The Gujarat Water Supply and Sanitation Board (GWSSB) of the Govt. of Gujarat and the Government of Netherlands have entered into an agreement to implement what is known as the Ghogha Regional Water Supply and Sanitation Project in Bhavnagar Dist., Gujarat State

Objective

The objective of the project is to provide 78 problem villages falling in parts of Ghogha, Bhavnagar and Talaja talukas with perennial, sustainable and cost effective water supply and sanitation facilities. Ground water has been identified as a reliable source for drinking water for 90% of the villages in the project area and its sustainability to be strengthened by later artificial recharge and water resources management programmes

Description

Indian Resources Information and Management Technologies Pvt. Ltd. (IN-RIMT), Hyderabad have been retained as consultants by the IWACO, Netherlands for supervising the entire operations right from the inception stage of the project involving hydrogeological surveys aided by surface geophysical surveys, satellite remote sensing techniques for preparation of hydrogeomorphological map of the project area, selection of sites for drilling and litho-logging of boreholes followed by pump tests.

The project area is mainly underlain by Deccan Trap (449 km2) in the western and southern portions, coastal Alluvium and other Quaternary and Tertiary formations in the northern half of the coastal tract (165 km2) adjoining the Gulf of Khambhat. By using satellite remote sensing techniques precise delineation of hard rock and soft rock areas, hydrogeomorphological units for groundwater targetting and groundwater irrigated areas was made.

Groundwater occurs mainly under water table conditions both in Deccan Trap and sedimentary rocks. Feeble semi-confined conditions have been noticed locally along joints and fractures in the trap and when the aquifers are underlain by thick layers of clay in the sedimentaries. Yields of 50m3/day to 150m3/day from dug wells have been reported in the trap area. In the soft rock area the yields range from 50m3/day to 350m3/day. The bore wells/tubewells yield from 150 m3/day to 700 m3/day. The water table is 10-25 metres below ground level.

In the coastal area, generally the sedimentary aquifers are found to be saline in nature due to sea water intrusion rendering water unsuitable for drinking purposes. In contrast, the quality of groundwater in the hard rocks is good, although in a few villages a higher incidence of fluoride has been reported.

Drilling operations / under the supervision and direction of IN-RIMT team of hydrogeologists commenced in April 1999. (4th mission) and was completed in all the villages (except those where the existing open wells were found to meet the drinking water requirements) by the third week of February 2000. (5th mission) In the hard rock areas (basalts) a total of 186 boreholes were drilled while in the coastal sedimentary tracts 10 exploratory boreholes were drilled by employing DR rig. As the quality of groundwater in this area was saline due to sea water intrusion into the aquifers, these exploratory boreholes were drilled mainly to see if any freshwater aquifers occurred at deeper levels below the overlying thick clay beds. The depths of boreholes in the basalt area ranged from 60.0m to over 170.0m while in the sedimentary areas the boreholes were limited to depths of 60.0 to 90.0m only.

Yields ranging from 25 lpm to as high as 1450 lpm were obtained during drilling operations from the basalts. It was found that boreholes drilled along lineaments/faults, and in highly fractured rocks generally gave higher yields. A success rate of 35-40% was achieved at the end of drilling operations in the first phase. At the same time 25 villages were shortlisted where it is proposed to take up a second phase of drilling. These villages are those where boreholes did not yield adequate quantities of water in the first phase.

Yields ranging from 25 lpm to as high as 1450 lpm were obtained during drilling operations from the basalts. It was found that boreholes drilled along lineaments/faults, and in highly fractured rocks generally gave higher yields. A success rate of 35-40% was achieved at the end of drilling operations in the first phase. At the same time 25 villages were shortlisted where it is proposed to take up a second phase of drilling. These villages are those where boreholes did not yield adequate quantities of water in the first phase.

Drilling operations taken up in the coastal area has proved that there was no possibility of getting fresh water from deeper aquifers and as such only dugwells may have to be constructed to tap sweet water from the shallow water table aquifers.

Pumptests are being conducted on all the successful borewells for determining the safe yields. Analysis of data of pump tests conducted so far has shown that safe yields from 20m3/day to as much as 3840 m3/day could be obtained from the successful boreholes drilled in the basalts. The quality of ground water in terms of TDS ranged from as low as 360 ppm to as much as 2840 ppm