Abstract
With the increasing use of groundwater for various activities the fast decline in groundwater takes place. In order to prevent the aquifer from fast depletion, the artificial recharge is resorted to. Keeping this in mind to avoid fast decline in groundwater levels in various parts of Tamil Nadu, a study has been undertaken to identify the favourable areas for artificial recharge and suggest suitable recharge structures to augment the aquifer system. The analysis was carried out blockwise for the entire state of Tamil Nadu using Remote Sensing data and GIS techniques. The various thematic maps such as Geomorphology, Geology, Soil, Slope, Landuse, Drainage, Drainage density, Lineament density, Runoff isolines, Depth to weathered zone, Depth to Basement, Groundwater level fluctuations and water quality were used in the analysis. The above maps were prepared using IRS-1C LISS III satellite data and other collateral information collected from the field and digitized. Criterion tables were generated considering the importance of different themes and necessary ranks and weights were assigned to each theme. Using ARC/INFO GIS software, the above themes have been integrated and the areas suitable for artificial recharge have been identified. Considering the 1-sigma criteria, the favourable areas for artificial recharge has been categorized into highly favourable, moderately favourable, less favourable and poor for recharge and verified in the field. Considering the terrain conditions and favourable zonation, the suitable artificial recharge structures such as percolation pond, check dam, recharge pit, recharge shaft, contour trench, nallah bund, recharge tube wells and subsurface dyke were recommended. These recommendations were communicated to district administration for implementation.
Introduction
With the increasing use of groundwater for Agricultural. Municipal and Industrial needs, the annual extraction of groundwater are far in excess of net average recharge from natural resources. Consequently, groundwater is being withdrawn from storage and water levels are declining resulting in crop failures, seawater intrusion in coastal aquifers, land subsidence etc., Vagaries of monsoon and indiscriminate development of groundwater often result in declining trend of groundwater levels. There is an urgent need for artificial recharge of groundwater by augmenting the natural infiltration of precipitation into subsurface formation by some suitable method of recharge. Artificial recharge is one method of modifying the hydrological cycle and thereby providing groundwater in excess of that available by process. Keeping this in mind to avoid fast decline in groundwater levels in various parts of Tamil Nadu, a study has been undertaken to identify the favourable areas for artificial recharge and suggest suitable recharge structures to augment the aquifer system. The analysis was carried out blockwise for the entire state of Tamil Nadu using Remote Sensing data and GIS techniques.
Objectives
The following are the objectives of the study:
- to delineate areas favourable for recharge by integrating various themes with different recharge possibilities and
- to recommend suitable recharge structures.
Procedure Adopted
This study was carried out for the entire state of Tamil Nadu to improve the overall groundwater level so as to prevent the wells extracting groundwater to a larger extent. Special thrust is given for the wells extracting water for drinking water. The description of the study area and the various procedures adopted in this study is briefly explained below:
Description of the Study Area
The Tamil Nadu has a geographical area of 1,30,000 sq.km. Majority of the area of Tamil Nadu was covered by the two major domains of geological formations namely hardrock and sedimentary. More than 70% of the area of this state falls under hard rock domain. The sedimentary formations occurs all along the coastal zones consists of coastal sandy zones, river alluvial sandy formations. The average annual rainfall is around 1000mm. In this project, it was contemplated to harness the excess surface water and allowed to recharge the aquifer.
Description of the Study Area
The Tamil Nadu has a geographical area of 1,30,000 sq.km. Majority of the area of Tamil Nadu was covered by the two major domains of geological formations namely hardrock and sedimentary. More than 70% of the area of this state falls under hard rock domain. The sedimentary formations occurs all along the coastal zones consists of coastal sandy zones, river alluvial sandy formations. The average annual rainfall is around 1000mm. In this project, it was contemplated to harness the excess surface water and allowed to recharge the aquifer.
Data Used for Integration
In this Project both satellite data as well as extensive field data were used for preparation of various thematic maps . As far as satellite data is concerned IRS-1C LISS III data has been procured for the entire state and used in the analysis. In addition to LISS III data IRS-1C PAN data also consulted for better interpretations. In addition to the above satellite data, the following collateral data namely daily rainfall, groundwater levels, geophysical data, borehole data and water quality were used in the analysis.
Spatial data used for Integration
In this analysis, 12 layers of thematic information are used. Among the 12, the following seven basic maps namely (a) Geomorphology (b) Geology (c) Soil and Hydrological soil (d) Slope (e) Landuse (f) Drainage and (g) Transport network and settlement are used. The above maps were prepared using both the satellite data and toposheets. In addition to the above basic layers, the following derived layers such as drainage density, lineament density, maximum groundwater level variations, depth to weathered portion and water quality were used. These maps were generated using ARC/INFO and SURFER softwares.
Processing of Data
The thematic information generated through
visual analysis were digitized using ARC/INFO
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echarge. The first
rank classes are considered as most favorable zone for recharge and the fourth rank is for poor
recharge. These ranks were assigned to each theme. Apart from the ranks, weights among the
parameters were assigned based on group
discussions and expert opinion. The different
criterion tables are developed for hard rock,
sedimentary and alluvial formations. The
criterion table developed for hard rock formation
is shown in the Table - 1.