TELEMAC Model Research Articles

Assessing hydrodynamic impacts of tidal range energy impoundments in UK coastal waters

Tidal range energy comprises a vast theoretical resource of 9,220 TWh per year, globally, with advantageous characteristics of predictability, generation flexibility and reliability. Approximately 13% of this resource lies within the United Kingdom’s (UK) coastal waters, where it could supply up to 12% of annual electricity demand. Tidal range energy conversion traditionally involves constructing and operating large-scale coastal or offshore impoundments (O10-100 km2), which will redefine near and far-field water levels and flow patterns. The relationship between the scale of the impoundment area and hydrodynamic impact has not been investigated for UK sites. To address this, we develop a two-dimensional (depth-averaged) TELEMAC model of the Irish Sea, and simulate six scenarios involving tidal range schemes of increasing basin area, from 25 to 150 km2, located on the North Wales coast in an open coastal basin setting. Results indicate that far-field (30−150 km) changes to the amplitude of the semi-diurnal (M2) tidal constituent exhibit a linear relationship with impoundment area and volume (correlation coefficient R=0.95 and R=0.96, respectively). The largest impoundment (150 km2) caused far-field changes in maximum surface elevation (2<ηmax<3 cm); near-field surface elevation was reduced (ηmax>3 cm).

Surface water quality modelling with data scarcity in semi-enclosed coastal regions encompassed distributed islands

Water quality variation in semi-enclosed urban coastal areas with different pollutant sources is a substantial issue. Pollutant entrapment has a significant impact on the lives of the local people. Surface water quality modelling often requires large datasets covering bathymetry, fluid and pollutants boundary conditions, sources and sinks. This is particularly challenging in regions with complex features and poor data availability, such as coastal water bodies featuring a large number of widely distributed islands and estuaries. In this paper, we developed a model of surface water quality and hydrodynamics for Ha Long Bay, in the North of Vietnam and includes 1969 islands, for a one-year period using a water quality dataset obtained for this study. The model utilized extracted bathymetric and geometric data from Admiralty Charts and Admiralty Tide Tables. Water quality coupled with the TELEMAC Model (WAQTEL) Biomass Module was employed to predict pollutant transport in the domain using point and diffused sources while field studies were conducted to collect data for the setting up and calibration of the water quality model. Thirty scattered sampling points were selected, and the water quality parameters were measured during two campaigns. The predicted water level and velocity values matched the local observation data well with a small error (RMSE = 0.19 and 0.16). Both NO3−-N and PO43--P were high near the shoreline and decrease gradually offshore. The maximum concentrations of NO3−-N and PO43--P reached 0.476 mg/L and 0.048 mg/L at the end of 2021 with the RMSE = 0.13 and 0.011, respectively. The levels of NO3−-N and PO43--P and their distributions showed that Ha Long Bay was eutrophic even during the COVID-19 lockdown period.

Using the TELEMAC model for analyzing the hydrodynamic regime in the Vam Nao River, Vietnam

The Vam Nao River is located Vietnamese Mekong Delta’s upstream, plays the role of transferring flow from the Tien River to the Hau River and balances the discharge for two of these main branches. Hence, the hydrodynamic regime is very complicated. In 2017, there was a severe riverbank failure, resulting in the loss of many houses and negative impacts on the local people. So, in this research, the TELEMAC model was applied to simulate flow and bed change, combined with field surveys, thereby analyzing the hydrodynamic regime of this river. The model was calibrated using the water level, discharge and suspended load data. The simulation results show that the flow has only one direction from the Tien River to Hau. The maximum velocity in the flood season is 1.66 m/s, the discharge is 8298 m3/s (in 2017), the flow after the confluence appears the vortex. Moreover, the confluence area has a rather high erosion rate, up to 1.2 m/year. According to data collected nearly 30 years, the Vam Nao River’s topographic data signify the riverbed is growing to expand and deepen, over 43 m after the confluence and distributed near the riverbank. With this development trend, it is necessary to continuously monitor to provide early warnings to minimize damages due to the risks of riverbank failure.

The application of big data in the analysis of the impact of urban floods: A case study of Qianshan River Basin

In recent years, with the acceleration of climate change and urban modernization, the flood risk of economic and social development has increased. The problem of urban flood disasters needs to be solved urgently. It is particularly important to conduct flood disaster loss assessment research for further flood control and disaster reduction, and emerging big data have opened a new direction for solving the problem of urban flooding. In this study, the Qianshan River Basin in Guangdong Province was used as an example. The TELEMAC model was used to simulate the inundation process under the design rainstorms of 50a and 100a in the Qianshan River Basin. Based on the heat map service, route planning service, and search service functions of Baidu Maps and Amap open platforms, this study used crawler technology to integrate multi-source data, including traffic survey data, geospatial data, population heat map data at different times (day/night) on weekdays and non-weekdays, and point of interest (POI) data from various industries. A dynamic assessment model of flood disaster loss for traffic, population, and POIs was constructed. The research results could greatly improve the timeliness and accuracy of urban flood disaster analysis, early warning, monitoring, and disaster risk assessment.

Effect of Open Boundary Conditions and Bottom Roughness on Tidal Modeling around the West Coast of Korea

The aim of this study was to investigate the effect of open boundary conditions and bottom roughness on the tidal elevations around the West Coast of Korea (WCK) using an open-source computational fluids dynamics tool, the TELEMAC model. To obtain a detailed tidal forcing at open boundaries, three well-known assimilated tidal models—the Finite Element Solution (FES2014), the Oregon State University TOPEX/Poseidon Global Inverse Solution Tidal Model (TPXO9.1) and the National Astronomical Observatory of Japan (NAO.99Jb)—have been applied to interpolate the offshore tidal boundary conditions. A number of numerical simulations have been performed for different offshore open boundary conditions, as well as for various uniform and non-uniform bottom roughness coefficients. The numerical results were calibrated against observations to determine the best fit roughness values for different sub-regions within WCK. In order to find out the dependence of the tidal elevation around the WCK on the variations of open boundary forcing, a sensitivity analysis of coastal tide elevation was carried out. Consequently, it showed that the tidal elevation around the WCK was strongly affected by local characteristics, rather than by the offshore open boundary conditions. Eventually, the numerical results can provide better quantitative and qualitative tidal information around the WCK than the data obtained from assimilated tidal models.

Application of parameters and paradigms of the erosion and deposition for cohesive sediment transport modelling in the Lingdingyang Estuary, China

Suspended sediment and the surficial sediment in most estuaries throughout the world consist of fine particles. Modelling cohesive sediment transport is an important way to explore the morphological evolution of estuaries where cohesive sediment is dominant. Various values for critical shear stress and deposition paradigms for cohesive sediment transport were evaluated here by analysis of field samples combined with numerical simulation in the Lingdingyang (LD) estuary in China. A UMCES-Gust Erosion Microcosm System (U-GEMS) experiment using field samples suggests that the experimental average value of critical shear stress for erosion (τce) is 0.26 N/m2. Two conflicting paradigms, i.e. mutually exclusive versus simultaneous erosion and deposition, are commonly used for cohesive sediment transport. Simulations of tidal currents and sediment transport during the wet season of 2007 and dry season of 2016 in the LD estuary were conducted under these two paradigms using the TELEMAC-2D hydrodynamic module and the sediment module SISYPHE in the TELEMAC model. Model verification under these two paradigms was carried out, and the τce parameters in the TELEMAC model were revised based on a U-GEMS experiment. The results showed the following. (1) The simulation results of the model in the LD estuary were satisfactory when an experimental average τce value of 0.26 N/m2 was used. (2) The simultaneous paradigm using a τce value of 0.26 N/m2 well explained the changes in the field-observed depth-averaged suspended sediment concentrations under all tidal regimes during the dry season, whereas the simultaneous paradigm using a τce of 0.15 N/m2 was more similar to observations in the LD estuary during the wet season.

Downscaling Future Longshore Sediment Transport in South Eastern Australia

Modelling investigations into the local changes in the shoreline resulting from enhanced atmospheric greenhouse gas concentrations and global climate change are important for supporting the planning of coastal mitigation measures. Analysis of Global Climate Model (GCM) and Regional Climate Model (RCM) simulations has shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in south-eastern Australia, is situated in a region that may experience noticeable future changes in longshore winds, waves and coastal currents, which could alter the supply of sediments to the shoreline. This paper will demonstrate a downscaling procedure for using the data from GCM and RCM simulations to force a local climate model (LCM) at the beach scale to simulate additional nearshore wind-wave, hydrodynamic and sediment transport processes to estimate future changes. Two types of sediment transport models were used in this study, the simple empirical coastline-type model (CERC equation), and a detailed numerical coastal area-type model (TELEMAC). The two models resolved transport in very different ways, but nevertheless came to similar conclusions on the annual net longshore sediment transport rate. The TELEMAC model, with the Soulsby-Van Rijn formulation, showed the importance of the contribution of storm events to transport. The CERC equation estimates more transport during the period between storms than TELEMAC. The TELEMAC modelled waves, hydrodynamics and bed-evolutions are shown to agree well with the available observations. A new method is introduced to downscale GCM longshore sediment transport projections using wave-transport-directional change parameter to modify directional wave spectra. We developed a semi-empirical equation (NMB-LM) to extrapolate the ~3.7-year TELEMAC, storm dominated transport estimates, to the longer ~30-year hindcast climate. It shows that the shorter TELEMAC modelled period had twice as large annual net longshore sediment transport of the ~30 year hindcast. The CERC equation does not pick up this difference for the two climate periods. Modelled changes to the wave transport are shown to be an order of magnitude larger than changes from storm-tide current and mean sea level changes (0.1 to 0.2 m). Discussion is provided on the limitations of the models and how the projected changes could indicate sediment transport changes in the nearshore zone, which could impact the coastline position.

Residual flow, bedforms and sediment transport in a tidal channel modelled with variable bed roughness

The frictional influence of the seabed on the tidal flow in shelf seas and estuaries is usually modelled via a prescribed, spatially/temporally invariant drag coefficient. In practice, the seabed exhibits considerable variability, particularly spatially, that should in principle be included in simulations. Local variations in the seabed roughness (ks) alter the flow strength and, hence, local sediment transport rates. The effect of using a spatially/temporally varying ks is assessed here with reference to a tidal channel (Menai Strait, N. Wales) in which the variability of the bedforms has been monitored using multi-beam surveying. The channel not only exhibits strong tidal flow, but also a residual induced flow that is used here as diagnostic to assess various bed roughness formulations tested in a Telemac model. Tidal simulations have been carried out with both constant and temporally/spatially variable ks, and the predicted residual flow is shown to be sensitive to these representations. For a mean spring-neap (SN) cycle with variable ks, the average residual flow is calculated to be 525m3s−1, consistent with observations. This residual flow can be recovered using imposed, constant values of ks in the range 0.15m to 0.3m. The results suggest that the overall, effective roughness of the seabed is less than half of the maximum local roughness due to the dunes in mid-channel, but more than the spatially-averaged ks value in the channel as a whole by about 50%. Simulations carried out with an M2-alone tide using variable ks produce a somewhat smaller (by 7%) residual flow of 491m3s−1. The use of an ‘equivalent M2’ tide of amplitude enhanced by 7.3% reconciles these estimates. The main contribution to ks is made by dunes which are modelled using Van Rijn's (2007) formulation subject to an additional ‘history effect’. The modelled ks is found to equal approximately the observed height of the dunes along mid-channel transects rather than half the height as expected. This is attributed to the non-equilibrium nature of the bedforms in the reversing tidal flow, which exhibited shorter wavelength and more symmetrical profiles than dunes in steady flow.

Oscillatory flows around a headland by 3D modelling with hydrostatic pressure and implicit bed shear stress comparing with experiment and depth-averaged modelling

Tidal flows around headlands with recirculations have long been of environmental importance and are now considered for tidal stream turbine deployment as flow accelerates around a headland tip, interacting with the recirculation zones, giving high kinetic energy. The 3D TELEMAC model with hydrostatic pressure and k-ε turbulence modelling where bed shear stress is implicit (part of the boundary layer computation and not defined by a friction coefficient) is compared with experimental measurements of surface velocity vectors and fluid velocity time series for rough turbulent conditions. The magnitudes of tip velocity are predicted with reasonable accuracy while the velocities in the recirculation zones are only predicted approximately. The bed friction coefficient around these recirculation zones may be magnified by an order of magnitude over the background level as was previously found for island wakes. The boundary layer thickness is generally less than the water depth and a two mixing length model with the horizontal about six times the vertical gives slightly better recirculation zone velocity prediction but requires an estimate of boundary layer thickness. The experiment has a distorted (exaggerated vertical) scale and relaxing this in the model while imposing non-dimensional roughness typical of field conditions gave results very similar to those for experimental conditions indicating that the distorted scale physical modelling is justified for these conditions although this should not be assumed to be a general rule. Results from widely used depth-averaged modelling overestimated the tip velocities markedly, particularly for the smallest oscillation amplitude, presumably associated with the necessarily fixed friction coefficient and absence of secondary flow allowing artificially high velocities in the recirculation zones generating higher velocities near the tip after flow reversal. This form of relatively simple 3D modelling thus appears useful for assessing energy capture from tidal stream turbines around headlands.

Estudo da hidrodinâmica de diferentes geometrias de sítios de conversão de energia das correntes

&lt;span&gt;O crescente aumento da população mundial acarreta em um consumo de energia elétrica cada vez maior, sendo a maior parte da energia do mundo gerada a partir de combustíveis fosseis, intensificando a busca pelo desenvolvimento de tecnologias de geração de energia por fontes alternativas. A energia das correntes marinhas é uma fonte alternativa bastante viável, mas que ainda apresenta um alto custo de implementação. Com o desenvolvimento tecnológico este custo tenderá a baixar, então devemos desde já realizar pesquisar para definir os melhores locais de instalação. Na Plataforma Continental Sul Brasileira, existem duas regiões propicias, sendo uma mais adequada. A partir da modelagem numérica utilizando o modelo hidrodinâmico, TELEMAC, com um modulo de conversão de energia, podemos determinar qual seria a melhor geometria para os sítios de turbinas de conversão de energia. Este estudo demonstrou que um sítio com 10 turbinas estando a 45° em relação à costa apresenta o melhor rendimento.&lt;/span&gt;

Assessment of hydrodynamic impacts from tidal power lagoons in the Bay of Fundy

The Bay of Fundy located in eastern Canada is home to some of the world’s largest tides. Currently there is renewed interest in harnessing these very large tides for power generation in ways that avoid upsetting ecosystems, infrastructure and human activities that are presently well adapted to existing conditions. This paper investigates the hydrodynamic impacts due to tidal power lagoons, an approach to power generation that involves temporarily storing seawater behind a circular engineered dyke and generating power by gradually releasing the impounded seawater through conventional low-head hydroelectric turbines. This paper describes a study in which a two-dimensional, depth-averaged hydrodynamic model based on the TELEMAC modelling system was developed, calibrated, and applied to analyze, predict, and quantify the potential changes in tidal hydrodynamics (water levels, tide range, circulation patterns and tidal currents) throughout the Bay of Fundy and Gulf of Maine due to the presence of a single tidal lagoon and multiple lagoons operating at various locations in the upper Bay of Fundy. The sensitivity of the hydrodynamic impacts to changes in lagoon type, size, location, the number of lagoons, and their operating mode have also been investigated. The methods employed in this study and the main findings are presented and discussed herein. These results will help inform future decisions concerning development of the vast tidal energy resources in the Bay of Fundy.

Application of a coastal model to simulate present and future inundation and aid coastal management

This paper describes the application of coastal hydro-informatic modelling (using the TELEMAC Modelling System) to address management issues arising from projected hydrodynamical and morphological changes within a shallow, sandy estuarine environment. The model incorporates the complex interaction of ocean, terrestrial and atmospheric processes. The case study of the Dyfi Estuary, on the west coast of Wales, is highlighted here. As sea levels have risen locally and are predicted to rise further, a National Nature Reserve (Borth Bog), which has been reclaimed from tidal waters by embankments, will be at increasing risk from flooding episodes due to overtopping of these embankments at high tide. Present and predicted future tidal-fluvial scenarios have been modelled in the Dyfi Estuary in order to estimate the potential for flooding. In addition, areas of greatest velocity change and potential for sediment erosion/accretion have been identified. A further process that has been investigated is how salt marsh migration is affected by sea-level rise. This case study exemplifies some fundamental and complex physical processes inherent to estuaries, and shows how different management options can be assessed, before their implementation, through a modelling approach.

Morphological controls in sandy estuaries: the influence of tidal flats and bathymetry on sediment transport

The morphodynamics of shallow, vertically well-mixed estuaries, characterised by tidal flats and deeper channels, have been investigated. This paper examines what contributes to flood/ebb-dominant sediment transport in localised regions through a 2D model study (using the TELEMAC modelling system). The Dyfi Estuary in Wales, UK has been used as a case study and, together with idealised estuary shapes, shows that shallow water depths lead to flood dominance in the inner estuary whilst tidal flats and deep channels cause ebb dominance in the outer estuary. For medium sands and with an artificially ‘flattened’ bathymetry (i.e. no tidal flats), the net sediment transport switches from ebb-dominant to flood-dominant where the parameter a/h (local tidal amplitude ÷ local tidally averaged water depth) exceeds 1.2. Sea level rise will reduce this critical value of a/h and also reduce the ebb-directed sediment transport significantly, leading to a flood-dominated estuarine system. A similar pattern, albeit with greater transport, was simulated with tidal flats included and also with a reduced grain size. This suggests that analogous classifications for flood/ebb asymmetry of the tide in estuaries as a whole may not represent the local sediment transport in sufficient detail. Through the Dyfi simulations, the above criterion involving a/h is shown to be complicated further by augmented flow past a spit at the estuary mouth which gives rise to a self-maintaining scour hole. Simulations of one year of bed evolution in an idealised flat-bottomed estuary, including tidal flow past a spit, recreate the flood/ebb dominance on either side of the spit and the formation of a scour hole in between. The erosion rate at the centre of the hole is reduced as the hole deepens, suggesting the establishment of a self-maintaining equilibrium state.

Flood/ebb tidal asymmetry in a shallow sandy estuary and the impact on net sand transport

Flood/ebb tidal dominance plays a pivotal role in estuarine sediment transport. The Dyfi Estuary, mid-Wales, UK, is used as a case study, together with an idealized trumpet-shaped estuary morphology, to illustrate key processes giving rise to flood/ebb dominance. Observations made in the main entrance channel to the Dyfi indicate that the system is presently ebb-dominant with regard to both the relatively long duration of the ebb tide and also the faster ebb velocities. Predictions made across the mouth of the estuary using the Telemac Modelling System suggest further that the net sand transport presently occurs out of the estuary. In contrast, due to the varying distribution of channels and flats within the estuary, the tidal flow in the upper estuary is flood-asymmetric and here the net transport is up-estuary. Flood versus ebb dominance is shown to be attributable to the relative extent of the channels and sandflats in relation to the mean water level. An attempt is made to develop a simple metric to determine present-day transport pathways within an estuary in response to its cross-channel flow asymmetries.

Methods for medium-term prediction of the net sediment transport by waves and currents in complex coastal regions

Medium-term prediction of sediment transport and morphological behaviour in the coastal zone is becoming increasingly important as a result of human interference and changing environmental conditions. The interaction of waves and tides is shown to play a pivotal role in the net (annual) sediment transport and morphodynamics of the coastal zone. The Telemac Modelling System has been applied to the Dyfi Estuary and neighbouring coastline, mid Wales, to recreate the annual wave–current conditions and the resulting sediment fluxes. ‘Input reduction’ methods have been required to produce realistic schematisations of events in practical computation times. A field campaign carried out in 2006 provided data for validation of the flow module ( Telemac-2D) and also observations to verify the patterns predicted by the wave module ( Tomawac). To improve model accuracy refinements were implemented with regard to the sand transport formulation used in the sand transport module ( Sisyphe). Here, a parameterisation of the results from the UWB 1DV sand transport ‘research’ model, for the conditions in the Dyfi Estuary, has been introduced, allowing Sisyphe to provide greater realism in the morphological predictions. The model predictions are presented along with a discussion of the success/failure and limitations of the modelling methods applied.

Compatibility between finite volumes and finite elements using solutions of shallow water equations for substance transport

AbstractThis paper formulates a finite volume analogue of a finite element schematization of three‐dimensional shallow water equations. The resulting finite volume schematization, when applied to the continuity equation, exactly reproduces the set of matrix equations that is obtained by the application of the corresponding finite element schematization to the continuity equation. The procedure allows the consistent and mass conserving coupling of the finite element Telemac model for three‐dimensional flow with the finite volume Delft3D‐WAQ model for water quality. The work has been carried out as part of a joint development by LNHE and WL∣Delft Hydraulics to explore the mutual interaction of their software. Copyright © 2006 John Wiley &amp; Sons, Ltd.