Causal model window

Physical parameters Your choice Result
Flow velocity
Water depth
Flow velocity heterogeneity
Depth heterogeneity
Instream habitat heterogeneity
Amount of gravel banks
Shoreline heterogeneity
Local sediment transport capacity
Sediment transport
River bed degradation
Fine sediment accumulation
Frequency of (unnatural) discharge fluctuations
Frequency of (unnatural) water level fluctuations
Frequency of (unnatural) fluctuations of flow velocities
Frequency of (unnatural) fluctuations of wetted river width
Wetted usable area for aquatic animals
Water temperature
Water quality
Need for sediment flushing
Naturaleness of flow regime
Access to important habitats, e.g. for spawning
Habitat fragmentation
Genetic diversity
Barriers for re-settlement and re-immigration
Potential for injury and death by hydropower plant turbines

Fish community

Species: Nase Chondrostoma nasus (L.)
Biomass: > 300 kg/ha
FRI: 5.9
Density: > 600 Ind/ha
FIA: -

Typical species

Natural epipotamal to hyporhithral river sections are populated by a wide variety of different fish species (up to a total number of ~45 species for e.g. the Wachau section of the Danube). The river system provides the hydromorphological features (seasonal discharges, habitats for all seasons and age classes, connectivity in all four dimensions) needed for them to build up sustainable populations and species communities. They appear in river type specific densities and biomasses according to the fish regions, with typical age class distributions, where juvenile stages are dominating with exponentially decreasing abundances towards adult age classes (‘Allen curve’).
Adult grayling, Thymallus thymallus (L.)
Adult grayling, Thymallus thymallus (L.), a sensitive rheophilous species with low structural needs conducting migrations up to 3o km. This species is especially sensitive to hydropeaking, a loss of river a loss of gravel banks due to channelization and reduction of flow velocities in impoundments and water abstraction sites.
Juvenile grayling, Thymallus thymallus (L.)
Juvenile grayling, Thymallus thymallus (L.), a sensitive rheophilous species with low structural needs conducting migrations up to 3o km, only rarely found in river sections subjected to significant hydropeaking.
Adult barbel, Barbus barbus (L.)
Adult barbel, Barbus barbus (L.), a typical dominant rheophilous species of epipotamal rivers, with low structural needs, conducting typical mass spawning migrations between 30-300 km distance. Adult individuals especially react negatively to water depth and flow velocity reductions in water abstraction sites.
Juvenile barbel, Barbus barbus (L.)
Juvenile barbel, Barbus barbus (L.),a typical dominant rheophilous species of epipotamal rivers, with low structural needs, conducting migrations between 30-300 km distance.
Adult nase, Chondrostoma nasus (L.)
Adult nase, Chondrostoma nasus (L.), a typical dominant rheophilous species of epipotamal rivers, typically conducting mass spawning migrations between 30-300 km distance. This species is especially sensitive to a loss of river connectivity, a loss of gravel banks due to channelization and reduction of flow velocities in impoundments and water abstraction sites.
Juvenile nase, Chondrostoma nasus (L.)
Juvenile nase, Chondrostoma nasus (L.), a typical dominant rheophilous species of epipotamal rivers, especially sensitive to the loss of gravel banks as habitats.
Danube salmon Hucho hucho (L.)
Danube salmon Hucho hucho (L.), represents a top predator in hyporhithral and epipotamal rivers. This species is endangered by extinction, and has been severely affected by all types of hydromorphological pressures, especially the loss of river connectivity and habitats due to river channelization.In addition, in the past overfishing also might have been responsible for the decimation of its abundance.
Juvenile Danube salmon Hucho hucho (L.)
Juvenile Danube salmon Hucho hucho (L.).The juveniles start to feed on other fish very early in development. As the Danube salmon spawns in March/April, a successful development of their offspring depends on the successful and abundant reproduction of typical prey fish species like nase and grayling, that also spawning very early in the year.

Explanation window

Natural rivers develop as are rivers with only very minimal anthropogenic influence (Fig. 1). They are part of the natural hydrological cycle, with water generally received from precipitation through a catchment from surface runoff and other sources such as groundwater, springs, and the release of stored water in natural ice and snow (e.g. from glaciers). Without human intervention, depending on the climate region, its situation in the river network and the geomorphological setting, rivers naturally develop different morphological forms being dynamically maintained over time ('dynamic equilibrium'). This allows specific biotic communities to adapt to these conditions and build up sustainable populations. Natural rivers are moreover characterized by a natural flow regime, and un-impacted transport of sediment and woody debris. This results in a typical, dynamically maintained habitat configuration as a basis for the sustainable development of river type specific biotic communities (Fig. 2). Fig. 1: Natural river with unimpaired transport of sediment and woody debris. Fig. 1: Natural river with unimpaired transport of sediment and woody debris. Fig. 2: Nature-like dynamic river section. Fig. 2: Nature-like dynamic river section.