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Paper for International Shallow Water Conference

Rapid Assessment of the Fresh-Saline Groundwater Interaction
in the Semi-arid Mewat
District (India)

Nicholas Thomas1, Rebecca Sheler1, Benjamin Reith1, Sean Plenner1, Lalit Mohan Sharma2,
Salahuddin Saiphy2, Nandita Basu1, Marian M. Muste1
1Department of Civil and Environmental Engineering,
The University of Iowa, USA
2Institute of Rural Research and Development,
The University of Iowa, USA

Salinization of groundwater sources is an increasingly significant issue specific to agroeconomies tightly linked to freshwater resources. Rural India agricultural communities in the Mewat District, Haryana continually see an influx of saline groundwater into historically fresh areas. Recharge structures offer some resistance to the saline intrusion in most areas, but increasing abstraction for agricultural purposes counteracts the inputs from recharge basins. A lumped hydrologic model for a localized area analyzes the total flux of water through the ground to identify possible improvements to current practices. A framework is identified for hydrologic modeling of saltwater fresh water interactions in the study and for future developments.

1. Introduction
Groundwater salinization has been cited as the biggest single threat to aquifer sustainability (Foster and Chilton, 2003). Salinization can be caused by saltwater intrusion resulting from aquifer drawdown (primary salinization), or by agricultural intensification (secondary
salinization). It has been estimated that 20% of the world’s irrigated areas are affected by secondary salinization, with India, China, Pakistan and Australia accounting for some of the most salinized soils.

In India, 5.5 million ha area is saline soil and 3.88 million ha area is alkali soil, totaling 9.38 million ha area of salt-affected soils (IAB, 2000). Salinity is currently growing in the region at a 10% per year (FAO, 2009). Saline zones can increase over time due to several factors related to the regional geomorphology and human intervention. Those factors include the natural salinity of the soil in the region, accumulation of salts in the top layer due to evapotranspiration, excessive use of chemical fertilizers, poor drainage conditions, and excessive uncontrolled irrigation.

The paper focuses on the Mewat District in Haryana, India where groundwater salinization issues have debilitated the already struggling local economy that relies primarily on groundwater irrigation for farming. The location of the district and a recent survey of the saline groundwater delineation are provided in Figure 1. The area is devoid of perennial surface water sources making availability of groundwater the critical factor in defining the sustainability of the agroecosystem. The water-driven crisis in the district determined the Institute of Rural Research and Development (IRRAD), a Non-Government Organization (NGO), to initiate a series of multifaceted
on-the ground actions to address the issue of fresh water availability in the District with consideration of the hydrologic and socio-economic aspects within a sustainable watershed development framework.

Figure 1: Mewat District June 2008, a) Location in India; b) Mewat District; c) Groundwater salinity map of Mewat District.

Figure 1: Mewat District June 2008, a) Location in India; b) Mewat District; c) Groundwater salinity map of Mewat District.

A group of thirteen multidisciplinary students from the University of Iowa and the IIHR has been hosted for two weeks by IRRAD as an integral part of the International Perspectives in Watershed Sciences and Management course in the winter of 2011-2012 ( Preliminary discussions between the course instructors and IRRAD posed the essential elements of the Mewat District water problem to be tackled by the students during their visit with IRRAD. After the arrival in India, the student research team was further familiarized with details about the salinization issues through discussions and site visits (Figure 2). The site visits offered a dramatic illustration of the severity and extent of the problem, while further motivating the group of young researchers. The student team self-organized around their academic backgrounds and embarked on fast-paced activity throughout their term in India. The rapid assessment study was organized into the four following themes: a) water sustainability indicators; b) data collection, assembly, and synthesis; c) numerical simulation framework to understand groundwater flow; and d) water quality and health-related aspects of water use.

The paper aims to illustrate the background of this challenging water issue and display the steps that the IIHR short international course students took to quickly grasp some insights into the issue. The immediate targeted result was to provide practical information on the migration of the saline groundwater as a function of natural (e.g., climate dynamics, soil characteristics) and anthropogenic (e.g., human water use, IRRAD interventions) forces. Adoption of this approach was constrained by the lack of resources, data, and time.

The simple approach adopted for developing a hydrologic model that captures the essential elements of the groundwater dynamics in the Mewat District area is described in this paper. The history of the region and solutions implemented by IRRAD is described in Section 2, while the issues to be addressed is identified in Section 3. In Section 4, a framework for numerical modeling is described. Preliminary data synthesis to quantify recharge, abstractions and hydraulic gradients is described in Section 5. Finally, future work is discussed in Section 6.

Figure 2: The University of Iowa's course team during the visit to Mewat and IRRAD offices.

Figure 2: The University of Iowa’s course team during the visit to Mewat and IRRAD offices.

2. Regional Water Issues and Interventions
The Mewat District is one of the poorest regions in India. A semi-arid climate, limited surface water, and salinization have resulted in a severe shortage of fresh water. Groundwater is the primary source of fresh water, but available groundwater is limited to a few freshwater pockets and the remainder is saline. Freshwater pockets provide water to only 61 out of 503 villages in Mewat. Saline groundwater cannot be utilized for domestic or agricultural purposes because of high levels of total dissolved solids (TDS). Despite this, most villagers continue to use saline water for their livelihoods. Many other problems arising from the limited freshwater supply are
exacerbated by the mass extraction of fresh water, which is outpacing the natural water recharge. If exploited at the current rate, fresh groundwater in the Mewat district is expected to be depleted within the next 10 to 15 years (CGWB, 2007).

The geographical area of the Mewat district is 1860 km2 and consists of alluvial plains with elongated ridges and hillocks. Ridges and hillocks lie to the west, south, and east sides of the region creating a bowl-like shape. The hydrology of the area is characterized by flashy runoff events whereby precipitation falling on the ridges and hillocks in the area is quickly conveyed as runoff into ephemeral streams, which settles in the central flats dominated by saline soils and brackish groundwater. The principal precipitation occurs during monsoon period from June to September when about 80% of the rain is received. The average rainfall varies from 336 mm to 440 mm in the district, with the maximum in July. Even the most extreme rain events on record do not produce enough runoff to convey water flows outside the Mewat district boundaries.

Since there are no existing rivers in the Mewat district, precipitation is the only source of fresh water for recharging the local and regional aquifers. The soil of the district is light in texture (i.e., sandy, sandy- loam and clay-loam) and poor in water and nutrient retention. Almost all the soils of the district are low in organic carbon and phosphorus, with a soil pH in the 7.0 to 8.5 range (Chauban, 2008). These adverse factors combined with the increased access to pumping equipment in recent years have led to an extension of the irrigated area from 72% to 88% during 1990-2004. Several studies have been conducted to assess the increasing rate of groundwater
exploitation in Mewat (CGWB, 2007; Chauban, 2008). These studies observed that the depth to water table below ground level ranges from 5 to 29 meters over the region. During the monsoon season, the water tables have shown to rise by a few meters; however, long term data over ten years has shown a general decrease in water table depth from 0.2 to 4 meters. The quality of ground water that is rising or stagnant is becoming increasingly brackish. Within 30 meters of the surface, it has been estimated that only 26% (500 km2) of the land bears fresh water and the salinity increases with depth (CGWB, 2007).

Given that precipitation is the only source of water for direct use, water harvesting is critical. Historically, the upland areas of the district were fit with water harvesting structures aimed at either recharging the groundwater aquifers or storing it for direct use. Most of these structures are currently not functional, abandoned, or silted (Chauban, 2008). IRRAD has made Mewat a focus of their development and education endeavors, working in the region since 1999. IRRAD has been continuously preoccupied with the multi-faceted aspects of fresh water availability in the District including the socio-economic impacts and the sustainable watershed development. The agency has searched and implemented innovative rainwater harvesting techniques to address issues of salinization and water availability in the area. Previous IRRAD interventions in the area include:

  • Renovation and upgrading of the historical water retention recharging structures
  • Rainwater harvesting measures (roof systems for larger building such as local schools)
  • Rainwater storage and conservation at the foot of the hills
  • Implementation of innovative solutions for bio-filtering bacterial contamination
  • Water education and training activities targeting multi-level water users (villagers, management authorities, agricultural agents)

While making great strides in communicating and educating communities on the issues of water availability and quality in Mewat, IRRAD activities can be considered local (i.e., at the village rather than basin level) with incomplete understanding of the natural and man-induced influences on dynamics of the surface and subsurface water flow through space and time.

3. Problem Statement and Selection of the Study Site
Several factors are responsible for the rapid depletion of fresh groundwater in Mewat, and some of which are attributable to Mewat’s ground conditions. First, saline aquifers are located in lowlying areas which contain saline soil. Most runoff flows down into these saline soil areas, continuously recharging saline aquifers and raising saline water tables. Second, most fresh groundwater tables are contained in foothills with higher ground gradient. Although a large amount of runoff is generated in the uphill areas, it flows rapidly through the high-gradient freshwater areas and, due to its low concentration time, freshwater percolation into the ground is minimal. The result is the poor recharging of fresh groundwater pockets. Third, fresh groundwater tables are found deeper than saline groundwater tables. Due to the difference in depth between the two groundwater tables, saline groundwater flows towards fresh groundwater tables. As a result, saline water areas are encroaching over freshwater pockets and thereby existing freshwater pockets are shrinking.

Another factor for the rapid fresh water depletion is the extraction of fresh water by villagers at a rate which outpaces that of natural water recharge. In the current situation a limited amount of fresh water must supply the requirements of local and neighboring villages. Further exacerbating the situation, some villagers indiscriminately use available fresh water for domestic and agriculture purposes. For example, wealthier farmers purchase small patches of land located above fresh groundwater tables, install tube-wells to pump fresh water to irrigate fields located in saline the groundwater areas. The result of these combined factors is enlarging saline groundwater areas, which poses a challenge to the water resource management in Mewat.

To address these issues, IRRAD has been promoting rainwater harvesting techniques to increase fresh water availability within the saline groundwater zones. This is achieved by constructing check dams at the foothills of the mountain ranges. Water stored in ponds behind check dams is given additional time to infiltrate into the groundwater. In addition, IRRAD has constructed recharge wells in these ponds that provide a faster passage of water from the surface to the subsurface. These interventions enhance the natural water recharge at the foothills, increase freshwater storage, and can potentially lead to the retraction of the saline zones. However, the degree to which such interventions are effective is a function of both climatic factors as well as human water use.

The check dams in some locations within Mewat have been observed to be beneficial in terms of shrinkage of the saline zones. In other areas, saline zones have continued to expand despite the check dams. One such location where saline zones have continued to expand despite the construction of check dams is the area between the villages of Ghagas and Karhera in the eastern part of the district. Ghagas is a freshwater village with an area of 7.3 km2 and is situated at the base of the Aravali Hills. Approximately 1.75 km2 area of the Aravali Hills contributes runoff to Ghagas. Karhera sits to the east with an area of 3.8 km2, and lies entirely in a saline area, see Figure 5.

IRRAD has installed four check dams in Ghagas, as well as recharge wells to enhance groundwater recharge. Additionally, they have minimized the practice of deforestation in the hills that has helped increase natural infiltration and decrease runoff. Despite these efforts, IRRAD has detected encroachment of the saline groundwater into the fresh groundwater zones. In 2002, Ghagas was located entirely in a freshwater region. By 2008, a portion of the village was located in a moderately saline zone as shown in Figure 3. The intriguing dynamics observed in the groundwater of this region are motivation for further study.

Figure 3Figure 3: Saline ground water encroachment from 2002 to 2008 in the Ghagas-Karhera general area

4.0 Conceptual Model
Flow of water precipitated in the hill areas is depicted in Figure 4 and is explained conceptually as the flow through three zones. Zone 1 represents the Aravali Hills, Zone 2 represents the village of Ghagas that lies in a partially fresh groundwater region, and Zone 3 represents the village of Karhera that lies in a region of saline groundwater.

Steep slopes and high rainfall intensities result in low concentration time and minimal infiltration in Zone 1. Water flows from Zone 1 to Zone 2 in the form of surface runoff where it recharges the groundwater. Natural recharge is enhanced by artificial recharge promoted by IRRAD using features such as ponds and/or recharge wells. Runoff not recharging Zone 2 enters Zone 3 and recharges the saline zone thus making it unusable. Creation of check dams and recharge wells in Zone 2 further enhances natural recharge and leads to less water entering Zone 3 and becoming saline. Water is also abstracted from Zone 2, and used either for domestic or agricultural
purposes. A large portion of the water abstracted from Zone 2 is transported to Zone 3 and used for irrigation. This leads to rise in the water table in Zone 3 and flow of saline groundwater from Zone 3 towards Zone 2. Abstractions lower the ground water table in Zone 2 which also increases flow of saline water from Zone 3 to Zone 2. Increasing recharge in Zone 2 by artificial means can raise the water table in Zone 2, slowing the migration of the saline groundwater from Zone 3 to Zone 2. If there is sufficient rise in the water table in Zone 2, it is possible to develop a movement of fresh water from Zone 2 to Zone 3, leading to contraction of the saline zone. The objective of this initial assessment is to quantify the natural and enhanced recharge due to interventions by IRRAD, as well as the abstractions by the farmers, with the overall goal of understanding the fresh water and saline water dynamics in the area.

Figure 4: Typical cross-sectional view of surface and groundwater dynamics.

Figure 4: Typical cross-sectional view of surface and groundwater dynamics.

5. Data Assembly and Collection
The multi-disciplinary student group joined IRRAD in initiating a fast-paced, yet comprehensive, effort to approach the water problem in in the Ghagas-Karhera area during the course time spent in India. The first activities targeted quantification of key variables involved
in the groundwater recharge using a variety of field measurements. Preliminary groundwater recharge values are identified through estimation of artificial recharge, natural recharge, and abstractions. Data acquisition and modeling was limited to the domain delineated in Figure 5.

Figure 5: 90-m resolution digital elevation model of: (left) the area of interest in Mewat and (right) Ghagas pump and boundary information.

Figure 5: 90-m resolution digital elevation model of: (left) the area of interest in Mewat and (right) Ghagas pump and boundary information.

Hydraulic gradients were determined using the monthly groundwater table depths available on record, see Figure 6. It can be observed that the groundwater levels increase during monsoon season (June to Septempter) which induces an increase of recharge. Decreases of groundwater during all other times of the year are due to groundwater usage. The hydraulic gradient (dh/dx) between Zone 2 (Ghagas) and 3 (Karhera) is identified as the difference in groundwater elevation over the distance between zones. The average difference in depth to ground water is 16.4m, the difference in surface elevation is 15m, and the distance between Zone 2 and Zone 3 is approximately 3 km, yielding a hydraulic gradient of 0.0005 m/m. Currently the groundwater table in Karhera (saline zone) is greater than in Ghagas (fresh zone) identifying a migration of the saline zone towards the freshwater zone. Increase in freshwater levels in the Ghagas village will lead to a proportional decrease in the hydraulic gradient and a slower migration of the saline zone. In the following sections, attempts to estimate the ground water fluxes (recharge and abstraction) that lead to an alteration in the water table depth in Ghagas village are discussed.

Figure 6: Monthly water table depth below ground surface for Ghagas and Karhera (2011).

Figure 6: Monthly water table depth below ground surface for Ghagas and Karhera (2011).

Estimation of water abstraction for irrigation utilized site specific land usage. Irrigation practice information was acquired from surveys of eight local farmers. Specific pumping data recorded include hours of operation during monsoon season, hours of operation for non-monsoon season, and type of pump used. Mustard, wheat, onion, and tomato are the most common crops for this village. The volume of water per acre was calculated for each crop type using the quantity of irrigations per season. Irrigation practices of the specific farmers interviewed were used to estimate land use for the entire Ghagas area. Assuming a majority of the water pumped is utilized for irrigation purposes, abstraction values were identified. Abstraction rates ranging from 18.3 to 29.5 m3/hour with a mean of 23.5 m3/hr were found using the results from the farmer questionnaires.

A secondary technique utilizing well locations, pumping rates, and pumping times returns a comparable abstraction rate. For this technique a stop watch was used to determine the time it took to fill a 210 L bucket. The flow rate was calculated and compared for two different types of pumps. The 7HP electric pump forces a flow rate of 24 m3/hour whereas the 10HP diesel pump produces a flow rate of 33 m3/hr. The spatial distribution of these pumps is shown in Figure 5. Using the flow rate data from the pumps and the average hours of operation per day, an estimated 151 m3 of water is pumped every day from each tube well. Using these different techniques and statistically analyzing the results of the two methods, an average abstraction rate of 25.2 m3/hour was obtained; however, each of the identified abstraction rates fail to address water pumped to locations outside of the modeling domain.

Figure 7: Photos taken during data collection from local farmers.

Figure 7: Photos taken during data collection from local farmers.

Artificial recharge is the practice of recharging the groundwater reservoir at a rate greater than the natural rate by allowing the water to pond for longer (by using check dams), or more focused recharge using recharge wells. Both storage (check dams) and recharge ponds (check dams and recharge well) were implemented at Ghagas. Pond sizes were estimated through rough GPS cross sections and measurement of the outlet structure height (3.02 m). Since the transverse pond width (120 m) was the only available measurement, longitudinal distances from 100 to 350 m were used to calculate the pond area assuming an ellipsoidal shape and trapezoidal cross section with 1:0.165 (H:V). The time for each pond to drain is acquired from intermittent monitoring by the local population, approximately 3 days for the recharge pond and 1 year for the storage pond. Therefore, the recharge rates could be calculated assuming infiltration through the bottom surface of the pond. Since this method assumes no recharge occurs until the pond is full, a range of possible volumes is shown in Figure 8.

Figure 8: Artificial recharge rates for varied pond volumes.

Figure 8: Artificial recharge rates for varied pond volumes.

Figure 8: Artificial recharge rates for varied pond volumes

Natural recharge consists of water that travels to the groundwater table originating from the unaltered process of rainfall, runoff, and infiltration without artificial ponding. This recharge occurs at locations outside of the artificial recharge drainage areas. Natural recharge is estimated using the Chaturvedi formula shown which is based on an annual value of precipitation in an arid or semi-arid region where P is the annual precipitation and R is the net recharge due to annual precipitation.

R = 1.35(P – 14)0.5

Ghagas receives 594 mm of precipitation each year, utilizing Eq. (1), 32.5 mm will recharge naturally. The natural recharge rate is 32.5 mm/year, while artificial recharge rates can vary between 490 mm – 600 mm/year for recharge ponds.

6.0 Future Work
The preliminary values and simplified modeling presented herein are based on short term, inconclusive data sets. Further exploration into alternative estimation techniques and more field information can yield significantly improved groundwater recharge estimation. Possible techniques include a soil water balance, water fluctuation method, Darcy’s Law, tracer methods, and other physical measurement techniques. Through the addition of spatially descriptive recharge, precipitation, evaporation, and abstraction data, two and three dimensional modeling software can be implemented to better explore the subsurface fresh-saline groundwater interactions. Two dimensional (i.e. MODFLOW) or three dimensional (i.e. HydroGeoSphere) modeling software are considered for this purpose. The information provided by the analysis of various water-use scenarios (pre- and post-structure environments) will allow for an increased
understanding of effect of the surface water retention structures on groundwater recharge. Furthermore the effects of land use, additional structures, recharge technology, and climatological alterations can be further assessed. The results of the hydrological modeling will be evaluated in the context of sustainable development with due consideration to socio-economic aspects of the water usage.

Tackling a real and complex water resource problem during the short duration of this course posed challenging educational aspects for students and instructors. The initial efforts, insights, and conceptualization of the fresh-saline water interactions described in this paper illustrate, however, the potential of these intensive, short-term educational courses to engage students in new and challenging studies through a team effort. The study will be continued through longterm collaborative research involving current and future students of the IIHR International Course and IRRAD. Each course offering will continue to engage ten to fifteen U.S. students in this valuable style of first-hand professional experience. Paralleling host-country particularities with the American perspective in water resources management will add an international dimension to existing curricula, preparing the students for careers that are becoming increasingly

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Last modified on September 10th, 2015
Posted on August 26th, 2012