Ri-Bhoi and West Khasi Districts
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क� द्र�यू�म भ जल बोड셍 जल संसाधन, नद� �वकास और गंगा संर�ण मंत्रालय भारत सरकार Central Ground Water Board Ministry of Water Resources, River Development and Ganga Rejuvenation Government of India AQUIFER MAPPING REPORT Parts of Ri-Bhoi & West Khasi Hills Districts, Meghalaya उ�र� पूव� �ेत्र, गुवाहाट� North Eastern Region, Guwahati AQUIFER MAPPING AND MANAGEMENT IN PARTS OF RI-BHOI & WEST KHASI HILLS DISTRICTS, MEGHALAYA CONTENTS Page No. 1. INTRODUCTION 1 2. MAJOR GROUNDWATER ISSUES IN THE AREA 1 3. MANIFESTATION AND REASONS OF ISSUES 1 - 2 4. AQUIFER GEOMETRY AND CHARACTERIZATION 2 - 3 5. AQUIFER MANAGEMENT PLAN 3 – 4 MANAGEMENT STRATEGIES MANAGEMENT PLAN ANNEXURE9 Maps 5 - 19 Map 1 Administrative map Map 2 Soil map Map 3 Isohyet map Map 4 Drainage map Map 5 Geological map 1 Map 6 Depth to water level map (Pre-monsoon), Shallow aquifer Map 7 Depth to water level map (Post-monsoon), Shallow aquifer Map 8 Location of exploratory boreholes Map 9 Bore hole logs showing disposition of aquifer Map 10 Distribution of conductivity in ground water Map 11 Distribution of iron in ground water Map 12 Distribution of pH in ground water Map 13 Location of VES point Map 14 Location of springs Map 15 3 D Aquifer disposition Table 20 - 61 Table 1: Litholog Table 2: Aquifer Parameters Table 3: Aquifer wise water quality data Table 10 Water Level Monitoring Data Table 11 Rainfall data Table 12 VES/TEM Data FIELD PHOTOGRAPH 62 - 66 2 AQUIFER MAPPING AND MANAGEMENT IN PARTS OF RI-BHOI & WEST KHASI HILLS DISTRICTS, MEGHALAYA 1. Introduction An area of 1000 sq km falling in parts of West Khasi Hills district (650 sq. km) and parts of Mairang Block under West Khasi Hills district (350 sq. km) of Meghalaya was covered as per the Annual Action Plan 2012-13 and 2013-14 of Central Ground Water Board, North Eastern Region, Guwahati. The study area falls under Survey of India Toposheet No. 78O/9 & 78 O/13 lies between North latitudes 25º45/00// & 26º00/00// and East longitudes 91º30/00// & 92º00/00//. The study area lies in the central part of the Meghalaya. The study area is shown in Map No.1 As per census 2011, Ri-Bhoi had population of 258,840 of which male and female were 132,531 and 126,309 respectively. As per census 2011, Mairang Block had population of 82437 of which male and female were 41394 and 41043 respectively. The area under study is hilly in nature. It includes a series of hill ranges, which gradually slopes towards the North and finally joins the Brahmaputra Valley. Central part of the area is traversed by hill ranges which run parallel from East to West with an average altitude of about 1400 meters. The area is having exposures of Archaean Gneissic Complex, meta-sedimentary of Shillong Group, Granitoids and Recent sediments.The assemblages of different formations play important role in controlling occurrence, distribution and movement of ground water. 2. MAJOR GROUNDWATER ISSUES IN THE AREA Major groundwater related issues found in the study area are low stage of ground water development and presence of high iron content both in shallow and deeper aquifer in some pockets. Power supply is irregular and in places non-existent. 3. MANIFESTATION AND REASONS OF ISSUES To understand water level behavior in the area 12 dug wells and 16 bore wells ( CGWB EW / OW) were monitored. Ground water occurs under the phreatic conditions in the weathered formation and in semi-confined conditions in the fractured zones. Pre-monsoon depth to water level in the shallow aquifer ranges from 0.3 to 4.97 m bgl while post-monsoon depth to water level ranges from 0.8 m to 3.58 m bgl. Water level recorded from deeper aquifer shows pre- monsoon depth to water level ranges from 2.35 to 11.21 m bgl while post-monsoon period depth to water level ranges from 1.09 to 5.42 m. bgl. The hydrographs of this ground water monitoring 3 welll shows no significant rise or fall in the water level trend. Most probable reason for this is groundwater development in the study area is almost negligible. The details of key wells have given in table no-10. The study area experiences different types of climate ranging from tropical climate in the areas bordering Assam to the temperate climate towards south. The study area mainly receives rain mainly from Southwest monsoon from June to September. The average annual rainfall in the area is 1900 mm with an average of 190 days of rainfall. The average relative humidity in a year is 70 % in the study area. Infrastructure for irrigation in the study area is very meager. In the study area falling in Ri-Bhoi district out of the total net sown area of 5917 ha, 5911 ha is covered under surface water irrigation. Minor irrigation schemes involving flow and lift irrigation schemes are in vogue in the area. Flow irrigation involves diverting streams and rivulets and irrigating the fields by gravity. In the lift irrigation schemes, water is lifted from the rivulets or streams at convenient places to irrigate the fields in the adjoining areas. But, study area falling in the Mairang block where out of 2082 ha net sown area only 591 ha has been brought under surface water irrigation till date. A detail of the irrigation area in the study area is shown below in table. District Covered area Net Sown area Net irrigated area Non-irrigated area ( in hectare) ( in hectare) ( in hectare) ( in hectare) Ri-Bhoi 65000 5917 5911 6 West Khasi 35000 2082 591 1491 Total 60000 7999 6502 1497 Piped water supply schemes and spot source of water schemes are the main source of water supply in the area. Spring water also play a major role to meet the water requirement of the people especially in the rural areas settled in the hill top. Discharges of the springs are found to vary between 1 – 40 liter / minute. Dwindle discharge, especially in the winter season, in the river source and population growth creates drinking water shortage in some villages. To understand ground water quality 12 samples from shallow aquifer 16 samples from deeper aquifer and 27 samples from springs were collected and analised in the Regional chemical Laboratory of CGWB, NER. .The pH of the Ground water varies from 6.6 to 8.8. The value of EC varies from 52 to 662 µs/cm at 250 C. Except iron rest of the quality parameters are within permissible limit. 4 In the western part of the study area covering Pathrkhamma, Warmawsaw etc. villages where both shallow and deeper aquifers as well as in the springs iron content is more than permissible limit. Maximum iron content recorded from dug well is 1.11 mg/ lt, from springs 2.24 mg/ lt and in the exploratory bore hole at Warmawsaw as high as 8.08 mg/ lt. Location of higher concentration of iron in groundwater is depicted in Map (annexure). Summary of results of chemical analysis data showing concentration of iron in groundwater is shown in table below The area under study is hilly in nature. It includes a series of hill ranges, which gradually slopes towards the North and finally joins the Brahmaputra Valley. Central part of the area is traversed by hill ranges which run parallel from East to West with an average altitude of about 1400 meters. Part of two major basins which are Brahmaputra and Meghna covers the area. Drainage pattern of annular, trellis, sub-dendritic types are found in the area which indicates both topographic and structural control. The important rivers in the study area are Umtrew, Umsiang, Umran and Umiam rivers. 4. AQUIFER GEOMETRY AND CHARACTERIZATION The main objective of the study is to delineate the horizontal and vertical disposition of aquifer as well as to study the aquifer character. In this connection 55 key wells including existing CGWB monitoring stations (Dug well) and springs were monitored in different season. Locations of the monitoring stations are shown in Map No-6. To know the aquifer disposition in the study area, exploratory wells data, VES data available with CGWB were utilized. CGWB has drilled 26 EWs within a depth range of 61 to 239 m bgl. It can be deciphered from the lithologs that two aquifer group systems occur in the area. First aquifer consisting of top soil and weathered granite upto 50 m depth and the second aquifer consisting of fractured granite / quartzite upto 239 m bgl (explored depth). Formation and depth wise fractured zone encountered , the second aquifer, is given below in table. Productive zones (fractures encountered) Discharge 0 to 50 50 to 100 100 to 150 150 to 200 200 to 250 (in lps) m bgl m bgl m bgl m bgl m bgl Archaean gneissic complex (Granite Gneiss) 0 to 2 F 0 to 2 F 0 to 2 F 0 to 2 F 1 F 0.43 to 12 Shillong Group (Quartzite/ phyllite) 0 to 2 F 1 F 1 F 0 to 2 F Not explored 2.53 to 10 Granite Pluton (Nongpoh Granite) 0 to 2 F 0 to 3 F 0 to 4 F 0 to 2 F Not explored 0.03 to 8 5 The deep tube wells constructed by CGWB show yield of the wells ranges from 18 to 43 m3/hr for a drawdown of 1.39 to 40 m. In general discharge in this gneissic complex is greater than the discharge found in the Nongpoh Granite.