The diversity in hydrological and hydrogeological conditions in the Kolwan valley, including variability in the rain-fall across the river basin is clearly evident from the results of the study on artificial recharge on three different scales. Although understanding the processes of recharge on the three scales is not simple, studies at the aquifer or recharge structure scale reveal that artificial recharge takes place from some of the structures, although the magni-tude of augmented water is limited. Surface runoff is the single largest component of water balances on all three scales, significantly different from water balances in other areas of the Deccan basalt where groundwater abstraction is the single largest component of the water balance (Macdonald et al., 1995). A comparison of these two extreme scenarios from the Deccan basalt is presented as conceptual diagrams (Figure 7).
Small structures meant for artificial recharge in microwatersheds contribute small quantities to the overall water budget of the microwatershed or river basin. However, in limited storage aquifers (such as the Chikhalgaon aquifer), where the total aquifer storage is less than 100 mm, this may be a significant contribution where ground-water resources are concerned, despite the relatively small proportion of infiltration to the rainfall or runoff.
T O P I C 6 Region issues and ar tif icial recharge case studies / Case studies 711
A B
Figure 6. Isohyets (A) for Kolwan valley showing annual rainfall variability and monthly rainfall variability for the year 2004 (B)
Component Quantity Proportion to rainfall
Rainfall (average from 7 stations) 1,920 mm 100%
Soil moisture 50 mm 2.6%
Infiltration 200 mm 10.41%
Pumping (mainly from rivers) 100 mm 5.2%
Surface runoff and evapotranspiration 1,470 mm 76.56%
Average annual input to minor irrigation tank storages 110 mm 5.73%
R E F E R E N C E S
Athavale R. N. and Rangarajan G. R. (1990). Natural recharge measurements in hard-rock region of semi-arid India – tritium injection. In: Groundwater Recharge- A Guide to Understanding and Estimating Natural Recharge, D.
N. Lerner, A. S. Issar and I. Simmers (eds.), International Contributions to Hydrogeology, IAH, vol 8, Verlag Heinz Heise, Hannover, pp. 235-245.
Badarayani U., Kulkarni H. and Phadnis V. (in press). Groundwater recharge from a percolation tank to a Deccan basalt aquifer: a case study from western Maharashtra, India. ISMAR2005: International Symposium on Managing Artificial Recharge, Berlin, Germay, June 2005.
Bondre N., Dole G. S., Phadnis V. M. Duraiswami R. and Kale V. S. (2000). Inflated pahoehoe lavas from Sangamner area of the western Deccan Volcanic Province. Curr. Science, 78(8), 1004-1007.
Deolankar S. B. (1980). Deccan basalts of Maharashtra- their potential as aquifers. Ground Water, 18(5), 434-437.
Deshmukh S. S. (1988). Petrographic variations in compound flows of Deccan Traps and their significance. Mem.
Geol. Soc. India., 10, 305-319.
Gale I. N. (Ed.), Neumann, I., Guha, P, Macdonald, D. M. J. and Calow, R. C. (2003). Augmenting Groundwater Resources by Artificial Recharge. AGRAR Guidelines for Field Work. British Geological Survey, Commissioned Report, CR.03/167N. UK.
Gunston H. (1998) Field hydrology in tropical countries: a practical introduction. Intermediate Technology Publications, ©Institute of Hydrology, UK.
Kaila K. L., Tewari H. C. and Tewari P. L. N. 1981. Crustal structure and deep sounding studies along Navibandar-Amreli profile in Saurashtra, India. In., Deccan volcanism and related basalt provinces in other parts of the world, K.
N. Subbarao, R. N. Sukeshwala (eds.), Geological Society of India, Memoir 3, Bangalore, pp. 218-232.
Kale V. S. and Kulkarni H. (1992). IRS-1A and LANDSAT data in mapping Deccan Trap flows around Pune, India:
implications in hydrogeological modeling. Archives Int. Soc. Photogramm. and Rem. Sensing, 29(B-7), 429-435.
Kulkarni H., Deolankar S. B., Lalwani A., Joseph B. and Pawar S. (2000). Hydrogeological framework for the Deccan basalt groundwater systems, west-central India. Hydrogeology Journal, 8 (4), 368-378.
Kulkarni H., Badarayani U. and Sharma S. (2003). Inception report for the research site at Kolwan valley, Pune district, Maharashtra, India. Augmenting Groundwater Resources by Artificial Recharge (AGRAR), Project funded by DFID and co-ordinated by British Geological Survey, UK, 52p.
A B
Chikhalgaon aquifer Pabal aquifer
Figure 7. Comparison between Chikhalgaon and Pabal aquifers from the Deccan basalt
• Limited groundwater abstraction;
• Infiltration is about 6% of annual rainfall;
• Infiltration results in recharge and increased baseflow.
(after Macdonald et al., 2005)
• Case of groundwater overabstraction;
• Infiltration is some 25% of annual rainfall;
• Very minor baseflow.
Kulkarni H., Badarayani U. and Phadnis V. in preparation. Final case study report for Kolwan valley, Pune district, Maharashtra, India. Augmenting Groundwater Resources by Artificial Recharge (AGRAR), Project funded by DFID and co-ordinated by British Geological Survey, UK.
Macdonald D. M. J., Kulkarni H., Lawrence A. R., Deolankar S. B., Barker J. A. and Lalwani A. B. (1995). Sustainable Groundwater Development of hard-rock aquifers : the possible conflict between irrigation and drinking water sup-plies from the Deccan Basalts of India. British Geological Survey (NERC) Technical Report WC/95/52, UK.
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an overview of results obtained using tracers.Hydrogeology Journal, 4(3), 50-70.
Sutcliffe, J. V. 2004. Hydrology: a question of water balance.IAHS Special Publication 7, UK.
T O P I C 6 Region issues and ar tif icial recharge case studies / Case studies 713
Abstract
The aim of this study is to understand the hydrologic mechanisms effecting the recharge of the over-exploited alluvial fan Prato aquifer (Tuscany, Italy) and to evaluate strategies for the re-equilibrium of the groundwater balance. The Prato aquifer plays a key role for the water supply of the Pistoia-Prato-Florence urban area, with a total drinking water demand of more than 100 millions of cubic meters per year. A series of strategies has been evaluated, acting on both the input and the output terms of the groundwater balance. Several field investigations have been carried out to acquire information for an artificial recharge trial program in the northern part of the fan body. As a tool to validate such experimental plan a physical model has been developed and tested both in steady state and transient conditions. The results of an artificial recharge scenario simulation (400 l/s for 8 months a year), for the next 10 years, show that such a recharge program will allow the recovery of the ground-water levels, although only 120 l/s are sustainable for the system at the recharge selected site. For this reason multiple recharge sites along with new strategies are becoming necessary to achieve the re-equilibrium of the balance.
Keywords
Artificial recharge, groundwater balance, groundwater management model, overexploitation.
I N T R O D U C T I O N
The intent of the project for the recovery of the groundwater levels of the Prato (Tuscany) (Figure 1) aquifer is to define the feasibility and the effectiveness of different strategies aiming to enhance the recharge of the aquifer by improving the positive term of the water balance, such as river bed losses and vertical infiltration. Several studies have been undertaken to plan and develop long term policies also for decreasing pipeline losses and for a 50% reduction of well abstractions by promoting the re-use of treated wastewater, for non civil purposes. These objectives are included within the ‘Programs of the water resources protection’ of the Water Protection Plan of the Region of Tuscany – to be adopted according to the UE Framework Directive 2000/60, the D.Lgs. 152/ 99 in force in Italy and the ‘Master Plan’ of the Regional Water Regulation Authority.
The Prato aquifer is mainly formed by an alluvial fan body (Figure 2), which contains an upper unconfined layer, strongly overexploited (Figure 3), underlayed by gravel lenses of semi-confined or confined minor aquifers (Figure 4).