The groundwater in Yamuna flood plain of Delhi (India) and the management options

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1 Final copy of the author submitted version to the journal for the article given below (only for archiving): Shekhar Shashank and R K Prasad The groundwater in Yamuna flood plain of Delhi (India) and the management options. Hydrogeology J. 17(7): , (DOI /s y). Springer publication original article available at link: The groundwater in Yamuna flood plain of Delhi (India) and the management options 1* Shashank Shekhar and 2 R.K.Prasad 1. Scientist 'B', Central Ground Water Board, 18/11 Jamnagar House, N.Delhi Chairman (Retd.), Central Ground Water Board, Govt. of India, India. * Corresponding author shashankshekhar01@gmail.com Keywords: India, Yamuna flood plain, groundwater management, groundwater recharge, saline water upconing Introduction: The National Capital Territory (NCT) of Delhi, India is a water scarce state with deficit in drinking water supply to its residents. Delhi Jal Board (DJB), which is custodian of drinking water supply to Delhi, supplies around 650 million gallons per day (MGD) (1066 million m 3 /d) of potable water against the need of 900 MGD (1476 million m 3 /d) leading to a deficit of 250 MGD (410 million m 3 /d).the total drinking water requirement as assumed by DJB grows in magnitude with every passing year because of ever increasing overall population of Delhi. The volume of water being supplied by DJB currently is derived by diversion of surface water from the neighboring states of Uttar Pradesh and Haryana and groundwater sources. When the city is not able to supply even the drinking water requirement of the population, it is difficult to meet the water supply needs of the other sectors, like agriculture and industry in particular, which partially sustain their requirements from this overall supply mechanism. It is therefore quite common that different localities of Delhi are not able to get their share of water supply because of the conflicts in demand and supply. The groundwater resources of Delhi are highly stressed as this source of water is easy to exploit and its exploitation can be accomplished by any individual. The people who are not able to receive adequate water from DJB sources resort to their own schemes to exploit groundwater. This leads to pumping of groundwater much more than the annually rechargeable quantity in most parts of Delhi. Thus, out of nine districts, seven districts of NCT Delhi have been categorized as overexploited with regards to the dynamic groundwater resources (CGWB 2006a). Yamuna River is a perennial river flowing through the eastern part of the territory (Fig.1). The occurrence of fresh groundwater in Delhi is mostly restricted to the Yamuna flood plain, the quartzitic ridge (popularly known as Delhi Ridge), Chhatarpur Basin and along water bodies like canals, drains etc (Fig.1).The Yamuna flood plain of 1

2 Delhi is the most promising area with regards to fresh groundwater resource potential. Thus an insight in to groundwater resources, groundwater recharge potential, and groundwater management options in the Yamuna flood plain of Delhi is a necessity. The Yamuna flood plain of Delhi: The Yamuna flood plain of Delhi comprises younger and older alluvium. The younger alluvium overlies older alluvium. The thickness of the younger alluvium varies from nearly 70 m in the northern part of the flood plain to nearly m in the southern part of the flood plain (Fig.2). The alluvium (younger and older) overlies quartzitic basement. This basement is exposed at Wazirabad and near to Okhala in the flood plain (Fig.1). In areas close to surface exposure of hard rocks, the depth to basement is at shallower level, and the thickness of overlying alluvium is reduced. The younger alluvium mainly comprises medium to coarse sand admixed with silt, clay and heterogeneously colored gravels in places (Fig.2). The younger alluvium has been classified as unconfined aquifer (CGWB 1996, Shekhar 2006, Rao et al 2007). The older alluvium is mostly finer sediments; these are clay predominant and admixed with silt and Kankar (calcareous concretions). The fresh groundwater in Yamuna flood plain is mostly restricted to younger alluvium, while saline groundwater is mostly restricted to clay predominant older alluvium. The depth to the fresh/saline interface in groundwater is found at the deepest level in the northern part at approximately 70 m below ground level (m b.g.l)) in Palla area (Fig.1), while it is shallower in the southern part (approximately 40 m b.g.l). In general the depth to water level in the active flood plain of Yamuna in Delhi is found in the range 3-7 m b.g.l (CGWB 2006b); mostly the depth to water level in the flood plain is within 5 m b.g.l. The fresh groundwater of Yamuna flood plain in Delhi can be imagined as an elongated semi cylindrical lens underlain by saline water. The water flowing through Yamuna River, the groundwater in bank storage of the river and other dynamic components of groundwater in underlying aquifers and water bodies in the flood plain of Yamuna River are generally in dynamic equilibrium. It implies that significant change in attribute of any one or more components of the equilibrium may affect other components of the equilibrium. In a broader holistic perspective the biotic and abiotic components of the whole flood plain are in equilibrium as an ecosystem. Groundwater resources and groundwater recharge potential in Yamuna flood plain of Delhi: Since the depth to water level is shallow, the recharge potential of the active Yamuna flood plain under the current scenario is quite low. Any forced further recharge may lead to water logging conditions which may also lead to salinity enrichment. 2

3 In normal circumstances, it has been observed that the average post monsoon water level rise in Yamuna flood plain of Delhi is approximately 0.37 m (assessed on the basis of representative water level data for years 2006 and 2007). The annually replenishable dynamic groundwater resources (V) in normal circumstances can be calculated using water level fluctuation data and the formula: V = F x area x specific yield of formation (1) Where F is average annual post monsoon water level rise. The total area of the Yamuna flood plain is estimated to be 97 km 2. With specific yield of the aquifer derived as 0.2 and average water level fluctuation measured as 0.37 m, the annually replenishable dynamic groundwater resources works out to be 7.2 million m 3. This annually replenishable dynamic groundwater resource can be significantly enhanced in the Yamuna flood plain of Delhi by carefully dewatering to create additional subsurface storage space in the underlying aquifer system. This will make provision for enhanced groundwater recharge in the flood plain using the concept of augmentation of subsurface storage by engineered techniques. In view of the water scarcity in Delhi and good freshwater potential in Yamuna flood plain, the Central Ground Water Board (CGWB 1996) proposed a scheme for calculated dewatering of Yamuna flood plain (by withdrawing fresh groundwater to augment drinking water needs of Delhi) and creating additional subsurface storage space to be eventually replenished by rainfall, flood induced recharge from flood water and river water. CGWB (1996) indicated that Delhi gets 724 million m 3 of water from Yamuna River through interstate agreement; out of this allocation, monsoon runoff accounts for 580 million m 3. Nearly half of this (about 280 million m 3 ) is not being utilized at present and flows out of Delhi during the monsoon period itself. Thus there is a need to store a portion of this water in artificially created subsurface reservoirs for utilization during the non monsoon period. CGWB (1996) suggested 4 m dewatering (with reference to pre-monsoon water level) of the Yamuna flood plain in Delhi by groundwater extraction. The report proposed that 78 million m 3 of surplus monsoon runoff can be recharged to the dewatered aquifer (the aquifer is dewatered initially by withdrawing 78 million m 3 of groundwater) on the assumption of 20% specific yield of the aquifer and 97 km 2 area of the flood plain. This 78 million m 3 of recharged groundwater is available for further withdrawal. The CGWA (2000) notified Yamuna flood plain as a protected aquifer with the vision of keeping scope for dewatering and refilling the aquifer to augment drinking and domestic water needs of NCT Delhi. 3

4 The northern most part of the Yamuna flood plain, popularly known as Palla sector (occupying an area of nearly 12 km 2 ) (Fig.1) was developed by DJB. Nearly 100 tubewells are being operated by DJB to augment drinking water supply to Delhi. In the perspective of aquifer potential, and of hydraulic considerations, nearly MGD (66-74 million m 3 /d) of fresh groundwater can be withdrawn from these tubewells. The CGWB, in collaboration with the National Institute of Hydrology (NIH), Roorkee carried out a system simulation and numerical model study (Rao et al 2006a, 2006b, 2007) leading to an operational model for groundwater pumping at Palla well field. The study suggested that nearly MGD (41-49 million m 3 /d) of fresh groundwater can be drawn safely during both monsoon and non monsoon seasons to meet drinking water standards (salinity less than 1000 mg/l). More groundwater extraction could be limited by quality and not quantity, and may lead to enhanced withdrawal of water from the river boundary. It is to be noted that MGD (41-49 million m 3 /d) of yield from Palla well field has been decided for the existing tubewells and the study was conducted with the constraint that the tubewell locations were already fixed. The study can be extended to assess system behavior in a scenario where some more tubewells are put at different locations. If the results are encouraging, some more tubewells can be installed with optimal spacing to augment drinking water needs of Delhi. It will also be useful if a model scenario is created with the approach that the total present groundwater withdrawal from Palla area is distributed equally or in the best possible way in to the whole Palla area and model results are examined in the perspective of groundwater salinity variations, river boundary withdrawals, etc. Soni (2007) opined that sands have 50-60% water holding capacity, although this seems to be on the high side for naturally occurring sandy formations, where compaction and admixing are natural phenomena. This study (Soni 2007) gives a figure of 1 billion m 3 as the water holding capacity of the Yamuna flood plain in Delhi. It assumes 20 m of unconsolidated sand in Yamuna flood plain to be available for recharging and considers that 50% of surface water in the flood plain gets absorbed/recharged. This implies that the present water level in Yamuna flood plain, occurring at a depth of 5 m b.g.l, needs to be further lowered to 25 m b.g.l. According to Soni, this will result in 20 m of aquifer material being available for recharge, which implies dewatering 20 m of the aquifer. The feasibility of this approach needs to be examined in further detailed study of the Yamuna flood plain in the perspective of sustainable yield. Groundwater management options: 4

5 The optimal pumping of groundwater from the aquifer of Yamuna flood plain should cater to socio-economic, ecological and political considerations. The socio-economic considerations emphasize the fact that water level lowering during peak demand periods should not affect the discharge of farmers tubewells, which may lead to greater costs in crop production. Lowering of the water level will also increase the cost of groundwater abstraction. The ecological considerations emphasize the fact that water level lowering during peak demand periods should not lead to saline water up-coning from below, and the soil moisture content in the flood plain should be enough to cater to the requirements of the root zones of the different biota present there. Since the flood flow of Yamuna River in the area under consideration is significantly larger than the water required to replenish the dewatered aquifer, there will still be a large volume of flood water for downstream flood plains, water bodies, wetlands etc. The political considerations emphasize water sharing agreements between the riparian states and other bodies. Pumping from any well field within the Yamuna flood plain should also consider the flow from river boundaries in to the aquifer, and due consideration should also be given to the rights of the upper and lower riparian states. Having recognized that the process of dewatering and refilling aquifers will have socio-economic, ecological and political considerations, any massive dewatering of Yamuna flood plain aquifer can not be attempted in the prevailing situation. A reasonable balance between these considerations will determine the optimal storage and withdrawal of additional groundwater. The optimal withdrawal of groundwater from the aquifer (or sustainable yield from the different sectors of the Yamuna flood plain) should be arrived at by detailed study incorporating concerns of all stake holders. An estimate may have to be made to quantify optimal storage of surplus monsoon river flow diversion in to subsurface reservoirs of the Yamuna flood plain in Delhi. The study can be initially taken up with an analytical approach based on a detailed database of groundwater withdrawal, recharge, aquifer parameters and groundwater quality in different parts of the flood plain, considering the system/systems as an individual lump/s. This should be followed by a system simulation and numerical modeling study aimed at a decision support system. There is a need among planners and water resource engineers for development of a comprehensive decision support system such that both surface and groundwater are fully developed and managed as an integrated and sustainable resource (Dr. S.V.N Rao, Danish Hydraulic Institute India, personal communication, 2008). The system simulation and numerical modeling approach should be adopted to prepare a computer based distributed parameter numerical model, incorporating the details of the Yamuna flood plain system of Delhi, with a provision for studying solute transport. The study should focus on groundwater development and replenishment (by 5

6 recharge) in the perspective of sustainable flood plain management policy. Some of the factors to be considered in the study are: saline water up-coning on account of fresh groundwater withdrawal; fixation of ecologically viable optimal flood water to be used for recharging groundwater; and the amount of sustainable storage and pumping of groundwater in the flood plain. The study should also consider that water in Yamuna River downstream of Wazirabad barrage is highly contaminated; how this contamination will affect the groundwater regime, and its treatment, needs to be studied. Babu et al (2003) had done ecological and economic evaluation of a stretch of the active Yamuna flood plain in Delhi from Wazirabad to Okhala barrage. The approach used by Babu et al (2003) could be integrated with the numerical modeling study of the flood plain at different stages so as to cater to social, economic and ecological concerns. Rao et al (2006b) visualize the use of skimming wells in order to control upconing from underlying saline waters, and suggest that the pumping schedule from such tubewells must be staggered in space and time. Rao and Manju (2007) suggest that such skimming wells most be operated from optimal locations such that they are staggered in space and time to obtain least saline water. The proposed functional model should be in the custody of a central agency, which should keep it updated in the light of emerging new field data. Some of the issues which the model can assess/examine are: behavior of the flood plain system under different stress scenarios; sustainable recharge potential of the flood plain under different groundwater abstraction schemes; effect on the groundwater system of different permutations and combinations of civil structures (which have either been constructed in the flood plain or are planned to be constructed); effect of peak floods on the groundwater system at different time intervals etc. The computer based numerical model will serve the decision support system for planners, relevant government institutions and other stake holders. As discussed earlier the preliminary study indicates that the Yamuna flood plain of Delhi can yield annually around million m 3 of groundwater (subject to further confirmation and improvement by detailed study). This volume of groundwater or the resultant new scenario can significantly augment drinking water supply to Delhi. The NCT of Delhi, being the capital of India, may be in emergency situations where the installations that supply drinking water may be threatened by natural disasters like earthquake etc., war, or deterioration in quantity/quality of Delhi's share of the river water coming through the open canal system. In such situations the drinking water supply system to Delhi may be jeopardized. The fresh groundwater from the Yamuna flood plain can then be pumped and supplied to different affected parts of Delhi by tanker. It may be worthwhile to assess the 6

7 maximum abstraction of groundwater from Yamuna flood plain in emergency situations and the amount of diversion of floodwater needed to replenish subsurface aquifers in such cases. Acknowledgements: The discussions with Shri G.C.Saha, Shri A.K. Bhatia, Shri P.N.Singh, Dr. Uma Kapoor, Shri Rana Chatterjee, Shri Raja Ram Purohit, Scientist from Central Ground Water Board is duly acknowledged. The authors are grateful to peer reviewers and editorial team of Hydrogeology Journal for their comments which helped in improving the manuscript. The authors are also grateful to Dr. S.V.N Rao, Consultant, Danish Hydraulic Institute- India, Delhi for his personal communication which helped in improving the manuscript. The authors are also very grateful to Sue Duncan, International Association of Hydrogeologists, for careful technical editing of the manuscript. References: Babu, CR, Kumar, P, Prasad, L, Agarwal, R (2003), Valuation of ecological functions and benefits: A case study of wetland ecosystem along the Yamuna river corridors of Delhi Region, Report, India Gandhi Institute of Development Research, Goregaon (East), Mumbai (India). CGWB (1996), Development and augmentation of groundwater resources in NCT of Delhi, Report, Central Groundwater Board, Ministry of Water Resources, Government of India, Delhi. CGWB (2006a),Groundwater resources of NCT, Delhi, Report, Central Ground Water Board, Ministry of Water Resources, Government of India, Delhi. CGWB (2006b), Hydrogeological frame work and groundwater management plan of NCT Delhi, Report, Central Ground Water Board, Ministry of Water Resources, Government of India, Delhi. CGWA (2000), Public Notice No. 9/2000, Sub: Declaration of the "Yamuna Flood Plain Area" within the NCT of Delhi as "Notified Area", Central Ground Water Authority, Ministry of Water Resources, Government of India, Delhi. Rao, SVN, Kumar, S, Sinha, SK and Shekhar, S (2006a), An operational model for groundwater pumping at Palla Well Fields, NCT, Delhi, Project Report, Joint study by National Institute of Hydrology, Roorkee and Central Ground Water Board, Delhi. Rao, SVN, Kumar, S, Shekhar, S and Chakraborti,D (2006b), Optimum pumping from Skimming Wells, J of Hydrologic Engineering, 11: Rao, SVN, Kumar, S, Shekhar, S, Sinha,SK and Manju,S (2007), Optimal pumping from Skimming Wells from the Yamuna river flood plain in north India, Hydrogeology J, 15: Rao, SVN and Manju, S (2007), Optimal pumping locations of skimming wells, Hydrological Sciences J, 52(2): Shekhar, S (2006), An approach to interpretation of Step Drawdown Tests, Hydrogeology J, 14: Soni, V (2007) Three waters An evaluation of urban groundwater resources in Delhi, Current Science, 93 :

8 Fig.1 : Map showing location of the study area (NCT Delhi) with relevant hydrogeological features and localities. 8

9 Fig.2 : A cross section transverse to River Yamuna in the active Yamuna flood plain to the south of Palla area. The interface between fresh and saline groundwater is shown as dotted lines in the lowermost formation. Different formations are shown by distinct hatching, along with labeling on the figure itself. 9