KNP Hydrological Survey
GROUNDWATER IN KIRTHAR NATIONAL PARK

General
The climate of Khirthar National Park (KNP) is hot and arid with average rainfall of about 150 mm/a and evaporation of more than 5000 mm/a. Most of the rainfall is intense during a short monsoon season in July and August. Daily rainfall of more than 100 mm has been recorded at a station near KNP in January, June, July and September, but the wettest month is usually August with an average 2.1 rainy days.

The hydrology of KNP has not been studied in detail in this or any other investigation. However, it is evidently similar to that of areas with "range and valley" landforms in warm to hot arid areas that have been studied in southwest USA and parts of inland Australia.

Intense rainfall on catchments with large areas of bare rock results in high runoff from the ranges. Moreover, the steep gradient of the beds of these streams, and the small catchments ensure that there is flow for only a short period following rainfall, providing little opportunity for infiltration to rocks within the ranges.

In the flatter valleys, flow velocities are lower, and the streams deposit sediment and lose water by infiltration into sands and gravels. This infiltrated water sustains aquifers in river alluvium, poorly consolidated recent sediments, and older limestone and sandstone formations beneath the valleys of KNP.

There are no permanent streams in KNP, and consequently all forms of life depend on water storage in the top few metres of soils, or the aquifers. For most of each year, groundwater drawn from wells, or discharging from natural springs provides the only source of water for wild and domestic animals, irrigation and human use throughout the park.

The groundwater component of the KNP baseline study has the objective of determining water quality at selected sites, collating existing hydrogeological information, and developing a preliminary model of groundwater storage and flow.

Water Quality
Water samples taken from selected springs and wells before and after the 2000 monsoon season have been analysed at the University of Karachi for a range of chemical and bacteriological characteristics. The sampling program was limited by access, time and budget. Twenty-two sites were selected on each occasion with limited repeats. The sampling ensured a reasonable spatial coverage of the park and provides some evidence of changes over time.

Most of these samples fail to meet bacteriological guidelines for domestic water supplies, and many of them are sufficiently saline to reduce the yield of some irrigated crops.

Nearly 20 years ago, 158 wells in KNP were inspected for the Pakistan Water and Power Development Authority. Of these, four wells provided water described as saline. Chemical analyses of water from 31 of the wells resulted in salinity (total dissolved solids) ranging from 400 to 3440 mg/L and averaging 1290 mg/L. The analyses show variable chemical composition of the water. Sodium and chloride were the dominant cation and anion respectively in most (61%) samples, with calcium the dominant cation in around 13%, and magnesium in around another 13%. There was detectable carbonate in 19% of samples and bicarbonate was the dominant anion in 13% of them. Sulphate was the dominant anion in 19% of the samples. Sodium and chloride are common in marine sediments, and calcium and magnesium are associated with limestone rocks.

The abundance of natural isotopes (2H and 18O) in some spring water samples has been determined in Australia. The results show that the water has been subjected to minimal evaporation, which is consistent with rapid runoff and infiltration following rainfall.

Flow from Springs
In February and March 2000 (about 6-months after the previous monsoon season) springs ranged from small stagnant pools to lakes of 1 ha or more with substantial discharges. Flow from these large springs is channeled up to 5 km for irrigation and domestic use. Flow in channels from three of the springs was estimated to be more than 1 ML/d, with the largest being about 7 ML/d. Karstic limestone is evident in the strata at one spring that was inspected.

Yield of Wells
Groundwater is drawn from a very large number of dug wells for irrigation, and stock and domestic water supplies in KNP. The dug wells are typically of order 100 m2 in area with no lining or structural support of the walls. Where the strata are not sufficiently consolidated, sections of the wall were seen to have collapsed.

In 2000, most of these wells were equipped with centrifugal pumps powered by a diesel engine. A few drilled boreholes were seen equipped with electric-submersible pumps supported by a nearby diesel-powered generator.

The earlier report to the Pakistan Water and Power Development Authority provides valuable statistical data on groundwater levels, and the yield of wells. Most of the wells were dug to a depth 1 to 3 m below the water table, which was 3 to 26 m below ground level. The wells were pumped at rates of less than 1 L/s for domestic use, or 2 to 3 L/s for irrigation.

Storage within the wells is important in most cases. Wells pumped at rates of about 8 L/s were pumped dry in less than 24 hours, but the water level was reported to recover in about half the time taken to pump the well dry. A few wells were reported to sustain pumping rates of more than 15 L/s with drawdown of about 0.5 m indicating locally high transmissivity of the aquifer.

Groundwater Model Development
The groundwater model collates quantitative information relevant to groundwater recharge and flow in the Taung Valley. This area was chosen because as a first-estimate it is assumed that there is no groundwater flow beneath the surface divides of the hills, and there appears to be a fault at the bottom of the valley, that causes groundwater to be discharged to the surface (Tikho Spring). The model assumes steady flow conditions, or average water levels and rates of flow.

A groundwater model can never be more reliable than the information used in its development, and there has never been a suitable hydrogeological study of KNP. For the current model, aquifer properties are estimated from descriptions of the strata; groundwater recharge beneath the streams is estimated from the area of catchments in the ranges; groundwater withdrawal from wells is estimated from the area of irrigated land; and groundwater levels are estimated from ground elevations as inferred by the digital elevation model (DEM).

By its nature, a steady-state groundwater model ensures mutual consistency of groundwater recharge/discharge and aquifer properties data. However, the absolute values of these parameters cannot be determined reliably without a major investigation at the site.

Expected Benefits of Developing a KNP Groundwater Model
A reliable groundwater model provides the best available tool for predicting potential impacts of any proposed changes of land use, groundwater production, etc on groundwater levels and flows. Such a model is now considered to be an essential aid to development of groundwater management policies and plans.

However, at this stage of development, the major benefit of the KNP groundwater model will be a better understanding of the hydrogeology of the area, and specifically the parameters that would need to be determined more accurately to improve that understanding and the reliability of a revised model.

A specific benefit is that it may be possible to relate chemical water quality and the location of springs to regional hydrogeology and land use.

Bacteriological water quality is likely to be intimately related to sources of animal and human contamination relative to unprotected water sources.