....tSPECIAL PUBLICATION NO. 43
SEASONAL VARIATION IN SANDY BEACH
SHORELINE POSITION AND BEACH WIDTH
by
James H. Balsillie, P. G. No. 167
ABSTRACT
Annual cyclic fluctuations in beach width due to seasonal variability of forcing elements
(e.g., wave energy) have been a subject of concerted interest for decades. Seasonal variability can be used to 1) identify and evaluate the accuracy of historical, long-term shoreline data interpretations, 2) aid in the identification of the boundary of sovereign versus private land ownership, and 3) predict expected seasonal behavior of beach nourishment projects, which
should be a stated up-front design anticipation.
In this paper, data representing monthly averages are used to compare "winter" and
"summer" wave height and wave steepness as they relate to seasonal shoreline shifts. Coupled with astronomical tide conditions and beach sediment size, two quantifying relationships are
proposed for predicting seasonal shift of shoreline position (i.e., beach width).
INTRODUC77ON span distances of from 450 to 700 meters, and such features often migrate alongshore The configuration of the beach in at time scales on the order of days or weeks profile view is primarily due to tidal (Morisawa and King, 1974). As the bay fluctuations which cause periodic changes in between cusp horns passes a profile line, the sea level, and shore-breaking wave activity, beach becomes narrower, and as a horn Any change in wave characteristics and passes, the beach widens. A prediction direction of approach will, depending on tidal model for daily shoreline change has been stage, result in a change in the sandy beach suggested by Katoh and Yanagishima configuration. (1988).
Systematic beach changes through a Of the possible cyclic changes, single astronomical tidal cycle are well noted perhaps the most pronounced is that (Strahler, 1964; Otvos, 1965; Sonu and occurring on the seasonal scale. During the Russell, 1966; Schwartz, 1967). Cyclic cut "winter" season, when incident storm wave and fill associated with spring and neap tides activity is most active, high, steep waves (Shepard and LaFond, 1940; Inman and result in shoreline recession. Generally, the Filloux, 1960), and the effect of such berm is heightened with a gentle foreshore phenomena as sea breeze (Inman and Filloux, slope, although erosion scarps may form. 1960; Pritchett, 1976), can contribute Sand removed from the beach is deposited additional modifying influences, offshore in one or more submerged longshore bars. During the "summer" Beach changes are noted to occur at season lower waves with smaller wave time intervals longer than a tidal cycle (e.g., steepness values transport sand stored Dolan and others, 1974). Smaller beach offshore back onshore, resulting in a wider cusps, for example, may range from 10 to beach. It should be noted that along some 50 meters apart, while sinuous forms may coasts such as the approximately east-west
1