**2. Case study**

The growing need of water supplies for both domestic and irrigation purposes has led to the exploitation of surface and groundwater resources in the Soan watershed of Indus basin. In the last drought of 1999–2002, the groundwater abstractions have been increased due to rapid increase in the number of private tube wells for irrigation purpose. Excessive pumpage of groundwater from these wells causes a gradual decline in water table. The decline in ground‐ water levels in the Rawalpindi area has imposed not only a threat to the livelihood of the residing communities but also a significant influence on the sustainable development of the watershed as a whole. Therefore, understanding and investigation of the groundwater dynamics in the target area have great significance in facilitating the socioeconomic and ecological development, as well as the sustainable development of the water resources. The watershed contains metropolitan areas of major cities of Islamabad and Rawalpindi, the combined population of which is about 2.8 million, with a density of 880 persons/km2 . Surface water supplies are maintained from Rawal and Simly reservoirs, which provide 21 million gallons per day (MGD) to Rawalpindi city and 17 MGD to Islamabad city. Groundwater supplies are 24 MGD from about 200 public tube wells in Islamabad, and 27 MGD from about 300 public tube wells in Rawalpindi. The average needs of Islamabad and Rawalpindi are 65 and 175 MGD, respectively, which exceed the capacity of available water resources.

#### **2.1. Description of the study area**

in the system [5,6]. The Indus groundwater system is also facing the temporal as well as spatial impacts of changing environment. A detailed appraisal of the subsurface aquifer system is thus vital in the context of prevailing conditions of drought/flood and the growing demand of water for sustainable development in the region. In recent years, groundwater numerical simula‐ tion models have been widely applied to groundwater dynamic simulation and as a manage‐ ment tool. The development and application of a groundwater model is a common practice for themanagementofgroundwaterresources[7].Manyscientificeffortshavebeenmadetodevelop more comprehensive and computationally efficient models involving complex hydrogeologic processes [8,9]. In many numerical models of a groundwater aquifer, for example, Feflow and MODFLOW, the continuous domain of groundwater system is replaced by a discretized grid network and the governing groundwater flow equation is solved at the network nodes. The inverse modeling (also called parameter optimization) is capable of assigning approximate values to the hydrological parameters by employing approximate methods to solve the partial

Pakistan is in the grip of a water crisis. This involves a hydroelectric power shortfall, per capita

in metropolitan areas, including the twin cities of Rawalpindi and Islamabad. Because pumping exceeds recharge, groundwater reserves are becoming significantly depleted. Groundwater overdraft has caused the groundwater table to decline remarkably and resulted in a series of ecological issues such as deterioration of water quality, soil aridity, deterioration

In the present study, a three-dimensional numerical groundwater flow modeling using finitedifference Visual MODFLOW coupled with decision support tools of geoinformatics was applied to analyze the spatial and temporal behavior of groundwater in the valley plain of the sub-Himalayan watershed in Pakistan. The multilayered aquifer system of the watershed is recharged mainly by the surrounding dissected land and rocky mountainous terrain. The behavior of the groundwater system was predicted in response to probable hydrogeological

The growing need of water supplies for both domestic and irrigation purposes has led to the exploitation of surface and groundwater resources in the Soan watershed of Indus basin. In the last drought of 1999–2002, the groundwater abstractions have been increased due to rapid increase in the number of private tube wells for irrigation purpose. Excessive pumpage of groundwater from these wells causes a gradual decline in water table. The decline in ground‐ water levels in the Rawalpindi area has imposed not only a threat to the livelihood of the residing communities but also a significant influence on the sustainable development of the watershed as a whole. Therefore, understanding and investigation of the groundwater dynamics in the target area have great significance in facilitating the socioeconomic and ecological development, as well as the sustainable development of the water resources. The

, falling levels of groundwater, and limited water supplies

differential equation (PDE), which describes the flow in a porous medium.

water availability less than 1100 m3

4 Groundwater - Contaminant and Resource Management

stresses.

**2. Case study**

of vegetation, and land desertification [10,11].

The Soan watershed covers an area of about 1684 km2 with its longitude 72° 54′–73° 34′ E and latitude 33° 26′–33° 56′ N in the Pothwar plateau of Pakistan (**Figure 1**). In the north and northeast, it is bounded by the Margalla and Murree hills, which are covered with permanent mixed scrub and coniferous forest. The altitude in the watershed increases gradually from the southwest (<500 m) toward the northeast, near the Murree hills (>2000 m). The area is charac‐ terized by gentle to steep slopes. The dominant formations (e.g., the Murree and Kamlial belonging to the Rawalpindi Group of Miocene age) are composed of sandstone, shale, and lenses of conglomerates. The Lei Nullah conglomerates of Quaternary age consist of poorly sorted pebbles and boulders of mostly Eocene limestone strata [12]. The most important aquifers are composed of gravels and boulders in the unconsolidated sediments of Pleistocene and Recent age. Alluvium (the channel-fill deposits) consists of dominantly silt and clay with subordinate amount of gravel and sand. The soils are mainly gravelly, medium to fine textured over calcareous material in the north and northeast and medium to coarse textured over sandstone in the south (**Figure 2**). The main perennial stream in the watershed is the Soan, whose primary tributaries are the Ling, Gumrah Kas, Korang, and Lei Nullah. The Korang and

**Figure 1.** Location of Islamabad watershed and study area.

Soan rivers are dammed at Rawal and Simly reservoirs, respectively. Due to high urban sprawl, a major area has been converted into various degrees of built-up category in the model domain (**Figure 3**).

**Figure 2.** Dominant soil classes in the Soan watershed.

**Figure 3.** Major land cover/land use in the study area.

Appraisal of Groundwater Flow Simulation in the Sub-Himalayan Watershed of Pakistan http://dx.doi.org/10.5772/63324 7

**Figure 4a.** Trend in annual precipitation at Islamabad Airport (1960–2013).

Soan rivers are dammed at Rawal and Simly reservoirs, respectively. Due to high urban sprawl, a major area has been converted into various degrees of built-up category in the model domain

(**Figure 3**).

**Figure 2.** Dominant soil classes in the Soan watershed.

6 Groundwater - Contaminant and Resource Management

**Figure 3.** Major land cover/land use in the study area.

**Figure 4b.** The mean monthly precipitation at Islamabad airport.

Lei Nullah extends approximately 30 km from the Margalla hills in the northwest to the Soan River at the southeastern edge. The Lei catchment area is composed of 239.8 km2 (169.0 km2 in Islamabad and 70.7 km2 in Rawalpindi) [13,14]. The total rainfall during the monsoon rainy season is about 60% of the annual average rainfall, that is, about 1169 mm. The annual and mean monthly rainfall trends at Islamabad for 1960–2013 periods are shown in **Figure 4a** and **b**, respectively. Floods in the Lei Nullah basin occur during the monsoon season, which usually starts near the end of June with peaks in August and finishes by September. In June, the daily maximum temperature reaches 40 °C, while the daily minimum temperature falls near 0 °C in December and January [15].

### **2.2. Hydrogeologic framework**

Silt and clay dominate the subsurface lithology where gravel deposits are present in discon‐ tinuous layers with silty clay. The gravel beds are generally 1–20 m thick and are composed of limestone and sandstone pebbles mixed with sand (**Figure 5**). The thickness of the gravel beds decreases in the south and west. In contrast to the gravels, the bedrock is usually considered to act as an aquitard rather than an aquifer since well yields are much lower than encountered in the gravels. The maximum thickness of the alluvium is more than 200 m, as encountered in the test holes RWP-6 and 8 in Dhok Khabba and Dhok Ratta, respectively. Individual beds range in thickness to 30 m or more. The thickness of alluvium probably exceeds 300 m, as indicated by a deep resistivity survey. They are grayish brown to reddish in color and appear to have been deposited from reworked loess, Siwalik, and Murree rocks. It can become difficult to differentiate rotary cuttings of bedrock formations from the alluvial clays and silts. Sand formations are comparatively rare. Generally, the sand is disseminated within the gravel lenses or constitutes a minor fraction of the clays and silts. The aquifers are composed of seven permeable geological horizons with a total average depth of 137 m. About 300 water wells are being pumped for about 18–22 h per day year round to meet the growing demand of the inhabitants of the city.

**Figure 5.** Schematic of lithological section in the study area.
