Managing Groundwater in Hard-rock Areas through Agro-well Design and Development

Water shortage in the dry season is a major problem facing agriculture in the dry and intermediate zones of Sri Lanka. Large diameter wells (agro-wells) have been introduced to use the groundwater as a supplement to rainfall. The underlying crystalline hard-rock formations have very low storage and transmissivity, which limit the groundwater resource. The haphazard development of agro-wells may seriously threaten sustainable groundwater use in the future. Based on field studies and a groundwater hydrological model, this paper explains a methodology for determining the dimensions of agro-wells that limit a farmer to abstracting no more than the volume of water recharged under his/her land. This methodology can be used to regulate groundwater in hard-rock aquifers by identifying the safe volume of water that can be abstracted, establishing the optimum well dimensions for constructing a new well, and matching crop-water requirements to the abstractable volume of water. Farmers themselves can regulate groundwater resources to limit exploitation to equal their entitlement.