Modifying the Residence Time and Dilution Capacity of a Reservoir by Altering Internal Flow-Paths

Tracers were released into a small oligotrophic reservoir to determine the tracer dilution ratio (the ratio of inflow to outflow concentration) and two residence timescales (the arrival time and the cleansing time) as a function of lake geometry. The dominant transport mechanisms were inferred by assembling lake-wide spatial and temporal fields of natural tracers such as temperature, pH, salinity, turbidity, and dissolved oxygen from a series of 37-stations. These stations were monitored three times a day during an 8-day field campaign and the field results were compared to numerical simulations of the system. The lake's hydrodynamic behaviour was successfully simulated with a hydrostatic three-dimensional numerical model (ELCOM) that was used to investigate the deflection from existing flow-paths by means of vertical impermeable curtains. Strategies were tested aimed at modifying the transport timescales and dilution capacity of the lake as may be required for the lake to act as a secure barrier against microbial contamination. Submerged curtains proved to improve the barrier capacity of the reservoir, described by the arrival time, the cleansing time, and the dilution ratio.