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groundwater manual for reference
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1. Security Classification
Unclassified
2. Distribution Restricted 3. Document (a) Issue 01
(b) Revision & Date
4. Report / Document Type
Technical Report
5. Report / Document No
NRSC-RSAA-GSG-MARCH 2015-TR-
6. Title Concepts of ground water prospects mapping for Rajiv Gandhi National Drinking Water Mission Project **7. Collation Pages: 57 Figures: 06 Tables: 04 References
Ministry of Drinking Water and Sanitation, New Delhi
14. Date of Project Initiation
December 1999
15. Date of Publication March 2015 16. Abstract (with Keywords) : This is the condensed version of manual tells about the concept of ground water prospects mapping prepared under Rajiv Gandhi Nation Drinking Water Mission Project for identification of potential zones for ground water occurrence and suitable locations for constructing the recharge structures using remote sensing and geographic information system.
Groundwater is a major source for all purposes of water requirements in India.
More than 90% of rural and nearly 30% of urban population depend on it for
drinking water. It accounts for nearly 60% of the total irrigation potential in the
country, irrigating about 32.5 million hectares. The dependency on the ground
water is expected to increase in future due to increase in population.
water requirements according to National Water Policy is about 43.2 million
available in the aquifer zones below the zone of water level fluctuation is about
1081.2 million hectare meters. The dynamic resource gets replenished every year
through natural recharge, so that the balance is maintained.
However, the occurrence and distribution of the ground water is not uniform
throughout the country and varies significantly based on geology, rainfall and
geomorphology. India is a vast country comprising of diversified geology,
topography and climate. The prevalent rock formations range in age from
Archaean to Recent and vary widely in composition and structure. Similarly, the
variations in the landforms are also significant. They vary from the rugged
mountainous terrains to the flat alluvial plains of the river valleys, coastal tracts
and the aeolian deserts. The rainfall pattern also shows similar region wise
variations. The topography and rainfall virtually control runoff and ground water
recharge.
The high relief areas of the northern and north-eastern regions occupied by the
Himalayan ranges, the hilly tracts of Rajasthan and peninsular regions with steep
topographic slope, and characteristic geological set-up offer high run-off and little
scope for rain water infiltration. The ground water potential in these terrains is
limited to intermontane valleys.
arid tracts of Rajasthan, the degree of mineralization in ground water is rather high
and salinity hazards are not uncommon. The salinity hazards in ground water are
also noticed in the inland areas of Punjab, Haryana, Uttar Pradesh, Rajasthan and
Gujarat, generally confined to arid and semi-arid tracts.
Ground water being a hidden resource is often developed without proper understanding of its occurrence in time and space. The total number of wells in the country has gone up from about 4 million in 1951 to more than 15 million at present, and the number of energised pump sets in the same period have grown from initially negligible to about 12 millions (Press Information Bureau, Govt. of India). Most of these wells are drilled indiscriminately based on the requirement. As a result, many a times, the wells have gone either unproductive or became failures causing financial loss to the users. In the over-exploited zones, the wells are getting dried up in due course of time. In some of the areas, the situation is so serious that there is a scarcity of water even for drinking purposes. In these areas, the ground water needs to be recharged artificially, as the natural recharge is not sufficient, to augment the resource and maintain the water table. On the other hand, the resource is not yet exploited to the optimum level in many areas in the country.
In many States, Public Health Engineering Departments (PHEDs) and Panchayath Raj Engineering Departments (PREDs) are engaged in rural drinking water supply. Potable water is provided to the rural population by these departments mainly through hand pump wells and piped water supply schemes by pumping of water from bore / tube wells and connecting to overhead tanks / ground level reservoirs. In water scarcity areas, water is also supplied to villages through tankers during summer season. These departments are having well established drilling and maintenance units supported by experienced hydrogeologists for selection of sites for drilling. However, scientific database on ground water, which facilitates identification of prospective ground water zones for systematic selection of appropriate sites for drilling, is not available in majority of the cases. They do not have enough time to select the sites by conducting systematic hydrogeological studies in the area followed by site specific investigations in the favourable zones.
Surface investigations and subsurface investigations will be carried out for end to end exploration activity.
i. Surface investigation
provides information on the parameters such as rock types, geological structures, landforms and recharge conditions which control the occurrence and distribution of ground water. Once these factors are precisely known, it is possible to understand the ground water regime better by visualizing the gross aquifer characteristics of the area. Based on the analysis of this data, geophysical surveys can be planned effectively.
to get information on geological structure, rock type and porosity, water content and water quality. The most commonly used geophysical surveys such as ‘the electrical resistivity surveying’ (‘profiling’ and ‘sounding’) is most popular and well established techniques for ground water exploration to know the resistivity of the subsurface hydrogeological condition for pinpointing the locations and depths for drilling bore wells. The other exploitation methods like seismic, gravity and magnetic are very rarely used.
ii. Subsurface investigation The subsurface investigations are comparatively expensive, but impossible to avoid if data on quality and quantity of the groundwater are desired. One or more, small diameter holes are drilled to supply information on the groundwater level and the geological substrata. The results of the drilling and sampling of material make it possible to establish a litho log with information from the different strata. It is also possible to take groundwater samples for chemical analysis. Any number of geophysical logs can be used, depending on the geological conditions, such as the spontaneous potential, resistivity logging, acoustic log and temperature logs.
The last and perhaps the most informative step in an investigation for a groundwater well is a pumping test. Pumping tests can be either short time (for information from the vicinity of the hole) or long time (for information from larger area). Geological formations have distinct physical properties that affect the flow of groundwater and determine the yield of a well. These properties include; − Effective porosity – the percentage of interconnected space in rock and soil that can contain water.
the geophysical surveys is quite cumbersome. Complex instruments and technical man power are required for conducting the survey. Lot of logistic support is also involved. The technology is not accessible to the common users, particularly to the private individuals who constitute the major section of ground water consumers in the country. Hence, it is not feasible to carry out these surveys at each and every place. Once the prospective zone is identified through other methods, the geophysical surveys can be conducted only to pinpoint the location for drilling the well in the prospective zone.
There is an inherent linkage between development and management of ground water resources. For an effective supply side management, it is essential to have full knowledge of hydrogeological controls which govern the yields and behaviour of ground water levels under abstraction stress. The effects of ground water development can be short term and reversible or long term and quasi-reversible which require a strong monitoring mechanism for scientific management. There is a need for scientific planning in development of ground water under different hydrogeological situations and to evolve effect management practices. Demand driven development of ground water resources by different user groups without any scientific planning and proper understanding of the behaviour of local ground water regime, leads to sharp depletion of the resources and also degradation of quality. Signals of mismanagement of ground water resources are seen in areas where ground water extraction rate has exceeded the natural recharge. Ground water management has become the foremost challenge for the Organizations dealing with ground water in India. The activities of the Organizations and policies affecting ground water need to reflect the priority issues with the overall objective to provide water security through ground water management.
Therefore, a comprehensive and a reliable scientific database on ground water for the entire country is a pre-requisite for proper management of ground water resource in the areas where it is over-exploited and for planning its optimum development and effective utilization in hitherto unexploited areas.
I. Background
The Government of India (Department of Drinking Water Supply), through the Rajiv Gandhi National Drinking Water Mission (RGNDWM) supplements the efforts of the State Governments to accelerate the pace of coverage of drinking water supply to Non Covered (NC), Partially Covered (PC) and quality affected rural habitations with mission approach by providing Central assistance under the Accelerated Rural Water Supply Programme (ARWSP). As per the estimation of the RGNDWM, there are nearly 4.4 lakh NC and PC habitations spread over in different States of the country, as on 01-04-1998, accounting for more than 30% of the total habitations. Taking this as a serious issue, the Govt. of India has included the supply of drinking water to these habitations in a time-bound-period in the ‘common minimum programme’ of the central Government.
As part of supplying the drinking water to these habitations, the RGNDWM has approached the NRSC/ISRO to provide scientific data on drinking water sources (ground water source) to the non-covered (NC) and partially-covered (PC) habitations, within the radius of 1.5 km in case of plain areas and within 100m elevation in case of hilly terrain, using the satellite data in a time bound period. The NRSC / ISRO has agreed to provide the same and taken up the project on priority basis. Later it is decided to cover all the habitations including the NC and PC for creating ground water database.
The objective of the project is mainly to provide the ground water prospects
information on 1:50,000 scale” by combining the information derived from satellite
data with conventional ground hydrogeological surveys for entire country. The
project work was commenced in the year 1999. It has been planned to implement
the project work throughout the country in a phased manner. In Phase-I six states
namely, Andhra Pradesh (eastern part), Chhattisgarh, Karnataka, Kerala, Madhya
Pradesh & Rajasthan were covered. In Phase-II four more states namely; Gujarat,
Himachal Pradesh, Jharkhand and Orissa were taken up for preparing the maps.
Convinced by the overwhelming success of this project in ten states, covering
nearly 50% of the country, the Ministry has extended it to the rest of the country
under Phase-III & IV programme. Accordingly NRSC has completed the
groundwater prospects maps for the entire country. Presently the GOI has
renamed this programme as National Rural Drinking Water Programme
(NRDWP).
The framework in which the ground water occurs is as varied as that of rock types, as intricate as their structural deformation and geomorphic history, and as complex as that of the balance among the lithologic, structural and geomorphic parameters. The entire column of subsurface acts as a three dimensional framework of groundwater conduits / aquifers and ground water barriers/ confining units. Finally, the ground water prospects in the unit depend on the availability of the recharge which in turn depends on the prevailing hydrological conditions. Hence, the ground water regime can be defined as a combination of four factors, i.e. 1) Lithology, 2) Landform, 3) Structure, and 4) recharge conditions. The
b. Hydrogeomorphological units The combined units in which the Lithology, landform, structure and recharge conditions are unique are called ‘hydrogeomorphic units’. They are considered as three dimensional homogenous entities with respect to hydrogeological properties and the recharge condition. In other words, they are treated as the aquifers. The ground water prospects are expected to be uniform in a hydrogeomorphic unit. However, some amount of heterogeneity may exist at micro level and it can be brought out only through large scale studies. It is basically depended on the scale of mapping. The degree of heterogeneity and the resultant variations in the ground water condition need to be accounted depending on the scale of study.
In order to study the ground water prospects of a hydrogeomorphic unit, inventory of the controlling factors i.e., rock type, landform, structure, and recharge condition, by which the hydrogeomorphic unit is made up of, has to be done and their hydrogeological characteristics need to be evaluated.
c. Relevance of Satellite Data
The hydrogeomorphic unit is evolved from the original rock formation due to structural, geomorphological and hydrological processes. These processes and the resultant changes are manifested on the surface. Satellite imagery is the best data base where the information pertaining to all these parameters is available in an integrated environment. Based on the interpretation of satellite imagery in conjunction with limited ground truth information, the extraction and mapping of spatial distribution of the rock formations, landforms, structural network and hydrological conditions can be done accurately. They can be better studied and understood in association with each other. This is not possible through
conventional ground surveys. Apart from this it takes lot of time and energy there by becoming the ground water survey costly. The geology maps showing rock types and major structures prepared by Geological Survey of India are being used for gross estimation of the resource and its distribution. Particularly, the data on the land forms, geological structures and recharge conditions are not at all available.
For example, an area occupied by granite gneisses intruded by dolerite dykes and cut across by a number of faults and lineaments, it is possible to draw conclusions on – the dolerite dykes act as barrier for movement of groundwater, whereas the lineaments/faults which cut across them act as conduits for groundwater movement. The weathered zones within the granite gneisses contain limited quantities of groundwater. The water bodies (tanks) which are seen on the imagery as black patches not only provide irrigation facility in the area but also contribute for recharge to groundwater. Thus, by providing appropriate hydrogeological information the satellite data facilitate proper identification and mapping of prospective groundwater zones. The satellite data by providing spatial distribution of irrigated crop land as bright red patches are not only useful in calculating where and how much of groundwater is being tapped for irrigation but also in classifying the entire area into over-developed, under-developed, optimally developed and undeveloped zones, indicating the status of groundwater development. Analysis of multispectral high resolution data clearly depict minor faults and lineaments indicated by slips/offsets and gaps and in the dyke ridges. These faults/lineaments act as conduits for movement of water below the ground and form the prospective groundwater zone. With the help of field boundaries, cart tracks, stream courses and other reference points, these zones can be more accurately demarcated on the ground. In addition, some minor fractures originating from these major faults/lineaments, and passing through water bodies (tanks) which also form potential sources for tapping drinking water to the nearby village could be delineated.
The methodology has been developed keeping in view the concept discussed above. It is basically a systematic procedure evolved to prepare a ground water prospects map using satellite data and GIS techniques in conjunction with limited field work. Various steps involved in the preparation of ground water prospects maps are furnished as a flow chart in Fig.1. The total methodology can be divided into two main parts. The first part deals with the delineation of hydrogeomorphic
a. Concept of Thematic layers for mapping As the occurrence and movement of ground water is a function of lithological, structural, geomorphical and hydrological parameters, each parameter exercises its control over the quality and quantity of ground water. Hence, a complete data on the parametres is a pre-requisite to understand the ground water regime and map the prospects properly. Missing of one element also leads to erroneous conclusions. To make sure that all the relevant data pertaining to each and every parameter are systematically studied and considered, it is proposed to generate the data on every parameter of all the five themes as a separate layer in an orderly manner. Different parameters in each theme that are to be considered for mapping are identified. Accordingly, all the rock formations, geological structures, landforms and recharge conditions occurring in the country are classified in to various types and an exclusive classification system for each of these themes has been evolved for this purpose. All the layers should be prepared in such a way that the contents in each map in all the four sides should match with the contents of the adjacent map layer in all respects. Finally, it should be possible to generate a seamless mosaic for the entire state/country.
Base map layers: It consists of four categories of information in four separate layers (fig-2). They are – a) Administrative units (maps covering areas that form a part of single administrative unit may not have this coverage) b) Settlements, c) Road network, d) Railway lines (maps covering areas where railway lines are not present may not have this coverage). Total number of coverage may vary depending on the study area. The administrative units are mapped as polygon coverage, the settlements are mapped as point coverage, the road net work and railway lines are mapped as separate line coverages. Fig-
Road network Coverage
Railway lines Coverage
Administrative units Coverage
Settlements
Lithology layer: All the rock formations occurring in the study area are mapped in a single layer are represented as polygon features and are annotated with respective numeric codes as per the RGNDWM rock types classification system (fig-3). While preparing the lithology layer based on the interpretation of satellite imagery, the existing geological / hydrogeological maps and literature need to be consulted. It helps in understanding general geological setting of the area and different rocks types that occur or likely to occur in the area. Where previous maps and literature are not available and differentiation of rock types is very difficult / not possible, a reconnaissance field visit will be useful. With this “priori knowledge”, the satellite imagery has to be studied to correlate the different image characteristics with different rock types. Where contrasting rock types are occurring, the boundaries can be seen very clearly on the satellite imagery with different colours / tones or landforms. In other cases, complementary evidences have to be considered to demarcate the boundaries between different rock types. Where previous geological maps on 1:50,000 scale are available, the same may be considered. However, the maps need to be modified / edited and updated incorporating additional details that can be interpreted from satellite imagery. Fig-
Structural layers: The geological structures occurring in the area are treated as two major categories for mapping- i) faults, shear zones, thrusts, fractures, dykes, veins, etc., which occupy an area acting as conduits and barriers for the movement of ground water and ii) the structural elements such as bedding, schistocity / foliation, folds, etc., which can be represented as attributes to either
assemblage of different landforms corresponding to each rock type. Sometimes a single geomorphic unit / landform may exits in one lithologic unit and vice versa. It is to be noted that wherever the lithological and geomorphological boundaries are common, they should be made co-terminus.
The geomorphic units/ landforms which are further classified into shallow, moderate and deep categories based on their depth of weathering, thickness of deposited material, etc have to be verified on the ground by observing the nala / stream cuttings, well sections, etc. However, the contacts between shallow, moderate and deep categories are to be treated as gradational.
Apart from dissection in the hills, slope-form also plays an important role in ground water occurrence and flow in the hilly/ mountainous terrain. Therefore, the hills with concave slope, especially in the lower reaches, have to be delineated as separate units wherever possible, e.g. ‘highly dissected structural hills with concave slope (SHHc),’ ‘moderately dissected denudational hills with concave slope (DHMc),’ etc. In hilly terrains, since ‘mountain’ terminology is not used in the geomorphic classification system, a note need to be included in the layer and in the corresponding ground water prospects map at the bottom of the upper part of the legend that ‘the area forms part of the (local name of the range) Himalayan mountain range.’ Fig-
Hydrology layers: There are 7 items to be considered for mapping in hydrology
theme (fig-6). They are – 1) Drainage, 2) Water bodies, 3) Canals, 4) Rainfall
data, 5) Irrigated areas, 6) Springs, 7) Wells. The drainage is represented as line
as well as polygon features, the water spread area of the water bodies is
represented as polygon features whereas the bunds are marked as line features,
the canals are represented as line features, the rain fall data is considered in the
form of rain gauge station with average amount of rainfall and marked as point
feature, the irrigated area as polygon feature, the springs and wells are
represented as point features. Each item is mapped as separate layer using
appropriate symbols and colours. The number of layers may vary depending on
the availability of items in the study area.
In the drainage layer, all the rivers/streams (entire drainage up to first order
streams) both perennial and ephemeral are to be mapped. In case of hilly areas
and highly dissected terrain where drainage density is very high, some first order
streams can be omitted to reduce the clumsiness in the map. The total drainage
from toposheet may be taken first and then some of the 1 st^ order drainage may be
omitted over the hills and high relief areas, but none of the 2 nd^ order streams should
be omitted. Along major rivers and streams where changes in the river / stream
courses are more common, necessary corrections in the drainage courses may
be made by referring the satellite image. Hanging drainages lines, if any, should
be connected using image control.
In alluvial terrain, the ephemeral and perennial streams are to be shown
separately with different symbols. In hilly terrains, the snow-covered areas as
seen on the satellite image (preferably of lean period) have to be demarcated and
shown in geomorphological layer. In the final ground water prospects map, in the
‘map unit’ column of the legend, such areas will be represented as SC, and in the
‘remarks’ column, it will be written as “it acts as recharge zone.” No ground water
structures required to be suggested in this unit. Satellite image is the primary
source of data for mapping water bodies. However, the boundary of water spread
area has to be taken from SOI toposheet and to be used for delineating perennial
and ephemeral catagories. Canal network is to be mapped basicallyfrom SOI
