HYDROLOGIC AND WATER RESOURCES MODELLING FOR THE GANGES BASIN Public Disclosure Authorized A Compilation and Bibliography Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized 1 TABLE OF CONTENTS Introduction ............................................................................................................................................ 3 Compilation of Recent/ Current Modelling Work ................................................................................. 4 Bibliography ........................................................................................................................................ 58 2 INTRODUCTION The Ganges River Basin is one of the largest river basins in the world, covering around 1.2 million km2. The basin spans India (84%), Nepal (12%), Bangladesh (3%) and China (1%). It rises in the Himalayas, traverses the fertile plains of India and Bangladesh, and flows into the Bay of Bengal through the world’s largest mangrove ecosystem, the Sundarbans of the Ganges Delta. Its major tributaries are the primarily rain-fed Himalayan rivers of India and Nepal. The delta is characterized by extensive series of distributary channels, including the Damodar-Hooghly River, but the main basin outlet is the main stem of the Ganges – called the Padma in Bangladesh – that merges with the Brahmaputra before flowing into the sea. The hydrology of the basin is dominated by the annual monsoon that delivers about 80% of annual inflows in just three months of the year. On average, around 1200 billion m3 of precipitation fall in the basin each year, of which around 500 billion m3 becomes stream flow. The extensive and high-yielding alluvial aquifers of the basin are critical part of the hydrologic system and the water resource. The Ganges is the world’s most populous river basin, home to more than 655 million people with high population density and poverty is widespread. It is also one of the world’s most revered rivers with deep spiritual and cultural significance for millions of people both within and beyond the basin. The basin resources are hugely significant economically for the riparian countries. Agriculture dominates water use, with irrigation currently representing about 90% of the basin’s combined surface and ground water uses. However, agricultural productivity in the basin is low compared to global averages. Improving water productivity would significantly contribute to food security, poverty reduction, and economic growth in the basin. Hydropower generation is critical to the economy of Nepal, and developing the untapped hydropower potential in Nepal is an ongoing development challenge with major transboundary dimensions. With increasing in urbanization and industrialization, the magnitude and sector balance of water demand is changing, giving rise to increased competition for water and increased stress on water dependent ecosystems. Flooding is a frequent occurrence in many parts of the basin with serious loss of life and economic damage. There is great potential for economic development and poverty reduction through more balanced and sustainable management of the water resources of the basin, but charting a trajectory towards this future requires a sound analytical basis. There are many analytical approaches that can help inform policy directions for the Ganges Basin. One important category of analytical tools are models of the hydrological processes and water resources systems. This report provides an introduction to the modelling work of this type undertaken to-date. The report pulls together two resources: (i) a compilation of current and ongoing modelling efforts, and (ii) a bibliography of over one hundred published papers on hydrologic or water resources modelling relevant to the Ganges Basin. The report is intended as a resource document for technical experts interested in water modelling for the Ganges Basin. The modeling efforts to-date have informed hydrologic characterization, water resource assessments, water resource planning, flood management, water quality assessment, groundwater management, climate change impact assessment, sedimentation and environmental management. Perhaps the biggest challenge faced in hydrologic and water resources modelling for the Ganges Basin pertains to the adequacy and accessibility of data. Much of the data required for setting up and calibrating reliable hydrologic or water resources models is either of poor quality (spatially or temporally sparse, unverified, etc) or not available because of government controls on water data. This has pampers the ability to build robust well calibrated models, which in turn leads to uncertainty and lack of agreement on issues such as flow patterns, surface-groundwater interactions, water availability, consumptive use and sharing. Without improved transparency on water data and knowledge, it will be difficult to move towards more efficient, cooperative and sustainable water management across the Ganges Basin. 3 COMPILATION OF RECENT/ CURRENT MODELLING WORK Snowmelt contributions to discharge of the Ganges. Quantify and clarify current Title/Purpose temporal and spatial contributions of snowmelt to runoff in the Ganges basin. C. Siderius1, H. Biemans1, A. Wiltshire2, S. Rao3, W.H.P. Franssen1, P. Kumar4, A.K. Author(s) Gosain3, M.T.H. van Vliet1, D.N. Collins5 1Wageningen University & Research Centre, 2Met Office Hadley Centre, 3IIT Delhi, 4Max Institution(s) Planck Institute for Meteorology, 5University of Salford Model(s) VIC, JULES, LPJmL and SWAT Currency 2013? Unknown duration Scope Surface water quantity simulation (snowmelt contributions) Model/Data Description The article delineated the Ganges basin using gridded cells with a 0.5-degree resolution (for all models except SWAT). It discusses four models: SWAT, Jules, LPJml and VIC. In all, only natural streamflow was modelled. No account was made for water allocation or demand management. Runoff was generated from water percolating through the soil column as a result of rainfall and snowmelt. Since the components were not treated separately when they entered the soil column, the proportion had to be calculated each month for each grid cell. To account for losses in the soil column, the snowmelt runoff did not exceed the total snowmelt from the previous month. Moreover, the proportions of snowmelt runoff did not exceed the snowmelt to rainfall ratio. The WATCH dataset (0.5° X 0.5°) was used to drive the hydrological models. SWAT runoff modelling used the Soil Conservation Service (USDA NRCS) methodology, while the Jules, LPJml, and VIC models were based on the water balance equation. Snowmelt and total runoff were routed using the STN routing scheme. Availability/Accessibility Model Public domain (but requires proprietary ArcGIS) Input data files published: Not Published Data files Output data files: Not published Report(s) Technical report produced: Unknown Report on inter-comparison of the relative performance of the three modelling Other publications approaches {Collins, 2012 #19} Spatial and Temporal Boundaries Spatial Extent Ganges Basin Outlet Point Farakka Barrage Temporal Monthly Resolution Time Period 1971-2000 Data Requirements Component Source Publicly Available DEM GTOPO30 Yes MODIS Yes University of Maryland Global Land Cover Yes Land Use/Cover US Geological Survey Yes IWMI Yes 4 Global Environment Monitoring Yes Soils FAO, International Soil Reference and Information Centre Yes Meteorological Center for Ecology and Hydrology Yes Global Runoff Data Centre Yes Runoff Data Wadia Institute No Key Assumptions and Limitations Reservoirs have no major effect on streamflow. Assumptions Conversion from snowmelt to runoff are the same for glaciers and snowmelt. Air temperature and discharge data are scarce in the Himalayan Region. High altitude climate stations are lacking including Tibetan plateau. No account of water demand and allocation estimates is provided. Data Limitations Coarse grid cells are used for Tehri. Models are affected by heterogeneity of mountainous areas. Global soil thickness database can affect formation of runoff and evaporative losses. SWAT has only a simplified snowmelt model. There is a lack of elevation bands for LPJmL Model Limitations and JULES. In VIC, only natural stream flow is used; groundwater is not accounted. A Hydrodynamic Approach to Address the Yamuna Riverbed Development in Delhi. Title/Purpose Assess channel improvements to the Yamuna River to reduce flooding. Author(s) Ritesh Vijay, Aabha Sargaonkar, and Apurba Gupta Institution(s) National Environmental Engineering Research Institute Model(s) RiverCAD (HEC-RAS) Currency 2008? Unknown duration Scope Hydrodynamic modelling and water simulation Model/Data Description The modelling was performed on the 23 km reach from Wazirabad to Okhla Barrage. Flood frequency flows were determined using the Gumbel Extreme Value for the 10, 25, 50, 100-year storm based on 41 years of record. Surfer was used to generate a DEM using 101 field survey cross-sections with a spacing of 200-300 meters. Seven bridges barrages were included based on hydraulic geometry. Manning’s coefficient values were obtained from the literature value. HEC-RAS were used to determine the water surface profile applying the energy equation an iterative process called the standard step method. Availability/Accessibility Model Public domain but requires proprietary interface Input data files: Not published Data files Output data files: Not published Report(s) Technical report