The Drying of the Arkavathy River: Understanding Hydrological Change in a Human-Dominated Watershed
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The drying of the Arkavathy river: understanding hydrological change in a human-dominated watershed by Gopal Penny A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering - Civil and Environmental Engineering in the Graduate Division of the University of California, Berkeley Committee in charge: Associate Professor Sally E. Thompson, Chair Professor Fotini K. Chow Assistant Professor Iryna Dronova Veena Srinivasan, PhD Summer 2017 The drying of the Arkavathy river: understanding hydrological change in a human-dominated watershed Copyright 2017 by Gopal Penny 1 Abstract The drying of the Arkavathy river: understanding hydrological change in a human-dominated watershed by Gopal Penny Doctor of Philosophy in Engineering - Civil and Environmental Engineering University of California, Berkeley Associate Professor Sally E. Thompson, Chair Human interventions in the hydrologic cycle have intensified to the extent that water re- sources cannot be managed and understood in isolation from anthropogenic influences. New approaches are needed to understand the effects of humans on hydrology, especially in re- gions of the world with limited hydrologic records. This dissertation focuses on a case study of the Arkavathy watershed adjacent to Bangalore, India, which has been transformed by rapid urbanization, intensification of agriculture, and over-exploitation of water resources over the last 50 years. During this time, the disappearance of streamflow in the watershed was largely overlooked as Bangalore shifted from Arkavathy-sourced water supply to im- ported water and farmers from surface water to groundwater irrigation. With Bangalore continuing to expand its water footprint and local groundwater resources drying up, moving towards sustainable water resources management in the Arkavathy requires overcoming the general absence of local hydrological records to develop an understanding of the changing hydrology of the watershed. To this end, a multifaceted research approach is developed and applied to the Arkavathy watershed to identify the dominant hydrologic dynamics within the watershed and understand the conditions under which hydrologic change occurred. This research reveals a number of important findings. First, humans are the primary drivers of change in this watershed, as neither precipitation variability nor increases in temperature can explain the observed changes in hydrology. Second, hydrologic change within the water- shed is spatially heterogeneous, with drying occurring in the northern part of the watershed and increased surface water availability downstream of Bangalore. Third, streamflow decline in the northern Arkavathy has most likely been caused by extensive groundwater depletion driven by groundwater irrigated agriculture. And finally, management strategies designed to reverse groundwater depletion by constructing check dams within the surface water network are unlikely to succeed on the scales pertinent to watershed management. In addition to understanding water resources within the Arkavathy, this work serves as a foundation for understanding the trajectory of water resources in the region. This research also presents an approach for investigating historical hydrologic change in a poorly monitored watershed, un- 2 derstanding human-water interactions, and supporting long-term predictions for sustainable water management. i Contents Contents i List of Figures iv List of Tables vi 1 Introduction 1 1.1 The need to study coupled human-water systems . 2 1.2 The Arkavathy watershed . 2 1.2.1 Regional context . 3 1.2.2 Potential drivers of change . 5 1.2.3 Climate and geography . 6 1.3 Research approach . 8 1.3.1 Conceptual framework . 8 1.3.2 Summary of chapters . 10 2 Multiple hypotheses of change 13 2.1 Introduction . 13 2.1.1 Challenges in rapidly growing, data-scarce regions . 13 2.1.2 Use-inspired science in data-scarce regions . 14 2.2 Drying of TG Halli reservoir . 15 2.2.1 Study area and the problem . 15 2.2.2 The debate about causes and solutions . 18 2.2.3 The multiple hypotheses approach . 19 2.3 Methods . 21 2.3.1 Data sources and quality assurance . 21 2.3.2 Analysis techniques . 21 2.4 Results . 26 2.4.1 Lack of evidence of climatic drivers . 26 2.4.2 Evidence of human drivers . 27 2.5 Discussion . 29 2.6 Conclusions . 30 ii 3 Spatial changes in surface water 32 3.1 Introduction . 32 3.2 Methods . 35 3.2.1 Study area and remote sensing analysis . 35 3.2.2 Statistical model of tank water extent . 37 3.2.3 Hydrologic change and land use . 40 3.3 Results . 41 3.3.1 Accuracy assessment . 41 3.3.2 Heterogeneity of long-term hydrologic change . 42 3.3.3 Streamflow decline and agricultural practices . 43 3.4 Discussion . 44 3.4.1 Long-term hydrological trends and human drivers of change . 44 3.4.2 Assessing the classification and model uncertainty . 46 3.5 Conclusions . 47 4 Process-based reconstruction 48 4.1 Introduction . 48 4.1.1 Typology of hydrologic reconstruction . 49 4.1.2 A process-based reconstruction approach . 52 4.2 Methods . 53 4.2.1 Study area and runoff generation in semi-arid catchments . 53 4.2.2 Field instrumentation and experiments . 56 4.2.3 Storm event analysis . 58 4.3 Results . 59 4.3.1 Overland flow . 59 4.3.2 Saturated hydraulic conductivity . 60 4.3.3 Storm dynamics and timing . 60 4.3.4 Open well survey . 61 4.4 Discussion . 63 4.4.1 Contemporary streamflow generation . 63 4.4.2 Historical streamflow generation . 64 4.5 Conclusions . 66 5 Check dams and groundwater recharge 68 5.1 Introduction . 68 5.2 Methods . 69 5.2.1 Study area . 69 5.2.2 Field instrumentation and data analysis . 70 5.2.3 Thirumagondonahalli watershed simulation . 72 5.2.4 Simulation of synthetic check dam networks . 73 5.3 Results . 75 5.3.1 Observed streamflow dynamics . 75 iii 5.3.2 Effect of check dams in the Thirumagondonahalli watershed . 76 5.3.3 Features of synthetic check dam networks . 77 5.4 Discussion . 78 5.5 Conclusions . 80 6 Conclusion 82 6.1 Summary of findings . 82 6.2 Future work . 83 A Supporting information for Chapter 3 85 A.1 Remote sensing analysis . 85 A.1.1 Remote-sensing images and supplementary data . 85 A.1.2 Classification method . 89 A.1.3 Validation of classification method . 92 A.2 Statistical model design . 95 A.2.1 Dry season analysis . 95 A.2.2 Collinearity analysis . 95 A.3 Statistical model analyses . 96 A.3.1 Precipitation timeseries . 96 A.4 Hydrological trends and agricultural land use . 103 B Supporting information for Chapter 4 104 C Supporting information for Chapter 5 105 C.1 Check dam water balance . 105 C.1.1 Evaporation . 105 C.1.2 Recharge . 106 C.2 Precipitation variability . 106 References 108 iv List of Figures 1.1 Arkavathy watershed location map . 7 1.2 Conceptual framework of sociohydrologic system and research approach . 9 2.1 Important features of the TG Halli watershed . 16 2.2 Changes in hydrology and hydrometeorology from secondary data . 17 2.3 Irrigation water supply over time . 18 2.4 Change in Eucalyptus area, 1973{2001 . 28 3.1 Arkavathy map and Landsat scene boundaries . 33 3.2 Aerial photos of a small tank before and after runoff events . 35 3.3 Map of major subwatersheds and tank cluster watersheds . 39 3.4 Tanks-scale validation of classification . 41 3.5 Long-term hydrologic trend for each tank cluster . 43 3.6 Agricultural land use and hydrologic change . 44 4.1 Typology of hydrologic reconstruction . 49 4.2 Map of study watersheds and instrumentation within the TG Halli watershed . 53 4.3 Framework for investigating streamflow generation mechanisms . 55 4.4 Deuterium concentrations throughout two storm events . 59 4.5 Saturated hydraulic conductivity and precipitation rates . 60 4.6 Probability of runoff based on storm size and soil moisture . 61 4.7 Hydrologic variables for a large runoff event on 07 October 2014 . 62 4.8 Time lag from peak inflow to peak soil moisture . 62 4.9 Elevation of wells compared with elevation of the nearest stream channel . 63 4.10 Depth to the bottom of dry wells in 2014 and water table depths c. 1970 . 65 5.1 Locations of check dams in study watersheds . 70 5.2 Photos of a check dam under empty and near-full.