![]() Individuals in low amplitude unsteady flow performed as well as fish in steady flow. Using intermittent-flow respirometry, we measured critical swimming speed (Ucrit), oxygen consumption rate (O2) and pectoral fin use in steady flow versus unsteady flows with either low (0.5 body lengths per second BLs(-1)) or high amplitude (1.0 BLs(-1)) velocity fluctuations, with a 5 s period. We examined how cyclic changes in water flow velocity affect the swimming performance and energetics of a labriform swimmer, the shiner surfperch, Cymatogaster aggregata. Unsteady water flows are common in nature, yet the swimming performance of fishes is typically evaluated at constant, steady speeds in the laboratory. Wave-mediated sediment delivery may be the mechanism involved, with wave-sheltered areas experiencing relative sediment deficits, such that some salt marshes in Puget Sound are already suffering sea-level rise impacts that are reflected in their channel network geometry. Four case studies, each with paired regions of similar tidal range and contrasting wave environments, further indicated wave environment affected channel geometry. Channel size and complexity were positively related to tidal range and negatively related to wave height. Y-intercepts of allometric relationships showed geographic variation, which multiple-regression indicated was associated with tidal range and storm significant wave height. Tidal channel allometry showed similar scaling exponents for channel planform metrics throughout Puget Sound, simplifying comparisons between locations. Salt marsh area was the independent variable for all dependent channel planform metrics. To develop allometric models predicting the number and size of tidal channels that could develop following salt marsh restoration, channels were digitized from aerial photographs of Puget Sound river delta marshes. Tidal channels are central elements of salt marsh hydrodynamics, sediment dynamics, and habitat. The conclusion is that wave energy is a second-order factor in determining eelgrass density at this location. The longshore pattern of eelgrass density was correlated with beach aspect, which itself is correlated with wave entrainment, but the direct correlation between longshore eelgrass density and longshore wave exposure was low. There are strong vertical gradients in both wave energy and eelgrass density that may be correlated, however, a number of other limiting factors for eelgrass are also correlated with beach elevation (i.e., dessication and photo-damage) so it is difficult to identify the specific role wave energy plays in setting the upper limit of eelgrass on the beach face. A sediment entrainment parameter used as a proxy for seabed disturbance of eelgrass was compared with high-resolution maps of eelgrass density. Sediment transport outside of this zone may be limited.The concentration of wave energy high on the beach foreshore results in a reduction, due to wave attenuation, of shear stress across the low-tide terraces of Puget Sound. An appropriate response model for morphodynamic change on low-energy, macro-tidal environments must include the effects of tide level distribution in concentrating wave action and hence sediment transport, to a vertical corridor determined by the tide level distribution. The most important sediment transport events are associated with infrequent, strong storms which may have a return interval of several years or more. At Cama Beach, Washington, wave energy is concentrated in a narrow band on the foreshore located just above mean sea level as a result of the long-term distribution of tides. ![]() However, these morphotypes do not appear to be correlated with estimates of storm wave height, period, fetch or tidal range suggesting that they are controlled primarily by antecedent morphologic conditions.The low-energy beaches of Puget Sound are dominated by swash processes. These beaches can be grouped into four profile morphotypes based on foreshore sediment and morphological characteristics. Puget Sound beaches are distinct from low-energy beaches previously studied in terms of their mixture of sand and gravel sediments, their profile morphology (which is steeper and more concave) and their tidal environment.
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