Controls on Formation and Form of Barred Nearshore Profiles

Abstract

Linear regression is used to examine effects of maximum fetch length and nearshore slope in controlling characteristics of barred nearshore profiles. Data came from twelve sites in the Great Lakes and two in the Gulf of St. Lawrence. Fetch length is a good predictor of height of the outer bar, depth to the crest, and offshore distance; bar number correlates significantly with decreased nearshore slope. Incident waves are the dominant control on nearshore bar formation and maintenance during storms. THE purpose of this article is to examine the extent to which the variation in several morphological parameters of barred profiles can be explained by fetch length and nearshore slope. The approach is empirical, with data from sites in the Great Lakes and the Gulf of St. Lawrence, and the strength of the explanation is tested by linear regression. Barred profiles exist year-round at the two locations. This condition allows definition of a characteristic profile for each site and avoids complication induced by the seasonal change from a barred to a nonbarred profile that occurs on some oceanic coasts. Data for the analysis came from twelve sites in the lower Great Lakes and two in the Gulf of St. Lawrence (Fig. 1). Thirteen of the sites have one or more nearshore bars year-round, but the other site has a nonbarred profile throughout the year. My research was the source of data for ten sites; data for three other sites were taken from published studies (Hands 1976; Owens 1977; Gillie 1980), and John Coakley of the Canada Centre for Inland Waters provided data for one site. Typical profiles for each site appear in Figure 2, and selected characteristics of each site and profile are contained in Table I. The sites were chosen to encompass a wide range of fetch lengths, nearshore slopes, and nearshore-profile characteristics. However, short, steep storm waves dominate at all sites, swell waves having limited importance. During a period of years, the wind climate at all the Great Lakes sites should be very similar, and conditions at the two gulf sites are probably comparable. The actual wave climate at each site varies with orientation and fetch, but the magnitude of the dominant storm waves is controlled largely by fetch length and is generally independent of orientation. The Great Lakes sites are virtually tideless, although water level fluctuates seasonally by 0.3 to 0.4 m. Both sites in the gulf are microtidal, with a mean tidal range of less than 1 m. * Grants from the Natural Sciences and Engineering Research Council of Canada since 1977 supported the fieldwork on which this article is based. * Department of Geography, University of Guelph, Guelph, Ontario, Canada N1G 2W1. This content downloaded from 207.46.13.101 on Sat, 08 Oct 2016 05:42:06 UTC All use subject to http://about.jstor.org/terms 186 THE GEOGRAPHICAL REVIEW