT and MODFLOW, and the results compared togeather.
Considering the amount of surface recharge of groundwater in the MODFLOW model consists of infiltration from precipitation, agriculture, drinking, and industrial return flow, as well as infiltration from dam reservoir, at this stage, the pond recharge is not considered in the SWAT model; therefore, it was removed from the recharge values of the MODFLOW model. In this way, the recharge values of the two models were compared.
Surface recharge in the MODFLOW model, which consists of recharge from precipitation and return flow and infiltration from dam’s reservoirs, in the whole aquifer in 2011-2012 was equal to 232.98 million m3. Surface recharge rate MODFLOW in the common area with SWAT model in 1391-92 was equal to 78.96 million m3, which increased to 102.71 million m3 along with recharge from the river. The sensitivity analysis of the MODFLOW model showed that the parameters of surface recharge, hydraulic conductivity, and specific drainage coefficient were the most sensitive. Therefore, recharge parameter in groundwater flow modeling has a key role in determining the water balance. The results of SWAT to calculate the recharge to the shallow aquifer showed that the recharge in the common area with the MODFLOW model in 1391-2012 is equal to 136.27 million m3, which was estimated to be 138.34 million m3, including the recharge from the rivers.
One of the advantages of the SWAT model is that it considers surface water processes in calculation of aquifer recharge, while in MODFLOW, these processes are not considered. Therefore, the recharge values calculated by SWAT have higher accuracy. In addition, the recharge calculated with the SWAT model is more compatible with the trend of changes in recharge values than with MODFLOW because the patterns of precipitation, the release of the Sefidroud Dam, and the released of water in the water transfer channels are considered in the SWAT model. The comparison of the results showed that the total amount of surface recharge estimated by SWAT was more than the estimated amount by MODFLOW. Considering that the groundwater level values simulated by MODFLOW model were lower than the observed water level values, to reach answers close to reality, the recharge values from SWAT are evaluated in groundwater flow modeling.