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ABSTRACT
Sabarmati river basin is one of the 24 river basins on west coast of India covering the States of Rajasthan, Madhya Pradesh and Gujarat and catchment area extends over 21,674 sq km. This river originates in the Aravalli mountains and drain in to Gulf of Khambhat. The hydrological model used in the present study is Soil and Water Assessment Tool (SWAT) with Arc View GIS interface. SWAT is a river basin, or watershed, scale model developed to predict the impact of land management practices on water, sediment, and agricultural chemical yields in large, complex watersheds with varying soils, land use, and management conditions over long periods of time. The study adopts a GIS based distributed runoff model for the watershed to estimate the evapo-transpiration using Penman-Monteith method. The present study is an attempt to quantify the impact of the climate change on the water resources of Sabarmati watershed using a hydrologic model. In this study, Soil and Water Assessment Tool (SWAT) model for watershed (sabarmati) is used for obtaining evapo-transpiration and sediment yield. Daily rainfall, Maximum and minimum temperature data of six years (1998-2005) are used in the study. The weighted average value of parameters such as runoff curve number, surface slope, channel length, average slope length, channel width, soil erodibility factor and other soil layer data are taken for each sub-watershed (HRU) to verify the model. The study is useful to predict evapotranspiration at Dharoi Dam if there is any change in temperature, humidity or watershed management practices with respect to change in land cover or soil erosion which can be monitored on sub watershed basis or mini-watershed basis. SWAT model generate automatically delineate the watershed and 29 mini-watershed was generated. Average yearly (1998 to 2005) evapotranspiration at dharoi dam is estimated by using AVSWAT model.
INTRODUCTION
Evapotranspiration is a collective term that includes all processes by which water at the earth’s surface is converted to water vapor. It includes evaporation from the plant canopy, transpiration, sublimation and evaporation from the soil. Evapotranspiration is the primary mechanism by which water is removed from a watershed. Roughly 62% of the precipitation that falls on the continents is evapotranspired. Evapotranspiration exceeds runoff in most river basins and on all continents except Antarctica (Dingman, 1994). The difference between precipitation and evapotranspiration is the water available for human use and management. An accurate estimation of evapotranspiration is critical in the assessment of water sources and the impact of climate and land use change on those resources. The watershed management is also an integrative way of thinking about human activities on a given area of land (the watershed) that have effects on, or are affected by water. It has recently been widely acknowledged that water is a critical element of poverty in its many dimensions (World Bank 1993, World Commission on Dams 2000, Biltonen and Dalton 2003). The impact of current development activities on environmental degradation and resource depletion and the resulting implications on the social goals of the current and future generations are the growing concerns in recent years. Due to the dependency of mankind on the finite land and water resources for the basic needs, the sustainable development of these resources (viz. land and water) avoiding irreversible consequences, assumes paramount importance. The optimum utilization of these resources requires expert managerial decisions on the suitability of the developmental activities and their scope visa-a-versa, the environmental and ecological preservation of the land unit. A Watershed is considered as a unitary land unit in development and management strategies for the sustainable development programme. Ever increasing pressure of population coupled with poor management of land and water resources is responsible for the tremendous stress on our fragile environment. Hence, accurate and timely mapping, monitoring and assessment of conditions in the watershed area are essential for assessing land and water resources and their optimum utilization for sustainable development. The water and land resources need to be developed, utilized and managed in an integrated and comprehensive manner. Soil and water conservation on a watershed basis can play a decisive role in this strategy for a comprehensive land-water management.
OBJECTIVES OF STUDY
Study is taken up with objective as specified below:
General Objective:
• To setup AVSWAT hydrological model for river Sabarmati and compute the values of evapotranspiration and sediment loading from the basin.
Specific Objectives:
• To build GIS database required for AVSWAT based simulation.
• To setup ARS-AVSWAT hydrological model for the Sabarmati river.
• Validation of the AVSWAT model for evapotranspiration dataset.
• To take and check simulated output for evapotranspiration from sabarmati basin.
STUDY AREA
Sabarmati river is big river in India, It water deficit lies on the west coast of India between latitudes 22°N to 25°N and longitudes 71°E to 73° 30’E, and is spread across the states of Rajasthan and Gujarat. The altitude of area is starting from 762 m above MSL.
PHYSIOGRAPHY: The area is characterised by undulating topography with gentle sloping alluvial plain. The altitude of the area is around 762 m above mean sea level. At few places small rocky hills are observed.
HYDROMETEOROLOGY: The climate may be defined as composite physical state of atmosphere at specified locality for a specified interval of time. It is determined not by a single whether element but by combination of several of them operating simultaneously.
Temperature: The study area is situated in semi arid climatic conditions and hence the temperature reaches up to extreme levels. The temperature generally fluctuates during pre-monsoon to post-monsoon periods and after February temperature progressively rises and by the month of May and June it reaches maximum before onset of the monsoon. On an average maximum temperature reaches about 36.6°C. The study area experiences hot summer from April to June months. The winter period is very pleasant with an average temperature of about 16°C in the month of December/January.
Rainfall: The analysis of annual rainfall data for the period of eight years has been carried out by arithmetical calculations. Based on available rainfall data, the average yearly rainfall for the present study area is computed as about 666.9 mm. The maximum annual rainfall is recorded in the year 2005 as 1031.286 mm. The minimum annual rainfall is recorded in the year 2000 as 393.99 mm. More than 90% of the annual rainfall takes place during the monsoon period between June and September.