Figure 2.2 Mean annual water levels in Lake Erie, 1900-1987
Figure 2.3 Water Level Changes at Buffalo and Toledo during the April 1979 Storm.
Long and short term fluctuations in Lake Erie water levels have a strong influence on the physiography of Long Point and its associated marshes (Laidley 1962). Long term water levels on Lake Erie are a function of inputs (flow from the Detroit River, surface runoff and precipitation), and outputs (flow through the Niagara River and Welland Canal, and evaporation) from the lake (Figure 2.2), whereas short term and localized levels on the lake are a function of lake set-up and seiches caused by wind and barometric pressure (Figure 2.3)(Gillies 1958; Hunt 1958). While the vast size of the Great Lakes tends to smooth out the erratic extremes in lake inputs and outputs, strong winds or sudden pressure changes can have dramatic effects on water levels in Lake Erie (Anonymous 1973). Long term variations in Lake Erie water levels, caused by successive years of high or low precipitation, are about 2 m, within-year variation in water level averages about 0.5 m, while set-up can result in a 2.5 m increase in the lake level at Buffalo, New York in a few hours (Figure 2.3)(Anonymous 1976). Wind effects on lake levels are particularly extreme on Lake Erie due to the orientation of the lake along the axis of prevailing winds, as well as the shallowness of the lake itself. Seiches are induced when winds causing set-up subside, since the reduction in wind energy causes Lake Erie's water to oscillate from east to west and back until it returns to pre-disturbed water level (Bradstreet 1977). Seiches generally last for between 12 and 16 hours on Lake Erie (Platzman and Rao 1963).
The extremely forceful wave energy striking shore during high water levels, combined with wind set-up and seiches can result in dramatic short-term increases in shoreline erosion along the entire length of Long Point. During low water periods, the beach along the south shore of Long Point is extensive, thereby providing a buffer between wave energy and the Point. This dynamic balance ensures that, under natural conditions, the extensive marshes of the Inner and Outer Bay are protected from destructive wave energy, while permitting the marshes to experience the water level fluctuations required to remain productive (Ball 1985; Kaminski et al. 1989; Neill 1990). During high water periods, the south beach is so narrow that the Point is sometimes breeched during storms, with the result that inter-dunal wetlands are often scoured and/or filled with large amounts of sand. In the short-term, this reduces wetland quality, but long-term effects are unknown and may be neutral or positive.