The importance of morphodynamic processes at riffles used as spawning grounds during the incubation time of nase (Chondrostoma nasus)

Earth Surf Processes Landf

2009

This paper investigates the impact of a 1000-year flood in August 2002 on floodplains and valley morphology of an Austrian mixed alluvial bed rock river. Discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains. After the 1000-year flood, those morphologically affected areas were at random intervals documented over the whole longitudinal profile. In addition to overbank erosion in curved sections (cutoffs), the river bed locally widened, floodplain stripping occurred and local overbank scours were documented along straight parts of the river. A hydrodynamic-numerical model, combined with field measurements, was used to analyse the cause of these erosional landforms. Based on the modelled hydraulic conditions for a one-year flood ), the numerical results allowed a cause-effect study with 19 parameters. Deterministic and statistical analysis (ANOVA, discriminant analysis) showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the Kamp River, which led partially to supercritical flow during flood constriction. These processes were in some cases also anthropogenically influenced. Lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event. These morphological features were therefore responsible for the elongated scour holes in the floodplains.

mentioning

confidence: 99%

Morphodynamics of a 1000‐year flood in the Kamp River, Austria, and impacts on floodplain morphology

Hauer

Earth Surf Processes Landf

2009

“…In the next modelling step the described low-energy habitats (MH: 0 Ã ) are divided into backwater (MH: 1) and shallow water habitats (MH: 0) using the depth criteria of class 1 (g 4 ) ( Table IV). Finally, the six mesohabitats are tested for their stability by using a stability ratio (Hauer et al, 2007) of calculated bottom shear stress (t) and the critical shear stress (t cr ) of stratified sampled subsurface sediments using the formula of Meyer-Peter and Müller (1949).…”

Section: Mesohabitat Evaluation Model (Mem)mentioning

confidence: 99%

Hydraulically related hydro‐morphological units: description based on a new conceptual mesohabitat evaluation model (MEM) using LiDAR data as geometric input

Hauer

Mandlburger²,

2008

River Research & Apps

A new conceptual mesohabitat evaluation model was developed and applied to the Kamp River, Austria. The model uses a functional linkage of three parameters (velocity, depth and bottom shear stress) to distinguish six different mesohabitat types (riffle, fast run, run, pool, backwater and shallow water) based on two-dimensional depth-averaged hydrodynamic-numerical modelling. The results clearly revealed the variety and change of mesohabitat-units under various flow conditions (3.6-89 m 3 s À1 ). In particular for low-energy habitats, a shift from shallow-to backwater habitats was recognized at increasing discharges. Fast runs featured a larger percentage of the total wetted area (9-33%) as discharges increased, whereas pool habitats showed low variability (means of around 15%). A velocity-depth-bottom shear stress relationship (VDSR) was most suitable to differentiate between mesohabitat patterns; this relationship was compared with Froude numbers and with velocity-depth ratios using ANOVA statistical analysis. This study also documented that the accuracy of river geometry plays a decisive role in habitat descriptions. Different height tolerances for the computation mesh (0.2 m, 0.5 m, 1 m accuracy) based on LiDAR significantly reduced important mesohabitats.

“…At the same time, Shields and Abt (1989), for example, concentrated on hydromorphological problems, particularly sedimentation, associated with reconnecting meanders to the flowing channel. Reconnection of meanders is incorporated into river restoration in Austria as a key component of river restoration where the river historically possessed a meandering style (Hauer et al, 2007). Figure 1 summarizes different variations of meander reconnection.…”

Section: Reconnection Of Meandersmentioning

confidence: 99%

A model‐based analysis of meander restoration

Krapesch

Tritthart

2009

River Research & Apps

Self Cite

Meander reconnection is becoming a widely applied river restoration measure, aiming to enhance the ecological status of river systems. Based on a physical model study and a 3D hydrodynamic-numerical simulation, the effects of different forms of meander reconnections on flow dynamics, water level and river morphology are investigated in present study including retention of the old main channel for flood protection when the bankfull discharge is exceeded. The distribution of total discharge between the reconnected meander bend and the flood channel during floods decreases flow velocity and bed shear stress and leads to aggradation. At higher discharges, the flow velocity decreases in the meander bend whereas it increases in the flood channel. The controlling parameter for flow diversion-hence for flow velocity and bed shear stress-is the elevation of the ramp diverting the flow.Using the hydrodynamic model RSim-3D a particle tracing study simulated the trajectories of conservative particles at six vertical levels. The vertical movements of the particles on trajectories going through the reconnected meander were investigated by calculating the number of level changes of each particle. This novel approach in simulating particle movement in channels facilitating qualitative decision-making in the framework of river restoration issues. In particular, it reveals information regarding heterogeneity and turbulence of the water and also nutrient movements under variable flow conditions and can thus help answer restoration-related ecological questions.