Lebrenz, Henning
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Henning Lebrenz
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- PublikationInvestigating river-restoration-effects on riverbed-stability by physical modelling(17.04.2024) Unrau, Silas; Venuleo, Sara; Derungs, Guido; Lebrenz, HenningThis 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.06 - Präsentation
- PublikationNew estimation models for determining the Q347(17.04.2024) Dups, Yanick; Santolamazza, Daniela Pavia; Staufer, Philipp; Lebrenz, HenningIn Switzerland, low flows are described by the five percent quantile denoted by Q347. This threshold value not only has consequences for the planning, but also necessitates authorities to adjust the operation of pertinent infrastructure to mitigate ecological impacts on watercourses. Given a discharge timeseries spanning at least a ten-year period, determination of the Q347 can be done using the duration curve. Typically, said timeseries are not available for smaller catchments necessitating the estimation of the threshold value Q347. In Switzerland, the utilization of multiple linear regression has been established to estimate the area-specific discharge q347. The primary objective of these investigations is to estimate the Q347 value for 383 ungauged catchments in the Canton of Solothurn, each covering an area less than 100 km². Daily discharge, precipitation and temperature timeseries ranging from 1990 to 2020 were collected from 56 gauged catchments smaller than 500 km² surrounding the target area. 30 “static” parameters delineating geometry, topography, geology, land use, and drainage along with nine “climatic” parameters describing temperatures, precipitation distributions, and potential evapotranspiration were defined and computed to characterize gauged and ungauged catchments. Alongside comparing three regression methods, coupled with two adjustment techniques supplementing truncated discharge timeseries, three parameter selection methods are evaluated. The validation of the proposed models shows reduced errors and increased linear correlations between estimated and observed values compared to currently applied models. Notably, a spatially more homogeneous yet catchment-specific distribution of estimated values is observable. Particularly when timeseries remain unadjusted or adjustment is done using the Antecedent Precipitation Index (API) and the flow duration curve from a donor basin (Ridolfi, E.; Kumar, H.; Bárdossy, A., 2020), the proposed models yield promising results. Furthermore, the temporal variability of low flow events for the glacier-free catchments in the study area has been analysed. The frequency of low flow events below the threshold systematically increased over the last 30 years, while the 10-year Q347 value of said catchments has systematically decreased in the same period. The increase in low flow days leads to large errors in the estimation of the Q347 value, especially when its estimation is based on truncated timeseries. As further changes in runoff behaviour are to be expected due to climate change, extending the definition of "low flow" to include event duration and intensity alongside a fixed threshold value could offer a more suitable description.06 - Präsentation
- PublikationSemi- or fully automatic drainage regulation as a mean to recharge groundwater(17.04.2024) Venuleo, Sara; Unrau, Silas; Staufer, Philipp; Lebrenz, HenningClimatic 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.06 - Präsentation
- PublikationFliessgewässer im Nordwestschweizer Jura in Zeiten der Trockenheit und des Klimawandels(Geographisch-Ethnologische Gesellschaft Basel, 2022) Lüscher, Peter; Weingartner, Rolf; Pavia Santolamazza, Daniela; Lebrenz, Henning [in: Regio Basiliensis]Trockenheit und Niedrigwasser sind aus hydrologischer Sicht der Gewässer eine der grössten Herausforderungen in der Schweiz. In diesem Beitrag werden die Niedrigwasserverhältnisse im Nordwestschweizer Jura untersucht. Dabei steht die Frage der heutigen und zukünftigen Trockenheitsanfälligkeit im Mittelpunkt. Die Resultate belegen, dass signifikante Unterschiede zwischen Ketten- und Tafeljura bestehen, wobei die Fliessgewässer im Tafeljura insgesamt trockenheitsanfälliger sind. Gelingt es nicht, die Treibhausgasemissionen wirkungsvoll zu begrenzen, wird die Trockenheitsanfälligkeit gemäss dem Szenario ohne Massnahmen (RCP 8.5) bis Ende des Jahrhunderts deutlich zunehmen.01A - Beitrag in wissenschaftlicher Zeitschrift