Abstract:
The rate of decrease in mean sediment size and weight
per square metre along a 54 km reach of the Credit River
was found to depend on variations in the channel geometry.
The distribution of a specific sediment size consist of:
(1) a transport zone; (2) an accumulation zone; and (3) a
depletion zone. These zones shift downstream in response
to downcurrent decreases in stream competence. Along a
.285 km man-made pond, within the Credit River study area,
the sediment is also characterized by downstream shifting
accumulation zones for each finer clast size.
The discharge required to initiate movement of 8 cm
and 6 cm blocks in Cazenovia Creek is closely approximated
by Baker and Ritter's equation. Incipient motion of
blocks in Twenty Mile Creek is best predicted by Yalin's
relation which is more efficient in deeper flows. The
transport distance of blocks in both streams depends on
channel roughness and geometry. Natural abrasion and
distribution of clasts may depend on the size of the
surrounding sediment and variations in flow competence.
The cumulative percent weight loss with distance of
laboratory abraded dolostone is defined by a power
function. The decrease in weight of dolostone follows a
negative exponential. In the abrasion mill, chipping causes the high initial weight loss of dolostone; crushing
and grinding produce most of the subsequent weight loss.
Clast size was found to have little effect on the abrasion
of dolostone within the diameter range considered.
Increasing the speed of the mill increased the initial
amount of weight loss but decreased the rate of abrasion.
The abrasion mill was found to produce more weight
loss than stream action. The maximum percent weight loss
determined from laboratory and field abrasion data is
approximately 40 percent of the weight loss observed along
the Credit River. Selective sorting of sediment explains
the remaining percentage, not accounted for by abrasion.
