Depletion percentage and nonlinear transmissivity as design criteria for groundwater-level observation networks

Intensive use of groundwater for irrigation has depleted available supplies in many areas of the world. Depletion reduces well yields, which negatively impacts agricultural productivity and profitability. The impact of groundwater depletion on wells depends on the relative changes in saturated thickness (depletion percentage) and the rates of change in transmissivity during depletion (nonlinear transmissivity). In heterogeneous aquifers of variable saturated thickness, the impacts on wells vary in time and space. An observation well network designed to account for these spatiotemporal variations is a key part of achieving sustainable development of groundwater. This paper presents a framework for incorporating estimates of depletion percentage and nonlinear transmissivity into GIS-based multicriteria analysis for observation-well network design. The workflow includes (1) selection of criteria using stakeholder input, (2) assessment of data quality, (3) interpolation of hydrogeologic surfaces with prediction standard errors, (4) estimation of hydraulic conductivity values, (5) calculation of saturated thickness and transmissivity using 3 and 4 above, (6) mapping of well densities, and (7) normalization of raster values and calculation of a priority index map. The framework is widely applicable, but flexible to adapt to local needs. By incorporating depletion percentage and nonlinear transmissivity, the methodology can help management agencies prioritize monitoring locations in areas where future depletions could have the greatest impacts on well yields.