Impact of Coastal Salinity Ingression and Assessment of Htl Ingression and Regression over a Decade in the Bhavnagar Taluka: a Gis Based Vulnerability Assessment

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IMPACT OF COASTAL SALINITY INGRESSION AND ASSESSMENT OF HTL INGRESSION AND REGRESSION OVER A DECADE IN THE BHAVNAGAR TALUKA : A GIS BASED VULNERABILITY ASSESSMENT

ABSTRACT

Climate change can have many impacts upon human societies. The impacts will vary from region to region. These impacts include sea-level rise, melting of mountain glaciers, floods, droughts, changes in storm intensities, changes in biological variables that have impacts upon human societies. This paper is however concerned with the ‘impact of sea level rise’ causing ‘salinity ingression’ in Bhavnagar Taluka; a part of Gulf of Cambay, Gujarat. Over last two and a half decades, a process of rapid sea water ingress (at some places as deep as 10–15 km. from the seacoast) is observed along the coastal belt of Gujarat. The major objective was to study the decadal changes in salt affected lands as well as agricultural lands. The change in High Tide Line along the study area was also studied using the same datasets of two periods. The resulted salinity ingress in the study area is mainly due to the large scale ground water extraction for agriculture as well as industrial purposes combined with intensive mining activity. Remote sensing data can be used in the objectives concerned with the monitoring changes in surface phenomena over time. In this study IRS LISS III data representing two different tidal conditions of the period 2000-2010 were used to compute and analyze the salinity ingression over a decade. The results indicate that there has been an increase in the ingress of sea water into the agricultural fields. This is one of the strong reasons of increasing soil salinity of coastal areas along the Bhavnagar Taluka. At some places in the study area it was also found that salinity is increasing not only because of natural causes but there is a big human intervention in it, the prohibition of which is necessary for long term coastal resource management. This sort of study could help in the monitoring of sea ingress and impact of salinity in an area over the successive periods.

INTRODUCTION:

The word salinity can be described as the saltiness i.e. the dissolved salt content of any water body. It includes levels of different salts such as sodium chloride, magnesium and calcium sulfates, potassium sulfate and bicarbonates. In oceanography, it has been traditional to express salinity not as percent, but as parts per thousand (‰), which is approximately grams of salt per kilogram of solution; other disciplines use chemical analyses of solutions, and thus salinity is frequently reported in mg/L or ppm i.e. parts per million. The typical seawater has a salinity of 35 ppt or 35‰. The average density of seawater at the surface is 1.025g/ml. Seawater is denser than freshwater because of the added weight of the salts (Source: Wikipedia). Salinity in ground water can be broadly categorized into two types, i.e. (a) Inland Salinity and (b) Coastal salinity. (a) Inland salinity in ground water is prevalent mainly in the arid and semi arid regions caused mainly due to practice of surface water irrigation without consideration of ground water status. (b) Coastal salinity is mainly caused by individual or combined effects of inherent salinity, tidal effect, irrigation by saltwater and by seawater intrusion due to flooding and extensive pumping.

Salinity ingress has been a typical environmental issue seen largely in coastal region of maritime nations. India is no exception to this. This problem has conspicuously been seen in the Upper Western Coastal Region (UWCR) of India. For long, salinity ingress has been a curse in Gujarat. Central Ground Water Board (CGWB) has carried out extensive studies which indicate that intrusion of sea water would continue because of over-exploitation of ground-water for drinking and agriculture purposes. Farmers in saline areas survive with rain-fed agriculture, growing 'jowar' and horticulture crops like chickoo...
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