Michael G. Skafel

Flume experiments on the erosion of till shores by waves

Abstract Hydraulic tests of the erosion by waves of a laboratory flume profile made from intact samples of till, a preconsolidated cohesive material, are described. Over 1000 h of testing were successfully completed using random breaking waves, varying conditions of sand cover, and varying mean water levels. Vertical erosion of the cohesive profile was measured with an optical bedplotter device. The sand layer covering cohesive shores can vary spatially and temporally, so erosion rates have been investigated under four different conditions of sand supply and the results are summarized here. In addition, two sets of tests were replicated in order to demonstrate their repeatability. Erosion rates compare favourably with results from unidirectional flow tests with a similar till material. During the tests, the unconfined compressive strength of the till surface was measured in a simple manner at selected locations.

Laboratory measurement of nearshore velocities and erosion of cohesive sediment (till) shorelines

Abstract The evolution of shorelines composed of consolidated cohesive sediments is dominated by irreversible erosion. In this note, measurements, under laboratory conditions, of bottom velocities, wave heights, and breaking characteristics over an actively eroding consolidated cohesive sediment shore are reported. Erosion is enhanced under breaking conditions, and plunging breakers are markedly more erosive than spilling breakers. The turbulence at the outer edge of the breaking zone has the −5 3 power high frequency dependence indicative of the inertial subrange.

Physical Processes Controlling Taste and Odor Episodes in Lake Ontario Drinking Water

Circulation and thermal structure of the coastal waters were studied as a part of an interdisciplinary program to investigate the taste and odor problem in drinking water along the north and western shores of Lake Ontario. The currents and temperature variations were found to be strongly linked to winds, with winds from the west causing upwelling and eastward flowing currents, and winds from the east inducing downwelling and warm westward flowing currents. The downwelling along the north shore during late August and early September of 2000 was associated with a pulse in concentration of the taste and odor causing compound geosmin. This study indicates that during this episode the onshore directed mean currents and cross-shore fluxes in the surface layer transported geosmin to the coastal waters of the north shore.

Transport of Sewage-Contaminated Sediment in Northeastern Hamilton Harbour

Abstract Dispersal patterns associated with sewage discharges from an STP outfall in northeastern Hamilton Harbour were obtained in 1992 and 1996 using coprostanol as a tracer. Both surveys revealed a distinctive shore-parallel pattern, characterized by a south-eastward trend and a second transport direction toward the northwest and southwest. As physical support for the tracer patterns, vertical profiles of currents near the outfall were monitored during four time periods from 1991 to 2000. Current data indicated the flow at the outfall was complicated; there was flow in all directions at all depths. However, the cumulative surface flow followed the prevailing wind (toward the east and northeast), while the bottom flow was approximately in opposition to the surface flow (to the west-northwest). Combining this circulation structure with the seasonal variation in buoyancy of the effluent discharge, the bi-directional transport pattern interpreted from the tracer distribution could be explained using a model in which the STP effluent plume was advected by local current at a position in the water column where the plume was stable. During January through August when the effluent was denser than ambient harbour water, it tended to be advected by flows lower in the water column moving the plume toward the north to west and into the central basin. During the rest of the year, it was lighter and more influenced by surface currents, which advected the plume onshore (toward the east and northeast) where it was deflected by shoreline geometry in a shore-parallel direction toward the southeast.

Exchange Flow Between Hamilton Harbour and Cootes Paradise

Abstract The flow between Hamilton Harbour and Cootes Paradise was monitored from April until December 1997 to provide background information for the operation of a fishway in the connecting channel. The flow was highly variable, and changed direction several times each day. Comparison with local meteorological and water level data revealed several interesting features. Outflow events of 4 hours or greater in duration were typically preceded by winds from the east usually lasting at least 6 hours. Similarly inflow events longer than 4 hours were typically preceded by westerly winds for at least 6 hours. There was evidence of diurnal and semi-diurnal flow reversals and of free surface oscillations of Lake Ontario, but not of Helmholtz resonance between Hamilton Harbour and the lake nor of exchange flow resonance between the harbor and Cootes Paradise.

LAGRANGIAN MEASUREMENTS OF ACCELERATIONS IN THE CRESTS OF BREAKING AND BROKEN WAVES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.