Physical modelling of the flow field in an undular tidal bore

Abstract

A tidal bore may form in a converging channel with a funnel shape when the tidal range exceeds 6-9 m. The advancing surge has a major impact on the estuarine ecosystem. Physical modelling of an undular bore has been conducted based upon a quasi-steady flow analogy. The experimental data highlight rapid flow redistributions between successive wave troughs and crests as well as large bottom shear stress variations. The results suggest a sediment transport process combining scour beneath wave troughs associated with upward matter dispersion between a trough and the following wave crest. The process is repeated at each trough and significant sediment transport takes place with deposition in upstream intertidal zones. The conceptual model is supported by field observations showing murky waters after the bore passage and long-lasting chaotic waves. RÉSUMÉUn mascaret peut se former dans un canal convergent en forme d'entonnoir quand la hauteur de marée excède 6-9 m. La vague qui avance a un impact important sur l'écosystème de l'estuaire. La modélisation physique d'un mascaret ondulé a été réalisée en se basant sur l'analogie avec un écoulement quasi-stationnaire. Les données expérimentales mettent en lumière des redistributions rapides d'écoulement entre les creux et les crêtes successives des vagues ainsi que des variations importantes du cisaillement au fond. Les résultats suggèrent un processus de transport sédimentaire combinant un affouillement de sédiment sous les creux associé à une dispersion ascendante de matière entre un creux et la crête de vague suivante. Le processus est répété à chaque creux et un transport significatif de sédiment a lieu avec dépôt dans les zones intertidales amont. Le modèle conceptuel est étayé par des observations en nature montrant des eaux troubles après le passage d'un mascaret et des vagues chaotiques durables.

Free-Surface Profiles, Velocity and Pressure Distributions on a Broad-Crested Weir: A Physical Study

“…In Figure 3, each data set regroups the flow depth measurements for 0.1 < x/L crest < 1, and they are compared with experimental results obtained above circular crested weirs (FAWER 1937, VO 1992 and in undular flows (CHANSON 2005). The present results showed overall a reasonable agreement between data and theory, in particular the solutions S1 and S3 ( < 0), along the entire weir crest (Fig.…”

Closure to “Minimum Specific Energy and Critical Flow Conditions in Open Channels” by Hubert Chanson

“…4 demonstrates conclusively the existence of the solution Sl for Ll<O, refuting the discussion's argument. (Chanson 2006) and experimental observations (Fawer 1937;Vo 1992;Chanson 2005) Last it must be stressed that only the critical flow solutions for Ll<O (rounded weir) and Ll=O (broad-crested weir) were found to match experimental observations of pressure and velocity distributions. For Ll > 0, the correct analytical solution of the critical flow depth is and it is shown in Fig.…”

“…In Fig. 4 hydraulic jumps with partially developed inflow conditions (Chanson 2005). Both wave crest and trough data are shown in Fig.…”

“…The basic data are regrouped in Table 1 (Chanson 2005). For the weir experiments, the term A/13 JI3/JA in Eq.…”

Explicit equations for critical depth in open channels with complex compound cross sections. A discussion

“…Comparison between analytical solutions (Eq. (4)), broad-crested weir data (Felder and Chanson 2012), circular crested weir data (Fawer 1937, Vo 1992) and undular flow data (Chanson 2005) Sections. A Discussion."…”