Graham S. Giese

Causation of large-amplitude coastal seiches on the Caribbean coast of Puerto Rico

Abstract Sea-level oscillations at supertidal frequency with amplitudes of the order of the mean tidal range have been reported from the Caribbean coast of Puerto Rico. Analysis of a 10-year time series of digital tide data from Magueyes Island, Puerto Rico, demonstrates that sea-level variance at the fundamental normal mode (sciche) frequency of the shelf has a pronounced fortnightly distribution with a maximum occurring 6–7 days after new and full moon. The sieche variance also shows a bimodal seasonal distribution with an inverse relationship to easterly wind stress. It is argued that the sciches are excited by internal waves generated by strong tides in the southeastern Caribbean. Support is provided by airborne radar imagery showing sea-surface patterns suggesting the presence of internal waves near the southern Aves Ridge, and by the results of two field experiments, carried out during times when large-amplitude sciches were expected, to search for evidence of internal wave forcing near the shelf br...

A Model for the Generation of Coastal Seiches by Deep-Sea Internal Waves

Abstract A dynamical mechanism for the generation of coastal sciches by deep-sea internal waves is investigated using a linear, two-layer coastal model in which internal waves from the deep ocean impinge upon a step-shelf bottom topography. For periodic incident waves, a pronounced peak in the shelf response occurs at each coastal seiche frequency. The maximum amplitude over the shelf is almost directly proportional to the degree of stratification, suggesting that sciche activity should vary with seasonal changes in the stratification. Based on the periodic solutions, Fourier transforms are used to determine the response to one or more internal-wave pulses, and the results are qualitatively consistent with observations. For geometry and gratification which are representative of the Caribbean coast of Puerto Rico, reasonably realistic incident pulses preferentially excite the basic seiche frequency, and a rather small amplitude pulse (10 m) can easily generate currents at the shelf break of 8–10 cm s−1. Fu...

RESIDENCE TIME OF SAND COMPOSING THE BEACHES AND BARS OF OUTER CAPE COD

When, under the strong impulse of Prince Henry, Portuguese maritime discoveries began, in the dawn of the XVth Century, methods of navigation were still those of coastal and estimated navigatxon and resulted mostly from the progress made in the Xlllth Century. During that period the knowledge of geometry of ancient Greece had spread widely and the mariners compass had been adopted on board the Mediterranean ships. These innovations had the following consequences: a) Rutters: to the former indication of the principal characteristics of the coasts, particularly as regards to ports and bars, and of the distance between the most remarkable accidents, was from now on added the indication of the magnetic azimuths between these accidents. b) Nautical charts: the nautical chart, nonexistent m Europe, was created at that time.Casual observations over a period of years of a long sand beach in the southern end of Monterey Bay, California, suggested that the sand elevation, while varying noticeably from one time to another, does not display the well-defined seasonal alternation between build-up in the summer and erosion in the winter that is now widely recognized on the exposed beaches of California. Accordingly, a program was established to measure the beach-profile changes by means of serial observations and to attempt to relate the changes to wave, tide, and beach conditions prevailing during the observation period. The results of the study, covering nine months, are presented herein.Sea tests of motion and mooring force were conducted on an LST (Landing Ship Tank) of about 44O0 long tons displacement. The LST was spread-moored by six 2-1/16 inch and one 1-1/4 inch (port breast) stud-link chains in simple catenary configuration in about 45 feet of water in the open Gulf of Mexico about 65 air miles south of New Orleans, Louisiana. Water-level variations at a single location, ship rotations and accelerations, mooring force, and wind were measured in sea states of 2 and 4. Three recordings of 38, 62, 67 minutes duration were analyzed, using timeseries techniques to provide apparent amplitude-response operators for all of the ships motions and seven mooring chains. Theoretical prediction of the operators using long crested regular waves was made also. In longitudinal plane, theory predicts motions 1/3 to 4 times and chain tensions 1/4 to 9 times those measured. The most probable maximum-motion amplitude responses in sea state 4 are found to be 1.7, 1.1, and 1.7 feet, respectively, in surge, sway and heave, and 3.4 and 0.5 degrees, respectively in pitch and yaw. Roll was measured only in sea-state 2 with a corresponding maximum of 2.1 degrees. Maximum wave-induced chain tensions in kips were: 85.1 and 48.0 in port and starboard bow chains respectively; 10.6 (sea state 2) and 19.7 in port and starboard breast chains; 13.9 and 4.3 in port and starboard quarter chains (sea state 2) and 9.7 in stem chain. Total tension in port bow chain was 116.1 kips (85.1 plus initial tension of 31.0 kips). Chain response operators vary directly with initial tension, whicl complicates design. It is concluded that: (i) moor was unbalanced, i.e., port bow chain took most of load; (ii) chains loaded lightly, e.g., maximum wave induced tension was 116 kips compared to new proof load of 300 kips for the particular chain, the port bow; (iii) water level should be measured at more than one point; (iv) discouragement over differences is balanced by encouragement over agreements between measurements and theoretical prediction of motion and chain tension; (v) toward improvement: Theory needs extension to include short crested waves and barge types; (vi) initial tension unique to problem of mooring design; (vii) propulsion devices may be needed toward maintaining design initial tension, especially in storm; (viii) if directional spectra had been measured and if theory involving short crested waves had been available and used, then discrepancies between observation and theory likely would have been less.At the moderate velocity of the pure water which lies on the quiet sal£ water stable internal waves appear at the interfac in the stratified flow, and these waves will break and violated surface will arise if the velocity of the pure water may be increased. In this phase of phenomena the shear stress at the interface has the most important part. However observed aalues of this shear stress have not been reported in the systematic style. Experiments have been conducted in our laboratory since i960. Some theoretical considerations could be served to get an empirical equation on the mterfacial shear using experimental results and data presented by other researchers.

The coupling between harbor seiches at Palawan Island and Sulu Sea internal solitons

Abstract Between 1989 and 1991 the authors made observations that confirm and elucidate the coupling between harbor seiches at Puerto Princesa on Palawan Island in the Philippines and tide-generated internal solitons in the Sulu Sea. Published tidal current predictions for Basilan Strait in the Sulu Archipeligo were used to produce an index to the daily ebb tidal flows near Pearl Bank where the solitons originate. The coherence between predicted maximum ebb tidal current speed and observed seiche activity was 0.60 and the phase lag between the two quantities closely matched published estimates of the time required for solitons to cross the Sulu Sea. Arrival of the Sulu Sea waves immediately offshore of Puerto Princesa in the form of internal bores corresponded in time to the initiation of harbor seiche activity. A more precise estimate of soliton travel time was determined from the time difference between predicted maximum ebb current and the initiation of seiche activity, and it was found to have a remar...

Evidence of internal swash associated with Sulu Sea solitary waves

Abstract Vertical temperature profiles were measured near the shelf edge off the coast of Palawan Island (Philippines) during the passage of several “rip bands” of choppy surface waves. Such rip bands are commonly associated with internal waves. Coincident with the passage of one of the rip bands, the temperature near the bottom decreased by 2.5°C within 1.4 min, becoming colder than any water on the shelf. Furthermore, the apparent depth of our CTD decreased by about 8 m despite the fact that the “line-out” was held fixed. We interpret these limited data, along with a sea-level record, as evidence of internal swash created by breaking internal solitary waves which are generated by tidal flow over a shallow bank in the southeastern Sulu Sea (described by Apel et al., 1985 , Journal of Physical Oceanography, 15, 1625–1651).

Discovery of Eocene Sediments in Subsurface of Cape Cod

Spores, pollen, and charcoal taken from two wells drilled near the tip of Cape Cod have been identified as Eocene. These are the first Eocene rocks to be identified in Massachusetts. Interpretation of seismic records taken in the Gulf of Maine and Cape Cod Bay will be influenced by this discovery.

Erosion of the cliffs of Outer Cape Cod : tables and graphs

Abstract : The following tables and graphs place in convenient storage the results of several years of careful surveying and at the same time provide rudimentary interpretation of results by comparing erosion rates. Listed in the bibliography are pertinant published papers which analyze these coastal erosion data in great detail. (Author)