Estimating renewal timescales with residence time and connectivity in an urban man-made lake in China.

Residence times and connectivity are computed for 12 subregions in an urban man-made lake in China using a high-resolution tracer-transport model. The renewal timescales are explicitly defined and computed for two groups of four freshwater inflow scenarios related to water diversion projects. First, the timescale values are computed and compared using different computational criteria for the upper limit of integration in the residence time equation. The sensitivity analysis suggests that a calculation time of 300 days is necessary to satisfy the relative error (0.001) and 5 % cutoff value criteria. Secondly, the residence times can range from 1.5 to 102 and 1.0 to 66 days under low and high flow conditions, respectively. Water in the inner lake would reside in the lake for less than 66 days prior to exiting the region of interest. The timescale values can be applied to impact studies that investigate the extent of sudden water pollution events that initially affect a subdomain of a lake. Finally, the lacustrine residence times are decomposed into the different subregion residence times, resulting in a connectivity matrix. This matrix can illustrate preferential connections among the individual subregions and reveal hidden patterns relating to local hydrodynamics in the lake.