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Despite the significance of river leakage to riparian ecosystems in arid/semi-arid regions, a true understanding and the accurate quantification of the leakage processes of ephemeral rivers in these regions remain elusive. In this study, the patterns of river infiltration and the associated controlling factors in an approximately 150-km section of the Donghe River (lower Heihe River, China) were revealed using a combination of field investigations and modelling techniques. The results showed that from 21 April 2010 to 7 September 2012, river water leakage accounted for 33% of the total river runoff in the simulated segments. A sensitivity analysis showed that the simulated infiltration rates were most sensitive to the aquifer hydraulic conductivity and the maximum evapotranspiration (ET) rate. However, the river leakage rate, i.e., the ratio of the leakage volume to the total runoff volume, of a single runoff event relies heavily on the total runoff volume and river flow rate. In addition to the hydraulic parameters of riverbeds, the characteristics of ET parameters are equally important for quantifying the flux exchange between arid ephemeral streams and underlying aquifers. Coupled surface/groundwater models, which aim to estimate river leakage, should consider riparian zones because these areas play a dominant role in the formation of leakage from the river for recharging via ET. The results of this paper can be used as a reference for water resource planning and management in regulated river basins to help maintain riparian ecosystems in arid regions.

Surface water–groundwater interactions in arid zones are characterized by water exchange processes in a complex system comprising intermittent streams/terminal lakes, shallow aquifers, riparian zone evapotranspiration, and groundwater withdrawal. Notable challenges arise when simulating such hydrological systems; for example, field observations are scarce, and hydrogeological parameters exhibit considerable spatial heterogeneity. To reduce the simulation uncertainties, in addition to groundwater head and river discharge measurements, we adopted remote sensing-based evapotranspiration data and lake area dynamics as known conditions to calibrate the model. We chose the Ejina Basin, located in the lower reaches of the Heihe River Basin in arid northwest China, as the study area to validate our modelling approach. The hydrological system of this basin is characterized by intensive, spatiotemporally variable surface water–groundwater interactions. The areas of the terminal lakes into which all river runoff flows vary significantly depending on the ratio between river runoff and lake evaporation. Simulation results with a monthly time step from 2000 to 2017 indicate that river leakage accounted for approximately 61% of the total river runoff. Our study shows that for areas where surface water and groundwater observations are sparse, combining remote sensing product data of surface water areas and evapotranspiration can effectively reduce the uncertainty in coupled surface water and groundwater simulations.

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Information on recharge value is necessary for solving different classes of hydrogeological problems. One of the methods of recharge estimation is simulation of flow in vadose zone. Soil hydraulic parameters are used to estimate recharge by flow in vadose zone. One of the hydraulic parameters is the pore connectivity parameter l. The sensitivity of estimated recharge to the value of pore connectivity parameter, especially under humid climate conditions, is studied insufficiently. In present study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest landscape on sand and field landscape on loam) were used to estimate recharge.Recharge estimation was also carried for the value of l=0,5 and for reported values of l parameter for certain type of sediment. Analysis of calculation results demonstrated that using fixed value of l=0,5 leads to significant overestimation of calculated recharge both for forest and filed landscapes, which emphasizes the importance of experimental definitions of soil hydraulic parameters for recharge estimation. The analysis of the water balance components showed that the increase of estimated recharge with enhancement of l value is mainly associatedwith the decrease of evaporation from the upper soil layer.