Decision Support System for the Elbe River Water Quality Management

A decision support system (DSS) for integrated river basin management of the German part of the Elbe river basin is currently under development, which involves taking account water quantity, chemical quality and ecological state of surface waters. The Elbe is one of the largest river basins in middle Europe having multiple land and water use demands. A hierarchical approach was developed to meet the various spatial and temporal scales when dealing with hydrologic, ecologic, economic and social aspects related to water systems. Four subsystems were defined: catchment, river network, main channel and floodplain. For each module, a system diagram was worked out which describes the properties, processes and data influencing the water flow and substance load. The modules are connected by water and substance flow, which guarantee the interactions between the different scales and consequences of measures on all subsystems. In close collaboration with the users, management objectives, scenarios and measures were defined. The DSS integrates models, spatial and non-spatial data and analysis tools under a user-friendly GIS-based interface, which confronts the decision maker with possible measures as well as multiple management objectives. Three conceptual models were selected and coupled to meet the user requirements. A model for the calculation of the long-term nutrient discharges in 130 sub-catchments from non-point and point sources, a simulation model of the waste water pathways (point-sources) and the aquatic fate assessment was coupled with a GIS-based discrete digitized river network of the Elbe. For the precipitationrunoff simulation, a distributed conceptual hydrological model was selected and calibrated for the same subcatchments. Long-term discharge time series from gauging stations are being used to calibrate the hydrological discharges. A transport and elimination model describes the downstream fate of the chemical. Temporal concentration distributions of chemicals in each river stretch can be calculated from variable and uncertain input data. With the example of phosphate attached to eroded soil particles the applicability of the Elbe DSS to support decisions for the improvement of the water quality is demonstrated.