Influence of bathymetric fluctuations on coastal storm surge

Natural events constantly alter nearshore bathymetric properties. Hurricanes particularly affect bathymetry as they pass over a body of water. To compute an accurate forecast or recreate a hurricane's effects through hindcasting techniques, an operational bathymetry data set must be known in advance. However, obtaining and maintaining current and accurate bathymetric data can be costly and difficult to manage. In this paper we examine the extent to which variations in nearshore bathymetry affect the storm surge at the coast. A common question for wave and surge modeling is, “how good is the bathymetric data?” If we can allow for a range of fluctuations in the bathymetry without significantly adjusting the results of the surge predictions, we can potentially save months of field work and millions of dollars. A one-dimensional (1D) analytical solution for waves and water level is developed for initial testing. In the 1D case we find that as long as the amplitudes of the bathymetric fluctuations are less than 60% of the original depth, the surge at the coast is within ± 10% of the surge generated on the initial bottom slope. If the fluctuation produces a hole, a deepening of the local bathymetry, within 80% of the local water depth, the coastal storm surge calculated is still within 10% of the unperturbed value computed for bottom slopes shallower than 1:20. In addition, we find there is an optimum distance offshore for each sloped profile that corresponds to a depth between 25 and 40 m, beyond which the effects of bathymetric fluctuations begin to decrease. A coupled 2D modeling system is implemented to test our hypothesis along a realistic coastline. After selecting three study sites, we vary the bathymetry at the selected locations by ± 20%. Consistent with the 1D tests, the storm surge at the shoreline varies by less than 5%.     

The physical hydrology of a lagoon system on the Pacific coast of Mexico

The annual hydrological cycle of the Caimanero-Huizache lagoon system on the Pacific coast of Mexico was investigated during 1977–1978. There is a well defined wet season during which the lagoons fill with water derived from fluvial inputs and direct precipitation. Water is lost by evaporation and outflow to the sea, the latter process starting as the wet season progresses and being facilitated by a falling mean sea level. Evaporation exceeds in situ precipitation and during the dry season complete desiccation may be prevented by a now rising mean sea level which promotes the flow of seawater into the lagoon basin. A quantitative estimate of the magnitude of these controlling processes is presented and processes bringing about mixing in the lagoons discussed. A brief comparison is made with other lagoon systems on the Pacific coast of Mexico.     

Mine-derived metal pollution in the Isle of Man

The sediments of rivers draining areas of past mining activity in the Isle of Man contained greatly enhanced levels of zinc, lead and, to a lesser extent, copper and cadmium. This contamination extended into the estuarine harbours where it was reflected in the metal content of four species of bivalve molluscs. Of the latter, Mytilus edulis was the most useful indicator species in that it occurred in all five estuarine harbours but Scrobicularia plana, although of more limited distribution, concentrated much higher levels of zinc and lead. Individual variation of metal levels was high in all species of bivalves examined; a negative correlation of dry weight: metal content was demonstrated in many cases, but other factors may also contribute to such variation.