Barrie Creeks, Lovers Creek, and Hewitt's Creek Subwatershed Plan

The Barrie Creeks, Lovers Creek and Hewitt’s Creek Subwatershed Plan
2.5 Fluvial Geomorphology
2.5.1 Introduction and background
Fluvial geomorphology is the study of the processes that influence the shape and form of
streams and rivers. It describes the processes whereby sediment and water are transported
from the headwaters of a watershed to its mouth. These processes govern and constantly
change the form of the river and stream channels, and determine how stable the channels are.
Fluvial geomorphology provides a means of identifying and studying these processes, which are
dependent on climate, land use, topography, geology, vegetation, and other natural and human
influenced changes.
An extensive understanding of geomorphic processes and their influences is required in order to
protect, enhance, and restore stream form in a watershed. Changes in land use, and
urbanization in particular, can significantly impact the movement of both water and sediment,
and can thus cause considerable changes to the geomorphic processes in the watershed.
Changes to the morphology of stream channels, such as accelerated erosion, can impact the
aquatic community, which has adapted to the natural conditions, and can also threaten human
lives, property, and infrastructure.
2.5.2 Geomorphic Processes
All streams and river systems are constantly in a state of transition, influenced by the flow of
water and the amount of sediment entering into the system, which in turn are influenced by
climate and geology. The amount of water delivered to the surface of a watercourse, as well as
how and when it arrives is influenced by climate. Typical patterns are high flow events during
the spring freshet, and low flow conditions during the winter and summer months.
The surficial geology of an area influences the path of water once it reaches the ground surface.
The underlying geology establishes the volume and proportion of groundwater and surface
water available to flow through a watershed through its effect on infiltration. Geology also
shapes the amount and type of sediment that enters a watercourse, and the strength and
erodibility of the surficial material through which the watercourse flows. A complex underlying
geology and topography can result in considerable variation in channel character, as well as
sensitivity to potential impacts, within the same drainage system.
Natural watercourses respond to continually changing conditions in flow and sediment supply
with adjustments in shape and channel position. These changes take place through the
processes of erosion and deposition. This ability to continually change is an inherent
characteristic of natural systems that allows the morphology of the channels to remain relatively
constant. The state in which flow and sediment supply are balanced to achieve this stable
channel form is referred to as “dynamic equilibrium.” While in a state of dynamic equilibrium,
channel morphology is stable but not static, since it
makes gradual changes as sediment is eroded,
deposited, and moved throughout the watercourse. For
example, many natural watercourses can be seen to
“migrate” within their floodplain over time. This is due to
the erosion of the outsides of channel bends, but with
corresponding deposition of material on the insides of
bends. This process maintains the balance between flow
and sediment supply in the system. Riparian and aquatic
biota are adapted to and depend on the habitats provided
by a system in dynamic equilibrium.
Chapter 2: Study Area: The Barrie Creeks, Lovers Creek and Hewitt’s Creek Subwatersheds 58