Simulatie van de regionale hydrologie in het stroomgebied van de Dommel

Abstract

The Dommel-life project aims to develop sustainable management plans for the catchment area of the river Dommel. One of the problems within the catchment area is the possible hydrological impact of socio-economic activities. To be able to assess the impact of these socio-economic activities, a regional hydrological model is developed. The model consists of two parts: a topmodel and a groundwatermodel. The topmodel is a waterbalance model, developed for the Life-Dommel project (Pieterse et al., 1998). This report gives a short summary of the construction and results of the topmodel because it is closely connected to the groundwater model. The topmodel calculates the net groundwater supply from precipitation and the spatial distributed dynamic stream discharge. Precipitation is discharged directly to the stream, to the sewer system in urban areas or percolates to the groundwater. The topmodel calculates a and phreatic groundwater dynamics for each timestep of 10-days. Discharge of effluent and transfer of stream discharge to other streams or to canals is accounted for. Because accurate discharge were available, an accurate calibration of the topmodel could be performed. Stream discharge is calculated adequately for the period 1990- 1996 with a Nashcoëfficient of 0.78 and a deviance between observed and simulated average discharge of 0.04 m3 sec-1 day-1. The groundwatermodel, implemented with the program MODFLOW, is linked with the topmodel. MODFLOW calculates the amount of seepage to- and from deep groundwater. This data is used as imput for the topmodel. The model parameters and (geo) hydrological data are identical for both models. The geohydrological schematisation of the groundwater model is based upon geological information from the REGIS database of TNO-NITG. The hydrological basis is defined as the basis of the Mioceen, consisting of the ‘Boomse klei’ and ‘Klei van Veldhoven’. The ‘Boomse klei’ is the first impermeable layer in the Belgian part of the modelarea. The schematisation method distributes the geological layers over regular rectangles. The thickness of each modellayer is applied with fining upward to the surface. The results of the waterbalance model represent very well the hydrology of the catchment. The deviation of calculated pheatic groundwater levels, compared with measurements from 1991, are in average 12 cm too high with a standard deviation of 67 cm.