A GIS-based Methodology for Assigning a Flux Boundary to a Numerical Groundwater Flow Model and Its Effect on Model Cali
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A GIS-based Methodology for Assigning a Flux Boundary to a Numerical Groundwater Flow Model and Its Effect on Model Calibration Satyendra Kumara, Vivekananda,*, Bhaskar Narjarya, Neeraj Kumara, Samanpreet Kaurb, R. K. Yadava, S. K. Kamraa a
ICAR- Central Soil Salinity Research Institute, Karnal - 132 001, India Punjab Agricultural University, Ludhiana - 141 004, India *E- mail: [email protected] b
ABSTRACT Groundwater flow modeling is an important tool for understanding and computing hydrology and water availability of an aquifer zone. However, an accurate representation of boundaries and their initial conditions are vital for simulation of the groundwater flow phenomena. In this study, efforts have been made to develop a GIS based methodology for estimating flux across boundaries of the study area using Darcy flow tool. The spatial maps of topography, bore log, transmissivity, hydraulic conductivity, porosity and groundwater levels for the study area were created in ArcGIS 9.3.1 using krigging method. A buffer zone of 1×1 km2 cell size was created on inner and outer side of the boundaries and Darcy flow model was used to estimate specified flux across boundaries. The groundwater behavior of the study area was simulated with specified flux boundary condition (Neumann boundary condition) and no flow boundary condition to assess importance and estimation accuracy of estimated flux. Darcy model output indicates that flux across the boundaries contributed about 36.20 mm in average annual change in groundwater table depth. With estimated specified flux, simulation accuracy of groundwater flow model (R2) increased to 0.97 from 0.90. The satisfactory level (R2=0.97) of simulation accuracy reveals that developed methodology can be used for estimating flux across boundaries in the absence of physical boundaries. INTRODUCTION Almost 97% of earth’s water is salt water in the oceans and of the remaining 3%, two-thirds occur as snow and ice in polar and mountainous regions, leaving only about 1% of the global water as fresh water. Of this, ~ 98% is stored in the aquifer, while the remaining is in streams and lakes, which often are fed by groundwater (Bouwer, 2000). In the last few decades, groundwater has become an important source of freshwater throughout the world. It provides about 50% of the current global domestic water supply, 40% of the industrial supply, and 20% of water use in irrigated agriculture (World Water Assessment Program, 2003). It has been estimated that global groundwater depletion increased from 126 (±32) km3 year–1 in 1960 to 283 (±40) km3 year–1in 2000 (Wada et al. 2010). Groundwater modeling is an important tool to design groundwater management strategies particularly in the areas where hydrological cycles are predicted to be accelerated under climate change (Singhal and Goyal, 2011). In previous three decades, numerous numerical modeling software have been developed and used globally such as finite element subsurface FLOW system (FEFLOW) (Diersch, 2005), groundwater modeling system (GMS) (Anon,
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