Sand exchange between groyne‐field beaches and the navigation channel of the Dutch Rhine: the impact of navigation versus river flow

Abstract

The morphodynamics of groyne-field beaches along the Dutch Rhine was studied from in situ measurements of hydrodynamics and sand transport, aerial photographs, and bed-level time series. From the analyses, it appeared that groyne-field beaches experience an alternation of periods of erosion and deposition. The erosion is due to navigation at low to moderate discharge; the deposition is due to floods. On a time scale of a few decades, periods of erosion and deposition are in equilibrium. Navigation-induced erosion is mainly due to vessels >60 m. The impact of passing vessels on the currents near the banks and the erosion of the beaches increases as underwater volume increases. Individually, loaded barge-tows have the greatest influence on groyne-field hydrodynamics and sand transport. On a yearly basis, however, the relatively strong influence of push towing is superseded by the higher frequency of passing motorized vessels. The erosion on a yearly basis, therefore, is driven by the effects of the large motorized vessels. The effects of push towing are negligible.Underwater volume and passing distance from the bank are the most important parameters of passages, insofar as their effect on groyne-field beaches is concerned. The effect of underwater volume is clearly reflected in the different behaviour of groynefield beaches on the north and south banks. Loaded vessels sailing along the south bank from Rotterdam to Germany have a much greater effect on the beaches on the south bank than do returning vessels, often empty or partly loaded, on the beaches of the north bank. As a result, beach erosion on the south bank is twice as pronounced as the erosion on the north bank. Remarkably, the greater erosion of the beaches observed on the south bank was compensated by a similarly larger deposition during the flood of 1998.The impact of navigation on groyne-field beach erosion increased strongly from

Human‐induced changes in bed shear stress and bed grain size in the River Waal (The Netherlands) during the past 900 years

“…This may be an effect of the increased navigation in Period 3, which is known to cause high τ values on the sandy groyne-field beaches along the Waal, whereas it does not strongly affect τ in the main channel (Ten Brinke et al, 2004). The high τ in the groyne fields evokes a net supply of fines to the main channel during low-flow periods.…”

“…However, analysis of thalweg measurements over the entire length of the river revealed that thalwegs measured left of the river axis were systematically finer than thalwegs measured right of the river axis (Figure 7d). According to Ten Brinke et al (2004) this is a result of navigation currents (see below).…”

“…Because the vessels sailing upstream in the left part of the Waal are fully loaded, whereas the vessels sailing downstream along the right bank are often empty, it may be clear that the fining effect of the navigation must be stronger in the left part of the Waal. The navigation thus probably is responsible for the cross-stream variation in bed grain size in Period 3 (Ten Brinke, 1997;Ten Brinke et al, 2004).…”

Transport of suspended sediments under the influence of bank macro‐roughness

“…(); Ten Brinke et al. (); Yossef and de Vriend (); Henning and Hentschel (). Recently, Sanjou and Nezu () analysed, for a constant planar configuration of rectangular embayments, the effect of bed slope on the mass and the momentum exchange between inner and outer flows.…”

Modelling spatio‐temporal flow characteristics in groyne fields

“…Hence, groynes are an example of human impact on the river system, resulting in a fixed river planform, a navigation channel that is relatively deep over a large part of its cross-section, and sandy beaches between the groynes (Ten Brinke et al, 2004). Early descriptions of this functionality of groyne structures date back to the 16th century (Vierlingh, 1576), and Leonardo da Vinci used them in plans to train the river Arno in the neighbourhood of Florence (Uijttewaal, 2005).…”