Abstract:
The streams flowing through the Niagara Escarpment
are paved by coarse carbonate and sandstone sediments which
have originated from the escarpment units and can be traced
downstream from their source. Fifty-nine sediment samples
were taken from five streams, over distances of 3,000 to
10,000 feet (915 to 3050 m), to determine downstream changes
in sediment composition, textural characteristics and sorting.
In addition, fluorometric velocity measurements were used in
conjunction with measured -discharge and flow records to
estimate the frequency of sediment movement.
The frequency of sediments of a given lithology changes
downstream in direct response to the outcrop position of the
formations in the channels. Clasts derived from a single
stratigraphic unit usually reach a maximum frequency within
the first 1,000 feet (305 m) of transport. Sediments derived
from formations at the top of waterfalls reach a modal
frequency farther downstream than material originating at the
base of waterfalls.
Downstream variations in sediment size over the lengths
of the study reaches reflect the changes in channel morphology
and lithologic composition of the sediment samples. Linear
regression analyses indicate that there is a decrease in the
axial lengths between the intial and final samples and that
the long axis decreases in length more rapidly than the
intermediate, while the short axis remains almost constant.
Carbonate sediments from coarse-grained, fossiliferous units
- iii -
are more variable in size than fine-grained dolostones and
sandstones. The average sphericity for carbonates and
sandstones increases from 0.65 to 0.67, while maximum
projection sphericity remains nearly constant with an
average value of 0.52. Pebble roundness increases more
rapidly than either of the sphericity parameters and the
sediments change from subrounded to rounded.
The Hjulstrom diagram indicates that the velocities
required to initiate transport of sediments with an average
intermediate diameter of 10 cm range from 200 cm/s to 300 cm/s
(6.6 ft./sec. to 9.8 ft./sec.). From the modal velocitydischarge
relations, the flows corresponding to these
velocities are greater than 3,500 cfs (99 m3s). These
discharges occur less than 0.01 p~r cent (0.4 days) of the
time and correspond to a discharge occurring during the spring
flood.
