2. Thesis and Dissertations
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Item Evaluation Of Irrigation Induced Hydrological Changes In The Malaprabha River Basin, Karnataka, India(National Institute of Technology Karnataka, Surathkal, 2022) A, Usha; NANDAGIRI, LAKSHMANWater and food are the two most essential needs for the survival of humankind. However, satisfying their increased demands for a growing human population remains a major challenge for several countries. The increasing demand for food can be fulfilled to a large extent by enhancement in agricultural productivity through the introduction of irrigation. Consequently, there has been a worldwide increase in irrigated agriculture during the past several decades. However, the introduction of large-scale irrigation in a region can bring about a wide variety of changes in the environmental, economic, and social domains. Since irrigation water withdrawals account for more than 70% of the total available water resources of the world, there is a potential for alteration of hydrological processes and regional climate patterns. Environmental impacts of irrigation in general and hydrological impacts in particular, which are usually detrimental in nature, have been a cause for concern given the rapid increase in irrigated agriculture across the world. Therefore, studies aimed at assessing irrigation impacts on regional hydrology are very essential to understand changes in the hydrological cycle and the magnitudes of water balance components. Improved understanding of such impacts will pave the way for developing plans for sustainable development and management of water resources. The primary objective of the present research work was to analyze the impacts of large- scale irrigation on river-basin scale hydrological processes. Accordingly, the Malaprabha River basin located in a semi-arid Karnataka State, India in which an irrigation project was established in 1972, was selected for the study. The sequential methodology adopted to evaluate the hydrological effects of irrigation consisted of 1) Characterizing the river basin using historical observations of hydro-meteorological variables 2) Analysing the likely effects of irrigation on long-term trend and variability of hydro-meteorological variables 3) Analysing the historical growth of irrigated agriculture in the Malaprabha river basin using CROPWAT 4) Identify and evaluate the contributions of major drivers causing the stream-flow change in the river using the SWAT model and 5) Evaluating the ii hydrological impacts of irrigation using plausible cropping pattern scenarios in the river basin. With the obtained historical hydro-meteorological data (rainfall, rainy days, average temperature, stream flows, and groundwater levels), a preliminary analysis was carried out using box-whisker plots and Spatio-temporal maps over the Malaprabha river basin. The analysis revealed that the large part of the basin experiences annual average rainfall between 544 mm to 700 mm, which is a typical range for a semi-arid climate. Streamflow regime at downstream gauging stations was significantly affected by the Malaprabha irrigation project in the study area causing increased low flows (LFI upto 111%) during summer months and decreasing amount of peak flows (HFI upto 37.4%) during monsoon. Also, higher GWL fluctuations (10 to 20 mbgl) were observed in the downstream command area during all seasons. This defending the fact that excessive groundwater utilization for growing water-intensive crops in the immediate vicinity to the reservoir. Trend analysis for the historical hydro-meteorological variables was carried out from 1960 to 2015 using nonparametric Singular Spectrum Analysis (SSA) and conventional Sen’s slope Estimator (SE) methods. The results demonstrated the ability of SSA to capture the trajectory of nonlinear trends over the entire time series of hydro- meteorological variables. The traditional SE and MK methods, on the other hand, provide information on linear monotonic trends. The temporal variability of the data was analyzed using the Coefficient of Variation (CV) statistic. Variability study revealed that the presence of the reservoir has resulted in the occurrence of rainfall events with higher intensities in its vicinity. Also, wells located in irrigable command areas are subjected to greater variability. The trend analysis indicates non-significant decreasing rainfall and rainy days till the year 2000, but an increasing trend thereafter. A significant increasing trend in mean temperature was observed for all the stations and all the seasons of the basin with an average magnitude of 0.2⁰ C per decade. The annual stream-flow trends for downstream gauging stations were subjected to variability as these are regulated flows and showed decreasing trends corresponding with the progression of irrigation in the iii command area. Groundwater levels of most of the wells in the upstream region showed increasing annual trends. The two wells located in close vicinity of the Malparabha dam towards the downstream side showed significantly decreasing trends. On the other hand, the wells in the downstream command area indicated a combination of significantly increasing and decreasing trends. The analysis of the historical growth of irrigation in the Malaprabha command area revealed that the commissioning of the irrigation project has a significant role in the development of irrigated agriculture in the region. The contribution of canal supplies to irrigated agriculture was maximum until 1985-86 (61%) and decreased thereafter and the contribution of canal supplies to irrigated agriculture was maximum until 1985-86 (61%) and decreased thereafter. Also, the regions close to the reservoir appear to be fully benefitted by canal water supplies whereas regions located away from the reservoir seem to be benefitting from groundwater supplies. A shift from low water consuming crops to water-intensive crops is observed and the area under cash crops has increased significantly. Cropping-pattern violations, flood-irrigation, illegal water withdrawals, and poor maintenance of canal and associated structures are likely causing the current status. Overall, it appears from the performance analysis that the Malaprabha irrigation project has not been able to enforce the planned objectives and goals. The SWAT hydrological model was applied to study the combined and isolated effects of Malaprabha reservoir, LULC change, and climate change for the decades 1980s, 1990s, and 2000s. The combined effect of changes in all three drivers caused an increase in annual stream-flow in the basin by 53% between the 1980s and 1990s and a decrease in stream-flow by 38% between 1990s and 2000s. The study reveals that in a tropical river basin the presence of an irrigation reservoir can significantly alter temporal variability of stream-flow which is further exacerbated by changes in LULC and climate. On the other hand, the analysis of irrigation effect on stream flows revealed that when irrigation is withdrawn, water availability in the basin was found to be improved significantly. Also, increased low-flows during the non-monsoon period and decreased flows during the iv monsoon period have been noticed for irrigation conditions concerning no-irrigation conditions. The quantity of actual evapotranspiration (AET) in the study for existing irrigation conditions was increased by 4 to 26% concerning the no-irrigation scenario and 15% concerning the proposed irrigation scenario over the irrigated sub-basins. The present study demonstrated a sequential methodology adopted to evaluate the hydrological effects of irrigation over the Malaprabha river basin through statistical analysis as well as using a hydrological model. The information provided by this study will be useful in solving water scarcity issues in the river basin through the development of effective management strategies to improve the efficiency of the Malaprabha project and promote the sustainable development of natural resources in the study area.Item Assessment of Hydrological Impacts of Land Cover Changes and Climate Variability in the Geba Catchment, Ethiopia(National Institute of Technology Karnataka, Surathkal, 2016) Hailu, Gebremedhin Kiros; Shetty, Amba; Nandagiri, LakshmanLand use/land cover (LU/LC) and climate are the two main factors directly influencing catchment hydrological processes and consequently changes in these factors will result in significant hydrological impacts. Quantifying the magnitude and direction of these impacts is of great importance for land use planning and sustainable water resources management. The Geba catchment (5137 km2) located in the highlands of Northern Ethiopia; Africa contributes a significant portion of flow in the river Nile and forms an important source of water to a large population. In the past few decades, the catchment has experienced significant changes in LU/LC in the form of degradation due to anthropogenic activities and subsequent restoration brought about by conservation measures. Also, trend analysis of hydro-meteorological data carried out as part of this study provided evidence of changes in rainfall and temperature regimes in the catchment. Therefore, the present study was taken up to characterize the hydrology of the Geba catchment using available hydro-meteorological data and to apply and evaluate the potential of the Soil and Water Assessment Tool (SWAT) model to simulate major hydrological processes and sediment dynamics in the catchment. The objective was to use SWAT to simulate changes in hydrological processes brought about by changes in LU/LC and climate variability within the catchment. Accordingly, the research methodology adopted involved the following tasks: (1) Using historical (1971-2013) ground-based observations of rainfall, air temperature (7 climate stations) and streamflow (1 gauging station) statistical and trend analyses were carried out for monthly and seasonal time steps. Also, trends in several extreme climatic indices related to rainfall and temperature were analysed (2) LANDSAT satellite imagery acquired for multiple dates during the period 1971-2013 were subject to standard image processing and supervised classification procedures to derive LU/LC maps for the Geba catchment. These classified maps were used to detect changes in different LU/LC classesii during the periods 1973 – 1987, 1987 – 2000 and 2000 – 2013 (3) Using a variety of inputs (ground and satellite-based) related to topography, soils, LU/LC, rainfall and climatic variables, the ArcGIS version of the SWAT model (ArcSWAT) was applied to the Geba catchment. Given that the catchment experienced significant changes in LU/LC over the 40 year period considered, a novel model calibration/validation approach was adopted involving the use of different LU/LC maps for different time periods (4) Using observed streamflow records at the outlet of the Geba catchment, the SWAT model was subject to sensitivity analysis following which calibration and validation was carried out using both monthly and daily time steps. Model performance in simulating streamflow and sediment concentration at the outlet was evaluated using different statistical criteria (5) Using the validated SWAT model, a novel method to evaluate the separate and combined impacts of LU/LC changes and climate changes on major water balance components in the Geba catchment was implemented. Results of trend analysis revealed that during the study period (1971-2013), rainfall and streamflow exhibited a decreasing trend, while maximum daily air temperature had an increasing trend and minimum daily air temperature showed decreasing trend at 95 % confidence level. As regards LU/LC changes, during 1973–1987 and 1987–2000 time periods about 10.83 % and 9.13 % of the catchment area was transformed largely from shrub, forest and rangeland mainly to agriculture and barren land. During 2000–2013, about 18.37 % of the total catchment area was transformed from barren land and range to agriculture, shrub, forest and urban area. SWAT model validation using observed streamflow records yielded values of coefficient of determination (R2) between 0.86 and 0.96 and Nash-Sutcliffe efficiencies (ENS) between 0.73 and 0.83 for different simulation periods with a monthly time step. For daily streamflow predictions, R2 values ranged between 0.77 and 0.91 and ENS values were between 0.7 and 0.79. SWAT also provided reasonably accurate predictions of daily sediment concentrations during validation (R2: 0.81-0.895, ENS: 0.79-0.80). These results prove that the SWAT model is a reasonably accurate tool for simulation of hydrological processes in the Geba catchment, whereas R2iii and ENS for daily and monthly flow were very less (satisfactory) for the single static LU/LC (2000) map, mostly followed in many studies. Impacts of LU/LC changes and climate variability were evaluated by dividing the study period (1973-2013) into three phases based on LU/LC and climatic conditions: Phase (I) - LU/LC maps of 1973 and 1987, climate of 1974-1983 and 1984-1993 Phase (II) - LU/LC maps of 1987 and 2000, climate of 1984-1993 and 1994-2003 Phase (III) - LU/LC maps of 2000 and 2013, climate of 1994-2013 and 2004-2013. The SWAT model was run separately for four scenarios in each phase involving combinations of LU/LC and climate. Results indicated that the combined impacts of the LU/LC changes and climate variability increased streamflow and potential evapotranspiration in both Phases I and II, while available soil water contents decreased. Positive impacts in the form of reduced streamflow and increased soil moisture resulted in Phase III due to extensive conservation measures implemented after 2000. Overall, changes in LU/LC seemed to have a higher impact on hydrological processes than changes in climate. The present study has demonstrated the applicability and efficacy of a convenient methodology integrating satellite remote sensing and modelling to characterize hydrological processes and simulate hydrological changes in a heterogeneous tropical catchment. The proposed strategy may be adopted to formulate strategies for sustainable land and water resources management in the region, and in similar hydro-climatic settings elsewhere in Africa.Item Assessment of Variable Source Area Hydrological Models in the Upper Cauvery Basin, Karnataka, India(National Institute of Technology Karnataka, Surathkal, 2016) B. C, Kumar Raju; Nandagiri, LakshmanWith increased availability of spatial data-sets of catchment characteristics and hydrometeorological variables, distributed hydrological models are being applied to solve a variety of problems related to catchment hydrology and water resources management. However, experimental results obtained in recent decades have shown the possiblity of existence of runoff generation mechanisms other than the conventional infiltration-excess (Hortonian) mechanism. In particular, it has been shown that Variable Source Area (VSA) mechanism of runoff generation may prevail in humid steeply sloping and well vegetated watersheds. Accordingly, efforts have been made by previous researchers to incorporate this mechanism into distributed hydrological models and their performances have been evaluated in mostly humid temperate regions and not so much in humid tropical regions. The primary objective of the present study was to compare the performances of hydrological models which incorporate the Variable Source Area (VSA) mechanism of runoff generation with that of the Soil and Water Assessment Tool (SWAT) which employs the conventional infiltration-excess mechanism of runoff generation. One of the VSA based model used, SWAT-VSA, has been proposed by earlier researchers as a re-conceptualization of the SWAT model and uses a topography-based wetness index to identify source areas and simulates runoff in a manner consistent with VSA hydrology. In the present study, the topography-based wetness index was replaced with a Modified Normalized Difference Water Index (MNDWI) derived from satellite imagery resulting in a new VSA model version, SWAT-MNDWI. Performance evaluation of the models was carried out through their application in two humid tropical watersheds (Hemavathi – 2974 km2; Harangi – 538.8 km2) located in the Upper Cauvery River Basin (36,682 km2), India wherein previous studies have shown the existence of VSA hydrology. The other aspects addressed in this study include: assessment of significance and magnitude of trends in historical records of observed hydrometeorological variables in the Upper Cauvery Basin, evaluation of uncertainties associated with streamflowii predictions of the 3 hydrological models and simulation of the hydrologic impacts of hypothetical land use/land cover (LU/LC) changes in the Hemavathi and Harangi watersheds. The present study examined the significance and magnitude of trends in the monthly rainfall (33 rain gauges), maximum and minimum temperature (6 climate stations) and streamflow at 4 gauge sites in the Upper Cauvery Basin for the historical 30 year period 1981-2010. The statistical parameters - Coefficient of Variation (CV) and percentage departure were calculated for average monthly values separately for 3 decades. The Seasonal-Kendall and Sen’s slope estimator were used to calculate significance and magnitude of trends in rainfall, temperature and streamflow data. Detrended Fluctuation Analysis (DFA) method was used to detect long-term persistence in the time series data. As expected, the CV of rainfall shows a large variation in the month December to March, while the percentage departure also varies during these months for different decades. But there was no significant trend found for all rain gauge stations and sub basins except for the Arkavathi sub basin. For maximum temperature there was not much variation except in the months of May and June at the Hassan climate station. Statistically significant trend was observed in maximum temperature for Chikmagalur and Hassan stations. The CV of minimum temperature shows a large variability from November to March for all climate stations and also a significant increasing trend for Hassan and Bangalore stations, while for Madikeri a decreasing trend was observed with a variation of -0.16 0C/year. There was not much variation found for streamflow except in K M Vadi gauge site and T.Narasipur gauge site which showed a significant decreasing trend of -0.778 m3/s/ year. Long range dependence analysis revealed a weak persistence for both rainfall and streamflow of the basin. Using relevant data inputs pertaining to rainfall, climate, elevation, Land use/Land Cover (LU/LC) and soils, the SWAT, SWAT-VSA and SWAT-MNDWI models were applied separately to both watersheds using a daily time step. Models were calibrated for the historical period 2000-2003 and validated for the period 2004-2006 using observed daily streamflow records at the watershed outlets. The comparative assessment focused specifically on the following aspects for the six cases considerediii (3 models applied to 2 watersheds): 1) sensitivity of model parameters 2) accuracy of daily streamflow predictions at the watershed outlets 3) predictions of spatially and temporally averaged annual water balance components 4) differences in spatial patterns of source areas of surface runoff. Sensitivity analysis indicated that for the SWAT model, Curve Number (CN) was the most important parameter while for the VSA based models, parameters related to the unsaturated zone and shallow groundwater were important, a result consistent with the runoff mechanism incorporated in the models. The accuracies of streamflow prediction as determined from scatter plots and model performance statistics were more or less similar both in calibration and validation for all the three models with the models performing better in the forested Harangi watershed. Overall, the SWAT-MNDWI model proved to be the best one in simulating daily streamflow with Nash-Sutcliffe efficiency (ENS) of 0.85, coefficient of determination (R2) of 0.88, percentage bias (PBIAS) of 13.2% and root mean square error (RMSE) of 37.48 m3/s for the Hemavathi watershed and corresponding values of 0.88, 0.88, 1.09% and 16.67 m3/s for the Harangi watershed. All three models simulated spatially and temporally averaged major water balance components in a consistent manner resulting in a residual error of <5% of annual rainfall in the annual water balance. However, evapotranspiration loss as a percentage of rainfall appeared unreasonable (27% - 32%) for the wet Harangi watershed probably on account of it being predominantly forested. The spatial patterns of surface runoff generation were somewhat similar for the SWAT-VSA and SWATMNDWI models, but completely different for the SWAT model, again a result consistent with the runoff generation mechanism adopted. Overall results of this study have demonstrated that models incorporating VSA hydrology, and in particular the SWAT-MNDWI model proposed in this study, provide accurate and convenient tools for distributed hydrologic modelling in humid tropical watersheds. This study also focuses on assessing uncertainties associated with SWAT-MNDWI, SWAT-VSA and SWAT models using SWAT-CUP (Calibration and Uncertainty Programs) tool. Two multi-objective uncertainty techniques (Generalized Likelihood Uncertainty Equation (GLUE) and Sequential Uncertainty Fitting algorithm (SUFI-2)) were tested for the Hemavathi and Harangi watersheds. The goodness-of-fit and efficiency of the models have been tested using ENS as the objective function. GLUEiv and SUFI-2 techniques yielded good results in minimizing the differences between observed and simulated streamflows at the outlets of the Hemavathi and Harangi watersheds. The results show that GLUE performance was slightly better than the SUFI-2 technique for all models for both the watersheds during calibration and validation periods. The 95PPU estimated by the GLUE and SUFI-2 techniques are very close to each other and larger than 45% (P-factor) for all models for both the watersheds during calibration and validation periods. For GLUE, R-factor values during the validation phase for the Hemavathi watershed were 0.35, 0.38 and 0.34 for the SWAT-MNDWI, SWAT-VSA and SWAT models respectively with corresponding values for the Harangi watershed being 0.41, 0.39 and 0.40. It should be noted that that both GLUE and SUFI-2 cannot accurately quantify the prediction uncertainty of SWAT-MNDWI, SWAT-VSA and SWAT models. Overall results indicated that the GLUE technique applied on the SWAT-MNDWI model performed best in quantifying the prediction uncertainty of streamflow at the outlets of both watersheds. In order to simulate the hydrologic impacts of LU/LC changes in the study area, two hypothetical LU/LC change scenarios were formulated for Hemavathi and Harangi watersheds. The SWAT-MNDWI, SWAT-VSA and SWAT models were used to simulate the hydrologic responses under these scenarios. Values of average annual water balance components and their percentage change with respect to reference results were calculated for both watersheds using the three models. Additionally, an effort was also made to construct the Flow Duration Curves (FDCs) using daily streamflow values generated under each scenario. Differences in optimal parameters of an empirical model for the FDC, magnitudes of flow quantiles, high flow index and low flow index were computed for each scenario. For the Hemavathi watershed, with increase in agricultural land there is increase in water yield predicted by all three models. With increase in forest cover there is decrease in water yield predicted by SWAT-VSA and SWAT models while for SWAT-MNDWI an increase in water yield was found. For Harangi watershed, with increase in agricultural land or forested area there is decrease in water yield for all three models except SWAT-VSA model in scenario I. Both the scenarios appeared to have significant impacts on the runoffv regime as indicated by significant changes in FDC model parameters, flow quantiles and flow indices. Overall results of this study provide useful inputs with regard the magnitude and direction of likely future changes in important hydrometeorological variables which can be used to prepare plans for mitigation and adaptation to climate change in the Upper Cauvery Basin. The present study has demonstrated an overall methodology for application, performance evaluation and uncertainty analysis of distributed hydrological models using a variety of ground-based inputs and satellite data within a GIS framework. Since previous studies in similar watersheds in the Western Ghats region have identified VSA as a dominant mechanism of runoff generation, the spatial patterns obtained with the SWAT-VSA and SWAT-MNDWI models provide information which will prove to be extremely useful in soil and water conservation measures and in identifying source areas of non-point pollution. The SWAT-MNDWI model proposed in this study is particularly attractive since it employs satellite imagery to accurately identify areas of different wetnesses within the watershed and integrates this information into a distributed hydrological model. As the results of this study have demonstrated, such a modelling approach using VSA hydrology provides an accurate and convenient tool for distributed hydrologic modelling and impact assessment of LU/LC changes in humid tropical watersheds.