Venuleo, Sara
E-Mail-Adresse
Geburtsdatum
Suchergebnisse
Investigating river-restoration-effects on riverbed-stability by physical modelling
This study shows how experimental results provide fundamental insights in the challenge of river revitalisation, and thus represent a powerful tool to guide engineers’ actions. Results concerns a study case, namely the “Wiese Vital” project, a restoration project in Basel area (Switzerland), with the objectives of safeguarding Basel's drinking water supply while revitalizing its watercourse and providing flood protection. The planned revitalisation measures involve the reconstruction of the Wiese riverbed, the introduction of structures to improve its morphological variability and the replenishment of fine sediment to improve the spawning habitat of native fishes. The new Wiese riverbed will consist of a coarser sediment layer, about 1.2 meters deep, overlaying a layer of finer sediments, meant to protect the underlaying aquifer from undesirable water infiltrations and thus to ensure Basel's drinking water supply safety. The stability of the coarser layer was investigated using a physical model in scale 1 to 20, built in the hydraulic hall of the University of Applied Sciences and Arts Northwestern Switzerland. Experiments investigated the stability of the coarse protective layer in presence and in absences of revitalization measures: with and without “ecological” structures and before and after the addition of fine sediments. Results revealed that wrong placement of “ecological” structures can cause local erosion and threaten the stability of the riverbed. Moreover, they provided useful insights on the response of a coarser riverbed to the input of fine sediments.
Physikalische Modellierung des Geschiebetransports für «WieseVital»
Das Revitalisierungsprojekt «WieseVital» (BS) sieht den Einbau einer grobkörnigen Schutzschicht über die gesamte Gewässersohle sowie punktuell eingebrachtes, feinkörniges Laichsubstrat vor. Um die Interaktion der beiden Kornfraktionen, insbesondere den Einfluss der Feinsedimente auf die grobkörnige Schutzschicht zu beurteilen, wurde an der Fachhochschule Nordwestschweiz (FHNW) ein physikalisches Wasserbaumodell im Massstab 1:20 nachgebaut. Unter Beachtung von Skalierungseffekten und den abgeleiteten Rand- und Übertragungsbedingungen, konnten wertvolle Grundlagen und Hinweise für den Bau und den Betrieb des geplanten Flussabschnitts gewonnen werden. Das eingebrachte feinkörnige Laichsubstrat verteilt und vermischt sich bis zur Vermischungstiefe, die durch «kinetische Siebung» (z. B. beim HQ100) deutlich erhöht werden kann. Im Allgemeinen erleichtern die Feinsedimente den Bewegungsbeginn der grobkörnigen Schutzschicht, ohne allerdings ihre Stabilität zu gefährden. Ergänzend können erhöhte Kolkbildungen an geplanten ökologischen Einbauten durch lokale Sohlsicherungsmassnahmen begrenzt werden. Im späteren Betrieb kann das Modell von Wilcock & Crowe für die Abschätzung der gesamten Geschiebefracht angewendet werden, falls die raumzeitliche Verteilung der notwendigen Gewässersohleneigenschaften bekannt ist.
Parameterization and results of SWE for gravity currents are sensitive to the definition of depth
Rigorously derived shallow water equations (SWEs) are applied to results of large eddy simulation (LES) of a continuously fed gravity current in order to assess (1) sensitivity of current depth results to its definition; (2) coefficients in depth-averaged continuity and momentum equation due to the nonuniformity of density and velocity profiles; and (3) sensitivity of entrainment coefficient to definition of current depth. It is shown that using different definitions of the current depth may produce significantly different numerical results. The coefficients due to nonuniformity in the continuity equation are very close to unity, whereas the coefficients in the momentum flux and the pressure term in the momentum equation are different from unity by a margin that is very sensitive to the definition of current depth. The entrainment coefficient is more sensitive to the selected parameterization than to the definition of the current depth.
Semi- or fully automatic drainage regulation as a mean to recharge groundwater
Climatic change is decreasing water availability, all over the world. Regions which never faced water scarcity need to adapt their practises to face more frequent and severe droughts periods. Among others, agriculture is one of the sectors that will face the consequences of water scarcity. Indeed, while water availability decreases, the use of water for irrigation purposes becomes questionable. In many regions in Europe, cultivated areas have a sub-surface drainage system, which ensures that crops do not face water stress due to excessive soil water content. These drainage systems convey the water infiltrating during rainfall events to surface channels, reducing the natural water table recharge. Introducing drainage regulations units in existing drainage systems represent a mean to increase the soil water retention and, consequently, a mean to increase the natural water table recharge while decreasing the need of irrigation and while helping to reduce peak flow during intense rainfall events. Moreover, controlled drainage management can reduce the amount of Nitrogen and Plant Protection Products (PPP) discharged into surface waters. Given its environmental benefits, drainage water management is today an official conservation practice in the USA and the Conservation Practice Standard 554 (code 554) has been published by the United States Department of Agriculture to inform, advice and guide potential users of this practise. Drainage control units can be simple structures retrofitted in existing drainage networks outlets. They can consist of sliding weir systems or of a flashboard with adjustable height and they can be operated manually or automatically. In the present study an automatic drainage control unit has been developed and operated in a laboratory prototype. The objective of our experiment was understanding which technical and practical difficulties are faced in the use of a drainage control unit and thus which issues hinder its spread among farmers. Particular attention was given to possible issues associated with sedimentation.
Machbarkeit von smarten Drainagen in bindigen Böden
Smarte Drainagen, die temporär Wasser zurückhalten, können eine weitere Möglichkeit zur Anpassung an den Klimawandel sein. Sie reduzieren u. a. die Spitzen von Hochwasser und können bei ausbleibenden Niederschlägen zur Linderung der Trockenheit beitragen. Mithilfe von physikalischen Modellversuchen wurden Grenzen und aber auch die grundsätzliche Machbarkeit für Geländesituationen aufgezeigt, die in der Nordwestschweiz und Südbaden typisch sind.