A river habitat simulation model to quantify ecological effects of low discharges on the River Meuse (the Netherlands, Belgium).
Liefveld, W. M.; Schulze, F.
The free-flowing border stretch (45 km) of the rain-fed River Meuse suffers from low discharges, enhanced by upstream water abstraction (e. g. navigation, drinking water). A River HAbitat SImulation Model (RHASIM) was developed to gain insight into the ecological effects of these low discharges. The physical habitat is modelled in relation to river discharge through four major components: (1) discharge, (2) substrate, (3) water quality and (4) habitat simulation, relating the changes in the physical environment to effects on habitat suitability for target species. The integrated results indicate that adult life stages of rheophilic species like barbel (Barbus barbus L.) and chub (Leuciscus cephalus L.) are favoured by the conditions at higher discharges while early life stages of these fish species are favoured by lower discharges. This is mainly caused by the severely incised nature of the main channel resulting in a lack of shallow and slow-flowing inshore zones with increasing discharges. To assess the minimum discharge a threshold of 100 ha has been held to sustain minimum viable populations of barbel and chub. The results indicate that at discharges below Ô 10 m3 sec-1 the surface area of suitable habitat is declining rapidly and is expected to be restrictive for chub populations. RHASIM is a potential useful tool that enables decision makers to take into account the ecological effects of measures that affect water level at low discharges.