Coastal Oceanography and Littoral Warfare (1994) / Chapter Skim
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2. WORKING GROUP SUMMARIES
2. WORKING GROUP SUMMARIES
Pages 9-48
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1. What environmental information is needed to support special operations, mine warfare, antisubmarine warfare, and amphibious operations?
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10 SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE 5. What research and development is needed that will have direct impact on these problems?
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There are undoubtedly some harbors (e.g., on arid islands) that meet the quoted definition only to the extent of being "semi-enclosed." As a practical matter, however, the conduct of littoral warfare in these exceptional harbors would require the same information concerning tides and currents as its conduct in more typical estuarine harbors and approaches.
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While the influence of river flow can be unpredictable in harbors with small tributary drainage basins, river flows in large drainage basins, and particularly in those having a substantial ratio of dam storage capacity to river flow, generally follow well-defineci seasonal patterns. In contrast, the atmospheric forcing that dominates many large embayments (e.g., tropical lagoons and the Ob estuary in Russia)
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We should not, as a consequence of a pressing need to deal with the short time scales directly pertinent to naval operations, lose track of the place of estuaries in recent geological history. This context is necessary to understanding the structure and evolution of estuarine ecosystems, their sedimentology, and (to the extent that channel morphology controls circulation processes)
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Working Group Discussion The charge to the working group consisted of two primary tasks. The first concerned environmental information: What information is needed for littoral warfare operations, how is it presently acquired, and how can this process be improved?
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Consider as an example the transport of suspended matter that determines the optical properties of the water column and, in many environments, the character of the seabed itself. Existing sediment transport models uniformly fail to consider the effects of horizontal gradients in suspended sediment concentration.
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The smaller-scale models may be either two- or three-dimensional, and adapted to the character of the particular estuary; such models might inclucle, for example, wetting and crying of tidal flats, fluvial forcing, and sophisticated turbulence predictions, as appropriate. Given reasonable bathymetric data and proper boundary forcing, existing barotropic tidal models can predict ticlal
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Estuaries with both strong tides and strong river flow, for example, have timevarying stratification that drives substantial, nonlinear circulations that are poorly understood at present. Interactions of tidal currents with swell can substantially modify the tidal current and greatly increase wave amplitude.
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The advection of a plume by storms and other coastal ocean processes leads to highly intermittent internal tides. These and other examples of forcing of tidal currents by a time-varying density field indicate that tidal currents cannot be treated as a stationary process in many systems.
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Acoustic properties of "blue water" environments relevant to the cold war ASW in past decades are entirely determined by the thermal structure of the water column. This is not the case in littoral environments in general, and particularly not in harbors and approaches.
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While the present state of knowledge provides a basis for future research, it also emphasizes that sustained funding will be required to improve the present state of the art substantially. Cohesive sediment transport is particularly important, and is cliscussecl below in the subsection on scalar transport.
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They are also an important considerations in the use of dolphins for mine detection. As discussed above, suspended sediment transport plays an important role in determining water column and seabed properties of interest to CMW and ASW.
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Sediment transport merits particular mention because of its importance in all aspects of littoral warfare. Recent advances in fluvial transport of mixed-grain, noncohesive sediments provide a solid base of knowledge for construction of sediment transport models for sand-bedded systems.
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25 Discussion of information needs, research directions, and potential technological developments to assist in the Navy's littoral warfare mission in harbors and approaches led to the definition of three primary topical areas that unified the previously identified information needs and served as a basis for further discussion. The three areas were tides and currents, acoustic and electrical properties of the water and sediment, and pollutant and other scalar transport.
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focusing of surface waves both by the bathymetry and by winds steered by focal topography. Intense human activity further complicates naval operations, particularly with shipping, fishing, and installation of cables and pipelines.
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Consequently, once a particular strait is identified during a crisis, predictions for naval operations must rely on available data and models incorporating processes known or likely to dominate that strait. Straits and processes chosen for further study should be chosen on the basis of the reviews recommended above, but several issues are apparent now.
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Summary and Conclusions The Straits and Archipelagoes Working Group recommended that a number of issues be addressed as the Navy prepares for future littoral warfare. First, they
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Processes that are particularly important to study in straits include the generation of internal bores and solitary waves, the effect of bottom stress on flow dynamics, how surface waves are generated and focused, how secondary circulations develop incidental to the main flow, and the effect of bottom morphology and sediment dynamics on bottom stress and acoustic propagation. The working group identified several other studies related to modeling flow through straits and the information needed to study straits.
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This working group report starts with brief descriptions of the nearshore from academic and Navy points of view. There is considerable overlap between the processes studied by academics and the environmental information needed by the Navy.
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Additionally, wave breaking, swash processes, bottom boundary layers, and the generation of infragravity and far infragravity waves are subjects of ongoing 6.1 research efforts. The response of sediment to fluid forcing is less well understood than the fluid forcing itself.
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focused on ways of significantly improving existing capabilities rather than meeting predetermined levels of accuracy, and included tong- and short-term approaches and both direct measurements and modeling of environmental parameters. Bathymetry The nearshore bathymetry influences many surf zone processes important to amphibious operations, including the spatial distribution of wave breaking and wave-driven steady currents.
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Technologies for measurement of the wave field outside the surf zone are readily available. Robust, easily deployed single pressure sensors can provide wave data for initializing models for wave heights in the surf zone.
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However, given measurements of the wave field at a few representative deep-water locations, models for wave propagation across the shelf could provide estimates of the wave field over the entire shelf and near the surf zone. The processes important to surface wave evolution across the shelf are probably different from those in very deep and shallow water depths, and are yet not well understood.
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One of most important is the incorporation of bottom-mounted pressure sensors (and associated telemetry systems) for measurement of wave height and direction.
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Summary and Conclusions The Surf Zone Working Group made recommendations about research and development needs related to improving our abilities to measure and understand the processes controlling nearshore bathymetry, waves and currents, shelfwide propagation of surface gravity waves, acoustical properties, sea level variations, and "trafficability" through the surf zone. The working group noted that several instruments now used in academic research could be used by the Navy to improve littoral zone environmental prediction, and thus Navy operations.
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Philip Vinson, CNO (N096) , Assistant Environmental Information Needed to Support Special Operations' Mine Warfare, Antisubmarine Warfare, and Amphibious Operations Several groups of experts have already listed the environmental information needed to support littoral operations.
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Pollution o Noise Anthropogenic 0 Geoacoustic properties * Bottom strength and stability o Pressure wave transmission (Shock wave propagation)
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Research to provide more and better environmental information is a vital first step, but this must be coupled to education of naval personnel in the use of the data. There is a general need for performance prediction and assessment for all sensors deployed in naval operations, but in particular for sonar and radar.
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Acoustic techniques have promise, but environmental information is essential for developing and predicting the performance of these sensors. Such information is needed on the following subjects, for example: spatial and temporal coherence of the medium; ambient noise from breaking waves, bubbles, organisms, or precipitation; volume scattering clue to bubbles or suspendecl particles; and the shock wave propagation mechanism in sediments.
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special warfare units, or installed on AUVs. 41 Antisubmarine Warfare Both passive and active sonar performance prediction and assessment capabilities in shallow water are essential, even if extensive local databases are not available.
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Specia/ Warfare anc/ Amphibious Operations Assessment and prediction of subsurface currents is a particular need for the Naval Special Warfare Command, although they are also important to other aspects of littoral warfare. Hull-mounted or bottom-deployed (and upward-Iooking)
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Research to understand better the fundamental oceanographic processes responsible for key environmental variables must underpin research targeted on specific problems such as sensor performance in a particular region. More and better environmental data from littoral zones is needed, but it is even more important to place these data in a context of research that will lead to an unclerstanding of the processes which yield and interrelate atmospheric, oceanic, and seafloor properties.
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For example, salinity is much more variable spatially and temporally in the littoral zone than in the open ocean. Although it is readily measured from surface ships using conductivity sensors, there is no technique for remote
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Important General Issues for Future Navy Operations in the Littoral Regime Func/amenta/ Differences Between the Littoral and Oceanic Environments Must Be Recognize c/. 45 In the past, large environmental databases and predictive models have served an important purpose in naval operations in deep-ocean basins.
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or predict oceanographic variables relevant to littoral warfare? At present, some predictive capability exists for tides, surface waves, and low-frequency alongshore velocity, but there is no corresponding predictive capability for cross-shore flow and the three-dimensional density structure over the continental shelf.
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ideas for Co//e ction anc/ Use of Environmenta/ Data for Operations in the Littoral Environment The worI |
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The working group also noted relevant problems in mine countermeasures, antisubmarine warfare, special warfare, and amphibious operations that could benefit from increased research effort. Finally, this working group listed a set of key research needs to improve operations in the littoral zone, highlighting the need to acquire basic environmental knowledge before sensor development is pursued.
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