BOTANICAL EVALUATION OF THE GOAT ISLAND COMPLEX, NIAGARA FALLS, NEW YORK
In 1811, Augustus Porter applied to the State of New York for ownership of Goat Island, said in that document to be about 100 acres (Porter, 16 Ann Rep Comm, 1900). Maude (1826) reported Goat Island having one hundred and fifty acres in 1800. Maude was reassured by a guide that "much of the Island has fallen down since he first was acquainted with it."
In 1893 Goat Island was said to have been around 63 acres with a circumference of about one mile (Niagara Book, 1893). The same source also indicated that at one time the Island comprised 250 acres, and that there was another elevation, Gull Island, south of the island which "is said to have contained two acres of land in 1840. There is hardly a trace of it now" (Niagara Book, 1893).
In the Gardner (1880) survey for the year 1879, an island matching the foregoing description was drawn in the Horseshoe channel in 1842 - by 1875 it had disappeared according to the U.S. Lake Survey.
Of all the margin area exposed to the river current "it is fortunate that the southern shore only has been seriously affected by the water" (7 Ann Rep Comm, 1891). Superintendent Thomas Welch in the second report of the Commissioners, 1886, reported that "the southern shore of Goat Island, although protected at some points by piers and timber structures, is being gradually worn away in many places by the force of the current." In the Olmsted and Vaux plan of 1887 for improvements to be made on Goat Island, evidence was given that a major slope collapse had occurred on the island's south end, taking away all the vegetation, presenting a "raw surface" (see section on the south slope). The profile of the slope they describe is typical of a slumped sedimentary surface (Olmsted and Vaux, 1887).
River induced erosion was also happening elsewhere in the complex, notably on the Sister Islands. "Within a year or two the action of the water has opened a fissure nearly half way through the western portion of the Third Sister island, and trees growing on the islands, undermined by the current, have fallen into the stream. Gull Island, south of Goat Island, said to have had an area of two acres in 1840, has virtually disappeared" (2 Ann Rep Comm, 1886). "It is stated that a storm ... occurring in the year 1847, entirely washed away Gull Island, about two acres in extent. Gull Island was situated south of Goat Island and just above the Horseshoe Falls " (6 Ann Rep Comm, 1890). The washing away was attributed to sudden elevation of the water levels of the river by southwestern winds in Lake Erie.
Erosion in the Goat Island complex generally refers to:
a) erosion due to bedrock failure at the brinks of the Horseshoe, Bridal Veil and American Falls, and the west-facing bluffs on Luna and Goat Islands.
b) erosion on the margins of the islands where elevations in the levels of the river are such that soil is washed away,
c) slumping or landslides of the soil masses on the banks to the north, west and to a lesser degree the southern elevations on Goat Island - perhaps due to seepage within the bedrock and sedimentary masses, or to the accumulation of atmospheric moisture within them, especially in the spring,
d) scour by ice in winter (see section on ice below), and
e) runoff on slopes and river banks denuded by trampling.
The only area in the complex where this is happening is on the channel banks between the First Sister Island and Goat Island where people feed waterfowl, in certain path areas on the Three Sisters and where the thickets are removed on the bank on the south side of Goat Island. In the first example, actual runnels are eroded into the exposed, mineral soil.
The energy of erosion within the bedrock, which accounts for collapse of rock on the west-facing gorge wall exposures and gorge wall behind the falling water of the cataracts is partly due to the degree of hydrostatic pressure from ground water flow throughout the jointed calcareous bedrock (Krajewski & Liberty. 1981). Ground water percolates vertically through and horizontally along joints in the bedding plane. Jointing in the Lockport dolostone caprock increases with proximity to the falls crest line, as does hydrostatic pressure and hence ground water (Krajewski & Liberty, 1981).
This weakening of the bedrock is most significant at the brinks of the cataracts and the gorge walls where weathering also is an erosional factor, and certain of these areas on Goat Island have been modified by dynamiting the weakened outer faces and mechanically strengthening the resulting outer layers of rock (see sections on Terrapin Point and Luna Island).
The channel of the Niagara River as it eroded its seven-mile gorge narrowed and broadened throughout the course of its history. New gorge is formed at the weakest point in the subtending caprock, currently in the center of the Canadian Horseshoe Falls. At present, the Horseshoe Falls section of the river is developing a narrow gorge:
"This narrowness of the channel is due to the concentration of the water at the center of the stream. It is easy to see that Goat Island and the other islands owe their existence to this concentration of the water; for at one time, as shown by the shell-bearing gravels, these islands were under water. The channel above the Horseshoe Falls has been cut more than 50 feet below the summit of Goat Island at the falls, while the upper end of the island is still at the level of the water in the river" (Grabeau, 1901).
Throughout the first decade of the Reservation's existence, there were problems with the south shore erosion - this was due to slumping of the sediments from undercutting of the banks indicative of the higher energy of the river in the southern river channel, due both to the higher river volume there (90 percent of the river) and the fifty foot drop in the river bed from the brink of the falls to the preceding mile of river (6 Ann Rep Comm, 1890).
Early depictions of the south side of Goat Island show a bluff leading down to the water's edge denuded of vegetation on its lower margin (11 Ann Rep Comm, 1895). To protect the south shore of Goat Island timber, crib-work and docking, filled with stone was built there in 1890 (7 Ann Rep Comm, 1891). To restore it to its "natural condition" there was intent to cover the embankment with loam, planting it with "vines, shrubs, willows and other suitable trees."
Before river levels were lowered and river bed on the south side of Goat Island became exposed in this century, there was a layer of "quicksand" above a basal layer of gravel on the south side of Goat Island which was vulnerable to scouring when the river was high, particularly during storm surges in the winter months.
Today, when water levels in the river are high, soil is washed away on low lying areas, as on the west end of the Third Sister, which is now nearly barren rock. Some breakwater is afforded by logs laid down on the marshy west end of the Second Sister, and a moss (bryophyte) community has established itself on the rotting wood.
Landslides on Goat Island have been referred to for various places in the Commission reports, as when the "high bank" or west boundary of Goat Island, south of the Biddle Stairway collapsed (20 Ann Rep Comm, 1904). Slumping and landslides on the west end were the most serious as this area was were the highest concentration of visitors were, and beyond which was a drop of over 100 feet to the talus slopes below.
A new source of erosion has to do with ground surface conditions:
"... in certain instances, where man-made structures or artificial surfaces have been installed, water collects in low-lying areas after heavy precipitation, or runoff is directed into channels down unprotected slopes causing erosion. The earth slump which occurred in April of 1980 along the Niagara Gorge above the Cave-of-the-Winds walkway illustrated this phenomenon. Here, it appears that runoff from the blacktop area at the top of the bank has been concentrated into a relatively small linear section, worsening natural conditions. During heavy precipitation the top layer of gravels is eroded quickly and also carries water down to a layer of silty clays which became saturated and flow down the slope" (Otis, 1982).
Slumping today occurs in the soils of seepy, shaded areas in the northern, north-facing wooded slopes of Goat Island. Numerous culverts here together with the existence of muddy seeps and a running stream or two may indicate a higher degree of subsurface water here than elsewhere on the island. Here and there north-slope walls have been reinforced by stone shingles layered into the elevations so that they resemble the natural fracturing of limestone. Occasionally the bole of a tree has been laid sideways against the bases of trees at the water's edge to protect the walker from the proximity of the river. A twenty four percent increase in the flow in the American (north) channel of the Niagara River (The American Falls International Board, 1971) and a presumed corresponding increase in flow velocity and river height may have something to do with accelerated erosion on these slopes. The north island margin is not buffered from the level of the river by a swathe of land and quieter water which the south side of the island presently enjoys.
Mature specimens of Sugar Maple and Canoe Birch on the north side have pitched forward due to slumping so that their crowns are in the river.
As already mentioned, winter storms in Lake Erie, which under certain circumstances drives up the mass of water in the river, have contributed to erosion events on Goat Island, particularly with the layer of "quicksand" above a basal gravel layer on the southern margin of the island. "Ordinarily the water in the river does not rise above the lower layer of gravel, which averages about two feet in thickness." During a storm on January 9, 1889, "where the southwestern portion of the island juts out into the river the swollen current washed away about ten feet of the bed of the island for a distance of 300 feet ... the washing away of the shore caused the embankment to cave in, undermining the footpath ...." "The tendency of the current is to wash away the southwestern portion of the island which curves outwardly into the rapids" (quotes from 6 Ann Rep Comm, 1890).
When the water is high in the Great Lakes, as after heavy rains in the system, more water appears to flow around the islands. Also if there is a south-western wind across Lake Erie, especially during winter storms, a greater than normal mass of water may flow into the Niagara River raising its level temporarily. There is a layer of "quicksand" above a basal layer of gravel on the south side of Goat Island which is vulnerable to scouring when the river is high. With the development of various control structures in the Grass Island Pool regulating the amount of water accumulation there, it is not clear how much control is exerted over these storm surges and their erosional impact on the islands downstream from these structures.
Reduction in flow in winter and elevation in summer due to diversion are factors affecting rates of erosion in the islands.