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Integrated Water Resource Management (IWRM) has become a significant policy objective worldwide. In India, the government plans to apply the IWRM protocols through different projects under Prime Minister Krishi Sinchayee Yojna (Watershed Development Component), with stakeholder participation, to achieve sustainable economic growth. The programs adopt a common strategy of multi-resource management involving all stakeholders within the watershed who, together as a group, co-operatively identify the resource issues and concerns of the watershed and develop and implement a watershed plan with environmentally, socially, and economically sustainable solutions. However, evaluating the performance of watershed projects is challenging as the diverse socio-economic characteristics influence project goals. Commonly, watershed managers face a major problem: identifying key performance evaluation variables for a participatory appraisal to assess ‘the’ disparity in performance against planned importance. In this paper, a participatory performance evaluation framework is proposed from a base-line study of three Integrated Watershed Management Program projects in the lower Brahmaputra valley zone of Assam, India, namely, the Satpokholi, Kaldia, and the Turkunijan. The framework contains 65 variables divided into eight categories of developmental goals built on IWRM principles, priorities in planning, project goals, and regional socio-economic settings focusing on community information. Based on the framework, a structured questionnaire survey, using a four-point ratio scale field surveys are conducted amongst the community in the selected projects. Performance Index (PI) of each projects are obtained by analysing the data. The results show that besides providing better bottom-up performance evaluation in watershed management, this model would provide inputs to design intervention against the nonalignment of project performance and planned importance by policy-makers.

ABSTRACTRiverbank and in-stream protection are crucial in numerous river stretches, where erosion of banks and bed material instigates river course alterations, consequently leading to land and property damage. In large Indian braided rivers like Brahmaputra, implementing tetrahedron frames commonly referred to as ‘porcupines’ has emerged as a cost-effective strategy for river training, yielding commendable outcomes in near bank sedimentation. Using flexible river training structures, such as porcupine, presents an appealing option for managing braided river channel networks in areas where permanent control structures like groynes or dams prove excessively costly or potentially ineffective, particularly in systems exhibiting highly dynamic flow regimes and morphology. This work aims to develop a hydrodynamic model that integrates the porcupine systems within its framework. The model’s effectiveness was assessed through a field test near Nematighat, Brahmaputra River, in collaboration with Assam’s Water Resources Department. The mathematical modelling provided some valuable insights regarding the flow characteristics surrounding the porcupine structure, shedding light on its hydrodynamic behaviour.

The conservativeness, stability, and robustness of the numerical models applied in braided river systems is primarily influenced by morphological complexities adverse, flow pattern and the channel roughness. Two-dimensional flow modelling over an undulating bed profile is critical on account of the existence of subsequent wet-dry regions in the flow domain. This work provides the applicability of the conservative and non-conservative form of two-dimensional unsteady flow equations in braided river system. Both models are solved by TVD McCormack predictor corrector finite difference method and applied in the Brahmaputra River near Majuli Island, Assam India. The computed outputs are compared with the field observed results for validation. Results indicate a satisfactory agreement between the computed and measured value. Two statistical indices are used in the model performance evaluation.

Submerged flexible vegetation modifies the open-channel dynamics by altering the hydrological and ecological characteristics. The velocity profiles at the top and bottom of the vegetation layer indicate the stochastic nature of the flow and hydraulic parameters. The randomness in the velocity profile at different degrees of submergence and vegetation density is explicitly represented by the channel entropy parameter. This study proposes a novel entropy-based vertical velocity distribution model by linking the 2D shallow-water model (SWM) with Shanon’s entropy theory. The convergence of the coupled model at different flow depthvegetation heightis investigated by comparing the computed model results with the mixing length model and the published experimental data. Results indicate that the predicted velocity profiles from the entropy model agree with the experimental results than the mixing length model. Although the channel entropy parameter (M) is invariant with the flood dynamics, the submerged vegetation influences the drag force and modifies the flow-entropy nexus. The relationship between the vegetation densities and the channel entropy parameter at different flow depthvegetation heightis derived, and a power-law profile is observed.

Climate change impacts are evident in the Brahmaputra River Basin (BRB). With over 1 million people relying on the river, and several water infrastructure projects being planned on the basin, understanding these impacts at the basin level is crucial. However, geopolitical complexities hinder comprehensive basin-wide research in the BRB, resulting in limited studies on the effects of climate change. This study aims to enhance understanding of climate change impacts on BRB by investigating future climate and precipitation extremes over the basin. Earlier studies did not focus on extreme events in the entire BRB. Focusing on the southwest monsoon season (June to September) under RCP 4.5 and RCP 8.5 emission scenarios, the research employs high-resolution, statistical downscaled data from NEX-GDDP project to understand the future changes. According to the results, monsoon precipitation is expected to increase by 7.7% and 10.7% by 2050 under RCP 4.5 and RCP 8.5, respectively. Consequently, under RCP 4.5 and RCP 8.5, respectively, there will be an increase of 18.1% and 38% by 2099. Both scenarios projected considerable increases in the maximum 1-day rainfall (2.2 mm decade−1and 4.5 mm decade−1) and the highest 5-day rainfall (2.33 mm decade−1and 4.9 mm decade−1). It is anticipated that the frequency of consecutive wet days (CWD) will increase throughout the monsoon season particularly in the upper part of the basin. These findings emphasize the need to consider the growing risk of extreme precipitation events when several hydropower projects are planned in the basin.

Any watershed project is a multi-stakeholder endeavour incorporating diverse socio-hydrological dimensions of a region. The project’s worth is correlated with the stakeholders’ willingness to continue. Identifying the most desirable watershed parameters is challenging for watershed managers. This research aims to explore critical parameters and construct a watershed project desirability indexing framework to examine the congruence of stakeholders’ perceptions on a hypothetical watershed parameter list. It contains 31 critical operational areas (or sub-domains) in eight domains incorporating different management mechanisms and socio-economic and environmental activities covering diverse watershed inventories based on watershed management protocols, including the Integrated Watershed Management Programme (IWMP), Integrated Water Resource Management Programme (IWRM), World Bank directives and government guidelines, and relevant literature. Stakeholders’ agreeability was recorded from two stratified stakeholder groups at the Satpokholi watershed project in the Brahmaputra Valley, India, using a structured questionnaire based on a 5-point Likert Scale. Subsequently, the degree of alignment of the perception of stakeholder groups regarding the sub-domains and domains and the relative desirability are evaluated by applying statistical and mathematical operations. Results reveal that this watershed project desirability indexing (WPDI) would help identify the congruency of views regarding adopted watershed domains and sub-domains. Applying the same WPDI, stakeholders’ desirability in two other adjacent watershed projects (Kaldia and Turkunijan) was evaluated. Findings were validated by a series of expert interviews, which shows the potential of this WPDI to assess different watershed projects operating in an analogous environment. This indexing method might be modified to manage and reengineer multi-stakeholder projects where incongruent perceptions exist.

Using various GCM (general circulation model), the present study attempted to analyze the impact of climate change on the entire stretch of one of the major rivers in South Asia, the Brahmaputra river basin. Initially, we identified a suitable GCM based on some statistical measures of the interpolated and bias-corrected variables. The results of the trend analysis show a significant impact on the climatic variables during future periods. The Brahmaputra basin is likely to experience an increase in rainfall, maximum temperature, and minimum temperature at the rates of 2.5 mm/year, 0.062 °C/year and 0.05 °C/year, respectively, corresponding to representative concentration pathway (RCP) 8.5 scenarios till the end of the current century. Moreover, the climate change impact analysis on streamflow indicates a rise of up to 13.06% in annual discharge at Pandughat, India. The findings of this study will provide a basis for water resource management of the transboundary Brahmaputra basin in the coming decades.

Two-dimensional modelling in a river having undulating bathymetry is challenging in terms of numerical stability, accuracy and robustness. The main reason behind the model stability is the oscillations in the solutions due to nonlinear and hyperbolic form of the flow equations. Sometimes, it is observed that using of primitive variables as temporal derivatives in conservation equation is a source of model instability, especially in a braided river. In this work, the surface form of two-dimensional hydrodynamic equations of shallow water is solved using a five-point TVD Mac-Cormack predictor-corrector scheme. The water surface gradient is used as a gravitational force component in the source term to overcome the possible error that may occur during bed slope discretisation in case of undulating bathymetry. Model is then applied over a wide range of problems including irregular bed, dam breach flow and mix flow with a hydraulic jump. Model outputs are validated with the available experimental data.

ABSTRACTSand mining changes river morphology, which alternatively has adverse impact on hydrology, environment, and ecology of the river system. Quantitative analysis of migration speed of pit and erosion in the mining zone is necessary for both sustainable mining operation and channel bed stability. Sediment transport mechanism in a river also gets affected due to in-stream mining activities. In this research a numerical model has been developed to estimate migration of mining pit by using flux vector splitting finite difference scheme. One-dimensional shallow water hydrodynamic equations and sediment mass conservation equation of bed material for equilibrium bed load sediment transport have been used for simulation of channel bed profile. Here, the applicability of various bed load transport formulation on pit migration has been studied. The use of different bed load transport formulation shows different migration speed of mining pit and downstream erosion. The model is verified by using laboratory flume experiment data for mining pit migration of rectangular and trapezoidal pit. High-resolution experimental data of bed profile obtained from ultrasonic ranging system shows migration and downstream erosion of mining pit. Numerical model developed in this study manifests good agreement with the characteristics of propagation of mining-induced erosion for different bed load transport formulation, while quantitative agreement is achieved only for the Van Rijn approach of bed load transport equation as a closure of the governing equations. The present experimental and numerical analysis shows that channel morphology due to mining can be predicted by using one dimensional numerical model within the acceptable limit.

The conventional urban stormwater management practices focus on carrying away runoff quickly by lined conveyors, which increase the surface runoff and reduce the time of concentration, subsequently causing floods in downstream areas. Ecological Management Practices (EMPs) provide nature-based solutions for reducing flood risks in a sustainable and economically viable manner. However, in the rapidly urbanizing setups in developing nations, the application of EMPs is limited due to space availability, data scarcity and limited funding. This study uses a Non-Linear Programming Optimization Technique to provide modelling solutions in optimizing the land-use and costs under EMPs to reduce flood risks in the Quebrada Aries watershed in the Municipality of Heredia in Costa Rica. Depending on the availability and ease of execution, a combination of three EMPs (bio-retention areas, infiltration trenches and green roofs) were tested. The effect of the application of derived optimal combinations has been analysed. The optimal combination of EMPs analysed for different channel capacity was able to reduce the peak discharge for the worst flood causing event of 50 years return period from 16.86 m3/s (under current land-use) to 9 m3/s, 9.51 m3/s, 8.38 m3/s and 9.13 m3/s in four hypothetical scenarios considered. In urbanized catchments, EMPs cannot be applied indefinitely to avoid floods. However, an optimal combination of EMPs can drastically reduce the requirement of large capacity drainage channels. This information can help policy-makers to analyse trade-offs between urban development and flood control measures. The study is suitable for other data-scarce regions as well.

Existence of piedmont zone in a river bed is a critical parameter from among numerous variations of topographical, geological and geographical conditions that can significantly influence the river flow scenario. Downstream flow situation assessed by routing of upstream hydrograph may yield higher flow depth if existence of such high infiltration zone is ignored and therefore it is a matter of concern for water resources planning and flood management. This work proposes a novel modified hydrodynamic model that has the potential to accurately determine the flow scenario in presence of piedmont zone. The model has been developed using unsteady free surface flow equations, coupled with Green-Ampt infiltration equation as governing equation. For solution of the governing equations Beam and Warming implicit finite difference scheme has been used. The proposed model was first validated from the field data of Trout Creek River showing excellent agreement. The validated model was then applied to a hypothetical river reach commensurate with the size of major tributaries of Brahmaputra Basin of India. Results indicated a 10% and 14% difference in the maximum value of discharge and depth hydrograph in presence and absence of piedmont zone respectively. Overall this model was successfully used to accurately predict the effect of piedmont zone on the unsteady flow in a river.