BOTANICAL EVALUATION OF THE GOAT ISLAND COMPLEX, NIAGARA FALLS, NEW YORK
Ice accumulates during winter in the Maid-of-the-Mist Pool (a section of the river in the upper gorge extending from the cataracts to the Whirlpool or Railroad Bridges). The river may become bridged by this ice mass to 70 feet above water level. Ice builds on the talus at the base of the American Falls to the level of the brink (184 feet). Freezing mist and spray accumulates on all surfaces, including all vegetation (The American Falls International Board, 1971). The force of this ice accumulation is mechanically powerful, weighing down and scouring whatever it comes in contact with, from island margins and river banks, to wiers, to international bridges (collapse of Falls View or Honeymoon Bridge, 1938).
Ice scour on those island margins with exposed bedrock, such as on the eastern end of the Three Sisters, the old Terrapin Rock area, and ledges on the north side of Goat Island may have benefited the unusual types of vegetation once or presently found there, renewing each winter erosion cycles which prevent the development of typical growing conditions and the invasion by plant species and communities typical of the region.
During winter, seventy five percent of the river volume is diverted, and twenty five percent is allowed to pass over the cataracts at the head of the Niagara River gorge. Devil's Hole, a natural cove in the gorge wall on the American side several miles north or downriver from the falls, was formed by the annual sloughing off of the exposed face of the dolomite caprock, according to James Hall, New York State Geologist (1843): "when we take into consideration the fact, that the water [from the stream called Bloody Run which empties into Devil's Hole] penetrates all the fissures of the rock, and then during fall and winter, expands by freezing, we shall find means of explaining the mode of operation," whereby this indentation in the gorge wall had been developed." At Niagara Falls, however "the action of frost is not to be taken into consideration, as the water, probably, never freezes in the fissures behind the fall," "the recession is by undermining and breaking down of the upper masses" (Hall, 1843).
As long as the flow of water at Niagara Falls was free, the processes of erosion by hydrostatic pressure and widening of joints in the dolomite bedrock by dissolution by action of acids on the calcareous rock prevailed. Reducing the flow of water in winter might then expose the bedrock at the falls to the same processes as Hall thought developed the Devil's Hole cove. This seems to be implied in the statement that "low flows [in the Niagara River] in the winter period expose the rock to freezing and thawing processes, thereby contributing to the disintegration of the caprock through ice jacking and plucking" (The American Falls International Board, 1971). "Now I consider it as an established fact, that small streams, which freeze during winter, will excavate their beds more rapidly in proportion than large bodies of water which never freeze" (Hall, 1843). Although beyond the present study to investigate, the possibility exists that before the present diversion regime, conspicuous erosion at the falls might have been due to different processes than those that prevail today. Certain kinds of erosion may have been checked by the modification of erosional processes, such as concentration of water mass in the central channel of the Horseshoe Falls, however, such checking may have exacerbated erosion in other areas by other means, such as frost heaving.
Formation of the ice masses seen on postcards at the American Falls, and their effects, however, is not altogether a natural, primeval phenomenon, but is, to some extent, a cultural artifact of water diversion. Lower water levels in the Maid-of-the-Mist Pool (15 feet in the tourist season and 26 feet thereafter) "have exposed considerable areas of previously submerged talus at the base of the American Falls and large areas of foreshore around the perimeter of the Pool." "This growth in exposure of talus has been progressive since 1922" with diversions to the Sir Adam Beck power generating facility, up until the present level of diversion. "This series of events have created the impression that rock fall from, and deterioration of, the American Falls is occurring at a faster rate than is actually the case." The force of the original magnitude of falling water probably destroyed the ice formations as they accumulated, much as the violence of the rapids below the Lower Arch Bridges breaks up the ice formation in the Maid-of-the-Mist Pool. But with the exposure, up to 100 feet in breadth as well as its height, of the dry talus, atmospheric moistures "condense, settle, and freeze, building up through the winter to ... imposing masses" (all quotes from The American Falls International Board, 1971).
Ice bridges, however, seem to have always been a natural annual event at the Falls. Ice develops in winter on the surface of Lake Erie. This ice enters the Niagara River at Buffalo and is borne down to and over the falls. The ice bridges are due to accumulations of this pulverized Lake Erie ice, which builds up from the lower shoreline until joining in the middle of the river. When the ice from the broad expanses of the upper river is dumped into the confinement of the plunge pool, the accumulation can be "6 to 15 times the volume of ice that the lower channel can ... carry away" (The American Falls International Board, 1971), especially if the water level in the river becomes lower due to changes in wind-direction on Lake Erie (Krajewski & Liberty, 1981). This buildup can create ice-jams in the Maid-of-the-Mist Pool up to 70 feet above the normal water surface.
To control this ice build-up, Ontario Hydro and the Power Authority of the State of New York built an ice-boom at the Lake Erie entrance to the Niagara River to keep ice from destroying or crippling power-generating facilities along the banks of the river above the falls, and to maintain "normal operating tolerances on the level of the Grass Island Pool." Authorization came at a meeting of the International Joint Commission in 1964 (Ontario Hydro in Holt, 1968). Only excessive or large masses of ice are allowed past the boom into the Niagara River before the first of April. Whether this reduction in the normal ice mass in the river has a significant effect on the quality of habitats in the Goat Island complex has not been determined as of this writing.