Module 5: Hydraulics - Impelling and resisting forces in river systems

Background

Why we’re covering it

A major part of reading local riverscapes is reading the water and flow. Often times, we make our observations at relatively low flows, when geomorphic work is not necessarily being done. However, the skillset for reading water at low-flows is the same for reading them at competent flows (e.g. high flows) when geomorphic work is being done. Moreover, many of the local controls on flow patterns are the same or similar for low and high flows, and you can infer what might be taking place at those higher flows.

Hydraulics is the study of mechanics of water flow and from our perspective the battle between the impelling forces of fluid flow, interacting with various resisting forces. The impelling forces have a lot of potential energy, that from the perspective of a geomorphologist, have the potential to do work. As water flows through a riverscape, it converts that potential energy into kinetic energy, but then a lot of energy is expended on things that do not do geomorphic work (e.g. friction losses creating heat, or air entrainment producing bubbles). As geomorphologists, we’re interested in those times when their is excess energy to do geomorphic work.

Learning Outcomes

Differentiate influence of external controls (e.g., climate and catchment) vs. local controls on form and process.
Recognize the primary controls on riverscape diversity, in which distinctive suites of physical and biotic processes (behavior) help shape the form and character of those landscapes.
Understand how hydrologic processes, give rise to hydraulic processes, which in local riverscapes.