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Hydropower dams can induce flash floods, leading to a severe cataclysm in flood-prone areas at downstream regions. On the catchment scale, flooding is not contributed solely by the reservoir releases, and there can be significant flow contributions from tributaries downstream of the dam. The major challenge in estimating the lateral flow contribution is that most tributaries are ungauged and situated in inaccessible areas. To overcome this inconsistency and to increase the precision of downstream flood warnings, a modeling framework was developed to quantify the flow contribution by ungauged tributaries to the mainstream using the drainage area ratio (DAR) method. The model parameters were estimated using optimization algorithms, and the best parameters were selected based on the error metrics. The modeling framework constitutes a reservoir operation model and hydrodynamic model developed in MATLAB version 2020b environment with the ease of coupling the two models. The estimated flow from the lateral tributaries based on the optimal model parameters of DAR and hourly inflow hydrographs were incorporated into the model. Two scenarios were analysed with and without lateral flow from ungauged tributaries. Results impart that the flood peaks have increased by more than 75% with the incorporation of the lateral flow. The model was validated with downstream stage and discharge data. The results indicated that the magnitude of the model generated and actual flow data were in the same range. Flooding downstream due to sudden release from a hydropower dam is a matter of serious concern worldwide. To evaluate the potential flooding situation downstream, a dam release is generally routed by a hydrodynamic model. However, because hydropower dams are mostly located in remote areas, the tributaries located at inaccessible downstream areas remain ungauged and, therefore, obtaining precipitation/streamflow data of such tributaries become difficult. In absence of downstream flow contribution, the water level obtained by routing the reservoir release underestimates flood magnitude. The dam release flood falls in the high-hazard category because of its suddenness characteristics and, therefore, adverse consequences of underestimation cannot be overemphasized. This paper presents a framework that couples a reservoir operation model, a hydrodynamic model, and a simplified area–proportionate model to estimate downstream tributary contribution, so that a more reliable estimation of the downstream flood situation can be made. The modeling framework has been tested in the Ranganadi Hydropower Project situated in northeastern part of India. The coupled model can be applied to any reservoir with proper calibration of model parameters. By applying this model, a disaster manager would be in a position to disseminate in advance a more reliable downstream flood warning. [ABSTRACT FROM AUTHOR]

This study detailed a novel semicoupled method for estimating the three-dimensional vertical velocity profile in an open channel with submerged flexible vegetation. A modified form of the two-dimensional shallow water equations coupled with the drag forces of the vegetation was derived by balancing the flux gradient and the source term. The bending profile of the flexible stems of different flow events was calculated based on the large cantilever beam theory. The vertical velocity profile in the free water and vegetation layers was estimated using Shannon's entropy and Reynold's stress equation theory, respectively. The derived semicoupled model was tested to replicate two popular laboratory flume experiments. The results showed that the model accurately predicted the velocity profiles under different flow conditions and patch density. The R2 values of 0.76 and 0.81 indicate that the proposed model is well established and can be applied in complex flow scenarios. [ABSTRACT FROM AUTHOR]

This article focuses on the assessment of climate change impacts on the hydroclimatology of the Subansiri River basin, which is the largest tributary of the Brahmaputra River in the northeastern part of India. Three representative concentration pathway (RCP) emission scenarios, namely, RCP2.6, RCP6.0, and RCP8.5, of three general circulation models (GCM) archived by the Geophysical Fluid Dynamics Laboratory (GFDL), were utilized for the projection of climatic variables (such as precipitation and temperature). Long-term (2011–2100) projections of precipitation and temperature for different emission scenarios were made using the statistical downscaling technique. The soil and water assessment tool (SWAT) hydrological model was used for hydrological modeling of the river basin. The observed streamflow series for the period of 2002–2013 has been utilized for calibration and validation of the hydrological model. Parameterization, uncertainty analysis, and parameter sensitivity analysis of the model were performed using a sequential uncertainty fitting (SUFI2) program. The coefficient of determination (R2) for the calibration and validation of the hydrological model on the monthly streamflow time series was found to be 0.86 and 0.80, respectively. Future projections of the precipitation and temperature suggest an increase in the annual average maximum temperature (Tmax), annual average minimum temperature (Tmin), and annual precipitation of the river basin. These projected climatic variables were used as the primary input in the hydrological model for the projection of the streamflow for the period of 2016–2100. The flow duration curve analysis of streamflow projections reveals an increase in the discharge for a particular percent of the dependable flow in the case of all the RCP scenarios. Water yield analysis also suggests an increase in the annual average water yield in all cases of emission scenarios. [ABSTRACT FROM AUTHOR]

It is important to estimate the quantity and quality of water resources in terms of spatial and temporal variability to utilize such resources sustainably. Change in future climate conditions affects the availability of water resources by modifying the magnitude of precipitation, groundwater recharge, surface runoff, actual evapotranspiration, lateral flow, water yield, and river flows, and provokes water stress in the downstream. Local government authorities around the globe have also emphasized water resource project exploration, design, planning, and management aspects within river basins. To assist such decisions, knowledge and understanding of water yield and water balance at basin and subbasin levels are extremely important. Water yield and water balance components of the Genale Watershed of Ethiopia are analyzed using the Soil Water Assessment Tool (SWAT) model under future climate change scenarios for the understanding of water resources status and to assist decision makers in adopting a sustainable management strategy. Potential areas of high water yield were identified to recommend water resources project planning and management. For detailed analysis, 25 subbasins and 464 hydrologic response units (HRUs) were created covering the Genale River Basin, a 54,942 km2 area. The soil conservation service (SCS) curve number (CN2.mgt), available water capacity of the soil layer (SOL_AWC.sol), saturated hydraulic conductivity (SOL_K.sol), and base-flow alpha factor (days) (ALPHA_BF.gw) were the most sensitive parameters to flow. Nash-Sutcliffe efficiency (NSE) for calibration and validation period was 0.81 and 0.78, and the coefficient of determination (R2) was obtained as 0.87 and 0.85 during calibration and validation, respectively, monthly, shows satisfactory performance in both the cases. Hydrological analysis of the Genale Watershed was revealed a high potential value of water yield at Subbasin 8 and Subbasin 12 under all scenarios. The assessment was done for the whole watershed, and the variation ranges from 7 to 2,124 mm. Average values of 421.17, 543.5, and 358.1 mm were found under baseline conditions, representatives concentration path (RCP)4.5, and RCP8.5, respectively. Under bias-corrected regional climate model (RCM)-coordinated regional climate downscaling experiment (CORDEX) data, the result shows there is a decline in precipitation and an increase in future temperature under representative concentration pathways (RCP8.5) and likely reduces the future production of water yield in the basin, which shows the RCP8.5 projection is warmer than RCP4.5. Based on this estimate, the regional governmental authority can prioritize projects to solve water-related problems of the community. [ABSTRACT FROM AUTHOR]

The hydraulic structures constructed for the benefit of society can cause perturbations in streamflows. Such disruptions to natural conditions may affect river ecosystems. The spatial scale of the impacts is further magnified in the case of interbasin water transfer (IBWT) projects, which can cause changes in the ecohydrological regime of donor as well as recipient watersheds. Assessment of the changes in the hydrological regime due to artificial structures requires a comparison of existing and counterfactual scenarios. In this paper, a methodological framework is proposed and applied to the Umiam Watershed to generate natural streamflow using postimpact data when preimpact data are not available. The Soil and Water Assessment Tool (SWAT) model is applied for simulating streamflow in the presence of a reservoir and water transfer out of the watershed. The Indicators of Hydrologic Alteration (IHA) method was used for the analysis of changes in streamflow. The results reveal a reduction in the monthly median flow rate by at least 21% in all months during the five-decade period. Large floods and small floods are found to be reduced in the presence of the reservoir, whereas it also causes more frequent low flows, which last longer. The extreme annual minimum flow conditions (1-, 3-, 7-, 30-, and 90-day minima) show low alteration, while the corresponding yearly maximum flow conditions show medium alteration. The frequency and duration of high and low pulses are greatly affected by the reservoir. The rising rate, falling rate, and number of reversals show a significantly decreasing trend. The results indicate a high overall degree of alteration in streamflow. [ABSTRACT FROM AUTHOR]