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  2. 2. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page i Table of Contents GENERAL 1 1 STEPS IN THE NETWORK DESIGN PROCESS 1-1 1.1 Introduction 1-1 1.1.1 Technical objectives 1-1 1.1.2 Location and depth of monitoring wells 1-1 1.1.3 Network density 1-1 1.1.4 Frequency 1-2 1.1.5 Phases in network design 1-2 1.2 Overview of steps 1-3 1.3 Purposes and objectives of the network (Step 1) 1-3 1.4 Inventory of available information (Step 2) 1-4 1.5 Evaluation and optimisation of existing network (step 3) 1-5 1.5.1 Effectiveness of the network 1-5 1.5.2 Evaluation using contour map 1-5 1.5.3 Evaluation using statistical techniques 1-6 1.6 Cost estimates and prioritisation (Step 4) 1-8 1.7 Implementation plan (Step 5) 1-8 1.8 Site selection (Step 6) 1-9 1.8.1 General considerations 1-9 1.8.2 Desk Study 1-10 1.8.3 Reconnaissance surveys 1-11 1.8.4 Field survey 1-11 1.8.5 Data interpretation 1-12 1.8.6 Finalisation of network sites 1-13 1.9 Network maintenance (Step 7) 1-13 2 CLASSIFICATION OF NETWORKS 2-1 2.1 General consideration 2-1 2.2 Network for groundwater resource assessment 2-1 2.3 Network for monitoring salinity ingress 2-3 2.4 Network for monitoring water level in canal commands 2-4 2.5 Network for monitoring water level in drought prone areas 2-6 2.6 Network for monitoring artificial recharge programmes 2-7 2.7 Integration of monitoring networks 2-8 2.8 Relevance of water-level data to groundwater quality issues 2-8 2.9 PRESENT STATUS OF GROUND WATER MONITORING NETWORK 2-8 Annexure I: Check List For Selection of piezometer Site 1
  3. 3. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1 GENERAL The Field Manual on Geo-Hydrology comprises the procedures to be carried out to ensure proper execution of design of the groundwater water level monitoring network, operation and maintenance of observation well and piezometers. The operational procedures are tuned to the task descriptions prepared for each Hydrological Information System (HIS) function. The task description for each HIS- function is presented in Volume 1 of the Field Manual. It is essential, that the procedures, described in the Manual, are closely followed to create uniformity in the field operations, which is the first step to arrive at comparable hydrological data of high quality. It is stressed that water level network must not be seen in isolation; in the HIS integration of networks and of activities is a must. • Volume 4 of the Field Manual deals with the steps to be taken for network design and optimisation as well as for its operation and maintenance. It covers the following aspects. • Part I deals with the steps to be taken for network design and optimisation. Furthermore, site selection procedures are included, tuned to the suitability of a site for specific measurement procedures. • Part II details with piezometer construction procedure with details of the different elements and the significance of different elements in the piezometer construction • Part III comprises the preparatory activities and procedures for carrying out aquifer tests. The procedures to be adopted for analysis of pumping test data is briefly discussed • Part IV comprises the testing and installation of DWLR’s. Procedures to be followed for procurements and installation are outlined in Volume 4 of the reference manual. • Part V deals with the need for carrying out Reduced Level Surveys and the procedures in carrying out the survey are outlined. • Part VI deals with the standardised procedures to be adopted for manual collection of water level data from open wells and piezometers. • Part VII deals with the standardised procedures to be adopted for retrieval of data from DWLR and integration with the software. • Part VIII, deals with procedures to be adopted for regular inspection and maintenance of piezometers and DWLR’s. The procedures as listed out in this manual are in concurrence with the ISO standards as far as available for the various techniques and applicable to the conditions in Peninsular India.
  4. 4. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-1 1 STEPS IN THE NETWORK DESIGN PROCESS 1.1 INTRODUCTION 1.1.1 TECHNICAL OBJECTIVES General aspects of groundwater monitoring are outlined in Chapter 4 of the Design Manual Volume 4. Technical objectives of the network depend on the general groundwater management strategy and information needs defined by the users. Once the technical objectives have been established and specific strategies have been developed for the respective monitoring programme, each strategy can be linked to a monitoring network design. The network design is basically a function of the location and density of monitoring points and measuring frequency. 1.1.2 LOCATION AND DEPTH OF MONITORING WELLS The positioning and the number of observation wells depend primarily on their specified representativity. Secondly, the location and the density of the wells depend on the possibility to determine the spatial trend of the groundwater levels and piezometric heads. To define the lateral distribution and depth of the observation wells information is required on: • Aquifer system and general groundwater flow, • Lithology of the aquifer and presence of aquicludes, • Additional information on all “natural” factors such as precipitation, surface water systems and “anthropogenic” factors such as abstraction, irrigation, etc. 1.1.3 NETWORK DENSITY To define the network density information is required on: • Monitoring objectives, • Complexity of the aquifer system which should be represented, • Magnitude and frequency of the variations in groundwater level and piezometric head. In general, monitoring of a local phreatic aquifer will need a relatively dense network of observation wells, while for the deeper confined aquifers less dense network is required. The selection of proper locations in consolidated formations with secondary permeability requires intensive input of geological expertise due to the complexity of the aquifer systems.
  5. 5. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-2 1.1.4 FREQUENCY To define the frequency of measurements quantitative data is required on: • Diurnal variations, • Short events (recharge and discharge changes), • Seasonal variations (dry and wet periods), • Anthropogenic impact variations (abstraction, irrigation). The fluctuation of water levels and piezometric heads in consolidated formations with secondary permeability might be large due to irregular flow patterns of groundwater. A proper understanding of lithology and structure of aquifers is needed to define the measuring frequency. 1.1.5 PHASES IN NETWORK DESIGN In the network design, several phases may be distinguished (Figure 1.1): Figure 1.1 Sequential phases in designing a monitoring network (from van Bracht, 2001) 1. Initial Phase of a new network, based (almost) solely on the deterministic “hydrogeological approach” of collecting and evaluating available information. Existing wells are adapted for monitoring purposes and new piezometers are designed in the representative hydrogeological units. 2. Juvenile Phase, in which some information about the groundwater level fluctuation is available. In this phase the groundwater level data are used to confirm the ideas developed during the hydrogeological approach.
  6. 6. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-3 3. Mature Phase uses time series of groundwater level measurements and information about the representativity of the spatial distribution of the observation wells. Various statistical methods are used to evaluate the functionality of the network. 4. Optimisation Phase is based primarily on the “statistical approach” of analysing the historical data. During the optimisation, monitoring points are either removed or added and the monitoring frequency is adjusted. In this chapter a general overview of steps in the groundwater monitoring network design process is presented. Guidelines are provided for the review of the network to get it tuned to the actual data need. 1.2 OVERVIEW OF STEPS The main steps in the network design process can be summarised as follows: 1. Define the purposes and objectives of the network, 2. Review available information, 3. Evaluate and optimise the existing network, 4. Estimate overall costs of implementation, operation and maintenance, 5. Prepare a phased implementation plan, 6. Select the appropriated sites for observation wells, 7. Establish a framework for regular periodic maintenance. These steps are further elaborated in the following sections. 1.3 PURPOSES AND OBJECTIVES OF THE NETWORK (STEP 1) In this step two question should be answered: • who are the data users and what will the data be used for? • what type of data is required and at what frequency? The specific objectives of water level monitoring include: • to detect impact of groundwater recharge and abstraction, • to monitor the groundwater level changes, • to assess depth to groundwater, • to detect long term trends, • to compute the groundwater resources availability, • to assess the stage of development, and • to design management strategies. Spatial distribution of the monitoring points and the monitoring frequency may vary for each of the above objectives. Since the implementation of a network is a time consuming and costly process, not only the current objectives but also anticipated future objectives should be included in design.
  7. 7. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-4 1.4 INVENTORY OF AVAILABLE INFORMATION (STEP 2) This step is crucial in the initial design phase. Also in the later phases, regular update of available information is required. The main questions to be answered in this step are: • Which geological formations occur in the area? • What are the hydraulic characteristics of these formations? • What is the recharge and discharge mechanism, which governs the groundwater flow? • What are factors that might influence the natural groundwater flow? The inventory can be accomplished by studying the historical water level data in the neighbouring areas, geological and hydrogeological maps, drilling data, geophysical exploration data and all relevant literature. This step towards design of the monitoring network for a specific area should result in: Identification of the number of aquifers in the vertical section and the extent of hydraulic connections among the adjacent ones. Characterisation of the individual aquifers in terms of permeability, depth to groundwater and chemical composition of groundwater. Specification of variation in thickness of each aquifer in its identified domain A global quantification of recharge and abstraction Identification of regional groundwater flow Description of groundwater problems specific to the area including quality issues The main hydrogeological units and their boundaries as well as the regional groundwater flow should be identified and defined on 1:250,000 topographical and geological maps of the State’s area of responsibility. These maps will form the base map for the network design. Smaller scale maps are of no use in this process other than to give a global picture of the network. On smaller scale maps it is not readily possible to identify the location of piezometer sites relative to watersheds and other key features. In addition to the basic maps other maps such as geomorphological map, soil map, land use map showing the physical features, soil types and land use information should also be referred to. The different maps that are made available in each of the Groundwater Data Processing Centres are: Theme Source Scale 1. Geology and Structures GSI 1:50,000 2. Land Use Derived from Satellite data 1:50,000 6. Administrative boundaries and communication Survey of India, toposheets. 1:50,000 3. Drainage and classification of drainage units upto watershed level Toposheet and updated through satellite data 1:50,000 4. Geomorphology Derived from Satellite data 1:50,000 5. Soil NBSS, 1:500,000
  8. 8. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-5 1.5 EVALUATION AND OPTIMISATION OF EXISTING NETWORK (STEP 3) 1.5.1 EFFECTIVENESS OF THE NETWORK In this step the existing network is evaluated in relation to the objectives defined in step 1. After the initial design is completed, the effectiveness of network should be evaluated in all subsequent phases to ensure that adequate water-level data are being collected for present and anticipated future uses. In the course of these evaluations, several questions should be asked: Is data being collected from areas that represent the full range in variation in hydrogeology, groundwater use, topography, climate and land-use environments? Have monitoring structures which are part of the network representing the different aquifer system the necessary hydraulic connection? Are the data-collection procedures following the prescribed norms? Is the data from the network providing the required information to designers, planners and water users? The effectiveness of the network needs to be periodically evaluated once every 3 years or at shorter intervals consistent with the changes taking place in the groundwater development scenario. Evaluation of the network should be carried out keeping in mind the broad monitoring objectives. The evaluation of the network should be carried out independently for different hydrogeological units. The evaluation should lead to identification of the data gaps (spatial and vertical) (statistical significance of groundwater level variations needs a longer period of monitoring, > 10 years). The evaluation should be based on water level and water quality data available from these networks. The yardstick for the evaluation shall be: • how well does the data emanating from the existing network permit an estimation of the mean water level elevation in a specified area. • how well does the data emanating from the existing network permit interpolation of the water level in areas having no monitoring structure. 1.5.2 EVALUATION USING CONTOUR MAP The simplest method to evaluate the representativity of the network is to generate a water-table elevation map based on data from the observation wells for different seasons. The map shall be visually analysed for determining the ground water level disposition, understanding the lateral flow directions and rates. Watertable/piezometric elevation contours permit an elaborate interpretation. In a number of cases the slope of watertable/piezometric surface shall be expected to be generally close to the topographical slope. The regional trend of the piezometric elevation may be governed by the static piezometric head at an upstream point of the basin and the stage of the outfall at the downstream end. Based on such analysis a qualitative idea of the network can be obtained. This interpolation capability also permits identification of such data points that are inconsistent with the rest of data. This may occur on account of some local phenomenon, which are not extensive enough. However, the other possibility is that the data may be erroneous or contains large data gaps. If no errors are detected and the inconsistency is detected consistently at various discrete times, it may be worth while to investigate the possible causative phenomena through statistical assessment.
  9. 9. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-6 1.5.3 EVALUATION USING STATISTICAL TECHNIQUES During the mature and/or optimisation design phase, when historical data is abundant, a so-called “statistical approach” can be used. The statistical approach is based on the principle that a process is governed by chance. This “probabilistic” process can be defined using statistical units derived from historical observations. The use of the statistics in the optimisation of a hydraulic head monitoring network is appropriate if: • The information content can be expressed in statistical units such as variance, confidence intervals, interpolation errors, probability on non-exceedence etc. • Sufficient data are available to quantify the spatial and/or temporal statistical properties of the variable to be measured. The statistical methods used in the optimisation of monitoring networks are described in detail by van Bracht (2001) and UN/ECE (1999). They can be broadly divided into: • Classical statistics. In the classical statistical approach, the observations are considered as a random number of measurements. The techniques include e.g. population mean and variance methods. • Geostatistics. In geostatistics, the variable property is viewed as a spatial random function. They include simulation techniques, variance-based techniques (e.g. Kriging) and probabilistic techniques. • Time series statistics. Time series statistics approach assumes that the measurements show an ordering in time and that they may have a serial correlation. Time series include regression analysis, auto-regressive integrated moving average models and spectral analysis. The statistical analysis of data from existing networks can provide useful guidance in evaluating the networks and also provide a firmer basis for network modifications wherever required. Statistical techniques have their limitation in the design/evaluation of water-level monitoring networks for several reasons. First, sufficient long records (preferably > 10 years) are needed to reliably estimate the parameters required by the techniques. Second, water-level monitoring networks typically have multiple objectives, some of which are difficult to express quantitatively. Because of these limitations, statistical analysis of data from existing networks must be carried out with care. The geostatistics method uses a set of probabilistic techniques for determining estimates of water levels at unmeasured locations based on combinations of nearby measured values. The method provides estimates of uncertainty that can be used to aid network design. Using this technique one can evaluate the relation between the number or density of monitoring wells and the uncertainty of a potentiometric map. A map of the water-table elevation based on data from the existing network of observation wells is to be initially generated. This should be followed by laying a regular geometric pattern over the area and randomly de-selecting from among the existing monitoring wells in each hexagon. A map of the water-table elevation based on the reduced network is generated and compared with the initial map to pick up deviations if any. This analysis will lead to the identification of areas with less than adequate coverage, areas where monitoring frequency has to be increased, as well areas where reductions in the number of monitoring wells is to be carried out. The limitations of this type of analysis should be kept fully in mind, however, in that the analysis focuses on the overall ability to accurately represent a regional potentiometric surface. Other objectives of the network might need to be factored into any decisions about network optimization, such as objectives to quantify drawdown in particular areas, to identify possible flow paths for water-quality analysis, or to evaluate the interactions of ground water and surface water. Likewise, geostatistical analysis assumes that further ground-water development will not greatly alter the estimated spatial correlation.
  10. 10. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-7 In case an existing network (in respect of a specific aquifer) is found to be inadequate, additional piezometers tapping that specific aquifer need to be provided. The first step towards planning of the enhancement shall comprise a macro-level planning, i.e., estimating the required number of additional piezometers and their location at a macro-level (say on a map of scale 50,000). The subsequent step shall involve pinpointing the sites for the additional piezometers on the ground, i.e., micro-level allocation. Depending upon the intended use of the data from the network, the macro-level planning of the network enhancement can be accomplished in the following ways: Coefficient of variation method The method requires the user to specify the maximum permissible error in the estimate of the mean water level. Subsequently, based upon an analysis of the concurrent data from an existing network, the required number of the piezometers is computed. Thus, the additional number of the piezometers is computed. The following procedure is adopted for locating the additional piezometers within the specified area. Employing the concurrent data from the existing network, draw contours of water level at a uniform interval. Divide the entire area into zones, each zone representing an area falling between two successive contours. Divide the required number of piezometers equally among all the zones. This will ensure a greater density of the piezometers in the regions of steeply sloping piezometric head and vice versa. Count the number of existing piezometers in each zone and hence estimate zone-wise, the required number of additional piezometers. Locate the additional piezometers in each zone in such a way that the piezometers (existing and additional) are uniformly distributed within the zone. Kriging Kriging is a powerful tool for evaluating an existing network. Kriging is used as a criteria for determining the ground water level monitoring network density. In Kriging the variance of interpolation error depends on the number of observation wells and their locations, independent of the actual measurements. The Kriging standard deviation of interpolation error (see figure 1.2) can be used as a measure of network effectiveness. It can also assist in the macro-level location of additional piezometers, in case the existing network is found to be inadequate. The steps involved shall be as follows: Specify the level of permissible interpolation error. Conduct Kriging on the concurrent piezometric data from the existing network. This shall yield contours of piezometric head and of the interpolation error. Study the error contours and hence identify the regions where the error is in excess of the specified permissible level. Additional piezometers are to be allocated to these regions. Locate additional piezometers in the identified regions tentatively, generally ensuring that the increase in the network density is consistent with the error excess. Conduct Kriging on the tentatively enhanced network and plot contours of the error. It may be noted that Kriging permits generation of such contours even though the data from the newly introduced piezometers do not yet exist. Study the modified error-contours and check everywhere whether the error falls below the specified limit and the enhancement has not been over-done. An over enhanced network shall display interpolation errors (far) less than the prescribed limit. Modify the network further, if necessary
  11. 11. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-8 Figure 1.2: Graphical impression of the Standard Deviation Interpolation Error in space (from van Bracht, 2001) 1.6 COST ESTIMATES AND PRIORITISATION (STEP 4) Once the preliminary design or evaluation of the network has been completed the capital cost of establishing new observation wells and the recurrent cost of operating the network should be estimated. The costs need not be itemised for each individual well location. Approximate estimates based on an average cost suffices. The manpower requirements should also be assessed. These should be balanced against existing establishments and budgets. Once this has been undertaken it should be possible to ascertain whether the proposed network is sustainable. This is extremely important. If there is any doubt about the ability to maintain the proposed network to a high level of quality then it must be reduced in size. The priority categorisations should be established during the review to assist in the optimisation process. The relative importance of the issue being monitored allows a categorization of the monitoring wells. Category Priority Issue to be monitored A High Groundwater resource estimation, drought/conjunctive use planning, coastal salinity ingress mapping B Medium Artificial recharge response monitoring, , monitoring natural/artificial contamination of groundwater C Low Groundwater estimation of smaller administrative units, monitoring localised groundwater issues Prior to abandoning an existing or proposed monitoring station from the network or upgrading the system, the main beneficiaries of the data (appropriate members of the HDUG) should be informed. 1.7 IMPLEMENTATION PLAN (STEP 5) Once the preliminary optimum network design has been completed a network implementation plan should be prepared. This should be realistic and achievable in the time scales allowed.
  12. 12. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-9 The plan should allow for the following: 1. Site location surveys 2. Preparation of piezometer/observation well designs 3. Land acquisition 4. Preparation of site specific plans 5. Invitation to tender for construction/drilling/preparing the agency drilling rig 6. Tender period 7. Evaluation of tenders and award of contract 8. Drilling/Construction 9. Development 10. Yield test 11. Monitoring of water levels (frequency and length of monitoring to be considered) 12. Construction of platforms and protective cover 13. Reduced Level Surveys 14. Fencing and other civil works 15. Installation of DWLR 16. Commissioning 1.8 SITE SELECTION (STEP 6) 1.8.1 GENERAL CONSIDERATIONS The location of a piezometer site should be such that it has to represent the specific hydrogeologic unit defined during the step 2. The sites selected should preferably be along the lines normal to rivers, canals and surface water drainage’s, so as to establish a relationship between surface water -ground water interaction, as well as along the basin outlet for computing the subsurface flow. In the areas where multiple aquifers are to be monitored in a single location, it is necessary to monitor the phreatic as well as the deeper semi-confined and confined aquifers for understanding the difference in pressure heads between different aquifers. Piezometer nests have to be constructed in such areas. In order to select the most appropriate site, considerable effort needs to be expended undertaking site selection surveys. The site selection surveys can be divided into four distinct phases, which are summarised in sub-sections below: 1. Desk study 2. Reconnaissance surveys 3. Field surveys 4. Data interpretation
  13. 13. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-10 In order to ensure that all the pertinent information is obtained during the site selection process and surveys and to assist with the work, a sample format has been prepared. A copy of this form is contained in the Appendix 2.1 to this Chapter. 1.8.2 DESK STUDY The target location for the monitoring station will have already been proposed on a 1:250,000 map or similar during the network design process, (step 2). However, this size of map is too small a scale for site selection purposes. The inspection of large-scale topographic maps (1:50,000) and hydro- geological maps if these are available, should be undertaken to identify possible sites within the target watershed unit. Relevant information can be obtained from: (a) Remote sensing interpretation map The Hydrology Project has been involved in the creation of GIS data sets in which thematic maps are generated using satellite data. The thematic maps should be used during the desk review for the locating the appropriate sites. The Remote Sensing maps have to be the basis for delineating the geological/hydrogeological boundaries, drainage units, faults, lineaments, etc. Using the GIS capabilities different themes should be combined. Based on the GIS studies and remote sensing interpretations inference on the subsurface soil moisture, recharge potentialities need to be estimated. The Remote sensing interpretations should be used to interpret features like karst topography, dykes, reefs, unconformities, buried channels, salt encrustation’s, tide levels, alluvial fans and abandoned channels etc. In the hard rock terrains the remote sensing studies should help in understanding the spatial distribution of rock outcrops and the catchment characteristics and the presence of structures and drainage systems influencing the groundwater movement. The likely thickness of regolith /overburden and the general groundwater potentiality may be derived from the nature of the landform and the slope. In this way, the most preferable location for the monitoring sites can be estimated. For this purpose, the GIS datasets related to Geology & structures, Geomorphology, drainage and soil should be integrated and interpreted. The satellite imageries especially provide a good overview of the drainage network for computing drainage density and lineaments. (b) Geological maps The geological map of the area permits good understanding of the rock type, the nature of consolidation and the distribution of the structures. The lithostratigraphic units shown in the geological maps lead to a broad understanding of the aquifer systems, groundwater flow systems and types and conditions of the boundaries, as controlled by geology and structure. Geological maps should be read with a three-dimensional perception for inferring the geometry of the aquifers and boundary compositions of the aquifer system. Based upon such an understanding, a hydrogeologist can identify the aquifers and aquitards. Geological maps are made available to all the Data Processing Centres as one theme under the GIS data set. (c) Hydrogeological maps These maps permit an understanding of the relationship between the groundwater and rock bodies. They comprise information on the different groundwater abstraction or monitoring structures, contours of the piezometric head/water level depth, direction of groundwater flow and variations in water quality. This information will enable a hydrogeologist to understand the extent of aquifers, together with geological, hydrogeological, meteorological and surface water features that are necessary for understanding the groundwater regime. Vertical sections, such as borehole data, are incorporated in the hydrogeological maps to illustrate the relationship between aquifers and non-aquifers in relation to depth. Isopach maps reveal thickness of individual aquifers and give information on their regional extent.
  14. 14. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-11 (d) Drilling Data Drilling logs of all the exploratory/production wells and piezometers in and around the area of interest can assist in identifying different formations/aquifers occurring in the area. The drilled wells/piezometers should be located on a working base map, preferably a topographic map of 50,000 scale. Such a location map along with the drilling logs permit preparation of cross sections and three- dimensional fence diagrams. These diagrams can assist a hydrogeologist in identifying various aquifers in the area and their domains in lateral and vertical dimensions. Superposition of the available water level/aquifer parameter data can lead to an understanding of the nature of the identified aquifers. Many of these wells need to be visited and information re-checked during the well inventory programme. (e) Study of Hydrographs and Contour maps Examine the water level hydrograph of all the monitoring wells in the neighbourhood of the proposed sites. Examine the water table elevation contour maps and depth to water table maps generated using two sets of data (pre-post monsoon). The desk study should result in a report describing the site-specific conditions. A plan for the reconnaissance survey should also be included. 1.8.3 RECONNAISSANCE SURVEYS The reconnaissance survey should be undertaken to the extent possible by foot for large part. It is important that the entire hydrogeological unit which would be represented by the network observation site should be inspected. Therefore, if travel by road is not possible there is no substitute for trekking the entire length of the target reach. An experienced geo-hydrologist at the senior scientist level along with young field officers who are responsible for data collection within whose office jurisdiction the monitoring site falls and who is familiar with the area should undertake the surveys. During the survey, interviews should be held with local people to try and build up a picture of local site conditions such as depth to groundwater, rate of groundwater abstraction and presence of irrigation structures. At sites of interest attempts could be made to ascertain who owns the land. On completion of the reconnaissance surveys, one or more sites could have been identified which are worthy of further consideration. However, it is often not possible to make final decisions on site selection until detailed well inventory of the neighbourhood site, and sometimes geophysical surveys and detailed water quality analysis are carried out. The reconnaissance survey should result in: • A specification of the potential constraints such as approach, access, safety, vandalism and land acquisition problems. • A plan for the field survey. 1.8.4 FIELD SURVEY Field surveys should include detailed well inventory, geophysical resistivity surveys, geophysical downhole logging, water quality sampling and pumping test (wherever required).
  15. 15. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-12 (a) Well inventory A detailed well inventory of the area that is to be represented in the network is intended to verify the hydrogeological concepts obtained during the desk study. The data to be collected in all wells which are close to the proposed site should include: • Administrative and technical information on the well construction (year of completion, depth of the well, depth of the screen, lithology encountered, water struck level etc). • Information on well use (irrigation, domestic use) including estimated rate of abstraction • Measured depth of well • Measured groundwater level • Field analysis for pH and EC. A standard well inventory format should be used and all the data collected during the inventory should be brought into an electronic format. (b) Geophysical Surveys Geophysical surveys need to be carried out as a standard procedure for getting a clear understanding at the proposed site of the depth to bed rock, the thickness of weathered zone, the extent of saturated zone, the approximate quality of water in the saturated zone, the thickness of different layers in layered formations and the type of layered formations. The influence of geological structures like faults, unconformities and dykes should also will be evaluated. Occurrence of saline and fresh water layers with the probable depth of occurrence also should be indicated. The geophysical survey results should be the basis for deciding the depth of the piezometer, aquifer position to be monitored and the piezometer design. (c) Geophysical downhole logging Geophysical downhole logging in existing wells provides valuable information on lithology and structure of rock formations and groundwater composition in the immediate vicinity of the well. The results from downhole logging are used for a calibration of surface geophysical methods. The most useful techniques include: resistivity, spontaneous potential and gamma logging. (d) Water quality sampling Two sets of representative sample for detailed laboratory analysis should be collected during the well inventory. The procedures for water quality sampling are described in Volume 6. (e) Pumping test A pumping test should be carried out in the existing wells to estimate the aquifer parameters. The principle and procedures regarding the pumping test are described in Part III of this Volume. 1.8.5 DATA INTERPRETATION Data interpretation should lead to a three dimensional picture of the representative hydrogeological unit which will be monitored. The procedure should be as follows:
  16. 16. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1-13 • Prepare lithological cross section/fence diagram using the data from the inventoried wells and geophysical surveys. • Delineate the prominent aquifers in the area with their thickness and aerial extent. • Describe the lithological and structural features of the representative hydrogeological unit and estimate the hydrogeological parameters. Describe all natural and anthropogenic factors, such as surface water structures, abstraction and irrigation, which might influence the groundwater levels and piezometric heads. 1.8.6 FINALISATION OF NETWORK SITES Based on all the studies and keeping in mind the logistical and safety consideration the potential sites has to be identified. Where more than one site is considered then a joint team of hydrogeologists should visit the area and identify the most favourable location. The site selected should be verified for its true representation of the area specific lithology and regime system. The interference from pumping wells, surface water sources, polluting sources, seepage from return flows should be avoided at all costs, unless the purpose of the observation well is to monitor the influences of these factors on the groundwater conditions in the area. Co-ordinates and proposed depth of the monitoring well should be specified and a location sketch of the proposed site should be prepared. 1.9 NETWORK MAINTENANCE (STEP 7) The design, implementation and operation of monitoring networks is a very costly and time-consuming process. To ensure a proper functionality of the observation wells, all monitoring sites should be regularly inspected and a preventive maintenance programme should be developed and implemented. The inspection and maintenance of monitoring wells and measuring devices is discussed in detail in Part VII of this Volume.
  17. 17. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-1 2 CLASSIFICATION OF NETWORKS 1.10 GENERAL CONSIDERATION While it is true that the observation sites would have more than one objective, it would be in- appropriate to believe that all the observation sites currently operational meet this criterion. In fact it is more than likely that many of the observation sites fail to meet any of the broad monitoring objectives. It is now time that all the monitoring agencies review the performance of independent monitoring structures that form part of the national network stations (CGWB) and State network stations (SGWD). The relevance of many of the hand dug wells has to be seriously questioned. Similarly piezometers with inadequate hydraulic connection or lack of required depth need to be replaced or rejuvenated. Wherever the open wells are still relevant the mechanism that can ensure their optimal performance to yield reliable data have to be identified. The need for additional observation sites should be based on a review of the existing network using appropriate norms. In areas where additional sites are being envisaged their main objective has to be clearly identified. Greater inter agency co-ordination can also reduce the need for additional monitoring wells at certain locations. Systematic analysis of all the historical records of water level and water quality data are basic pre- requisites for understanding the existing system as well as for forecasting changes in response to new ground water development and management strategies. Based on the monitoring objectives the design of monitoring wells/piezometers and the density of network should be considered. For all classes of monitoring networks the following points should to be kept in mind while selecting observation wells or designing the piezometers: static water level should be available for monitoring the aquifer tapped should be clearly identifiable the diameter of the monitoring structure should be small a fixed point should be used for measurement of water levels the selected structure should have adequate water column to ensure that it does not dry up in summer or drought years the location should be approachable at all times the structure should provide access for operating sampling pump for water quality monitoring The network density should be guided by the level of heterogeneity of the parameters influencing the water levels and water quality. This would require a good understanding of the relevant processes based on which, preliminary guesses can be made of the scale of the variability with respect to space and time. The frequency of monitoring should be in consonance with the dynamics of the measured processes. 1.11 NETWORK FOR GROUNDWATER RESOURCE ASSESSMENT There are a variety of ground-water resource availability problems that involve determining the state of ground water and detecting or predicting changes in the ground-water environment. Most approaches to ground-water monitoring network design avoid a rigorous formulation of the monitoring objectives and fail to consider the important processes controlling the movement of ground water and migration of ground-water contaminants. It is unlikely that such approaches to network design will be able to monitor effectively and efficiently the subsurface environment in the face of limited resources.
  18. 18. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-2 The majority of observation sites by CGWB and State Groundwater agencies have been established with the main objective of groundwater resource assessment. The GEC-97 has recommended the unit of assessment to be a drainage basin. This would call for a review of the existing network. The CGWB network would essentially need to cover all major drainage units so that the groundwater resource assessment can be carried out for all the major tributaries of river basins pertaining to different states. The state network has to cover all the watersheds. The network however has to cover all the major hydrogeological units as part of the drainage units. While a certain amount of duplication between the Central and state agency network is likely, an integrated network can totally avoid any duplication. The observation location in the case of resource monitoring should be a site that shall provide the true information on ground water reservoir through the water levels it depicts. These piezometers, are to be located in areas not influenced by major water production wells so that data collected is more representative of general conditions in the aquifer rather than conditions influenced primarily by the daily on-and-off cycles of the production wells. The observation well/piezometer has to faithfully respond to the natural or artificial input and outputs on the groundwater system. The groundwater reservoir being a dynamic system all changes in quantity and quality has to respond immediately with minimum lag time. This would demand that the monitoring well should have good hydraulic connection with the reservoir. The privately owned hand dug open wells serving as observation wells is being slowly replaced by dedicated piezometers. It would be appropriate to replace all the poorly performing observation wells with piezometers that will be owned by the department. Any hand dug open well that would still continue to be part of the monitoring network should be examined and a mechanism for ensuring regular upkeep needs to be discussed with the owner. Participation of the Central/ State agency in the upkeep through a nominal financial grant of private hand dug wells should also be considered. It has also to be ensured that integration of networks of Central and State Groundwater Organisations is a regular process in order to avoid any duplication. The different aquifers that are being exploited and the aquifers that offer potential for future groundwater development should be part of the network. In areas where more than one aquifer is vertically distributed cluster/nested piezometer should be constructed and incorporated into the network. The aquifer type should define the network density. The monitoring frequency is an issue that has to be considered at the time of site selection itself. “Periodic monitoring", are ground-water levels measured manually at selected intervals, usually with a steel or electric tape. These measurements typically are made once per month by many state groundwater agencies or once every season totalling five measurements per year. In any event periodic monitoring should not be less than five measurements every year. Periodic monitoring as a rule is confined largely to open dug wells. In the case of piezometers tapping formations with very poor hydraulic conductivity and small water level variations, the frequency can also be converted into periodic monitoring with one measurement every month. "Continuous Monitoring " of ground-water levels is done by using automatic monitoring devices like a DWLR with data stored in data loggers, and retrieved periodically from the field. The frequency of monitoring is now arbitrarily fixed at 4 measurements every day. Since DWLR have been installed for the first time in the country the optimal monitoring frequency could not be decided and hence six hourly measurements are being recorded. Now with availability of data for over three years for different sites, detailed analysis (spectral, harmonic) need to be carried out for arriving at the optimal monitoring frequency. The historical monitoring programmes for resource evaluations have been limited to water table aquifers. No norms have been developed for estimating resources of the deeper aquifers. This estimation is no doubt difficult due to uncertainties regarding the recharge zone, but lack of the piezometric head data has pre-empted its solution. The periodic monitoring of dug wells have never been able to provide a true water table hydrograph. As a result of this, recharge estimation by water balance of the unconfined aquifer became uncertain in many ways.
  19. 19. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-3 With the high frequency monitoring credible piezometric head data can be obtained which would provide the groundwater practitioners access to true piezometric head hydrograph. This is bound to inspire the practitioners to enhance the scientific/technical content of their prevailing practice of resource assessment and also to incorporaten in it many new analyses. Thus for groundwater resource assessment network, continuous monitoring frequency should be preferred in representative piezometers while the open dug wells can continue to have periodic monitoring. For groundwater resource assessment the following site selection guidelines apply: 1. Open to a single, known hydrogeologic unit 2. Known well/piezometer construction that allows good water-level measurements 3. Located in unconfined aquifers or near-surface confined aquifers that respond to climatic fluctuations 4. Minimally affected by pumpage and likely to remain so 5. Essentially unaffected by irrigation, canals, and other potential sources of artificial recharge 6. Long-term accessibility 7. Well/piezometer has never gone dry (not susceptible to going dry) 8. The location should be selected so that the site is never flooded with water. It is preferable that the site is near to a place that can be easily approached and protected from vandalism. This is obviously not always possible. However to meet these criteria none of the critical technical components should be overlooked. e.g. establishment of observation sites in police stations and electrical substations only from security consideration at times can generate inconsequential data which have very little scientific utility. 9. Wherever recording water level monitoring devices (DWLR) are to be installed. The likely water level fluctuation and the deepest water level should be understood clearly. 10. The water level measurement device should whenever possible be located in areas where it will not be obstructed by tree root and heavy concentration of minerals in the water. 1.12 NETWORK FOR MONITORING SALINITY INGRESS The threat of encroachment of salt water into aquifers containing fresh water has become cause for concern in the last few decades along the east and west coast of the country. The relation between the intrusion of saline water and declining hydraulic heads due to extensive aquifer development is a major problem in these areas. Ground water is the principal source of public-water supply in many coastal areas. Large ground-water withdrawals result in regional cones of depression, which if not checked can lower potentiometric surfaces of aquifers to below sea levels. The natural flow directions then get reversed and saline water can migrate toward pumping wells. This phenomenon is best explained by the Ghyben-Herzberg relation. The Ghyben-Herzberg relation states that under hydrostatic conditions, the weight of a unit column of fresh water extending from the water table to the freshwater-saltwater interface is balanced by a unit column of salt water extending from sea level to the same depth as the point on the interface. This analysis assumes hydrostatic conditions in a homogeneous, unconfined coastal aquifer. According to this relation, if the water table in an unconfined coastal aquifer is lowered by 1 m, the saltwater interface will rise 40 m. The first step in appreciating the problem of salt water intrusion is to evaluate the size and extent of the problems. This can be accomplished by establishing an exclusive network of groundwater monitoring wells in the form of dedicated piezometers which should enable to determine the boundaries of the salt/fresh water interface and the rate at which salinity levels are increasing. Using this data and information on the hydrologic and geologic properties of the contaminated aquifer,
  20. 20. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-4 numeric and computer modelling can be incorporated for predicting future conditions as well as to evaluate remediation alternatives. The piezometer design has to be perfect so as to record a water level response that is sympathetic to the changes taking place in the aquifer during pumping and recovery. Because of large ground-water withdrawals along the coastal, regional cones of depression are developed in each of the aquifers, which have to be completely recorded. The potentiometric surfaces of aquifers that are connected to the sea level, are to be determined by linking all the piezometers to a single datum. This will only enable monitoring the natural flow directions and reversals wherever they occur. Because of the potential threat of degradation of the freshwater in such areas, ground-water withdrawals need to be carefully monitored through a specialised network. The piezometer network for monitoring the saline water ingress has to be very dense comprising of a number of closely spaced piezometers located parallel to the coast which can closely record the cone of influence of the production wells and pick up the localised groundwater gradients. The elevation of each piezometer in the network has to be accurately surveyed to compare water levels from inland to the coast. Concurrent measurements of groundwater level in each piezometer allow the groundwater surface to be contoured and displayed on a map for inferring groundwater flow directions. A comparison of the contour plots for different seasons/ pumping events will show us whether there is any seasonal variation in groundwater flow directions. The contour pattern will also provide a good understanding of the dominant recharge sources and the groundwater outflow into the sea if any. The hydrograph of monitoring water levels should be plotted as water level elevation against time axis for comparing the water level elevation with respect to Mean Sea Level. Relation between reductions in heads from pumping and chloride concentrations also needs to be regularly monitored. The monitoring frequency in the coastal area has to be such that it provides the highest level of resolution of water-level fluctuations. The monitoring frequency should be such that it should be able to monitor the effects of water levels to various stresses and provide the most accurate estimates of maximum and minimum water-level fluctuations in aquifers. For these reasons continuous monitoring equipment such as a DWLR should be used with monitoring frequency of 1 hour or in critical areas at 10 minutes frequency. The monitoring frequency should be subject to review frequently. For the network in the coastal areas the following site selection guidelines apply: 1. Open to the hydrogeologic unit which has the fresh water 2. Piezometer/open dug well which are not production wells should only be part of the network 3. The piezometers/observation wells should clearly respond to sea level changes and withdrawals.
  21. 21. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-5 The continuous monitoring of groundwater levels is required for assessing seasonal trends in ground- water recharge and storage. The data should be used for periodically constructing potentiometric maps for picking up any significant changes in the size of the cones of depression developed in the aquifers. Water samples need to be collected from selected observation wells for analysis of chloride and dissolved-solids concentrations, and these data should be compared to monitor changes in the relation between hydraulic heads, ground-water-flow directions, and ground-water quality. Using this combined water level and water-quality monitoring program, the monitoring agency will be able to evaluate the effects of water-management decisions on the aquifers and carefully monitor the improvement or further degradation of water quality in the aquifers. 1.13 NETWORK FOR MONITORING WATER LEVEL IN CANAL COMMANDS In the major surface water irrigation projects in India the interplay between the surface and ground water system is getting complicated due to multiple interactions between the two systems. This has resulted in rising trends in groundwater water levels in many canal commands leading water logging and salinity conditions. A large percentage of the productive land in these irrigation commands appears to show rising water levels. Some of these areas are having seasonal water logging. The effects of high water table conditions gets aggravated in the events of high rainfall and flooding. In such areas there appears a need to tap the shallow productive zones through the construction of number of groundwater structures for limiting the rise of water levels. The future development of groundwater resources in the different irrigation commands needs to be systematically planned. Integrated groundwater development planning should take into consideration not only the present abstraction rate but also the trends in water level movement, the regional extent of the different aquifers in the area and the regional distribution of water quality in the area. Areas showing rising water levels have to be prioritized for extensive groundwater development even if the prevailing groundwater abstraction is high as compared to other areas. In the existing and the proposed irrigation projects commands the development of groundwater resources has to be substantially enhanced. Groundwater abstraction should be introduced in the ayacut area for supplemental irrigation, raising nursery and for rabi crop production. The groundwater abstraction should aim at lowering the water levels substantially in the rabi season so as to arrest the rising water levels in the Kharif season. The design of the groundwater abstraction structures should be related to the aquifer properties. In areas with high transmissivity and storage values large scale pumping should be taken up for conveying water to deficit areas or for mixing it with surface water. Conjunctive use of surface and groundwater need to be taken up. The concept of conjunctive use planning involves appropriate mix of groundwater along with surface water for meeting either the full requirements of water in certain time periods or over certain pockets for the whole year. This judicious mix of surface water and groundwater would help increase the irrigation intensity, make available water in tail ends / water deficit areas, control water level build up, prevent water logging and reduce the risk of salinity hazards. For the network for monitoring the influence of surface irrigation systems on the groundwater systems the following guidelines apply: • It has to be very dense in the canal commands and periphery, comprising of number of a shallow dug wells/ filter points/tube wells. • The elevation of each piezometer in the network has to be connected to a common datum. • The measurement of groundwater level in the different monitoring structures should be carried out to enable preparation of water level elevation contours for different periods prior to canal opening, mid way through the canal flow period and at the end of the canal flow. This would enable clear understanding of seepage losses from different canal sections, return flow form irrigation, total groundwater build-up during the canal flow period and the areas vulnerable to water logging. The contour pattern will also provide a good understanding of the groundwater outflow
  22. 22. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-6 into the surface water bodies or rivers. The hydrograph of monitoring water levels should be plotted to understand the water level trend and the rate of rise of water level every year, the rate of decline after the canal closure. The design of an optimum conjunctive use plan would require close monitoring of the water levels over a number of years. Analysis of the monitoring water level data will be useful for understanding the • impact of surface irrigation system on the groundwater resources, • Identify the areas that are vulnerable to water logging, • delineate areas that offer scope for ground water development, • develop a groundwater resource development plan that would optimise the available groundwater resources without resulting water logging conditions
  23. 23. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-7 The mo nitoring frequency in the canal commands has to be such that it provides a good picture of the influence of the surface irrigation systems on the groundwater reservoir. The monitoring frequency should be such that it monitors the effects of water levels to different recharges and provide the most accurate estimates of maximum water-level fluctuations in aquifers. The monitoring should be flexible so as to get near continuous water level measurements during the period when there are canals flows and periodic monitoring during the canal closures. For these reasons continuous monitoring equipment such as a DWLR should be used in a limited number of piezometers while in other monitoring wells the water level can be monitored by using tapes. 1.14 NETWORK FOR MONITORING WATER LEVEL IN DROUGHT PRONE AREAS Wide meteorological, hydrological, hydrogeologic and socio-economic diversity has led to perennial drought situation in different areas of the country. Droughts have generally resulted in a high abstraction of groundwater for agriculture as well as for meeting the increasing demands from urban users resulting in overdraft conditions. The areas prone to drought appear to be extending across all the states and in the different hydrogeological settings. The bulk of groundwater in the drought-prone peninsular India occurs in the weathered formations, which have been mostly tapped, and in the fractured rock aquifers much of which is still available for use. However, rates of groundwater movement and the response to recharge have not been clearly understood. Groundwater recharge response appears to be influenced by a number of factors including its location in the physiographic basin, the soil, geology of the area, thickness of the weathered mantle, the orientation of fractures and the hydraulic head distribution. There is a need to identify and develop better techniques for quantification of recharge, the recharge response to different rainfall intensities and the rate of release of recharge in different situations. The best watershed management options that can contribute to groundwater recharge have to be understood and effective structures that can enhance the vertical movement of groundwater need to be identified. The dedicated piezometers, DWLR and weather stations combined with the new analytical tools have enhanced our understanding, this needs to be carried to its logical end for developing improved watershed management techniques and units for enabling groundwater recharge in different hydrogeological units. Additional data generation should focus on some of the themes that can emerge as predictive tools for helping in decision making during the droughts as well as in times of reduced recharge quantification of the stress on the groundwater reservoirs during droughts. A dedicated network for drought monitoring is a worthwhile investment for improving our understanding on rainfall-recharge relationship in pre/post drought situation for different rainfall events and soil moisture conditions groundwater - surface water relationships extractive’ values associated with groundwater at times of shortage delineation of hydraulic compartments in the drought prone areas. water level fluctuation in different fractures systems. impact of overdraft on aquifer pore space and flow rates recharge response of aquifers after prolonged droughts rejected recharge merging as base flows in drought prone areas understanding fault/ fracture integrity The dedicated monitoring networks should also include different types of measuring tools and special techniques for tracking the flow regimes etc. Real time and near real time monitoring of water levels, recharge events, rainfall, runoff will be a requirement in certain areas. Continuous monitoring may not be required where the hydraulic response of an aquifer to stresses is slow and the frequency and
  24. 24. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-8 magnitude of water-level changes in a monitoring well are not great. However continuous monitoring would be advisable during droughts when hydraulic stresses may change at relatively rapid rates. 1.15 NETWORK FOR MONITORING ARTIFICIAL RECHARGE PROGRAMMES Groundwater recharge is a critical hydrogeological parameter that, depending upon the application may need to be estimated at a variety of spatial and temporal scales. Aquifer scale recharge is essential to water resource assessment and management where as local scale recharge is critical to assess the performance of different artificial recharge techniques as well as to quantify the amount of recharge. Estimation of recharge in such areas may be required on a temporal scale ranging from hours to days. Artificial recharge of groundwater is achieved by putting surface water in basins, furrows, ditches or other facilities where it infiltrates into the soil and moves downward to recharge aquifers. Artificial recharge is aimed at short and long term underground storage. Knowledge of the conditions that help in recharge in different areas would require field monitoring. An artificial recharge monitoring network is intended to be a regional/local network operational for long term/limited periods. It is essential for: • evaluating the additional recharge facilitated, • performance of different techniques, • quantifying the amount of recharge, • carrying out cost benefit analysis of the investment • understanding the overall ecological impact on the local micro-environment. Network monitoring design should be guided by the local geological setting, aquifer types and ground water flow regimes. The network monitoring to a large extent should be carried out using the existing groundwater structures, which are the main beneficiaries of the programme, supported by dedicated piezometers wherever required. The type of monitoring is to measure the shape of groundwater mound on the aquifer in response to recharge and decline in the mound after infiltration has stopped. Network monitoring need to be supported by additional studies for quantifying the recharge. Slug test, infiltration test, tracer techniques, environmental isotope monitoring etc are the additional methods to be taken up in specific areas for mapping the recharge rate and flow path. The monitoring programme should be so planned as to help planners to understand the long term effects of recharge on groundwater, the quantum of water that can be safely stored in the aquifers, the threat of water logging if any, and the amount of water that can be optimally recovered. The network for the artificial recharge monitoring should comprise of : 1. Dug wells/piezometers tapping a single lithological unit 2. Piezometer/open dug well which serve as production wells could also be part of the network The piezometers/observation wells should comprise of those clusters which have the potential to respond to artificial recharge
  25. 25. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-9 1.16 INTEGRATION OF MONITORING NETWORKS In the Hydrological Information System the following networks are operational: • ground water level network, • ground water quality network • hydro-meteorological network of rainfall and full climatic stations • hydrometric network • surface water quality network Various State and Central agencies operate these networks. To avoid duplication of work, to enhance availability of data and to reduce cost the networks operated by the various agencies have to be integrated, technically and organisationally. The hydro-meteorological network has to be considered in conjunction with the ground water and surface water networks. Integration of the different network will help in providing data on the different constituents of the hydrological cycle during the ground water resource assessment. Organisational integration of the networks implies that the networks are complimentary and that regular exchange of field data takes place to produce authenticated data of high quality. Review of the networks is also to be done in close collaboration. 1.17 RELEVANCE OF WATER-LEVEL DATA TO GROUNDWATER QUALITY ISSUES The role of water-level data in the investigation of ground-water quality or contamination problems is sometimes under appreciated. To a large degree, predictions about the speed and direction of movement of ground-water contaminants are based on determination of the gradient (slope) of the water table or potentiometric surface in the affected aquifer. While the data needed for these determinations typically are obtained by synoptic water-level surveys, longer term water-level measurements are often needed to develop an understanding of how ground-water contaminants migrate from their sources through the ground-water system. For example, an examination of water- level hydrographs and graphs of contaminant concentrations over time may reveal a relation between the occurrence of event-related or seasonal changes in ground-water recharge and fluctuations in the contaminant concentrations. During drought conditions, the effective management of ground-water resources, and monitoring of ground-water availability and ground-water and surface-water interaction, require the ability to rapidly collect water-level measurements and track trends. Therefore, more efforts should be made to construct climate-response and other observation wells capable of collecting “real-time” water-level measurements, and to make all collected water-level data more rapidly and readily accessible through electronic transmittal. 1.18 PRESENT STATUS OF GROUND WATER MONITORING NETWORK Conventionally ground water monitoring in India has been carried out by measuring water levels using privately owned open dug wells tapping the upper unconfined aquifers. In the monitored open wells the necessary well-aquifer hydraulic connection have not always beyond suspicion and all the parameters with respect to the aquifers could not be always be evaluated. Thus the water level data have only provided the piezometric head/water table elevation of the semi-confined/unconfined aquifers.
  26. 26. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2-10 Under the HP, a number of such non representative wells have been replaced by dedicated piezometers tapping unconfined and the deeper aquifers. In the construction of the piezometers it has to be ensured that the necessary hydraulic connection with the targeted aquifers are established and the tapped zones are suitably isolated from overlying/underlying aquifers. The newly constructed piezometers along with the historically maintained observation wells have become the upgraded monitoring network. The state ground water department network combined with the network maintained by CGWB have to be considered as an integrated monitoring network of the region/state. Evaluation of the integrated network will help in understanding its effectiveness as well as to identify areas with data gaps. It is stressed that once the network is operational, it has to be evaluated regularly to see whether (revised) objectives still match with the produced output in a cost- effective manner. A network, therefore, is to be seen as a dynamic system and should never be considered as a static entity. This requires some flexibility in establishing new stations and closing down others
  27. 27. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 1 Annexure I: Check List For Selection of piezometer Site 1. Location information Hydrogeology Geology Aquifer System Main Drainage Basin: Sub basin: Watershed Location map to be prepared and attached to the check list. 2. Objectives and purpose(s) 2.1 Need for the Piezometer/Observation well: Category Description What will the data from the site be used for Who will be the data users What type of data is required and at what frequency Data gaps in the existing network Is the proposed site a replacement/enhancement How long the station is likely to used for data collection Is there sufficient manpower for regular monitoring Is there transport facility available for monitoring Is there adequate budget available for maintenance and replacements 2.2 Main purposes and functions of data Please tick the appropriate boxes: Purpose/function ( ) Ground water Resource Estimation Drought Monitoring Salinity monitoring Conjunctive use Overexploitation Pollution monitoring Recharge Monitoring Other -
  28. 28. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 2 2.3 Nearest Observation well/piezometer State Agency site Site name: Distance from the proposed site Latitude: Longitude: Site name: Distance from the proposed site Latitude: Longitude: CGWB site Site name: Distance from the proposed site Latitude: Longitude: Site name: Distance from the proposed site Latitude: Longitude: 2.4 Data requirements Data type Tick approp. box(es) Frequency (e.g. continuous, daily, etc.) Remarks Water level Aquifer Parameters Water quality Surface flow Rainfall Weather station Other, please specify
  29. 29. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 3 2.5 Network design considerations Consideration Unit area ( km 2 ) Details a. Hydrogeological unit b. Geological unit c. Drainage Unit d. Administrative unit e. Rainfall zone (Thiessen Polygon) f. Others 3. Site Selection 3.1 Desk work Examine topographic maps and GIS data sets Yes/No Is there an existing observation well in the locality, i.e. is the station to be upgraded? Yes/No If yes, provide details. Is there any existing data available, e.g. water level/quality? Yes/No If yes, provide details for need for upgradation. 3.2 Well Inventory Dates undertaken:...................................................................... List details of wells visited and salient information collected: No. Location name Latitude Longitude Water level (m) Formation Remarks
  30. 30. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 4 3.3 Geophysical Investigations Dates undertaken:...................................................................... No. Investigation method Latitude Longitude Depth of investigations Formations inferred Recommendations Site Specific Details 4. Location Proposed Piezometer site, name of locality: Village: Latitude: Longitude: Description of access route: 5. General location considerations Consideration Details Remarks a. Is the location a government land/private property. Specify whether the location is decided based on security b. Is the site going to be submerged or water logged c. Is there any dumping activity/polluting source in the neighbourhood d. Distance of pumping well from the site e. Distance of surface water body from the site f. Distance of irrigated land from the site g. Distance from the drainage divide in the upstream h. Distance from the discharge area in the downstream i. Deepest open dug well j Deepest borewell/tube well k Casing depth Is the aquifer fully represented in the selected location l Time and distance reach from the nearest Data Processing Centre
  31. 31. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 5 6. Geological & Hydrogeological Considerations 6.1 Control Considerations Y/N Remarks a. Does the area represent the full range in variation in hydrogeology of the area b. Is there any rock outcrop or well exposure etc. close to the site which will act as a geologic control? c. Is there a good lithological section available as an exposure in an open well/ road section which will act as good lithologic control - d. Does the area show ground water development in more than one aquifer system / lithological unit for constructing piezometer nest e Is there another monitoring well in the neighbourhood which would facilitate cross checking of data f Does the area show any drilling problem Is the site a suitable location for the installation of a DWLR 6.2 Water Level / Water Quality ranges Parameter Units Minimum Maximum Water level m Discharge m 3 /s Water quality EC TDS Na Cl F 7. Piezometer Construction considerations Consideration Remarks a. Name of nearest town or village and its distance from the site. b. Extent of facilities like diesel, water, cement, steel, skilled labour available nearby. c. Is site approachable by drilling rig ? Is a four wheel drive vehicle required? d. Location of nearest inspection bungalow/rest house? e. How away is the nearest bench mark for RL survey? f. Is there a power line close to the site, which needs to be disconnected during piezometer construction? g. Is there a need to close/divert traffic around the site during piezometer construction? h. Is there a need for informing any authority/getting clearance before construction of piezometer.
  32. 32. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 6 i. Is there any school /hospital that will be affected with the noise during the construction of the piezometer. (suggest solutions) j. Is there a need for fencing the site k. Is there a need for providing a protective well head l Has the village community been informed about the proposed construction of the piezometer through a village meeting j Has the village community agreed to safeguard the observation site k Others 8. Possible measurement methods Method Suitability (yes/no/marginal) Remarks Manual Water Level Measurement DWLR RL Measurement Discharge Measurement Aquifer Parameters Water quality depth sampling Geophysical logging 9. Recommendation Type of observation site: Open dug well/ Piezometer Construction method: Manual digging/ Drilling (Rotary/DTH/Hand) Total Depth (m) Casing/Steining Depth (m) Diameter/Dimension (mm) Specify pressure sensor measuring range for DWLR. *Attach estimate of capital cost for construction, wellhead protection, fencing, monitoring instrument as well as the recurrent cost of operating the station. *Attach all survey reports, designs, maps.
  33. 33. Field Manual – Geo-hydrology (GW) Volume 4 – Part I Geo-hydrology March 2003 Page 7 Statement The piezometer/observation well site in _______________________________, Village ________________ Taluk ________________________, District ____________________ is recommended for implementation based on the detailed surveys carried out by a team comprising of Name Designation Technical Tasks Station Head