Abstract
This study develops a response-based hydrologic model for long-term (continuous) rainfall-runoff simulations over the catchment areas of big rivers. The model overcomes the typical difficulties in estimating infiltration and evapotranspiration parameters using a modified version of the Soil Conservation Service curve number SCS-CN method. In addition, the model simulates the surface and groundwater hydrograph components using the response unit-hydrograph approach instead of using a linear reservoir routing approach for routing surface and groundwater to the basin outlet. The unit-responses are Geographic Information Systems (GIS)-pre-calculated on a semi-distributed short-term basis and applied in the simulation in every time step. The unit responses are based on the time-area technique that can better simulate the real routing behavior of the basin. The model is less sensitive to groundwater infiltration parameters since groundwater is actually controlled by the surface component and not the opposite. For that reason, the model is called the SCHydro model (Surface Controlled Hydrologic model). The model is tested on the upper Blue Nile catchment area using 28 years daily river flow data set for calibration and validation. The results show that SCHydro model can simulate the long-term transforming behavior of the upper Blue Nile basin. Our initial assessment of the model indicates that the model is a promising tool for long-term river flow simulations, especially for long-term forecasting purposes due to its stability in performing the water balance.
Highlights
In order to simulate the continuous rainfall-runoff transforming behavior of big rivers, there are many methods and algorithms which can account for the soil moisture balance to produce long-term hydrologic simulations
The new approach consists of surface balance sub-module based on a long-term modification of the Soil Conservation Service curve number (SCS-CN) method and routing sub-module based on time-area (TA) unit hydrograph
The water balance is controlled at the surface, which ensures accurate surface hydrograph that does not depend on underground parameters
Summary
In order to simulate the continuous (long-term) rainfall-runoff transforming behavior of big rivers (e.g., the upper Blue Nile), there are many methods and algorithms which can account for the soil moisture balance to produce long-term hydrologic simulations. A major problematic issue in long-term simulations using the SMA approach is the difficulties encountered in estimating/calibrating the different soil moisture accounting parameters especially infiltration rates and storage capacities. Evapotranspiration is another problematic variable that cannot be estimated precisely since plants tend to adjust the water consumption based on the soil moisture available and on temperature and humidity Another issue that can be problematic in large basins is the routing approaches used to route both runoff and groundwater depths to the basin outlet. The above routing approaches can depart from reality in large basins with different sub-catchments that contribute at the basin outlet at significantly different times For such large basins, a time-area unit hydrograph (developed on a short-term basis) can better represent the transforming behavior [27,28,29]. The separated excess and groundwater depths are convoluted at the basin outlet (routed to the basin outlet) using a time-area unit-response approach that is developed on a short-term basis [27,28,29], which can better simulate the real responses of large basins
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