An intercomparison of remote sensing river discharge estimation algorithms from measurements of river height, width, and slope

The Surface Water and Ocean Topography (SWOT) satellite mission planned for launch in 2020 will map river elevations and inundated area globally for rivers >100 m wide. In advance of this launch, we here evaluated the possibility of estimating discharge in ungauged rivers using synthetic, daily ‘‘remote sensing’’ measurements derived from hydraulic models corrupted with minimal observational errors. Five discharge algorithms were evaluated, as well as the median of the five, for 19 rivers spanning a range of hydraulic and geomorphic conditions. Reliance upon a priori information, and thus applicability to truly ungauged reaches, varied among algorithms: one algorithm employed only global limits on velocity and depth, while the other algorithms relied on globally available prior estimates of discharge. We found at least one algorithm able to estimate instantaneous discharge to within 35% relative root-mean-squared error (RRMSE) on 14/16 nonbraided rivers despite out-of-bank flows, multichannel planforms, and backwater effects. Moreover, we found RRMSE was often dominated by bias; the median standard deviation of relative residuals across the 16 nonbraided rivers was only 12.5%. SWOT discharge algorithm progress is therefore encouraging, yet future efforts should consider incorporating ancillary data or multialgorithm synergy to improve results

A kinetic interpretation of the section-averaged Saint-Venant system for natural river hydraulics.

International audienceThe classical Saint-Venant system is well suited for the modeling of dam breaks, hydraulic jumps, reservoir emptying, flooding, etc. For many applications, the extension of the Saint-Venant system to the case of non rectangular channels is necessary and this section-averaged Saint-Venant system exhibits additional source terms. The main difficulty of these equations consists in the discretization of these source terms. In this paper we propose a kinetic interpretation for the section averaged Saint-Venant system and we derive an associated numerical scheme. The numerical scheme~-- 2$^{nd}$ order in space and time~-- preserves the positivity of the water height, and is well-balanced. Numerical results including comparisons with analytic and experimental test problems illustrate the accuracy and the robustness of the numerical algorith

Structural damage and recovery determined by the colloidal constituents in two forest soils compacted by heavy traffic

The role of colloidal constituents in soil structure and its resistance to compaction was studied in two acid forest soils of contrasting pH, clay type and texture. The soils were trafficked with an eight‐wheel‐drive forwarder, and undisturbed topsoil samples were taken on trafficked and control plots. Shrinkage analysis was used to assess the soil's physical behaviour, and in addition texture, organic carbon content and exchangeable Al3+ (Alex) and amorphous Al oxide (Aloxa) contents were determined. The effect of each constituent on the soil's physical properties was assessed with covariance analysis. The hydro‐structural stability and coarse pore (> 150 µm radius) and structural pore volumes of control samples were strongly determined by organic carbon and the forms of Al, whereas the plasma porosity was determined by clay content only. Organic carbon and Aloxa increased the structural pore and coarse pore volumes and modified their susceptibility to compaction; organic carbon provided a protecting effect, whereas it was the opposite with Aloxa. We observed contrasting effects of the colloidal constituents and of the behaviour of the pore systems on compaction. The situation is complex and we need to take into account the effects of the colloidal constituents to determine the effects of compaction on the soil's porosity. A simplified approach in which we used the water content at −10 hPa as a covariate predicted soil bulk density as accurately as with all the analytical covariates, and it seems to be an inexpensive way to assess compaction

Lateral coupling method for different one and two dimensional shallow-water solvers: application to the hydro-informatic Telemac-Mascaret system

We present a lateral coupling method between one-dimensional (1D) and two-dimensional (2D) shallow-water solvers dedicated to numerical simulation of river overflows. Both 1D and 2D models, respectively in the river channel and in the floodplains, can be solved with implicit scheme in order to limit computational cost. The 1D-2D exchange terms for mass and momentum between the river and the floodplains are computed with an explicit solver of Riemann problem over a local area that extends over the coupling interface. A distinctive feature of the approach is its flexibility in reusing available computation codes of 1D and 2D shallow-water models as black-boxes. The proposed method has been implemented with the integrated suite of solvers Telemac-Mascaret together with the dynamical coupling software OpenPALM. Numerical validations with respect to an analytical solution and experimental data as well as a first application for the historical 1981 flood event over the Garonne River are presented. The results showed that the overflow discharge is well estimated by the coupled model while it tends to underestimate the water height near the lateral boundaries. For the real application case, reasonable agreement was found between the full 2D simulation and the coupled model

Sensitivity of a one-line longshore shoreline change model to the mean wave direction

International audienc

Assessment, validation and intercomparison of operational models for predicting tritium migration from routine discharges of nuclear power plants: the case of Loire River

During last decades, a number of projects have been launched to validate models for predicting the behaviour of radioactive substances in the environment. The project of the "Aquatic" working group of the project EMRAS (Environmental Modelling for Radiation Safety) organised by the International Atomic Energy Agency (IAEA) was based on the validation and assessment of models for predicting the behaviour of radionuclides in the aquatic ecosystems. The present paper describes a blind test of models aimed at assessing the dispersion of tritium releases in the Loire River (France), on a large domain (∼350 km) and on a period of six months, by comparing the results obtained by operational-to-experimental values of tritium concentration at Angers, a city along the Loire River. The common conclusion is that the models used by the different participants namely 1D models and models based on a schematic hydraulic (box models) are reliable tools for tritium transport modelling. Nevertheless, the importance of proper and detailed hydrological data for the appropriate prediction of pollutant migration in water is demonstrated by the example provided during this study. © 2007 Elsevier Ltd. All rights reserved

On operational flood forecasting system involving 1D/2D coupled hydraulic model and data assimilation

International audienceIn the context of hydrodynamic modeling, the use of 2D models is adapted in areas where the flow is not mono-dimensional (confluence zones, flood plains). Nonetheless the lack of field data and the computational cost constraints limit the extensive use of 2D models for operational flood forecasting. Multi-dimensional coupling offers a solution with 1D models where the flow is mono-dimensional and with local 2D models where needed. This solution allows for the representation of complex processes in 2D models, while the simulated hydraulic state is significantly better than that of the full 1D model. In this study, coupling is implemented between three 1D sub-models and a local 2D model for a confluence on the Adour river (France). A Schwarz algorithm is implemented to guarantee the continuity of the variables at the 1D/2D interfaces while in situ observations are assimilated in the 1D sub-models to improve results and forecasts in operational mode as carried out by the French flood forecasting services. An implementation of the coupling and data assimilation (DA) solution with domain decomposition and task/data parallelism is proposed so that it is compatible with operational constraints. The coupling with the 2D model improves the simulated hydraulic state compared to a global 1D model, and DA improves results in 1D and 2D areas