Central Ground Water Board  North Central Chhattisgarh Region  Raipur
		WWW.CGWBRaipur.gov.in

Groundwater systems are dynamic in nature and adjust continually to short term and long term changes in climate, groundwater withdrawal and land use. Water level measurements from observation wells often called ‘ groundwater monitoring’, provide vital and much needed information about the hydrologic stresses, the aquifer undergoes and how these stresses affect groundwater recharge, storage and discharge. Long term systematic groundwater monitoring provides essential data needed to evaluate changes in the resource over time, to generate groundwater models and predict trends. These will in turn help design, implement and monitor the effectiveness of groundwater management, protection and conservation programme

Groundwater monitoring as defined by UN/ECE Task Force on Monitoring and Assessment, (1999)is the collection of data, generally at set locations and depths and a at regular time intervals in order to provide information which may be used.

• to determine the state of groundwater both in quantitative and qualitative sense.

• to provide the basis for detecting trends in space and time, and

• to enable the establishment of cause-effect relationships.

A groundwater monitoring network is a system of dedicated ground water monitoring wells in a geohydrologial unit at which ground water levels and water quality are measured at pre-determined frequency.

A monitoring cycle is a sequence of related activities that starts with the identification of information needs and ends with the use of information products. A schematic representation of the monitoring cycle for groundwater is given in fig.1. A detailed description of all steps in a monitoring cycle is presented in documents of UN/ECE Task Force on Monitoring and Assessment (UN/ECE TFMA 1999 and 2000) and is beyond the scope of this discussion here. It would suffice to mention here that each of the steps described above contribute significantly to plan, formulate and implement a sound groundwater management policy.

The design of an optimal network layout reflect the entire hydrogeological system of the area under consideration. The network provide long term information on the different aquifers being developed. Information on shallow aquifers tapped by open wells, deeper multi-layer aquifers tapped through open dug wells/dug cum borewell/borewell/tube wells and ground water development issues (declining water levels, rising water levels, coastal salinity, water logging in irrigated areas, ground water pollution etc) should be considered in the network design.

A minimum network should include a number of ground water monitoring stations in the recharge area, run off and discharge area, for each of the aquifer system within the considered drainage/administrative units. Since the ground water monitoring networks are of particular socio economic importance to the State and country, it is essential that all problems related to drinking water, irrigation, health and industrial demands of ground water are prioritised during the network design. It has to be kept in mind that the overall objective of the monitoring network is for understanding the dynamics of the ground water system, trends in ground water fluctuation so as to assess the total ground water resource within the reservoir that can be safely harnessed. Other requirements of the network are for understanding the ground water dynamics, flow patterns, recharge- discharge relationship etc.

Data requirement and availability of budget should guide the network density and frequency of monitoring. It has to be always remembered, that the establishment of monitoring stations is less expensive as compared to the long- term cost of regular data collection and maintenance and regular upgrading of the monitoring station. Authentic data can emerge only from networks, which are not starved of funds nor have shortfall of manpower.

Decisions made about the number and locations of observation wells and piezometers are crucial to any water-level data collection program. Ideally, the sites chosen for an observation well network will provide data representative of various topographic, geologic, climatic, and land-use environments. Decisions about the areal distribution and depth of completion of piezometers also should consider the physical boundaries and geologic complexity of aquifers under study. Water level monitoring programs for complex, mulitilayer aquifer systems may require measurements in nested piezometers completed at multiple depths in different geologic units. Large, regional aquifers that extend beyond State/basin boundaries require a network of observation wells distributed among one or more States. If one of all the purposes of a network is to monitor ambient ground- water conditions, or the effects of natural, climatic- induced hydrologic stresses, the observation network will require dedicated piezometers that are unaffected by pumping, irrigation, and land uses that effect ground-water recharge.

The basic principles for the location of monitoring wells can be summarized as follows :

• The location of the observation monitoring wells in terms of sites, depth, design (single or nests) should be based on geo-hydrological, social and economical considerations. Optimal design should include assessment of the density of the network through statistical algorithms which needs to be adjusted based on geo-hydrological conditions and monitoring objectives.

• The site selection for locating monitoring stations should be largely guided by local area conditions. The site selection should ensure that data collected should be unbiased and not subjected to interference from production wells, canals or surface water bodies in the neighbourhood.

• Round the year accessibility and foolproof protection to the monitoring station and the monitoring equipment’s should be considered during site selection.

The monitoring network is one of the most important tools for the management exploration and protection of the groundwater resources

The technical basis of a network consists of a number of observation wells which are either existing wells or are purposely designed piezometers tapping the groundwater body which has to be monitored. The design of a monitoring network is a part of the monitoring cycle, which starts with a request for information and ends with the use of information for various purposes. A generalised scheme showing the portion of the design and implement process of monitoring network in relation to the monitoring cycle is depicted in fig.2.

Ground Water Monitoring is a surveillance system based on sound scientific postulates to observe periodic and long term changes in ground water regime. To meet this objective a network of observation wells, till recently mostly dug wells, has been established throughout the state. The network provides a density and distribution of the stations in the region such that necessary and authentic information on groundwater regime is known. Interpolation of known data sets at different stations help determine the values of data at ungauged points. Establishment of network hydrograph stations commenced in 1969 with establishment of one station per degree sheet. The number of stations were increased both basin wise and district wise to 380 till march 2005. All the observation wells were open dug wells tapping the phreatic aquifers.

Limitations of the open wells: The use of privately owned open wells for water level and water quality observations became an increasing problem. Some tend to go dry before the end of the dry season and others fall into disrepair after being abandoned by their owners. The hydralic connectivity between the aquifer and the well cease to exist.

Monitoring of deeper aquifers: Existing networks were designed mainly for monitoring the shallow phreatic aquifers. It made no provision for monitoring of semiconfined or confined aquifers. Deeper aquifers are being increasingly exploited for rural water supplies, municipal supplies and irrigation. Thus water levels monitored were not truly reflective of the exact ground scenario.

Inaccuracy and infrequency of water level measurement: Data of questionable authenticity seemed to be emanating from the practice of relying mainly on manual measurement of water levels. The assiduity of the observer, missing of true peaks and troughs and the fact that the privately owned well may have been in use prior to the measurement being made, are collectively responsible for this existing scenario.

Groundwater quality sampling: The requirements for groundwater level monitoring and for water sampling for quality monitoring in an observation well are opposite. The level measurement should be indicative of the true piezometric head of the aquifer. This requires that the water levels in the wells should be undisturbed. On the contrary, water sample should represent the quality of the aquifer water in the location. The analogy is that the water in the well should be removed by pumping to enable sampling of fresh aquifer water in the well. The use of privately owned open dug wells for monitoring both water level and water quality carries the risk of flouting one or both the requirements

In 1995 the Government of India and participating states entered into a development and credit agreement with the world bank to implement the hydrology project. The over all delopment objective to which the project aims to contribute is to support major aspects of national water policy thrpugh improvement of the institutions and technical capacity to measure, process and disseminate quantity and quality data on surface water, groundwater and related climatic data.

The inadequacies outlined above have been sought to be removed by the implementation of the HP. The main objective of the groundwater component of the HP is the establishment of required infrastructure to improve the understanding of the groundwater systems both in terms of quantity and quality. The existing observation network of 380 dug wells in Chhattisgarh has been thoroughly reviewed and upgraded by replacing non-representative observation wells with specifically designed 134 pizometers. Piezometers are purpose built observation wells whicha re designed to measure the vertically averaged piezometric head of a single layer. They can’t be used for exploration purpose.

The improved network has been designed to get a good spatial and vertical coverage and representation of all the hydrogeological set ups, considering the present and projected states of groundwater development and water quality variations. As many as 75 piezometers have been provided with digital water level recorders (DWLRs) to ensure measurement of continuous piezometric head at 6 hour interval. The accurate and high frequency data will enhance the technical contents of the data.

	A DWLR troll(insitu) with the water barrier kit	High frequency water level data being retrieved with the help of a lap-top computer

The groundwater estimation committee has recommended a density of one well per 100 Sq.Km. In over exploited areas the density recommended is one well per 20 Sq. km. Till March 2005 a total of 380 dug wells and 134 piezometers were set up in different parts of the state as follows.

The geographical area of the state sans the forest and hilly areas is 113642 Sq. Km. The density is about 5 wells /1000 sq Km. With the plan of integration of CGWB network with that of the Ground Water Survey Department of the State of Chhattisgarh, the density is fairly well. Statistical techniques, though have inherent limitations have been used to evaluate the existing network and provide a firmer basis for network modifications.

The total number of hydrograph Stations in the network was 514 Out of these 514 stations, 380 were dugwells tapping shallow aquifer and 134 were the Piezometers tapping deeper and shallow aquifers. District-wise distribution of hydrograph stations is furnished in Table – 3.3.1. On an average each station represents an area of 255 sq. km

TABLE-3.3.1 DISTRICT WISE DISTRIBUTION OF NHS

In the operational area of the Region, there are 4 main river basins and 14 sub-basins. The rivers Mahanadi, Son and Tons are east flowing while the Narmada and Indravati are west flowing. Basin-wise break-up of observation wells are showing in the Table – 3.3.2

TABLE-3.3.2 DISTRIBUTION OF HYDROGRAPH STATIONS IN THE MAJOR RIVER BASINS

In the state of Chhattisgarh (16 districts), the net sown area was 35 lakh ha, in which a net area of 11.49 lakh ha. was irrigated. Out of the net irrigated area, an area of only 1.04 lakh ha. was irrigated through ground water source. Irrigation by surface water through canals is in practice in 12 medium to major command area. To monitor the behaviour of ground water levels in the areas of canal irrigation, the network of observation wells is also extended to the canal command area. Distribution of observation wells in the noted command areas is furnished in Table-3.3.3.

TABLE-3.3.3 DISTRIBUTION OF HYDROGRAPH STATIONS IN IRRIGATION COMMAND AREA

Different lithological groups representing almost all geological times underlie the eastern part of Madhya Pradesh and Chhattisgarh state. Distribution of observation wells in different formations is listed out in Table-3.3.4.

TABLE-3.3.4 DISTRIBUTION OF HYDROGRAPH STATIONS IN DIFFERENT LITHOLOGICAL GROUPS

Thus the network stations are uniformly distributed through the state in all the formations, command areas and basins.The location map of hydrograph stations is presented as Plate.1

The frequency of measurement is one of the most important considerations in designing of a water level and water quality monitoring programme. The development of a plan for monitoring is dependent on the objectives of the programme and the intended use of the data. The frequency of measurement should be adequate to detect short term and seasonal groundwater level fluctuation of interest and to discriminate between the effects of short and long term hydrologic stresses. The frequency of measurement is also dependent on several factors like aquifer type and position, groundwater flow and recharge rate, aquifer development and climatic conditions.

Water levels measurements are carried out for a number of reasons including :

• estimating the average piezometric head,

• understanding the groundwater regime,

• computing groundwater resource availability,

• design of groundwater management structures,

• Identify the short-term changes due to pumping, tidal effects, isostatic changes, tides, etc.,

• Ground-water investigations.

To achieve the above objectives one or more of the following attributes have to be estimated from the monitored water level data after generating the water level hydrograph.

• peak of the hydrograph,

• trough of the hydrograph,

• time of shallow water level i.e, time during which the water level rises above a stipulated shallow critical level,

• time of deep water level, i.e, time during which the water levels falls below a stipulated deep critical level,

• rate of rise or decline and

• response time after an event.

Statistical and visual analysis of water level hydrographs help provide information with regard to long term change in the ground water level and seasonal fluctuation.

For determining the measuring frequency, the intended use of the data and the length of water level data collection needs to be understood. Water-level date need to be collected over various lengths of time, dependent on their intended use (s). Short- term water level data are collected over periods of days, weeks, or months during many types of groundwater investigations. Water level measurements needed to map the altitude of the water table or potentiometric surface of an aquifer, are generally carried out within the shortest possible period of time-in days or weeks- so that hydraulic heads in the aquifer are measured under the same hydrologic conditions.

Long-term data are fundamental to the resolution of many of the most complex problems dealing with ground- water availability and sustainability. Significant periods of time- years to decades- typically are required to collect water- level data needed to evaluate the affects of climate variability, to monitor the effects of regional aquifer development, or for analysis of water-level trends.

Water-level measurements serve as primary data required for calibration and testing of ground-water models, and it is often not until development of these models that the limitations of existing water-level data are fully recognized. Further more, enhanced understanding of the ground-water flow system and data limitations identified by calibrating ground-water models provide insights into the most critical needs for collection of future water-level data.

In India the water level monitoring frequency have been common for all the different requirements, and the measurements are limited to few times in a year. These times are selected coinciding with premonsoon, monsoon, post-monsoon and winter seasons. Limited water level data originating from extensive monitoring networks has been used for getting a very broad regional picture of the groundwater regime. It is presumed that these water levels represent the troughs and peaks of the water table hydrograph. However, many a time these data have been too sparse to yield reliable and credible water table hydrograph.

Today, when groundwater development has increased far too rapidly, there is a need for better understanding of the localized changes in groundwater behaviour between seasons and between different aquifer systems within an area. The water level measurements need to be taken as frequently as needed to depict the fluctuations realistically. If the measurements are not frequent then the rise and fall of water levels are invariably underestimated. Typical characteristics of the hdyrogeological system will then be totally missed.

Currently, two types of monitoring are being carried out :

• periodic monitoring, and

• continuous monitoring

Periodic ground-water-level measurements are made at scheduled (daily, weekly, fortnight monthly, or season). Periodic water level measurements are usually carried out through manual measurement techniques, such as chalked metal tapes or water level indicator. The most popular periodic monitoring frequency in India by the groundwater agencies is either monthly or seasonal. In many situations, periodic monitoring tends to miss hydraulic responses of aquifers to short-term stresses, which may occur between measurements, also extreme water- level fluctuations cannot be determined with certainty. The trends revealed from these measurements are likely to be biased by the choice of measurement frequency. The frequency of seasonal monitoring should be based on the monitoring objective. The limitations of the seasonal observations should be well understood before they are used for any major interpretations.

Continuous monitoring is near real time monitoring, that is usually established in a certain fraction of wells within the monitoring network. The subset of wells so selected should :

• provide unambiguous and quantitative real-time information on unique and potentially damaging ground- water level events that are occurring and signal these events as early as possible:

• represent ground-water conditions over a substantial area of the aquifer.

• monitor specific areas where the aquifer may be more susceptible to water- level related problems, and

• provide information that aids in the assessment of saltwater intrusion in those areas of the aquifer where such considerations are relevant.

Continuous monitoring or near continuous monitoring is usually carried out using Digital Water Level Recorders (DWLR), which are programmed to make measurements at a specified frequency. The selected monitoring interval should be such that the monitored hydrograph resembles closely with the true hydrograph. This should be the most stringent and all encompassing anticipation while deciding the monitoring frequency. The monitoring intervals would depend upon the degree of the desired resemblance so as to ensure a high enough correlation between the true and the monitored hydrograph.

Water level monitoring in Chhattisgarh involves both periodic and continuous measurements. Periodic groundwater level measurements are carried out in 380 dug wells and 134 pezometers.At present, the national hydrograph stations are being monitored four times in a year simultaneously throughout the region during the following periods.

May - 20th to 30th of the month - represents water level of Pre-monsoon period.

August - 20th to 30th of the month - represents peak monsoon water level

November - 1st to 10th of the month- represents water level of Post-monsoon period.

January - 1st to 10th of the month- represents the recession stage of water level

Periodic water level measurements are made manually using metal tapes or electric sensor tapes. Potential drawbacks to periodic monitoring are that hydraulic response to short term stresses may occur between measurements and may be missed. Authentic water level fluctuations can not be determined with certainty.

Continuous monitoring in Chhattisgarh is carried out in 75 piezometers with the help of digital water level recorders (DWLRs). These DWLRs have been programmed to record water levels at six hourly frequencies. Continuous monitoring provides the highest level of resolution of water level fluctuations. True hydrographs generated from data of DWLRs can help identify the effects of various stresses on the aquifer system. It will provide most accurate estimate of maximum and minimum water level fluctuations in aquifers where the hydraulic response of an aquifer to stresses is slow and the frequency and magnitude of water level changes in an observation well are not great. However, it is often the best technique to use for monitoring fluctuations in ground water levels during drought and other critical periods like earthquake when hydraulic stresses may change at relatively rapid rates.

Under this programme the local people have been involved in monthly measurement of ground water level in some of the selected wells which are distributed in all the districts of the state. Around 80 dug wells are being minitored on monthly basis by the observers (fixed by the CGWB), who are basically the local people. The data thus recorded have been sent by the observers to the Regional Office at Raipur by post .

In Chhattisgarh, groundwater quality is studied once in every year on a regional scale. Samples are collected from all the 380 National Hydrograph Network Stations in the month of May when the probability of dilution (caused by rainfall) is the least. In general, the analysed parameters include EC, pH, Cl-, CO3--,HCO3-,S04--, N03-, Na+, K+, Ca++, Mg++, Si. On the basis of these studies detailed monitoring is carried out, where the temporal as well as spatial density of the samples are increased as per the need. Apart from this, groundwater chemistry is also studied in the samples obtained from the exploratory bore/tubewells constructed by CGWB.

The existing system of manual or very limited computerized data processing is being replaced by dedicated and user-friendly software. The primary module of groundwater data processing system (including water quality) is called Ground Water Data Entry Software (GWDES). GWDES 2.04 is the latest version of the software. The software has a Microsoft access data base structure at the back end. Front end has been developed using visual basic for Application. The software is GUI based and provides a user- friendly environment. This GWDES has been replaced by dedicated software (GEMS:Ground Water Evaluation And Management System). This software will use industry standard relational data base management system ORACLE. This is essential for long-term sustainability of the data sets and their efficient disseminations to the end users. Both raw and processed data sets are being stored and archived. Necessary features like data security, protection from data corruption and provision of controlled accessibility is a part of the system design. An efficient and user-friendly query system helps in data retrieval. The dedicated groundwater data processing software includes GIS support to visualize, manipulate and analyse spatial data.

The water level reflects cumulative effect of natural recharge-discharge condition and draft. The water table which forms the upper surface of the saturated zone is subjected to seasonal fluctuation. This fluctuation is dependent on rainfall infiltration, consumptive use, topography, soil characteristics, temperature, humidity, lithology of the formation etc.

Ground water levels, observed over a period provide valuable information on the behaviour of ground water regime, which is constantly subjected to changes due to recharge and discharge. The difference between these two factors results in the decline or rise in the ground water storage. When the recharge exceeds discharge, there will be rise in the ground water storage whereas decline in storage will be observed when recharge is less than discharge.

For every set of measurement, the data was analysed to prepare a report and maps for representing.

i.   Depth to water level in that particular month

ii.   Water level fluctuation in comparison to same month in the previous year.

iii.   Water level fluctuation in comparison to pre-monsoon.

iv.   Water level fluctuation in the month of measurement with reference to the decadal mean for the same month.

Similarly, the water quality reflects the chemistry of the aquifer and effect of anthropogenic activities on the ground water regime. Based on the analysed data, contour maps for different constituents are prepared and compared with the results of the previous years. Based on the analysis, poor ground water quality areas are delineated.

The manual process of map preparations have almost been done away with the availability of off- the- self sophisticated softwares like Surfer, MapInfo professional etc.

To ensure that adequate water-level data are being collected for present and anticipated future uses, observation-well networks and water-level monitoring programs at the local, state and federal level need to be evaluated periodically.