Modeling the hydrodynamics and salinity of the Pontchartrain Basin

The area of New Orleans was hit by Hurricane Katrina in August 2005. A large part of the city got flooded due to bad design, construction and maintenance of the levee system. In order to increase the level of protection of the city, the levees are heightened and strengthened in the framework of the Hurricane and Storm Damage and Risk Reduction System (HSDRRS). On the long term the restoration of coastal wetlands is also part of the program. Since the 1930’s wetland erosion in coastal Louisiana has been recorded. The main cause of the erosion is the canalization of the Mississippi River, land subsidence and sea level rise, and salt water intrusion by alteration of drainage patterns. One way of initiating wetland restoration is the construction of diversions. The Violet Diversion is the largest diversion planned in the Pontchartrain Basin. Water from the Mississippi River is diverted into Lake Borgne and the Biloxi marsh in order to decrease salinities in those target areas. In order to get more insight in the impact of the diversion on salinity (gradients), hydrodynamic and salinity modeling of the Pontchartrain Basin is desired. Due to lack of data and time, model calibration on salinity was not accomplished. The goal of this study is to model a dynamic equilibrium of yearly averaged salinity in the Pontchartrain Basin. The lessons learned from this study can be a start for subsequent modeling efforts of the Violet Diversion. In Delft3D-FLOW a grid was set-up to model tidal propagation in Lake Borgne. The grid consists of a little less than 53,000 nodes. The initial bathymetry and roughness are taken from the ADCIRC SL15 model. The model is forced with the amplitudes and phases of the ten most important tidal constituents. In order to calibrate the model, the tidal channels are enlarged and the bottom friction is decreased. The necessity of these changes was already proven by the application of the harmonic method on the Pontchartrain Basin, as well as the moderate results of previous model studies. The model is calibrated on tidal amplitudes (accuracy within 10%) and fluxes through the tidal passes (accuracy within 1%). Phases were considered less important. Salinity was implemented by simulating initial salinities and river discharges on top of the tide. Comparing 2D with 3D simulations, gravitational circulation occurs in the 3D modeling. This causes an increased salt water intrusion from the Gulf of Mexico towards Lake Borgne and the Biloxi Marsh. However, the salinities in this target area are too low in the dynamic equilibrium situation. This is explained by the underestimation of transport by tides and Mississippi River discharge towards Lake Borgne. Previous model studies proved that circulation around the continental shelf cannot be neglected for tidal transport. Also, the Mississippi River discharge can flow around the Birdfoot. Due to the choice of the model domain, that flow cannot occur in this study. Using the tide-calibrated model for salinity studies, it is recommended to model in 3D to simulate the gravitational circulation. Nontidal water level elevations and currents should be included in the boundary conditions. This can be achieved by enhancing the model domain to capture a larger part of the Gulf of Mexico and the Mississippi Birdfoot. Then the flow around the Birdfoot can also be simulated. Wind should also be added to the hydrodynamic simulations. The measured salinities and the target salinities show seasonal variation. Therefore future modeling should strive for real-time simulation by forcing the model with time-series. The diversion flow can then be varied per month or season.Hydraulic EngineeringCivil Engineering and Geoscience

A Network of Typologies: Redefining of and giving quality to the public space network as an urban restructuring element in order to permeate the borders of La Victoria and reconnect to the regional and metropolitan scale.

The development of a methodology for analyzing and restructuring the public space network of Santiago de Chile, aiming at the permeation of borders within the municipality Pedro Aguirre Cerda.DSD Urban Asymmetries SantiagoUrbanismArchitectur

Energiezuinig suppleren: Innovatie-initiatieven, Actorenanalyse en Interviews

De Nederlandse kust wordt veilig gehouden met zandsuppleties op de vooroever en het strand. Door autonome ontwikkelingen en door klimaatverandering wordt verwacht dat in de toekomst de benodigde suppletiehoeveelheden zullen toenemen. Daardoor zullen kosten, energiegebruik en emissies toenemen. Dat was voor RWS en Deltaprogramma Kust (DP Kust) de aanleiding om te inventariseren of er ontwikkelingen zijn op het gebied van energiezuiniger / duurzamer suppleren. Die inventarisaties zijn zowel intern binnen RWS als extern bij markpartijen en kennisinstituten uitgevoerd. Aansluitend op de inventarisaties is een workshop georganiseerd. Hier worden de resultaten kort samengevat. Uit de interne inventarisaties van RWS zijn duurzame alternatieven voor de energieopwekking naar voren gekomen (vanuit het WINN (WaterINNovatie) programma). Het opslaan en aanwenden van de energie voor suppleren vormden geen onderdeel van het WINN programma. Of het mogelijk is om die alternatieve energievormen te gebruiken is nog niet in technische en financiële zin onderzocht. De gevonden alternatieve ideeën voor energiezuinig suppleren zijn de Zandpunaise®, de Zandwindmolen®, Ecobeach, zand injecteren onder het strand en een leidingnetwerk voor de kust. De laatste twee ideeën zijn nog erg pril en niet uitgewerkt. Van de Zandpunaise is een prototype in bedrijf geweest. Het is niet geheel duidelijk waarom dat prototype geen vervolg heeft gekregen. Het concept Zandwindmolen wordt verder door Grontmij, IHC Merwede en Deme Dredging getoetst op technische en financiële haalbaarheid. Voor Ecobeach loopt een proefproject. Het resultaat wordt binnenkort gerapporteerd. Uit de externe interviews komt naar voren dat de baggerbedrijven energiewinst zien in andere contractvormen en dat de kennisinstituten energiewinst zien in het aanpassen van de suppletiestrategieën. Bij de workshop zijn nog enkele aanvullende nieuwe ideeën naar voren gekomen. De technische en financiële haalbaarheid van die ideeën is onbekend. Een eerste verkenning (samen met de inbrenger van het idee) kan uitwijzen of het zinvol is om die ideeën op te pakken. Naast de zoektocht naar nieuwe ideeën is ook globaal gekeken of de huidige suppletievorm met sleephopperzuigers verder verbeterd kan worden. De baggerbedrijven zien mogelijkheden in andere contractvormen. Bijvoorbeeld meer accent op langjarige onderhoudscontracten. Dan kan het voor de bedrijven lonend zijn om specifiek (energiezuiniger) equipement in te zetten. Dat beeld wordt bevestigd door de baggerequipementbouwers. De kennisinstituten zien mogelijkheden in het optimaliseren van suppletiestrategieën (in tijd en ruimte kijken waar winning en dumping het meest effectief is). Dat kan echter soms op gespannen voet staan met de huidige beleidslijnen (winning dieper dan NAP -20 m en handhaven Basis KustLijn). Ze verwachten echter dat er winst te behalen is door nog beter aan te sluiten bij de natuurlijke processen van sedimentatie en erosie. De inventarisatie heeft diverse inzichten opgeleverd. De vraag is hoe verder? RWS / DP Kust heeft de bedrijven uitgenodigd om met concrete voorstellen te komen. Voor de bedrijven is het dan van belang wat ze van de overheid kunnen verwachten. Hoe beloont de overheid initiatieven? Aspecten als intellectueel eigendom en terugverdienkansen zijn daarbij van eminent belang. Als die niet voldoende gewaarborgd zijn is het voor bedrijven niet aantrekkelijk om (samen met de overheid) in dergelijke risicovolle projecten te stappen. De overheid kan zelf ook initiatief nemen tot het initiëren van innovaties. Ze zal zich dan moeten beperken tot een begeleidende rol. Het onderzoek en de innovaties worden aan de markt overgelaten. Een concreet genoemd voorbeeld was het organiseren van kennisdeelsessies tussen verschillende partijen in een kleiner verband, met de hoop dat daaruit concrete initiatieven voortvloeien. Ook bij dergelijke kennisdeelsessies moet duidelijk zijn hoe intellectueel eigendom en terugverdienkansen voor de betrokkenen geregeld zijn

Estimating Pedestrian flows at train stations using the Station Transfer Model

Train stations play a vital role in the door to door travel experience of train passengers. From the passengers’ value of time perspective, the station is the weakest link in total time value of the journey. Within the station the transfer function – moving between the various transport modes and waiting at the next service - is the core function, because it connects all transport modes. Therefore, an optimal transfer process is a key requirement for a well performing station. The basic requirement for optimization of the transfer process is to understand how many passengers use the transfer facilities, and at what time. This information is delivered by the Station Transfer Model, which taps into data already available at the train operating and station management divisions of Netherlands Railways (NS). With the model, the volumes of pedestrian flows at platforms, escalators and stairs can be estimated for various time frames. The Station Transfer Model generates output that is useful for evaluation of the commercial performance of the station’s retail. It can also be used to estimate the required capacity of stairs and escalators between the platforms and the station hall, tunnels or bridges. When renewed data is available, NS intents to further develop the model to increase the quality of the output.Transport & PlanningCivil Engineering and Geoscience

Case study Piçarras Beach: Erosion and nourishment of a headland bay beach

Master project report. Piçarras is one of the touristic beaches of Santa Catarina state in Brazil. Piçarras beach is a headland bay beach. In the bay irregular features like an island, rocky outcrops and shoals are present influencing wave propagation. In the south Piçarras is bounded by Piçarras river. The river mouth has been fixated in 1970, after which erosion started. The part just a few hundred meters north of the river jetty has the most severe erosion. The erosion gradually decreases towards the north, where even some accretion has been measured. When the situation became critical a nourishment was executed in 1999, which has disappeared totally on some places. The decrease in beach width causes a devaluation of the houses and a decrease in tourism which consequently leads to a decrease of employment. It is therefore necessary to investigate the causes and the amount of the erosion and to generate measures to counteract the negative impact of the erosion. Prosul, a Brazilian engineering company, has designed a nourishment of which execution started in July 2008. The main goal of this study is investigate erosion at Piçarras beach and to design a nourishment to counteract the effects of the current erosion. A model has been built to represent the situation at Piçarras beach. With the model the evolution of the nourishment and the evolution of the existing plan of Prosul could be evaluated. The bathymetry has been composed of recent profile measurements and old nautical maps. They have all been related to the reference level of IBGE. To investigate the erosion at Piçarras beach the wave climate has been schematised. The available wave data was given for four direction (NE, E, SE, S) in the form of wave heights and periods. To be able to compare what the results of the incoming wave energy from these four directions were on the erosion and accretion on the beach, a schematisation has been made. A representative average wave per direction has been determined, that supplied the same energy input from that direction as did all the different waves from that direction. Headland bay beaches are historically formed in such a way that the incoming waves and thereby the wave energy, arrive perpendicular at the beach, thus absorbing the incoming wave energy in the most efficient way. This theory formed the basis of this schematisation. The mean tidal variation is 0.6m, at spring tide this is 0.9m. Storm surges lead to a set-up in water level of approximately 1.0m. Currents and wind are not taken into account. The sediment present at the beach has a D50 of 0.285mm. The sand used in the nourishment of 1999 was coarser than the native sand, which had a D50 of 0.260mm. Erosion processes can take the sand either in cross-shore direction or in longshore direction. Without looking at the underlying process, just to get a realistic idea of the erosion and accretion patterns, the amount of eroded sediment has been calculated with shoreline changes and deduced erosion rates [2]. The erosion of the past nine years is calculated to be 395,000 m3. To find out where the sediment is transported to at Piçarras beach a model has been build. First the nearshore wave conditions have been modelled with Delft3D (D3D) for the four wave scenarios. These conditions serve as input for Unibest (UB). This program is applied to model the shoreline changes.Hydraulic EngineeringCivil Engineering and Geoscience

The role of submerged aquatic vegetation in structuring the nearshore fish community within an estuary of the Southern Gulf of St. Lawrence

Artificial fertilizers are contributing to the replacement of eelgrass (Zostera marina) by sea lettuce (Ulva lactuca) in estuaries of Prince Edward Island (PEI), Canada. In this study, we found that the nearshore fish community differed between areas dominated by these two vegetations within an estuary in every month sampled (April–August). Adult northern pipefish (Syngnathus fuscus), threespine stickleback (Gasterosteus aculeatus), blackspotted stickleback (Gasterosteus wheatlandi), and Atlantic silverside (Menidia menidia) were most strongly associated with eelgrass, while mummichog (Fundulus heteroclitus), ninespine stickleback (Pungitius pungitius), and American eel (Anguilla rostrata) were often more numerous in sea lettuce. Sea lettuce stations tended to have more young-of-the-year mummichog, fourspine stickleback (Apeltes quadracus), and Gasterosteus sp. than eelgrass stations but fewer young-of-the-year northern pipefish and Atlantic silverside. Fish richness and abundance were significantly lower in the sea lettuce than eelgrass habitat during August when benthic hypoxia occurred. We conclude that the loss of eelgrass from PEI estuaries will result in significant declines in fish biodiversity