Man-induced regime shifts in small estuaries—II: a comparison of rivers
- 885 Downloads
This is Part II of two papers on man-induced regime shifts in small, narrow, and converging estuaries, with focus on the interaction between effective hydraulic drag, fine sediment import, and tidal amplification, induced by river engineering works, e.g., narrowing and deepening. Paper I describes a simple linear analytical model for the tidal movement in narrow, converging estuaries and a conceptual model on the response of tidal rivers to river engineering works. It is argued that such engineering works may set in motion a snowball effect bringing the river into an alternative steady state. Part II analyses the historic development in tidal range in four rivers, e.g., the Elbe, Ems, Loire, and Scheldt, all in northwest Europe; data are available for many decades, up to a century. We use the analytical model derived in Part I, showing that the effective hydraulic drag in the Ems and Loire has decreased considerably over time, as anticipated in Part I. We did not find evidence that the Upper Sea Scheldt is close to its tipping point towards hyperturbid conditions, but risks have been identified. In the Elbe, tidal reflections against the profound step in bed level around Hamburg seem to have affected the tidal evolution in the last decades. It is emphasized that the conceptual picture sketched in these papers is still hypothetical and needs to be validated, for instance through hind-cast modeling of the evolution of these rivers. This will not be an easy task, as historical data for a proper calibration of the models required are scarce.
KeywordsTidal amplification Hydraulic drag Dispersion equation Regime shift Elbe Ems Loire Scheldt
This work was carried within the framework of the LTV project, which is the acronym for the Long-Term Vision of Scheldt estuary with respect to Safety, Accessibility and Nature, in which the following subprojects are integrated: Maintaining fairways Scheldt estuary, Permits for disposal of dredged sediments and the so-called KPP (knowledge of primary processes) program of Rijkswaterstaat. The study was financed by the Flemish “Afdeling Maritieme Toegang” (Maritime Department) and Rijkswaterstaat, Waterdienst, and Directorate Zeeland (the Dutch Ministry of Infrastructure and Environment). The subject of the research in this paper was formulated by Mr. Youri Meersschaut requesting the analysis of the fine sediment dynamics in the Scheldt River. Further, we like to thank Dr. Henk Schuttelaars for his many constructive comments and ongoing discussions on this subject, and Dr. Tom de Mulder for reviewing an earlier report of this study. We also would like to acknowledge the help of Mr. Marcel Taal in organizing and coordinating our study.
The results in this paper are based on a large number of data from a variety of sources. Some data sets were available at Deltares in reports, or in digital form from studies carried out earlier. Other data have been prepared and made available especially for this project. We would like to thank the following people for their support and supply of data: Mr. Frederik Roose (Flemish Government) for Scheldt data; Dr. Luc Hamm (Sogreah) for information on the Loire; Dr. Harro Heijer and Mr. Jens Jürges (BAW) for data on the Ems, Weser, and Elbe river; and Prof. Ian Townend for data on the Thames and Severn estuaries. Furthermore, Dr. Holger Weilbeer (BAW) and Dr. Jens Kappenberg (Helmholz Centre) were helpful in some discussions on the Elbe and Ems Rivers.
- BAW (2012) Data received from Dr. Frank Kösters and Jens Jürges on Ems and ElbeGoogle Scholar
- Briere C, Crebas J, Becker A, Winterwerp J.C (2012) Analyse de la morphologie du chenal de Nantes et étude de sa restauration - Phase 3 : Etude de l’impact d’une intervention à l’amont de Nantes sur les caractéristiques de la marée. Deltares report 1201695 (in French)Google Scholar
- Herrling G, Niemeyer HD (2008) Comparison of the hydrodynamic regime of 1937 and 2005 in the Ems-Dollard estuary by applying mathematical modeling. Research project: INTERREG IIIB North Sea project HARBASINS; Work package 4: “Hydro-morphological impacts and pressures” Lower Saxony Water Management, Coastal Defense and Nature Conservation Agency, Coastal Research StationGoogle Scholar
- IMDC (2012) Analyse bodemgegevens Boven Zeeschelde. Note I/NO/11387/12.226/VBAGoogle Scholar
- Jay DA (1991) Green law revisited: tidal long-wave propagation in channels with strong topography. J Geophys Res 96(C11):20,585–20,598Google Scholar
- Kappenberg J, Fanger H-U (2007) Sedimenttransportgeschehen in der tidebeeinflussten Elbe, der Deutschen Bucht und in der Nordsee. GKSS report 2007/20; ISSN 0344–9629Google Scholar
- Krebs M, Weilbeer H (2005) Ems-Dollart estuary. Die Küste 74:252–262Google Scholar
- Kuijper C, Lescinski J (2012) LTV Veiligheid en Toegankelijkheid. Sub project B: Data analysis Western Scheldt. Report 1204405. DeltaresGoogle Scholar
- Plancke Y, Maximova T, Ides S, Peeters P, Taverniers E, Mostaert F (2012) Werkgroep O&M - Projectgroep Veiligheid. Sub project 1: Data analysis and hypothesis - Upper Sea Scheldt. Report WL2012R756_05_rev4_0. Flanders Hydraulics ResearchGoogle Scholar
- Schrottke K, Bartholomä A (2008) Detaillierte Einblicke in die ästuarine Schwebstoffdynamik mittels hochauflösender Hydroakustik. Tagungsband zum Seminar Ultraschall in der Hydrometrie: neue Technik; neuer Nutzen; FgHW / DWA, Koblenz, June 2008, 75–82Google Scholar
- Sogreah (2006). Expertise et connaisssance du systeme estuarien de Loire – Tome 1: Analyse historique, Report 1711457R2Google Scholar
- Talke SA, de Swart HE, de Jonge VN (2009) An idealized model and systematic process study on oxygen depletion in highly turbid estuaries. Estuar Coasts 32(4):602–620Google Scholar
- Van Braeckel A, Piesschaert F, van den Bergh E (2006) Historische analyse van de Zeeschelde en haar getijgebon den zijrivieren. 19e eeuw tot heden. INBO report INBO.R.2006.29Google Scholar
- Van Rijn LC (1993) Principles of sediment transport in rivers, estuaries and coastal seas. AQUA Publications, The NetherlandsGoogle Scholar
- Villaret C, Huybrechts N, Davies AG, Way O (2011) Effect of bed roughness prediction on morphodynamic modelling: application to the Dee estuary (UK) and to the Gironde estuary (France). Proceedings 34th IAHR World Congress-Balance and Uncertainty, Brisbane, Australia: 1149–1156, ISBN 978-0-85825-868-6Google Scholar
- Vroom J, van den Boogaard H, van Maren B (2012) Mud dynamics in the Eems-Dollard, research phase 2–analysis of existing data. Deltares, report 1205711-001Google Scholar
- Weilbeer H, Klöpper M, Bundesanstalt für Wasserbau (2011) Model validation and system studies for hydrodynamics, salt and sediment transport in the Elbe Estuary—basic information for the river engineering and sediment management. Draft Report A39550310069Google Scholar
- Winterwerp JC (2011) Fine sediment transport by tidal asymmetry in the high-concentrated Ems River: indications for a regime shift in response to channel deepening. Ocean Dyn 61(2–3):203–215Google Scholar