Improving the crop productivity in rainfed areas with water harvesting structures and deficit irrigation strategies
Watershed management practices aim at improving the agricultural productivity in rainfed agricultural areas by conserving rainwater for an extended period. The stored rainwater in the harvesting structures is used for meeting crop water demand. The water use efficiencies of these structures can be further enhanced through adoption of deficit irrigation management strategies. In this study, deficit irrigation scheduling is formulated using a simulation-optimization framework for a rainfed agricultural area with supplemental irrigation from a check dam in Kondepi IWMP area, near Kondepi Mandal, Prakasam district, Andhra Pradesh, India. The results from the study indicate that the adoption of irrigation management strategies have the potential to improve the productivity and bring more area under irrigation with an increase of 20% and 140% for yield and irrigated area respectively. The outcomes of this study indicate that the proposed method can be suggested for developing optimum irrigation strategies under water deficit in rainfed agriculture having water harvesting structures for an efficient utilization of stored rainwater.
Development of a hydrological model for simulation of runoff from catchments unbounded by ridge lines
Watershed hydrological models are effective tools for simulating the hydrological processes in the watershed. Although there are a plethora of hydrological models, none of them can be directly applied to make water conservation decisions in irregularly bounded areas that do not confirm to topographically defined ridge lines. This study proposes a novel hydrological model that can be directly applied to any catchment, with or without ridge line boundaries. The model is based on the water balance concept, and a linear function concept to approximate the cross-boundary flow from upstream areas to the administrative catchment under consideration. The developed model is tested in 2 watersheds – Riesel Experimental Watershed and a sub-basin of Cedar Creek Watershed in Texas, USA. Hypothetical administrative catchments that did not confirm to the location of ridge lines were considered for verifying the efficacy of the model for hydrologic simulations. The linear function concept used to account the cross boundary flow was based on the hypothesis that the flow coming from outside the boundary to administrative area was proportional to the flow generated in the boundary grid cell. The model performance was satisfactory with an NSE and r2 of ≥0.80 and a PBIAS of <25 in all the cases. The simulated hydrographs for the administrative catchments of the watersheds were in good agreement with the observed hydrographs, indicating a satisfactory performance of the model in the administratively bounded areas.
Hydrologic design of water harvesting structures through simulation-optimization framework
Watershed management in rainfed agricultural areas of arid and semi-arid regions aims at alleviating agricultural drought by employing water conservation measures. Water conservation measures serve as mechanisms for recharging groundwater, and also for surface storage. While the benefits derived from these structures is widely accepted, there is increasing concern regarding their sustainability and efficiency. The application of water conservation measures in upstream reaches contributes to reduced inflows to downstream reaches and structures. Currently watershed management is planned by considering elementary information about the hydrological regime and its associated impacts on the upstream reaches of the watershed. This approach may lead to inefficient water conservation structures, and there is also a significant probability that the structure may be under designed (or over designed). Therefore, careful planning that considers the hydrological changes that the conservation structure may bring in the watershed and the associated benefits/compromise for both upstream and downstream is essential for developing a successful watershed management plan. A simulation-optimization framework for optimal sizing of the water conservation structure considering the dual objectives of improving the benefits in the upstream reaches while maintaining flows in the downstream reaches is proposed in this study. The proposed method is demonstrated for optimal sizing of water conservation structures (check dams in this study) for an experimental watershed in Kondepi Mandal, Andhra Pradesh, India. The results indicate that the check dams of sizes obtained from both traditional method and simulation-optimization method increase moisture availability in the watershed. However, for check dam sizes obtained from the simulation-optimization framework, there is an increase in the flow to downstream reaches compared to the check dam sizes obtained from the traditional methods. The increase in downstream flows obtained by optimizing the check dam heights is at the expense of increased moisture stress days in the non-growing period, thus, not affecting the crop growth or productivity. The results from this study indicate that the proposed simulation-optimization framework can be of assistance in sizing of check dams for sustainable and effective watershed management.
Fuzzy inference system for site suitability evaluation of water harvesting structures in rainfed regions
Watershed management (WM) aims at enhancing the water availability in rainfed areas through water conservation structures, which facilitate storage of water and recharge to ground water. Identification of suitable locations for placing these structures play a major role in the effectiveness of the water conservation. Site suitability evaluation of water conservation structures is performed through an assessment of various biophysical and socio-economic factors. Many of these factors are expressed in linguistic terms rather than precise numeric values, and therefore the output of the evaluation gets subjective. In this study, a fuzzy inference system (FIS) is developed for site selection of water harvesting structures (check dams, farm ponds, and percolation tanks), owing to its capability to handle linguistic data effectively. The suitability zones were identified using the slope, soil permeability and runoff potential as input variables to the FIS. Trapezoidal membership function (MF) was considered for the input and output variables for the fuzzy model and MF parameters were obtained from literature and expert knowledge. The developed FIS is illustrated through an application to Kondepi watershed, Andhra Pradesh, India. The FIS categorized the majority of the watershed area into high suitability class for both farm ponds and check dams. However, the watershed characteristics were not conducive for percolation tanks according to the FIS. A sensitivity analysis of the FIS parameters suggested that the check dam suitability was sensitive to the soil permeability classes. The suitability maps from the FIS were in good agreement with the location of the existing structures in the watershed, suggesting potential use of the developed FIS in WM decisions.
Uncertainty of hydrologic simulation, and its impact on the design and the effectiveness of water conservation structures
The uncertainties associated with the simulation models are often ignored in operational hydrology. While many methods are available for evaluation of simulation uncertainty, most of them focus on construction of prediction bands, which alone may not be sufficient to make effective decisions. This is a serious concern in watershed management planning, especially in cases where the models are uncalibrated due to unavailability of observations. This study addressed uncertainty in hydrologic modeling, and its consideration in check dam design decisions. Size of the check dams were determined using a simulation–optimization framework by considering dual objectives of maximizing water availability for agriculture and minimizing the adverse effects on downstream reaches. The optimizer suggested distinct Pareto-optimal-front for different parameter sets of the model (in turn resulting in different simulations), indicating the influence of parametric uncertainty on the design. An analysis of the optimal solutions suggested varying check dam sizes (0.5–1.5 m) for similar objective function value, which plausibly indicate an economic impact. Nonetheless, the effectiveness of the structure (in terms of simulated wet and dry period lengths) did not exhibit significant variability across the designs (average wet period length of > 100 days). The median of the streamflow ensemble provided satisfactory performance (> 100 days wet period length and only 11–25% reduction of flow to downstream) and could be a viable choice for implementation. The results suggest that parametric uncertainty that is propagated to prediction uncertainty significantly influences the final design decisions and calls for careful assessment prior to implementation.