Author(s): Janos Jozsa; Tamas Kramer; Hannu Peltoniemi
Linked Author(s): János Józsa
Keywords: Residence time; Transport modelling; Lakes; Coastal flows; Impact assessment
Abstract: Water exchange mechanisms are assessed via modelling the spatial distribution of the mean residence time in lakes and coastal areas. A grid-based numerical solution of the deterministic advection-diffusion-reaction kinetics equation with the ageing of water as transport variable is applied. The composition of residence time from times spent over separate sub-domains is handled as multi-species transport. Numerical errors arising in the advection approximation at sharp gradients are reduced by robust upwind schemes. The spatial residence time distribution due to through-flow and wind-induced water exchange in a shallow sample lake with littoral reed is analysed by 2-D depth-integrated approach. Apart from the spatial distribution, the normalised volumetric distribution of the residence time is also considered. The impact of planned, large-scale landfill on the residence time in semi-enclosed bays at Helsinki coasts is evaluated by 3-D modelling.