An approach to assessment of flow regimes of groundwater-dominated lakes in arid environments

We investigate the conditions and criteria for identifying flow regimes in shallow groundwater-dominated lakes in arid environments. Relying on regional and local water-table configurations, we develop a steady-state model of lake-aquifer systems. Using dimensional analysis and numerical simulations, we investigate relationships between groundwater inflow and outflow. A new framework uses the concepts of gradient ratio G, defined as the ratio of regional-to-local head gradients, and the topohydrologic offset (THO), defined as the difference between actual lake level and regional groundwater level. It is shown that a critical value of gradient ratio, Gc, exists for each aquifer thickness and anisotropy in hydraulic conductivity. In cases where the regional gradient is larger than the local gradient and G > Gc, the lake is “flushed” in a flow-through regime. When the local gradient is larger than the regional head gradient and G < Gc, the lake gains and large evaporative losses occur. Gc becomes progressively larger with increasing aquifer thickness and anisotropy in hydraulic conductivity. Variation in the ratio of groundwater inflow-to-outflow as G approaches Gc is consistent with observed variability in lake salinity. Transition from flow-through conditions to other regimes in groundwater-dominated lakes in arid environments may occur with subtle changes in the gradient ratio, regional water-table slope, lake size, and THO. Finally, we discuss the feasibility of using a geographic information system to delineate the potential for lake to retain solutes in areas with numerous lakes, similar to Nebraska, USA.