Introduction

The South West district of the national capital territory (NCT) of Delhi, India (Fig. 1), has been required by the Government of India to regulate development of groundwater resources. The step was taken due to a rapid decline in groundwater level and quality (the current electrical conductivity of fresh groundwater is <1,500 µS/cm at 25°C). The district falls within a difficult scenario with regards to replenishable fresh groundwater resources. The study, reported here, tries to project future availability of fresh groundwater resources in the years 2007, 2012 and 2022. From a hydrogeologic perspective, the district has a simple geology comprised of Alwar quartzites in the east and fluvioaeolian deposits in the rest of the district (Fig. 2a). The borehole data of the Central Ground Water Board (CGWB) show alternate fluvial and aeolian bands distributed sporadically. The sediments are mostly silt with medium to fine sand and clay. The depth to bedrock (basement) is influenced by the steep escarpment at the margins of the hard rock area and mild undulation in the rest of the district (Fig. 2). On the fringes of the hard rock, the depth to bedrock is in the range of <30–300 m below ground level (m b.g.l.); the depth to bedrock increases as one moves away from the hard-rock exposure to the west (Fig. 2b). The depth to bedrock in the rest of the area is found in the range of 300–400 m b.g.l. Shekhar et al. (2005) describe the escarpment mentioned above as a fault zone and consider it to be one of the basic controls on variation in the depth to the groundwater fresh/saline interface in this district.

Fig. 1
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Map showing location of the study area

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Fig. 2
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a Geological map of South West district, NCT Delhi. b Depth to bed rock (basement) map of the South West district, NCT Delhi

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Premonsoon depth to water in the district varies in range of 2–50 m b.g.l. (Fig. 3a). The southwestern part of the district, comprising the Jhuljhuli and Roata areas (Fig. 3a), has shallow groundwater in a range of 2–5 m b.g.l. The area to the north of the above-mentioned zone, encompassing Dhansa and similar localities along the N–S stretch of the Najafgarh drain—including Dwarka Sector-3 and localities such as Amber Hai, Pochanpur and Bamnoli—has a depth to water in the range of 5–10 m b.g.l. The zone comprising localities such as Kair, Mandela Khurd, Bagargarh, etc. (Fig. 3a), has a depth to water in the range of 10–15 m b.g.l., and another zone to the east of the Najafgarh drain comprising areas such as Palam and Manglapuri, has has a a depth to water in the range of 10–15 m b.g.l. The central portion of the area to west of the Najafgarh drain, including localities such as Ujwah, Daulatpur, Chhawala, Kharkhari Nahar, Najafgarh, Jharoda Kalan and Dichaon Kalan, has a depth to water in the range of 15–20 m b.g.l. To the east of the Najafgarh drain, a narrow strip of region passes through Naraina and Bijwasan which has a depth to water in the range of 15–20 m b.g.l. The region with depth to water in the range of 20–30 m b.g.l. occurs to the east of the Najafgarh drain and passes through Shekhawati lines. The southeastern part of the area shows deeper groundwater levels in the range of 30–50 m b.g.l. (Fig. 3a). The deepest groundwater levels are observed in hard rock areas at higher elevations and in those areas adjacent to them.

Fig. 3
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a Map showing premonsoon depth to groundwater in the South West district, NCT Delhi. b Map showing the thickness of fresh groundwater zones in the South West district, NCT Delhi

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In a broader perspective, the deepest groundwater levels to the west of the Najafgarh drain are found towards the central part of the area and further north. The depth to groundwater in the region to the east of the Najafgarh drain shows an increasing trend moving from the west to the southeast (Fig. 3a).

Methodology

Shekhar (2004) and Shekhar and Singh (2005) talk about the availability of fresh groundwater in the district. Total available fresh groundwater in the district has been calculated on the basis of a map showing the thickness of fresh groundwater zones in different parts of the district. The same map (Fig. 3b) has been further classified here by giving nomenclature to different freshwater thickness zones to facilitate zonewise quantification of fresh groundwater resources. Thus, the methodology involves the microzonation of the district in terms of the thickness of fresh groundwater zones, and then projecting available resources in freshwater zones with the help of data from representative groundwater monitoring stations of the Central Ground Water Board (CGWB) that are located either within a fresh groundwater zone or near to it. Similar work has been carried out by CGWB for the Delhi subcity of Dwarka, wherein this methodology was used to evaluate the sustainability of fresh groundwater resources (CGWB 2003). In order to calculate the volume of the total available fresh groundwater resources in the district, areas having a thickness of freshwater zones in the range of 0–10 m (Fig. 3b) were not considered, because the majority of these areas have a thickness of freshwater in the range of 0 to <5 m.

Shallow groundwater is mostly saline in this area. Wherever a limited amount of freshwater (5 to 10 m thickness) is found, it cannot be utilized because the average drawdown in tubewells operating in this region is about 10 m, which is equal to or more than the available freshwater thicknesses. The zone with a thickness of fresh groundwater in a range of 30–40 m (zone E in Fig. 3b), contains a small patch with thickness of freshwater in the range of 20–30 m, which has been ignored for the purposes of calculation; the whole of zone E is considered to have a thickness of freshwater in the range of 30–40 m.

Utilizing the perspective of Shekhar and Singh (2005 ) on a local scale, an approach has been adopted to evaluate the total available fresh groundwater resources on a regional scale. The mean values of freshwater thickness ranges in respective freshwater zones, have been used to calculate the fresh groundwater resource for the district. The specific yield for the hard rock terrain has been determined as 0.015, and for alluvial/fluvioaeolian deposits the specific yield has been recorded as 0.1. The formulae used to assess the volume of available fresh groundwater are given below:

$$\begin{array}{*{20}c} {{v = A.T.Sy}} \\ {{and}} \\ {{T = M - D}} \\\end{array} $$
(1)

Where

V :

Volume of fresh groundwater available (m3)

A :

Areal extent of the zone (m2)

T :

Utilizable freshwater thickness (m)

S y :

Specific yield of the formation

M :

Mean of the freshwater thickness range (m)

D :

Average value of the assumed drawdown in a freshwater zone (m)

Results

With help of Eq. 1, the present availability of fresh groundwater resources of the district was calculated as 481 million m3 (Shekhar and Singh 2005). The projection of future availability of fresh groundwater resources in the district have been attempted on the basis of the yearly decline in water levels of different fresh groundwater zones shown in Fig. 3b. The average value of the yearly decline in the water level of the district was used to calculate the utilizable freshwater thicknesses (T) that would be available in the years 2007, 2012 and 2022. The likely volume of fresh groundwater available in the future was calculated from T, using Eq. 1.

Evaluating the future availability and sustainability of fresh groundwater resources was straightforward, due to the fact that there are a considerable number of groundwater monitoring stations (Fig. 4) more or less evenly distributed throughout the district. As mentioned earlier, the approach to this evaluation involved a zonal approach, where different freshwater zones (Fig. 3b) were studied separately to yield an average rate of decline in groundwater levels within different freshwater zones, based on the average change in groundwater over years 1997–2003 (Table 1).

Representative groundwater monitoring stations for each freshwater zone were selected based on their proximity to the respective freshwater zones (Table 1; Figs. 3b and 4). The two dugwells of Raota and Jhuljhuli (Fig. 4) that were used as groundwater monitoring stations are just adjacent to the Najafgarh drain. The trend in groundwater level given by these two monitoring stations (see Table 1) is not in tune with the general trend of the water levels observed in all the other groundwater monitoring stations of the area. Thus, for projection and quantification of fresh groundwater resources in the freshwater zones F3 and G3 (Fig. 3b), on the basis of proximity to the zones, these dugwells could have been selected, but because the general regional trends were contrary to the local trends given by these dugwells, for the purpose of regional quantification, the other groundwater monitoring station nearby (Daulatpur) was selected. The basic assumptions in the exercise presented are enumerated in the following:

  1. 1.

    The level of exploitation of groundwater resources in the coming years remains at the same level as it is today; this is likely to be so because the Government of India has notified this district regarding the regulated development of groundwater resources and thus, very few tubewells (nearly none) are permitted to be drilled in this district.

  2. 2.

    Recharge to groundwater by natural and artificial means will remain at the same level as of today for years to come

  3. 3.

    There has not been much change in geomorphic and land-use patterns in the district

  4. 4.

    Features like canal irrigation networks, huge surface water bodies, etc., will not be developed in the near future

Fig. 4
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Map showing location of key wells (groundwater monitoring stations) in the South West district, NCT Delhi

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Table 1 Premonsoon decline in water level (in meters) of representative groundwater monitoring stations
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The yearly decline in premonsoon water levels observed in representative groundwater monitoring stations for the period 1997–2003 was studied to arrive at an average value representing the rate of decline in respective freshwater zones (Table 1). Pre and postmonsoon water levels were studied on the assumption that if a decline in premonsoon water levels renders the aquifer unsuitable for groundwater exploitation, a rise in postmonsoon water level will not be of much use as regarding a sustainable exploitation of groundwater resources. Groundwater monitoring stations were grouped to represent regional areas in hard rock and other freshwater zones, and for each area, numeric values were derived that were supposed to represent the annual rate of decline in different freshwater zones of the district.

The different numeric values and their averages are given in Table 1. Examining data in Table 1, it becomes evident that the average rate of decline in hard rock areas of the district, represented by freshwater zone A, corresponds to 2.4 m/year. While the average rate of decline in the mid-eastern part of the district (zones B, C and D and zones E, F1 and G1) corresponds to 1.2 m/year. The average rate of decline for the F2 and G4 freshwater region (represented by Goela Khurd groundwater monitoring station in Fig. 4) equals 0.5 m/year. Similarly, for the freshwater zone in the Ujwah and Mandela depression, the average rate of decline has been assumed to be 1.2 m/year. On the basis of the present rate of decline in different zones, the number of years it will take for fresh groundwater resources to become unsuitable for exploitation is given in Table 2.

Table 2 Sustainability of the fresh groundwater resources based on average rate of decline for the period 1997–2003
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The mean of the yearly premonsoon decline rate averaged over different freshwater zones provides a simple tool for projecting groundwater scenarios for years to come. Thus, fresh groundwater pockets/areas of the district were studied and analyzed and the projection results are tabulated in Table 3; freshwater thickness in different freshwater zones was calculated for the years 2002, 2007, 2012 and 2022. On basis of the freshwater thicknesses for different years, new freshwater zones in different years were made. These freshwater zones were used for further quantification of fresh groundwater resources in the district. Table 3 shows how, in successive years, the future freshwater thicknesses (and ultimately volume of fresh groundwater) will decline on the basis of the past six years’ premonsoon behavior.

Table 3 A projection of the volume of fresh groundwater resources available in succeeding years
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As mentioned earlier, the present availability of fresh groundwater in the district was worked out by Shekhar and Singh (2005) to be 481 million m3 (see Table 3). It is estimated that 481 million m3 of available fresh groundwater resources will have reduced to 374 million m3 by year 2007 and to 303 million m3 by year 2012, and by year 2022, the district will have only 176 million m3 of available fresh groundwater resources. Figure  5 is a bar graph showing how, in successive years, the volume of fresh groundwater available in the district will decrease, while Fig. 6 is a composite bar diagram showing how the area underlain by saline and freshwater will behave in successive years. The projected figures provide a clue as to how the system will behave in the future with regards to availability of fresh groundwater. This will provide an important input for purpose of holistic and visionary planning in the district.

Fig. 5
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The bar graph shows the projected volume of fresh groundwater resources available in successive years in South West district, NCT Delhi

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Fig. 6
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The composite bar graph shows the relative areal extent of fresh and saline water in successive years in the South West district, NCT Delhi

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Discussion

With the approach used here, it becomes clear that the district has very poor utilizable fresh groundwater potential. Even so, the regions adjoining hard rock areas and traversed by the fault zone have better potentiality compared to other freshwater regions of the district. Similarly, freshwater zones along the Najafgarh drain, and one containing depressions, have somewhat better potentiality compared to other freshwater zones of the district, excluding the one mentioned earlier. These areas, having limited groundwater development potentiality, should be viewed with caution and treated as a buffer stock to meet emergency potable water requirements in the district.

At this stage, it would be appropriate to discuss the effectiveness of the methodology used here. There is an evenly distributed groundwater-monitoring network of stations in all formations of the district and in zones with different freshwater thicknesses. Once microzonation of the district with respect to freshwater thickness is complete, the groundwater monitoring stations act as effective control points for the quantitative assessment of fresh groundwater in different zones. Since the water level in these groundwater monitoring stations are regularly measured, and have been for a considerable period of time, the trend of the water level can be easily established. With the assumption that the system will behave in the future similarly to how it behaves now, and if other basic components of the system remain the same, prediction of groundwater scenarios have been possible.

The basic objective here has been to make individuals, communities, government bodies, planners, etc., aware of the approximate present and future availability of fresh groundwater resources in the district, so that individuals can become more responsible users of water, and the community and government can adopt developmental projects and water management practices with present and future fresh groundwater availability in mind. The objective has been accomplished in a very simple and effective manner. The objective could also have been achieved by simulation of the system on computer and then using numerical modeling techniques.

Simulating a complex system for the type of area mentioned here (where saline water occurs below freshwater at different depths, where there is a faulted zone on the fringes of the hard rock controlling the depth to the fresh/saline interface in groundwater, where there is a huge drain and where hard-rock exposures have considerable freshwater thickness underneath, etc.) would generally involve considerable simplification of the system. Verification of output of numerical modeling effort would again be provided by the same groundwater monitoring stations and historic data from those stations. Thus, to begin with, it was decided to adopt this methodology where field-based control points (groundwater monitoring stations) are key components. It is envisaged that the scope of future work in this area will be a computer-based functional numerical model that can act as a decision support system, incorporating all the minute details and complexities such as density dependent flow, fresh and saline water diffusion, heterogeneity and anisotropy in aquifer, groundwater draft and recharge pattern in the district, etc.. This will take considerable time and effort. Thus, a beginning has been made with a very simple approach. Having established that the fresh groundwater resources available at present and projected for the future are dismal, some suggestions with regards to water management in the district are proposed.

The water available to residents in the district should be used judiciously and in an efficient manner and water conservation habits should be incorporated into people's habits in daily life. The practice of dual water supply for residents of the district should be taken up in terms of freshwater for drinking purposes and saline groundwater for other domestic and horticultural activity. Wastewater and sewage should be prevented from going directly into village ponds in the area; instead local onsite treatment of wastewater should be taken up by the government and community on the scale of individual villages or group of villages. An attempt to recycle treated wastewater should be made. At the individual and community level, surface runoff from rural and urban parts of the district during monsoon times should be harvested and used for recharging the groundwater. Properly cleaned village ponds and parks in urban areas could be used at the community level for this purpose.

In hard-rock areas of the district there are numerous quarries, ponds and barren patches of land (observed during field survey) that can be utilized efficiently for recharging the groundwater by making suitable artificial recharge structures. The district does not have any canal irrigation facility and, in this respect, it will be desirable to have a canal network in rural areas of the district. This will reduce stress on groundwater in the district and, at the same time, the network of canals will locally recharge surface water to groundwater. Conjunctive use of surface and groundwater can then be taken up in command areas of the canal network. With regards to the Najafgarh drain carrying a large volume of water in the area, a pilot project study should be initiated to ascertain how this volume of water could be best utilized for recharging the groundwater in parts of the district in an eco-friendly manner and without contaminating the groundwater. Once this feasibility is established, then limited exploitation of groundwater utilizing only the additional recharged volume of groundwater can be planned on for meeting emergency water requirements of the district.

Lastly, there should be an emphasis on using salt tolerant varieties of crops. This will lead to utilization of shallow saline groundwater for agricultural purposes. Recharge to groundwater using excess surface runoff during monsoon time may create limited freshwater lenses above subsurface saline waters. The efforts of the individual, the community, and government bodies, working in harmony, can bring some hope to the residents of this water-scarce district.