Spatial Analysis of Data
Using the overlay module of ARC/INFO
workstation based GIS software, the above
thematic layers were overlaid with suitable ranks
and weights. The final map contains numerous
polygons having the characteristics of all the
above 12 themes. In order to group them in to
four classes, a statistical analysis was made
assuming the distribution is normal. Considering
the 1 - sigma criteria using the above criteria, the
final suitability map has been delineated into
four classes namely highly favorable, moderately
favorable, less favorable and not favorable.
Field Verification
The generated output maps were taken for field verification. The scientist verified the zonation created using GIS and also the suggested type and location of the water harvesting structures. In almost all the cases, the zonation generated as well as the type and location of water harvesting structures suggested are agreeable and the success rate is more than 90% while suggesting the suitable recharge structures, the zonation map, drainage pattern, site conditions etc., have been considered.
Recommended Recharge Structures
After detailed analysis of the zonation map generated using GIS techniques, the various suitable recharge structures such as check dams, percolation ponds, recharge pits / shaft, subsurface dykes, nallah bund, contour trench etc., were suggested based on the field condition.
The brief description of the different structures recommended are given below:
Percolation Pond in Dindigul
In Dindigul area the quality of water was
bad due to infiltration of tannery effluent in the
nearby places. Since the water was not completely affected and it is brackish in nature, if the groundwater is recharged through percolation pond, there is every chance in the improvement of the groundwater. Keeping this in mind, the percolation pond has been suggested near Dindigul in Dindigul block (vide Fig - 1a). Moreover, the structures has been suggested in the highly favourable zone to ensue more recharge. Similar types of percolation ponds were suggested wherever the highly favourable zone with suitable terrain conditions are exist.
Check dams in Chinnamanur block
The Odappatti village in the Chinnamanur block is suffering from water scarcity. The wells sunk in the area got dry and they did not give sufficient yield. In order to improve the groundwater potential three check dams have been proposed (vide Fig-1b). The location where the check dam proposed falls under highly favourable zone with good potential of groundwater.
Subsurface dyke in Bhavani River
The subsurface dyke is a semi permanent
structure constructed across the river where sand
thickness is more. The subsurface dyke will be
constructed above the bed level of river and upto
the sand thickness. This is normally recommended near the sea shore to prevent the subsurface flow from the river to the sea. But this subsurface dyke is proposed to prevent the movement of sand in the river. (vide Fig - 1c).
Recharge Pit in Kovilpatti
The recharge pit is normally recommended where the soil is having poor infiltration rate. If the clay layer is present above the shallow aquifer, the clay will be removed by constructing small pits. These pits will be filled
with pebble stone and sand. Whenver rain
occurs, the water seeps through the recharge pits
and recharge the aquifer. The Kovilpatti area
having full of black cotton soil lacks the recharge
capability. In order to improve the above aquifer,
the recharge pit (vide Fig-1d) has been recommended. If the depth of clay formation is more instead of recharge pit, recharge shaft has been recommended.
Similarly the other recharge structures such as nalla bund, contour trench etc., were suggested wherever feasible. Desilting of tanks were also suggested in some blocks.
Conclusions
At the present condition, the artificial recharge is to be resorted to sustainable development of groundwater. Hence, the results obtained from the present study fulfill some of the requirements of selecting suitable artificial recharge structures. Moreover, this is one of the first operational study made for identifying suitable sites for artificial recharge structures using Remote Sensing and GIS. The criterion table developed in this study should be slightly modified according to the site conditions.
Acknowledgement
- The authors thank Dr. K. Kasthurirangan,
Chairman, ISRO / Secretary., DOS and Mr. Nambiyar, the then Chief
Secretary to Government of Tamil Nadu for taking initiative for
commissioning the project.
- The authors are indebted to the
Secretaries to Government, Department of Municipal Administration
and Water Supply and Department of Rural Development, Government
of Tamil Nadu for sponsoring the project and the encouragement.
The authors wish to express their deep appreciation to the
Vice-Chancellor, Anna University for the encouragement given
during the execution of the project.
- The authors acknowledge the services
rendered by the consultants and the members of the Technical Committee and Quality Evaluation Team for successful completion of the project.
References
- Asano, T (Edited, 1985 Artificial
Recharge of Groundwater Butter worth Publishers, Boston.
- Bansky Vladimir (1983) Artificial
Recharge study in Madras Aquifer - The Hindu (Daily) June 1983.
- CGWB, Govt. of India (1992) Proceedings
of workshop on "Artificial Recharge of Groundwater Lowcost Rain
Water Management for increasing irrigation & Groundwater
Recharges in Chattisgarh Region" Held at Raipur, India.
- Chow. V. T. (Ed. 1964) Hand book of
applied Hydrology MoGrow Hill Book Company, New York.
- Edward, T. Ooksford (1985) Artificial
Recharge : Methods Hydraulics and Monitoring, Artificial Recharge
of Groundwater, Edited by Takashi Asano.
- Ramalingam. M. & Natarajan. T(2000) Identification of recharge areas using Remote Sensing and GIS" NNRMS Bulletin (B) 24. Bangalore, India.
Table – 1. Criterion Table – Hard rock Environs
|
Theme |
Rank 1 |
Rank 2 |
Rank 3 |
Rank 4 |
Weightage |
|
4 x weightage |
3 x weightage |
2 x weightage |
1 x weightage |
|
|
Geomorphology |
Buried Pediment (Deep), Flood Plain, Bazada, Valley Fills, Buried Channel, Palaeo Channel, Less Dissected Plateau |
Buried Pediment (Shallow), Medium Dissected Plateau |
Pediment, Pediment Inselberg, Highly Dissected Plateau |
Structural Hills, Denudational Hills, Deflection Slope, Ridges |
25 |
|
Hydrological Soil Group |
A |
B |
C |
D |
18 |
|
Slope |
0-3% |
3-5% |
5-10% |
>10% |
15 |
|
Runoff |
Moderate |
Less Moderate |
Low |
High |
12 |
|
Lineament Density |
High |
Moderate |
Less Moderate |
Low |
9 |
|
Geology |
Alluvium, Schisto Gneiss |
Charnockite, Kankar, Limestone |
Pegmatite, Laterite |
Dolerite, Granite, Quartzite |
8 |
|
Landuse |
Wet crop, Plantation |
Dry crop, Fallow, Harvested land |
Scrub, Barren |
Rock outcrops, Forest & Others |
7 |
|
Drainage Density |
Low |
Less Moderate |
Moderate |
High |
6 |
|
TOTAL |
100 |