Bed load transport processes at river flow power plants - hydraulic model test for the Lower Salzach River

River morphodynamics and sediment transportSediment-structure interactio

Airborne hydromapping area-wide surveying of shallow water areas

River engineeringInnovative field and laboratory instrumentatio

Calibration Strategies Designed For Long Term Sediment Transport Modelling

The presented work deals with the calibration of a 2D numerical model for the simulation of long term bed load transport. A settled basin along an alpine stream was used as a case study. The focus is to parameterise the used multi fractional transport model such that a dynamically balanced behavior regarding erosion and deposition is reached. The used 2D hydrodynamic model utilizes a multi-fraction multi-layer approach to simulate morphological changes and bed load transport. The mass balancing is performed between three layers: a top mixing layer, an intermediate subsurface layer and a bottom layer. Using this approach bears computational limitations in calibration. Due to the high computational demands, the type of calibration strategy is not only crucial for the result, but as well for the time required for calibration. Brute force methods such as Monte Carlo type methods may require a too large number of model runs. All here tested calibration strategies used multiple model runs utilising the parameterization and/or results from previous run. One concept was to reset to initial bed elevations after each run, allowing the resorting process to convert to stable conditions. As an alternative or in combination, the roughness was adapted, based on resulting nodal grading curves, from the previous run. Since the adaptations are a spatial process, the whole model domain is subdivided in homogeneous sections regarding hydraulics and morphological behaviour. For a faster optimization, the adaptation of the parameters is made section wise. Additionally, a systematic variation was done, considering results from previous runs and the interaction between sections. The used approach can be considered as similar to evolutionary type calibration approaches, but using analytical links instead of random parameter changes

Extension And Testing Of A 2D Hydrodynamic Model For Direct Rainfall Runoff Simulation

While the simulation of flood risks originating from the overtopping of river banks is well covered within continuously evaluated programs to improve flood protection measures, flash flooding is not. Flash floods are triggered by short, local thunderstorm cells with high precipitation intensities. Small catchments have short response times and flow paths and convective thunder cells may result in potential flooding of endangered settlements. Assessing local flooding and pathways of flood requires a detailed hydraulic simulation of the surface runoff. Hydrological models usually do not incorporate surface runoff at this detailedness but rather empirical equations are applied for runoff detention. In return 2D hydrodynamic models usually do not allow distributed rainfall as input nor are any types of soil/surface interaction implemented as in hydrological models. Considering several cases of local flash flooding during the last years the issue emerged for practical reasons but as well as research topics to closing the model gap between distributed rainfall and distributed runoff formation. Therefore, a 2D hydrodynamic model, depth-averaged flow equations using the finite volume discretization, was extended to accept direct rainfall enabling to simulate the associated runoff formation. The model itself is used as numerical engine, rainfall is introduced via the modification of waterlevels at fixed time intervals. The paper not only deals with the general application of the software, but intends to test the numerical stability and reliability of simulation results. The performed tests are made using different artificial as well as measured rainfall series as input. Key parameters of the simulation such as losses, roughness or time intervals for water level manipulations are tested regarding their impact on the stability

Innovative Dam Monitoring Tools Based on Distributed Temperature Measurement

Distributed fibreoptic measurements contain a number of particular features. Even though they are nowadays used for strain measurements, actually the most interesting parameter to be monitored by distributed fibreoptic measurements in dams is temperature. Due to their enormous mass, large structures such as dams usually show very slow behaviour in terms of temperature changes. It is well known that temperature measurements have to be carried out in concrete dams in order to observe the development of the heat of hydration. Furthermore, seepage flows affect the temperature field within the dams and their foundations. The Distributed Fibre Optic Temperature DFOT measurement was identified to be ideally suited for monitoring the temperature fields of dams, both for leakage detection and for the observation of concrete temperatures. For almost one decade, DFOT measurement has proven to be a powerful tool to detect and locate leakage in hydraulic structures. Leakage detection by means of DFOT measurements has been typically implemented through two major approaches: the gradient method, which employs the temperature as a tracer to detect anomalies in the flow field; and the heat-up method, which allows detecting the presence and movement of water by evaluating the thermal response after external heat is induced. In the past years more and more DFOT projects are under progress. As for today, the DFOT measurement has to be considered as a state of the art tool in dam monitoring. Nevertheless, especially in the field of leakage detection, there is still an enormous potential to improve effectiveness. New additional applications will be developed and important parameters as the seepage velocity in soil material will be measured with DFOT technology in the future. Being robust and gaining a high density of in-situ information out of the dam, DFOT technology has to be considered as one of the key technologies in tomorrow’s dam monitoring

Sanierung untere Salzach mit energetischer Nutzung

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 1" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

High Resolution Bathymetric Lidar Data To Hydraulic - Modelling A Mountain Stream By Bathymetric Lidar Data

Knowledge about the hydraulic situation in a mountain torrent is relevant to quantify flood risks, to study sediment transport and to assess the waterbodies’ ecology. To conduct reliable calculations, high-quality terrain data of riverbeds, riverbanks and floodplains are required. Typically, digital terrain models (DTMs) of floodplains are derived from classical airborne laserscanning (red wavelength) together with terrestrial surveys along riverbeds and riverbanks. Usually these are restricted to a limited number of cross sections. The terrestrial surveys are necessary because those laser systems cannot penetrate through the water column of the observed waterbodies. Consequently, data for the geometry of riverbeds and bank structures are hardly available at a high spatial resolution and extent, comparable to the airborne-laser scanning derived data for river floodplains. In this study, a newly available, water-penetrating airborne laser system (green wavelength, FFG research project between the University of Innsbruck and Riegl LMS) was used to survey a mountain torrent. Detailed and extensive data (~30 points/m² on topobathy side) of the riverbed, the riverbanks and the neighboring floodplains were acquired with this single sensor. The general applicability of such hydromapping data as a base for 2D- and 3D numerical simulations was investigated. For this, a detailed analysis was carried out by comparing results of 2D-calculations based on the new hydromapping data and 2D- calculations based on traditional terrestrially measured cross-sections. For example, the morphologic boundary conditions are significantly better defined when using the hydromapping data than they are when using cross-sections. This is already due to the original high spatial resolution and spatial data coverage of the hydromapping data, which saves the need of any interpolation, required when using cross-sections that can be tens to hundreds of meters apart from each other. Hydromapping delivers the entire structure of a riverbed and therefore a geometrical information about its friction