This earthcache brings you to a location with some interesting informational signage explaining the fluvial geomorphology of Whitemud Creek and surrounding ravine.
At this location, you can learn about how a meander is formed, and how an oxbow is created. You can also see a good example of a meander and an oxbow. From the signage, we learn and can see that Whitemud Creek swerves side to side across its valley in a series of bends called meanders. A meander forms when bars of sediment are deposited in the channel during periods of low stream flow and water is forced to flow around them. This creates a faster-flowing current which erodes deeper pools of water on the outside of the bend, and has the power to erode and undercut the adjancent banks. The sediment eroded from the bank falls into the creek and is carried downstream. Where the flow slows down on the inside of a bend, sand and gravel is deposited. This narrows the channel causing the flow to speed up. The fastest flowing water is diverted towards the outside of the bend, where further erosion occurs, follwoed by more deposition of sediment downstream.
An oxbow is created when meander bends come close together. When this occurs, erosion on the outside banks may be great enough to allow the creek to shortcut across the neck of land between them. Shortcutting can occur when stream flow is high, such as during spring snowmelt or heavy rainfall. When this happens, water will continue to flow slowly through the original bend, gradually depositing sediment and filling in the channel. However, most of the flow will follow the new channel which will get wider over time. Eventually the infilling of the old channel will cut it off from the new channel. The result will be a crescent-shaped oxbow lake with only limited throughflow of water.
To log this earthcache, please answer the following questions by sending me a message. Please do not post any answers in your logs.
(a) On the signage on the east side of the boardwalk is a photo of the landscape, with several letters marked on the photograph. Look for the letter "D". Based on what you know about meanders, do you think the river is eroding this location or depositing materials in this location?
(b) To the West is an Oxbow Island, and area of land surrounded by the current and former course of the creek. Do you think this oxbow was fairly recently formed or has been here for a long time? If you continue south down the path for another 60-70 meters, you will find another sign that explains how you can tell (N 53° 28.535 W 113° 33.387).
(c) Can you identify another location in Edmonton (or Alberta) where the same forces have occurred to change the course of a stream or river? Provide a description or coordinates, and explain why you believe the same process has occurred.
(d) (OPTIONAL) Post a photograph of yourself, your team, or your GPS on the boardwalk. Just be careful not to give away any information from the sign boards.
We hope you enjoy a leisurely walk in this very picturesque area and enjoy the flora, fauna (and geology) of the Edmonton River Valley and Ravine system!
Reference: Informational signage at site posted by the Edmonton Nature Club and the City of Edmonton