Firas Saleh

On the use of numerical modelling for near-field pollutant dispersion in urban environments − A review

This article deals with the state-of-the-art of experimental and numerical studies carried out regarding air pollutant dispersion in urban environments. Since the simulation of the dispersion field around buildings depends strongly on the correct simulation of the wind-flow structure, the studies performed during the past years on the wind-flow field around buildings are reviewed. This work also identifies errors that can produce poor results when numerically modelling wind flow and dispersion fields around buildings in urban environments. Finally, particular attention is paid to the practical guidelines developed by researchers to establish a common methodology for verification and validation of numerical simulations and/or to assist and support the users for a better implementation of the computational fluid dynamics (CFD) approach.

THE STEVENS FLOOD ADVISORY SYSTEM: OPERATIONAL H3E FLOOD FORECASTS FOR THE GREATER NEW YORK / NEW JERSEY METROPOLITAN REGION

This paper presents the automation, website interface, and verification of the Stevens Flood Advisory System (SFAS, http://stevens.edu/SFAS). The fully-automated, ensemble-based flood advisory system dynamically integrates real-time observations and river and coastal flood models forced by an ensemble of meteorological models at various scales to produce and serve street scale flood forecasts over urban terrain. SFAS is applied to the Greater NY/NJ Metropolitan region, and is used routinely by multiple forecast offices and departments within the US National Weather Service (NWS), regional and municipal Offices of Emergency Management, as well as the general public. Every six hours, the underlying H3E (Hydrologic–Hydraulic–Hydrodynamic Ensemble) modelling framework, prepares, runs, data-assimilates, and integrates results from 375 dynamic model simulations to produce actionable, probabilistic ensemble forecasts of upland and coastal (storm surge) flooding conditions with an 81-h forecast horizon. Meteorological forcing to the H3E models is provided by 125 weather model ensemble members as well as deterministic weather models from major weather agencies (NCEP, ECMWF, CMC) and academia. The state-of-the-art SFAS, a replacement of the well-known, but deterministic, Storm Surge Warning System (SSWS) that was highlighted during Hurricanes Irene and Sandy and more recently extratropical cyclone Jonas, has been operational since the end of 2015.

Reporting of Stream-Aquifer Flow Distribution at the Regional Scale with a Distributed Process-Based Model

Groundwater withdrawals can reduce aquifer-to-stream flow and induce stream-to-aquifer flow. These effects involve potential threats over surface water and groundwater quantity and quality. As a result, the description of stream-aquifer flow in space and time is of high interest for water managers. In this study, the EauDyssée platform, an integrated groundwater/surface water model is extended to provide the distribution of stream-aquifer flow at the regional scale. The methodology is implemented over long periods (17 years) in the Seine river basin (76 375 km2, France) with a 6 481 km long simulated river network. The study scale is compatible with the scale of interest of water authorities, which is often larger than study scales of research projects. Net and gross stream-aquifer exchange flow are computed at the daily time step over the whole river network at a resolution of 1 km. Simulation results highlight that a major proportion of the main stream network (82 %) is supplied by groundwater. Groundwater withdrawals induce a reduction of net aquifer-to-stream flow (−19 %) at the basin scale and flow reversals in the vicinity of pumping locations. Such an integrated model provided at the appropriate regional scale is an essential tool provided to water managers for the implementation of the EU Water Framework Directive.

Exploring Uncertainty in Uncalibrated Bioretention Models

Using SWMM 5.0.016, a case study of a street right-of-way bioretention system (ROWB) configured as a storage node is compared against SWMM’s “LID Controls”. Through a series of 1-yr continuous simulations, the uncalibrated models indicate that a storage node representation of a media-filled system substantially underestimates stormwater retention and detention compared to the LID Control. This is because the latter explicitly accounts for dynamic flow through porous media. Lined/underdrained ROWB may provide significant stormwater mitigation because the majority of storms are small, thus fully captured by the media without the need for exfiltration. As the storage node approach is typical of the current (USA) industry for green infrastructure or low impact development modeling, outcomes raise concern around over-design (and misspent resources). Sensitivity analysis of the LID Control parameterization indicates that the relative difference between the engineered media’s porosity and field capacity have the most significant influence on performance. This may be an artefact of the calculation procedure rather than actual physical phenomenon. Future work should prioritize calibration with observed data sets from multiple sites (i.e. multiple media), and actual measurement of field capacity and porosity for multiple examples of bioretention.

Distributed Simulation of Daily Stream-Aquifer Exchanged Fluxes in the Seine River Basin at the Regional Scale

The interaction between surface and groundwater is a complex process and depends on many physical factors that are directly related to topography, geology and climate. The description of those interactions in the simulation process is necessary to better assess hydraulic heads in near stream aquifer units and to improve the assessment of stream-aquifer water exchanged fluxes. This motivated researchers to focus on coupled models. Among the coupled models used by the scientific community, the EauDyssee modelling platform, jointly developed by Mines Paristech and UMR 7619 Sisyphe, couples existing specialized models to address water resources and quality in river basins. In the present study, we used 7 models based on the EauDyssee platform to quantify the daily spatially distributed water flow exchanged between aquifer units and surface water systems in the Seine river basin and Basse Normandie’s coastal watersheds (France). The modelled domain covers an area of 69,000 km2 and is composed of a 13,622 km-river network. Models simulations provide a description of the hydrosystem behaviour with regards to different anthropogenic (with and without pumpings) and climatic (dry, humid and pluri-annual) scenarios. Results of the simulation were synthesized in a database which provides a valuable tool to assess river water bodies [Water Framework Directive management units (E.U., Dir 2000)] vulnerability to potential groundwater contamination or groundwater resource depletion.