Rip Currents: Observations of Hydraulic Gradients, Friction Factors and Wave Pump Efficiency

Nielsen, Peter; Brander, Rob; Hughes, Michael G.

doi:10.1061/40566(260)49

Cited by 11 publications

(20 citation statements)

References 2 publications

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“…The overwash discharge was estimated using the wave pump concept. Bruun and Viggoson (1977) first introduced the non-breaking wave pump model that was extended to rip cells by Nielsen et al (2001). Callaghan et al (2006) applied Nielsen et al (2001) model to atoll flushing.…”

Section: Node 2 Nodementioning

confidence: 99%

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Ocean Driven Flooding of a Coastal Lake

Callaghan

Hanslow³

et al. 2014

Int. Conf. Coastal. Eng.

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Analysis of Lake Conjola flooding in April 2006, provided in this paper, attributes it to waves pumping water over a 300 m long beach berm and into Lake Conjola. This overwash, generated by the medium wave height swell occurring during this flooding, was able to lift the lake levels near the entrance, persistently over several tidal cycles, to well above the ocean water levels . The wave pump model was used to model this flooding. Lake Conjola water storage and dynamics were modelled by using a two-node continuity based model that a change in storage in time is driven by the net inflow to a node and these nodes and the ocean are linked by log-law. The extents of these two nodes were established from previous water surface measurements. While the qualitative flood behavior was reproduced by this remarkably simple model, the peak flood level was not satisfactorily predicted when using literature values for model turning parameters. One reason for this mismatch was that the waves pumped against a head including critical flow on the beach berm. Based on recent images of Lake Conjola wave overwash events, it may be concluded that pumping against critical flow is too harsh. Removing this from the model has halved the gap between the measurements and predictions. However, more research is definitely required to establish what components should be included in the hydraulic head pumped against.

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Section: Node 2 Nodementioning

confidence: 99%

“…Bruun and Viggoson (1977) first introduced the non-breaking wave pump model that was extended to rip cells by Nielsen et al (2001). Callaghan et al (2006) applied Nielsen et al (2001) model to atoll flushing. Nielsen et al (2008) provided comprehensive measurements for wave pump efficiencies ε (fig 4).…”

Section: Node 2 Nodementioning

confidence: 99%

Ocean Driven Flooding of a Coastal Lake

Callaghan

Hanslow³

et al. 2014

Int. Conf. Coastal. Eng.

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“…However, results from one-node model by Thuy et al (2011) show that the wave pump efficiency, ε, required to lift up whole lake level of ca 1 m, is 9 times the suggested value by Nielsen et al (2001) and Callaghan et al (2006a) for natural systems. This resulted in unrealistic velocity through the entrance and over the berm.…”

Section: Two Node Hydrodynamic Modelmentioning

confidence: 99%

“…The wave pump concept was introduced by Bruun & Viggosson (1977) for non-breaking waves and extended by Nielsen et al (2001Nielsen et al ( , 2008 for rip currents. This concept was applied successfully for studying atoll flushing by Callaghan et al (2006a).…”

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Aspects of inlet geometry and dynamics

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This thesis contains new analytical approaches as well as laboratory-and field experiments conducted to understand the hydrodynamic and morphodynamic responses of tidal inlets to forcing from tides, river flow and waves on the time scales of closure, flood or storm events. The thesis outcome is effective new tools for authorities managing coastal zones balancing navigation-, shore protection-and socio-economic development purposes.A new method of coastal inlet classification based on dimensionless parameters is presented. These parameters represent the relative strength of the three main forcing agents: tides, river flow and waves. This new classification is applied to 178 inlets along the NSW coast of Australia, and compared with other widely used classification schemes available in the literature.The inlet hydraulic analysis is presented in Chapter 2 with given inlet geometry and wave climate with overwash discharge (Q over ) added into the usual governing equations. The hydraulic analysis of inlets in terms of the frequency response function for the linearised system is illustrated for cases of monochromatic and mixed diurnal/semi-diurnal tides. This analysis quantifies the influence of the entrance invert level, river flow and bay surface area. A case of inland flooding at Lake Conjola, Australia is used to test different methods resulting in a successful illustration of the importance of wave overwash as a driving force.For each hydrodynamic condition, the inlet system and its elements have a corresponding morphological equilibrium state. New relationships for inlets in equilibrium were constructed based on dimensional analysis and tested on a data set of 36 natural inlets in the USA. These new relations depend not only on the tidal prism but also the tidal period, and mean annual significant wave height s H .During unusual weather, the morphology of tidal inlets runs out of equilibrium.Subsequently, they may return to the previous equilibrium or move towards a new equilibrium or get closed. Inlet morphodynamics analysis is ideally carried out from topographical surveys. These are however costly and usually not available. Process based numerical models are still unreliable. A more economical and reliable new method, a 24.5hour moving window method, is introduced to infer hydraulic-and morpho-dynamic changes from tidal records. The morphological time scales are thus determined from time series of mean water levels, standard deviation, or the gain of the primary tidal components. This analytical method is successfully applied to inlet closure events and flood or storm events.The morphological time scale, T morph has been derived from the 24.5hour moving window analysis for many closure events with bay area (A b <0.7km 2 ) in Australia. The results show a clear trend of T morph decreasing with increasing relative wave strength -i.e., more rapid closure with iii bigger waves. However, for larger inlets or inlets with training works the morphology changes, at the time scale of individual storms, are usua...

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Nearshore circulation over transverse bar and rip morphology with oblique wave forcing

Houser

Arnott

Ulzhöfer

et al. 2013

Earth Surf Processes Landf

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There is a paucity of field data to describe the transition in nearshore circulation between alongshore, meandering and rip current systems. A combination of in‐situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at Pensacola Beach, Florida in the presence of relatively low energy oblique waves. Current speeds vary in response to the relative wave height ratio (Hs/h), which defines the degree and extent of breaking over the shoal. In the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves. As waves begin to break across the shoal (0.20.5), the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone. The increase in wave dissipation is associated with an increase in very low frequency (VLF) variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow. The unsteady nature of the nearshore circulation is responsible for 55% of all surf zone exits under these more dissipative conditions. In contrast, only 29% of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore‐meandering current. While the currents had a low velocity (maximum of ~0.4 m s‐1) and would not pose a significant hazard to the average swimmer, the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low‐energy rip circulation systems under oblique wave forcing. Copyright © 2013 John Wiley & Sons, Ltd.

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Rip Currents: Observations of Hydraulic Gradients, Friction Factors and Wave Pump Efficiency

Cited by 11 publications

References 2 publications

Ocean Driven Flooding of a Coastal Lake

Ocean Driven Flooding of a Coastal Lake

Aspects of inlet geometry and dynamics

Nearshore circulation over transverse bar and rip morphology with oblique wave forcing

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