FUNDAMENTALS OF AQUIFER MAPPING

The water Resource Ministry of Government of India has released a notification and a fact sheet on National Aquifer Mapping Programme (NAQUIM). The Central Groundwater board and the State Groundwater Departments will act as the main functionaries in this programme. It is also decided by the government that national level aquifer mapping will progress substantially through the 11^th five year plan period. Considering the fact that those government departments alone cannot accomplish the job it has been decided that stake holders and NGOs would be involved in this endeavor.  This national level programme also has components like nation wise training and human resource development.

But, what is an aquifer map and what it is for?

The concept of aquifer mapping is not new. Many developed countries like Australia and USA have already completed aquifer maps in certain areas like Murray Darling Basin and Texas. They have already published some of the reports and maps. An aquifer map is not a single map, on the other hand it is a group of several maps that would describe the aquifer system and management criteria and options in an area.

In NAQIM programme of India it has been proposed that aquifer maps would include (1) Identification of Aquifer Management Units (AMU) (2) Evaluation of AMU, (3) Data preparation and generation of different categories (4) Prioritization of AMU, (5) Preparation of aquifer management plans and aqifer management and information system, (6)  Participatory groundwater management.

1.      IDENTIFICATION OF AQUIFER MANAGEMENT UNITS:

Aquifer management units are something different from a Hydrogeological unit. In a hydrogeological map generally geological units are described by its hydrogeological characteristics. But an AMU contains much more than that. It includes the 3 dimensional matrix of all information like extent of the aquifer, depth, thickness, geology, hydrology, land use on it, recharge and discharge related information and its political and social boundaries.

2.      EVALUATION OF OF AMU:

This is the most difficult task. Aquifer evaluations are conducted for various purposes including water supply development as well as groundwater contamination and remediation situations. They can range from fairly intense evaluations involving test drilling, geophysical investigations, installation of monitoring or observation wells, test pumping, physical and chemical water quality analyses, analytical and digital modeling to rapid evaluations based on existing data.

3.      DATA PREPARATION AND GENERATION OF DIFFERENT CATEGORIES:

The groundwater departments and states are generating groundwater data on regular basis. But those data are generally categorized on the basis of revenue boundaries and not on the basis of aquifer boundaries. So under NAQIM aguifer related data should be compiled and generated. A suggestive list of required data is given below.

   - Evaluation of existing data

   - Test drilling

   - Installation of monitoring or observations wells

   - Geoprobing and/or hydro probing

   - Geophysical investigations

   - Geophysical borehole logging

   - Groundwater gauging

   - Groundwater sampling and analyses

   - Test pumping

   - Slug testing

   - Analytical and digital groundwater modeling

   - Solute transport modeling

   - Groundwater monitoring

4.      PRIORITISATION OF AMU:

AMUs are basically aquifers subdivided into management units. These units are prioritized according to the demand and usage depending on the evaluated parameters of the aquifer. Before prioritization a management framework is required. The framework may include:

• Establish the baseline groundwater conditions and range of natural variability in the aquifer to facilitate enhanced knowledge and detection of change.

• Provide a consistent approach to understanding potential effects from all development activities on the surrounding environment.

• Facilitate projections of change based on future scenarios, such as expanding development or climate variability and change.

• Support and supplement the current pollution prevention and risk management principles as part of groundwater quality and quantity management.

 Prioritisation index:

Depending on the hydrogeology, quality of water and development status a prioritization index is to be developed by the groundwater authorities.

AMUs are initially ranked according to an index (equation 1) based on normalised current groundwater extraction, the fraction of groundwater allocation currently extracted , the fraction of sustainable yield currently extracted , a potential growth index and an index of the predicted future impact of groundwater extraction on surface water flow.

Apriority evaluation index has been attempted in Murray-Darling Basin Sustainable Yields Project (http://www.clw.csiro.au/publications/waterforahealthycountry/mdbsy/technical/Q-GMU-Prioritisation.pdf) Several other algorithms can be developed to prioritise aquifers in our country. In a GIS platform both raster and vector based analysis may lead to an efficient decision support system.

5.      MANAGEMENT PLAN

This initiative will seek to protect the long term water supply capacity of the aquifer by controlling average annual aquifer use and balancing it with average annual recharge.

                                i.            Aquifer Protection Plan: This initiative will seek to assess the quality of the water in the aquifer and then to protect it by encouraging activities that enhance water quality and by discouraging activities that degrade it.  The key components are

                              ii.            Maintain Status Quo where water level is alarmingly depleted.

                            iii.            Reduce withdrawal of water: Water withdrawal may be reduced by introducing innovative farming, recycling of water and reducing consumption. The management plan will address aquifer specific recommendation.

                            iv.            Enhance Natural Recharge: To enhance natural recharge proper steps should be taken. This may include afforestation, gully plugging, construction of sub surface dykes etc. This initiative will seek to maximize aquifer recharge with good quality water by encouraging beneficial land and water management practices and by investigating the potential to use stream flow.

                              v.            Monitoring plan: This initiative will seek to maintain a current and comprehensive scientific database on the aquifer by collecting, compiling and evaluating data. The current aquifer monitoring activities could be reviewed to coordinate and redesign them, focusing on the comprehensive protection of the Aquifer.

                            vi.            Manage Pollution Risks: Activities carried out in pits and dumping areas within the primary recharge area present a variety of risks to aquifer water quality. The risks associated with these activities could be assessed and, where required, action taken to manage them as part of an aquifer protection plan. Other risks like geogenic contamination like As and Fl should be properly addressed in the management plan to reduce public health hazards.

                                      vii. Reduce Incoming Salt Water: The regional salt water flow to the aquifer could possibly be intercepted by installing a set of management structures or through innovative engineering activities.

6.      AQUIFER EDUCATION PLAN

The potential long term success of this management plan depends on the understanding and cooperation of a diverse group of people.  It is believed that a better informed group makes better decisions.  Only common understanding will engender the cooperation needed to formulate,  implement and maintain a successful long term stewardship plan for the Aquifer. Additional study is required to achieve a better understanding.  Extension education is required to make knowledge gained available to all area residents.