Field Measurements of Impact Pressures in Surf

Miller, Robert L.; Leverette, Steve; O'Sullivan, Justine; Tochko, J.; Theriault, K.

doi:10.1061/9780872621138.106

Cited by 12 publications

(8 citation statements)

References 7 publications

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“…9 suggests that wave impingement effects on organisms have been just as inappropriately overlooked. Historically, although coastal engineers have devoted much effort to the study of impact forces (e.g., Miller et al 1974;Blackmore and Hewson 1984;Cooker and Peregrine 1990), intertidal biologists have typically discounted the importance of wave impact for two reasons. First, it has been believed that flows with high fractions of entrained air are less likely to produce large pressure transients, and breaking waves on rocky shores provide excellent examples of white water.…”

Section: Discussionmentioning

confidence: 99%

Biological implications of surf‐zone flow complexity

Gaylord

2000

Limnology & Oceanography

100

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Wave action imposes potentially large hydrodynamic forces on intertidal plants and animals, and can act as a primary agent of disturbance. It has also been proposed that rapid water accelerations produced by breaking waves might constrain the sizes to which intertidal organisms can grow. However, despite the proven ecological importance of surf-zone flows, few actual measurements of forces imposed on plants or animals by waves in nature have been conducted. In this study, real-time wave forces acting on individuals of the rockweed Pelvetia compressa and a sea urchin Strongylocentrotus purpuratus are recorded in the field. These measured forces are compared with values predicted from theory using laboratory-determined shape factors (i.e., drag and added mass coefficients) and simultaneous flow measurements conducted adjacent to the deployed samples. Results demonstrate that models predicting large contributions of force due to water's acceleration are likely inaccurate, most probably because such models fail to account for the small spatial scales of surf-zone accelerations. This likely eliminates any capacity for intertidal hydrodynamic accelerational forces to limit size, contrary to previous conjectures. Data also suggest that wave-induced forces predicted from simple fluid dynamic expressions can, but sometimes do not, reflect accurately the forces applied. Together these findings imply that although traditional hydrodynamic theory may indeed provide a valuable tool for predicting forces imposed on immersed surf-zone organisms, such approaches must be used with caution. Finally, the field recordings suggest that sharp, transient forces arising from the impingement of waves directly on non-submerged organisms may in general impose the most severe loadings experienced by intertidal plants and animals, a possibility that to date has received little attention. The precise consequences of such brief forces depend on the level of flexibility or rigidity of an organism's construction.In intertidal regions of rocky shores, forces imposed by breaking waves may act as one of the dominant mechanisms determining species presence or abundance, plant and animal diversity, and community structure (Lewis 1964;1968;Dayton 1971;Connell 1978;Paine and Levin 1981;Sousa 1984Sousa , 1985Ricketts et al. 1985). However, despite their importance, wave exposure and the magnitudes of imposed hydrodynamic forces have proven difficult to estimate. Most studies that have attempted to evaluate consequences of breaking waves for intertidal organisms have relied on standard fluid-dynamic theory coupled with idealized flow scenarios that may or may not accurately describe effects of the complex and rapidly evolving water motions of the surf zone (e.g., Koehl 1977;1986;Denny et al. 1985;Denny 1987;1995;Carrington 1990; Denny and Gaines 1990;Dudgeon and Johnson 1992;Bell and Denny 1994;Gaylord et al. 1994; Denny and Gaylord 1996;Blanchette 1997). Thus the validity of models designed to predict the severity or 1 Present address: Dept. Ec...

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Section: Discussionmentioning

confidence: 99%

Biological implications of surf‐zone flow complexity

Gaylord

2000

Limnology & Oceanography

100

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“…These measurements show a slowly varying force similar to that exerted by a nonbreaking wave, together with a very short duration rather large force that occurs just as the wave breaks at the pile, Figure 1. Some field measurements of forces induced on a circular pile by breaking waves in the surf zone are given in papers by Snodgrass, Rice, and Hall, 1951;Morison, Johnson and O'Brien, 1953;Miller, Leverette, O'Sullivan, Tochko and Theriault, 1974. Results of laboratory studies have been given by Hall, 1957;Goda, Haranaka and Kitahata, 1966;Watanaba and Horikawa, 1974. It is difficult to measure this "impact" force reliably owing to its very short duration combined with the dynamic characteristics of the test system.…”

Section: Breaker Forces On Pilesmentioning

confidence: 99%

“…(See the variation of dynamic pressure measurements with distance beneath the surface by Miller, et al, 1974 for the reason that this can be done).…”

Section: Breaker Forces On Pilesmentioning

confidence: 99%

“…It appears from the work of Snodgrass, et al, 1951;Hall, 1957Hall, , 1958and Watababe and Horikawa, 1974, that the Morison equation is adequate for waves that have not yet broken, insofar as any individual pile is concerned. A wave breaking in the plunging manner at a pile induces a greater force in the An, portion of crest (see Miller et al, 1974). "Foam lines" (bores) resulting from plunging breakers exert a very large force on a pile in the same manner, Figure 4.…”

Section: (3m /3x)mentioning

confidence: 99%

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Forces Induced by Breakers on Piles

Wiegel

1982

Int. Conf. Coastal. Eng.

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This paper consists of three parts. The first part presents a method for analyzing the forces exerted by breaking waves on a cirular pile. The force consists of two components, a slowly varying force and a much larger but very short duration quasi-impact force (probably of the order of 1/100 of a second). The second part is concerned with breaker characteristics, with emphasis being given to the few field data that have been measured. The third part consists of a presentation of some available data on surf zone bottom profile variations with time. Information on all three of these parts is needed for the proper design of a pile supported structure in the surf zone. If the bottom along the site of a proposed pier is sand, an estimate of the variability with time of the profile must be made. The effect of bottom depth and configuration on the height of waves moving shoreward, and the effect of this, in turn, on the wave loading is important in the calculations of wave-induced moments about the bottom. The ability of the structure to withstand these horizontal loads depends in part upon the depth of penetration of the piles. If the bottom varies with time, then calculations of wave characteristics and wave-induced loads on the piles should be made for appropriate bottom configurations.

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“…Miller et al (1974) failed to record impact pressure in the field. Theoretically high impact pressures also occur through water hammer.…”

Section: Erosion By Wavesmentioning

confidence: 99%

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand

2000

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Shore platforms on the Kaikoura Peninsula have been examined to determine the roles of marine and subaerial weathering processes in platform evolution. Erosion was measured to assess rates of development and processes of erosion. Lowering rates on platforms are presented from two years of monitoring using a traversing micro-erosion meter. Cliff retreats were calculated using aerial photographic interpretation. Marine processes were investigated by using deep water wave data, by measuring waves on shore platforms and by analysing measured tidal data. Weathering processes were investigated using tidal data, climate data, the Schmidt Hammer test, and a laboratory experiment on wetting and drying.Lowering rates over two years ranged from 0.07 to 19.80mm, and annual rates ranged from 0.154 to 9.194mm/yr. Rates of erosion varied with lithology and the type of platform.Erosion on Type A mudstone platforms was 1.98mm/yr; on Type B mudstone platforms erosion was 0.733mm/yr; and on limestone platforms it was 0.88mm/yr. The grand mean lowering rate for all shore platforms was 1. 13mm/yr . These rates fall in the middle of the range of published rates from previous studies at Kaikoura and at locations around the world. For the fITst time, erosion data from a traversing micro-erosion meter were presented as volumes of material eroded.The total volume of rock eroded from study sites having, each with an area of 45.4cm 2 , ranged from 1.20 to 92.50cm 3 • A significant finding was that rock surfaces swell up as indicated by a rise in surface level rather than lowering from erosion. The maximum measured swelling was 8.90mm. At some measurement sites as much as 90 per cent of measurements showed swelling over a period of 98 days. Values for erosion and swelling were higher during summer months.Both erosion and swelling were shown to be statistically related to season, suggesting that weathering is the group of processes causing both erosion and swelling. Summer provides better conditions for wetting and drying, which is thought to be the most important weathering process on shore platforms. Horizontal retreat rates were calculated over 52 years for cliffs, beaches and lagoon deposits backing shore platforms at Kaikoura, these ranged from 0.05 to 0.91mJyr.Investigation of marine processes showed that the deep water wave environment off the Kaikoura Peninsula is very energetic, but the amount of wave energy delivered to platforms is very low. A comparison of deep water wave energy flux with wave energy flux at the landward cliff of platforms, showed that there was a reduction by as much as five orders of magnitude. An analysis of the role of breaking waves revealed that these were ineffective as an erosional agent ii because the depth of water offshore causes breaking well before waves arrive on platform surfaces. Shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms. TIus showed that these forces never exceeded the compressive strength the platform rocks at Kaikoura. It was co...

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Field Measurements of Impact Pressures in Surf

Cited by 12 publications

References 7 publications

Biological implications of surf‐zone flow complexity

Biological implications of surf‐zone flow complexity

Forces Induced by Breakers on Piles

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand

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