CHAPTER 9 SUMMARY AND CONCLUSIONS

Transcription

1 CHAPTER 9 SUMMARY AND CONCLUSIONS The following are the important conclusions and salient features of the present study. 1. The evaluation of groundwater potential is a prerequisite for any kind of planning activity. Growing population in every part of the globe demands increase in the identification of the water sources and supply of freshwater. 2. The Bharathapuzha Basin is located between 75''54'38" E & if 12'31"E longitudes and 10 18'41" N & 11 12'26" N latitudes. It has got a total area of 6186 Sq.Km, out of which 4400 Sq.Km is in Kerala and the rest in Tamilnadu. 3. Bharathapuzha is the second longest river in Kerala. It originates from the Anaimalai Hills at an elevation of 1963m and flows into Kerala through parts of Coimbatore District of Tamilnadu, draining the districts of Palakkad, Thrissur and Malappuram before debouching into the Arabian Sea. 4. The River Basin is well represented by the major physiographic divisions of Kerala namely the highlands ( m), the midlands ( m), lowlands (10-20m) and coastal plains (0-lOm). 5. The irrigation and water supply in the Bharathapuzha basin is met with the help of surface water reservoirs built across the tributaries. The Malampuzha Reservoir, Kanjirapuzha Reservoir, Walayar Reservoir, Aliyar Reservoir, Tirumurthy Reservoir, Mangalam Dam, Pothundi Dam, Meenkara Dam and ChuUiyar Dam are the major reservoirs made in the basin for surface water facility. 6. The Bharathapuzha basin, with its varying physiography and the difference in climate, is home for a wide variety of vegetation. The forest cover within the basin encompasses the biodiversity spots of the Western Ghats including a part of the Silent valley Reserved Forest. 218

2 7. The Bharathapuzha river basin lies mainly over the crystalline Achaeans and the Palghat Gap region is considered to be a boundary between the northern Late Archaean Nilgiri Granulites and the dominantly Proterozoic block of Anaimalai granulites to the south. 8. The three major rock types are homblende-biotite gneiss, biotite gneiss, and chamockites. Both varieties of gneisses have very similar granitic composition and can be distinguished from each other by the presence or absence of homblende. The chamockite is distinctly more mafic than gneisses. 9..Within the Palghat Gap, the regional strike of foliation and banding are eastwest with steep to moderate dips to the south. 10. Morphometric Analysis of Bharathapuzha Basin has been carried out by demarcating the sub-basins. An analysis of the spatial distribution of fourth order streams joining with the main river has been done to demarcate the subbasins. Factor Analysis was done with the data of morphometric parameters and the results are presented 11. The Bharathapuzha river is found to be of 8th order river with three major sub-basins of order The number and length of streams of each order in the sub-basins follows the general law of Maxwell (1955). 13. The slope and relief of the terrain influence the number and length of the streams 14. The Bharathapuzha river is found to be of 8th order river with three major sub-basins of order

3 15. The remote sensing data is a strong supplementary tool in mapping the hydrogeomorphic units and lineaments. 16. The ground water prospect map has bee prepared from IRS-ID satellite imagery and the spatial data of geology, topography and drainage 17. The study of Shuttle Radar topographic Model (SRTM) satellite data has shown that there are areas within the river course of Bharathapuzha, which are below mean sea level. This elevation difference could be attributed to the intensive sand mining in the river and the subsequent change in the riverbed. 18. Like the other parts of Kerala state, the Bharathapuzha basin also experiences two distinct monsoons, namely, the South-West (June-August) and North- East (September-November). During these two monsoons, 90% of the annual rainfall is obtained. South-West monsoon accounts for about 60% of the aimual rainfall. 19. The Palakkad Gap region is receiving comparatively less rainfall due to the change in orographic conditions. 20..In the Bharathapuzha Basin, groundwater occurs in phreatic conditions in the laterites, alluvium and in weathered crystallines. It is in semi-confined to confined conditions in the deeper fractured rocks. Since the area experienced several episodes of tectonic deformations, a large number of intercormected fractures offer very good groundwater potential. Alluvium encountered along the banks of Bharathapuzha acts as potential phreatic aquifers. The thickness as well as the width of the alluvium increases towards west. 21. Areas of recharge and discharge have been delineated with the grid deviation water table map. The grid deviation contours in the discharge zone are widely spaced indicating the low gradient of the terrain. 22. In the present study, water levels measured during the pump tests were collected from the Groundwater Departments of Kerala and Tamil Nadu and 220

4 the transmissivity values have been calculated using Jacob's method and presented and the spatial variation of transmissivity was presented thematically. 23. The study of water levels and annual water level fluctuations shows that in some areas the bore wells and dug wells are in hydraulic continuity. 24. From the results, it could be seen that among the total fifty six VES locations, there are six 5-layer cases, thirty six 4-layer cases and fourteen 3-layer cases. The 3-layer case is representing the three layers viz. laterite, the weathered zone and the basement rock. The 4-layer case might be resulting from the abovesaid three layers together with a thin veneer of topsoil. The predominance of H-type (central low) curve may be due to the presence of a clay layer, the resistivity of which is comparatively low. 25. The results of geophysical data interpretation have been made use of in identifying the groundwater potential zones. The criteria selected were as follows. For open wells, areas with aquifer thickness less than 10m and resistivity (second layer) less than 100 ohm-m was chosen. For bore wells, areas with aquifer thickness of more than 20m and resistivity (third layer) less than looohm-m was selected. 26. The groundwater potential zones demarcated by geoelectrical investigation synchronise well with the productive hydrogeomorphic units of satellite imagery interpretation. 27. The comparative study of the resistivity data with the litholog indicates the suitability of resistivity methods for demarcating subsurface boundaries and thereby exploring the groundwater prospects. 28. Ground water chemistry of the basin is mainly controlled by the geology of the area. Towards the westem part of the basin, where the underlying 221

5 lithology is mainly chamockite and laterite, the quality is better than that in the eastern part, predominated by homblende-biotite gneiss. 29. The precipitation pattern in the basin also seems to be a controlling factor in the overall chemical quality of the basin. 30. Index of Base Exchange and ground water types indicate that the waters of this basin have stayed for a long time in the aquifers to get modified to the present quality due to rock-water interaction. 31. The chief mechanisms controlling the chemistry of ground waters of this basin are rock interaction (bore wells) and precipitation (lateritic dug wells). 32. The overall hydrogeochemical models (for post-monsoon and pre-monsoon) show that there is a variation in the quality of water in the eastern and western parts of the basin. In the post-monsoon, there is a shght reduction in the distribution of positive scores of the factors pointing to the possible effect of precipitation on the water quality. 33. Effective management of groundwater requires the ability to predict subsurface flow and transport of solutes, and the response of fluid and solute flux to changes in natural or human-induced stresses. 34. The groundwater flow model of the study area has been developed using standard finite difference technique and has been used for simulating the water level up to The Computer Programme has been written in Quick basic and executed. The At has been kept as 61 days Bimonthly simulations have been done. Resultant heads of selected nodes where observation well data are available have been taken as output and compared. 222

6 36. The calibration has shown a good match and the model has been used for simulating the water levels upto In this Computer code, statements have been included to compute the groundwater in storage of every period or time step using the predicted water level, this has been computed and the following are the aquifer water in storage: Groundwater in Storage (MCM) Year January March May July September November Predicted It could be seen that the water level of this basin gradually declines and the amount of Ground Water in storage also gets reduced during these periods. 39. An integrated approach is a must for the choice of sites of high yields and good quality waters for industrial and irrigational purposes. The strength of any scientific research is the dataset generated and used for the analysis. The different spatial themes generated could be utilized for further research as the Bharathapuzha Basin is occupying a highly complicated geologic terrain namely the Palakkad Gap. 223