ABSTRACT: Earth science and coastal management: natural hazards and climate change in the coastal zone.

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Coastal hazards (including tsunamis, rising sea levels, storm-surge flooding, storm waves, shoreline erosion,sediment movement, shore-ice impact, and related phenomena) can cause significant damage to publicinfrastructure, personal and business property, heritage resources, and personal security. Accelerated sea-levelrise expected to result from global warming will exacerbate many existing hazards, while climate change will affect regionally important factors such as reef health on tropical coasts and permafrost stability in high latitudes. Regions of highest vulnerability in Canada include the Fraser Delta and other local areas in British Columbia, the Beaufort Sea coast in Yukon and the Northwest Territories, and several low-lyingparts of the Maritime Provinces [Shaw et al. 1998a, 1998b]. Other small areas including fjord-head deltas and beach-ridge plains, occupied by communities such as Placentia, Newfoundland, are also vulnerable. This presentation emphasizes coastal hazard issues and climate-change impacts in Canada with limited reference to international experience. Coasts attract people for many reasons including marine food resources, convenient transportation, andrecreation. A very large proportion of the world’s population resides in coastal regions and many are unaware of the natural hazards they face, in part because the most severe and damaging events are rare and risks tend to be forgotten. Twenty-eight people were killed by a tsunami that struck the south coast of Newfoundland on 18 November 1929 following a major earthquake on the Grand Banks [Anderson et al.1996]. One life was lost along the Beaufort Sea coast during a severe storm surge in September 1970 and people are sometimes swept off rocks in Nova Scotia when large storm waves pound the Atlantic coast. These numbers pale in comparison to the human costs of storm surges and tsunamis in other parts of the world. The 1998 tsunami in Papua New Guinea, caused by a nearby submarine slump, hit more than 25 km of shore with a wave height over 10 m (locally up to 15 m), destroyed three villages, damaged others, and killed at least 2200 people [Tappin et al. 1999]. More than 600 000 have perished in repeated devastating storm surges striking the coast of Bangladesh since 1960 [Kausher et al. 1996]. In North America, the hurricane that struck Galveston, Texas, on the night of 8-9 September 1900 raised water levels more than 5m in the city centre, cut off all means of escape, took the lives of more than 5700 (20% of the population), and left large parts of the community in rubble [Dean 1999]. With growing population, wealth, and coastal development, socio economic vulnerability to natural disasters, including coastal hazards, is generallyincreasing with a concomitant increase in costs [van der Vink et al. 1998]. Climate change and sea-level rise in the coastal zoneGeological evidence points to large variations in global mean sea level (of the order of 100 m) as the climate has switched between glacial and interglacial conditions. Large parts of the present seafloor on the continental shelf off eastern Canada were dry land at 10 ka, rivers flowed far beyond the present coast, and Prince Edward Island was a part of the mainland. On the Pacific coast, people lived and travelled the coastallowlands west of the Coast Range mountains, which today rise directly from the sea [Josenhans et al. 1995]. The subsequent rise in sea level was accompanied in many parts of Canada by crustal subsidence, which continues to the present day [Shaw et al. 1998b], although areas closer to the centre of continental ice loading are still experiencing isostatic uplift. Tide-gauge records from Churchill, Manitoba, show relative sea level falling at a rate of about 8.5 mm/year while the tidal record at Halifax, Nova Scotia, indicates an average rise over the past 100 years of 3.3 mm/year [Forbes and Liverman 1996], of which approximately 1.2 mm/year may be global sea-level rise. It is now widely believed that increasing concentrations of greenhouse gases in the atmosphere are leading to global warming [Houghton et al. 1996]. The implications for the coastal environment in Canada include accelerated sea-level rise, warmer ground temperatures in high latitudes (therefore enhanced melting of permafrost and ground ice), reduced sea-ice extent in the Arctic and mid-latitude seas such as the Gulf of St. Lawrence (therefore increased wave energy), changes in large-scale circulation (e.g. El Niño/ SouthernOscillation and the North Atlantic Oscillation), and possible changes in storm frequency and severity. In particular, the current best estimate for the rise in sea level over the coming 100 years is a little less than 0.5 m with a range from about 0.2 to 0.9 m [Houghton et al. 1996]. Therefore a coastal location such as Halifax may experience a relative sea-level rise somewhere in the range between 0.4 and 1.2 m. Sea-level rise of this magnitude can produce significant impacts in the coastal zone. These include: · more frequent and extensive flooding of coastal lowlands and wetlands; · higher risk of overtopping dykes; · potential breaching of coastal barriers;· possible instability of tidal inlets; · enhanced coastal erosion. Storm impacts on the coast: waves and flooding Wave hazards are usually considered in the context of coastal erosion or marine navigation. Direct effects of waves at the coast are often overlooked but can be important, particularly when human lives are lost. This applies both to rare and extreme tsunami events as well as storm waves. Wave forces can damage coastalstructures and wave overtopping can cause flooding. Infrastructure located 20 m or more above mean waterlevel can be severely damaged in large storms, as documented on the island of Niue (South Pacific)following a tropical cyclone in February 1990 [Solomon and Forbes 1999]. Flooding of coastal properties is a hazard under present conditions when severe storm surges are superimposed on spring tides, particularly perigean high tides. A situation of this kind occurred over a wide area of the southern Gulf of St. Lawrence on 21-22 January 2000, when a very deep (95.5 kPa) winter storm passed north over Prince Edward Island, generating a 1.5 m storm surge on top of perigean high tides in a region of relatively small tidal range (1.1 to 2.9 m large tides). This storm, with an estimated returnperiod of >30 years, caused extensive flooding along the coast, including parts of the urban core in both Charlottetown and Summerside, PEI, as well as severe flooding along the gulf coast of New Brunswick. The surge was accompanied by strong ice pressure, producing high shore-ice pile-up ridges along parts of the New Brunswick coast and severe damage from ice ride-up at several small-craft harbours and alighthouse in Charlottetown. In the Bay of Fundy, the Saxby Gale of 1869 moved up the bay with high tide, generating a 2 m surge that flooded large areas. Storm surges up to 2.4 m or higher have been recorded along the Beaufort Sea coast in an area with 0.5 m tides. Rising relative sea level along these coasts contributes to more frequent inundation at specific reference levels and more extensive flooding for a givenprobability. Accelerated sea-level rise in response to global warming will enhance this impact. The correlation between mean sea level and coastal erosion has been documented empirically by Komar and Enfield [1987], among others. Bruun [1962] proposed a theoretical model, whereby for highly idealized conditions (including zero longshore gradient in sediment transport), the horizontal shoreline recession, Dx,required to maintain an equilibrium shore profile under a rise in sea level of Dz can be computed as the ratio of the sea-level rise to the mean nearshore slope, viz. Dx = Dz ·(l/h), where h is the maximum depth of exchange of sediment between the nearshore and offshore and l is the length of the profile from the shoreline to that depth. Although equilibrium shore profiles are rarely realized, other assumptions of this simple model are often violated, and the model is widely misused, it nevertheless clearly demonstrates the potential for a small rise in sea level to produce an order-of-magnitude larger change in shoreline position. When combined with other factors such as increased storms [Taylor et al. 1997; Forbes et al. 1997], human intervention through sediment removal or engineering works [Forbes and Solomon 1999], and/or thresholds in coastal morphodynamics [Forbes et al. 1995], the resulting coastal changes can be dramatic. The severity of erosion is strongly dependent on geological factors, including topographic setting, rock exposure and lithology, and sediment supply. Under conditions of high sediment supply, beaches may buildseaward even under rising sea levels. Furthermore, an excess sediment supply at one point on the coast is often dependent on a sediment deficit at another location. Beach growth (usually considered good) may result from nearby coastal erosion (probably considered bad). In some circumstances, erosion and accretion phases can coexist and flip back and forth along a coast with changes in wind regime caused by phenomenasuch as El Niño [Solomon and Forbes 1999]. Earth science in coastal management and hazard reduction Earth science can make significant contributions to improved understanding, prediction, reduction, and avoidance of coastal hazards. A knowledge of site-specific conditions and biophysical processes in the coastal zone provides a solid basis for recognizing hazards, assessing risks, and predicting effects of coastal engineering or management actions. Successful hazard reduction in the context of integrated coastal-zonemanagement must explicitly recognize the range of coastal processes operating at various time and space scales in the physical environment. This effort can be enhanced by new technologies such as airborne laser altimetry, which can provide high-resolution digital terrain models for flood-zone delineation using geographic information systems. When combined with new tools for numerical prediction of storm surges, such tools may also contribute to flood warnings and reduced losses from severe storm events. Many planning jurisdictions have instituted building set-back requirements in the coastal zone, typically based on estimated coastal retreat over a fixed time interval such as 50 or 100 years. The estimates of coastal recession rates used to establish set-back distance are often rudimentary and overlook the potential for more rapid erosion caused by climate change. Improved understanding of longshore variation in erosion andsediment transport processes, combined with enhanced funding for coastal monitoring, are critical requirements for more effective planning and hazard avoidance in coastal development.

Bibliography of Canadian Geomorphology