IS THE KARIZ WORTH SAVING? ASSESSING THE LONGEVITY OF ANCIENT WATER SUPPLY SYSTEMS IN AFGHANISTAN

In many arid to semi-arid regions including Afghanistan, hand-constructed sub-horizontal tunnels with vertical access shafts (kariz or qanat, or one of many other names depending on region) transfer groundwater from proximal alluvial fan toward distal alluvial fan using only gravity. For thousands of years, these constructs have supplied water to families and even small villages, the cost of which has only been maintenance of the tunnels. Flow of kariz water is generally fastest in the spring and early summer because alluvial-fan aquifer recharge is primarily from mountain snowmelt, but water supply has historically been year-round. Although an integral part of the local culture, the karezes in many areas have stopped delivering water due to recent, persistent drought. A dilemma exists in whether to deepen or otherwise attempt improvement of the kariz to reestablish water flow or to abandon and replace them with more modern wells and more costly mechanical pumping. We have used a groundwater model (Visual MODFLOW) to test how the kariz produces water and what factors are most important for sustaining water flow. The model demonstrates the vulnerability of the kariz to reduced snowmelt and suggests that, assuming recent trends in reduced mountain snowfall continue, abandonment is the preferred choice even though the impact of this choice on local societal structure may be severe. The model also suggests that, depending on the distance to the nearest groundwater discharge point (e.g., river) and the hydraulic conductivity distribution, there may be an enhanced groundwater supply created by kariz leakage over its lifetime. These approaches and findings may be helpful in guiding local hydrogeologists’ decisions about groundwater exploration and development in arid to semi-arid regions.