Hydrogeological Study of Karez System in Tehsil Karezat, Balochistan, Pakistan

Abstract or Introduction

Karez is an underground water canal that is connected to the ground surface with a series of upright shafts or dug-wells. The canal receives groundwater by natural aquifer discharge from piedmonts and flows to the valley floor by gravity. It’s an ancient invention, technically inclusive, sound in performance, excellent in design and diligent in construction. The main objective of the study is to evaluate geohydrological aspect of the karez system. Geohydrologically Nisai Formation limestone of Eocene, alluvial fans and piedmont sediments of Quaternary are comprised of high potential groundwater zones. In Karezat out of 106 karez systems, 37 are partially active, 65 dried out, and 4 demolished. Karezes were constructed during the past 25-600 years and dried during the last 3-20 years. The karezes are dried up due to droughts that hit twice during the last two decades. The study area comprised of 7 Union Councils, as per 1998 and 2017 census the population increased from 76,360 to 138,208 persons, a 55% increase in nineteen years. From 106 existing karezes 48,000 inhabitants used to irrigate their lands, which is about one-third of the total area population. Presently from 37 partially active karezes, only around 17,000 or 13% inhabitants benefiting from karezes. The area cultivated by karezes and tube wells is 20-631 Km2 which is 3-97%, respectively. During the last 20 years, the area irrigated by tubewells increased 338% while area irrigated by karez declined 80% in the last 50 years. The 90% of karezes have a command area < 1000 Km2, 50% have 340 Km2, and 10% of schemes < 80 Km². The depth of the groundwater level ranges from 60-118m from the ground surface. The discharge quantities of karez waters represent an increase from 2.9 to 3.7 L/s in four months, representing a positive impact of precipitation on groundwater. About 0.37 million m3 water is extracted daily by tube wells in Karezat for agriculture. The electric conductivity of karez waters ranges from 682-1240 µS/cm and TDS from 390-1000 mg/L, representing excellent to fair quality groundwater. Karezat used as rangelands, constituting 73% of the total area, supporting small ruminants and providing fuelwood to 80% of rural households. Rangelands serve as watersheds for valleys that generate 90% runoff which drain out through ephemeral streams, farmers divert < 10% runoff for rain-fed agriculture. An integrated watershed management strategy has also been proposed to increase the recharge of aquifers.