This EarthCache is placed for the Fraser Valley Cache Bash #2, and is intended to increase your knowledge of the geography of the Fraser Valley. Like all EarthCaches, please review the information, then answer the questions/tasks at the indicated coordinates, and submit your answers to the Cache Owner before logging a find.
A Floodplain Within a Floodplain
The starting GZ for this earthcache brings you to the location in Derek Doubleday Arboretum where you can observe that the Fraser Creek joins the meandering Nicomekl River, approximately 60m to the West of the starting point.
This bit of low-lying land is called the Fraser Creek Flood Plain
One of the cool things about this area is that it is a readily observable smaller instance of the what normally is a significantly larger area. In fact the entire fertile Fraser Valley stretching from Hope to Richmond.
This image from the Fraser Basin Council website illustrates the enormity of the Fraser River Floodplain and the various social, environmental, and economic impacts associate with living, working, and farming within it.
(https://www.fraserbasin.bc.ca/water_flood_fraser.html)
Why we’ve brought you to this location is because you can observe a floodplain in action at a scale that allows us to see the entire scope of events and impacts, and then better understand the larger scenario within which we are located.
Recognizing Floodplain Features
A floodplain (or alluvial plain) is “an area of land adjacent to a stream or river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.”*
What this means is that just like an ephemeral pond (see Earthcache GC6Y90D for more information about vernal or ephemeral ponds and how they are similar to floodplains), seasonal increases in the amount of water moving through the stream or river will overflow the banks, and then recede again.
This repeated seasonal action over hundreds of years results in two interesting and readily notable features.
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The body of water will be set in a “low land” area with low naturally occuring banks made of layers of silty material
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The path of the body of water is not straight, but “meanders” through the lowlands
These features continually build on each other over time, creating very erratic looking courses for the creek, stream or river. These should be readily noticeable from your observation point. Generally speaking, the longer a body of water has been active, given relatively similar volumes of water, the more pronounced the meanderings will be.
To Get Credit for This EarthCache
Please send your answers to these questions before logging your find. Feel free to include any photos of the area with your log, avoiding any that give away the answers.
Tasks:
Waypoint #1 (Earthcache Icon)
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Note where the Fraser Creek joins the Nicomekl River. Estimate the width of the creek, the river, and the floodplain.
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Fraser Creek and the Nicomekl River are set within a greater floodplain - what is it called?
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Estimate the elevation difference between the surface of the water and the tops of the banks
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Are there any noticeable man-made flood control structures in place here?
Waypoint #2
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Examine the area at waypoint #2. Looking at the ground near and in the creek, what do you observe about the materials deposited in and along the creek bed?
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Based on your observations at both waypoints, do you think the structure here remains above water all year?
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Compare the paths of the Fraser Creek and the Nicomekl River. Which has more pronounced meanderings, and why do you believe that is?
Homework!
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Using the new Geocaching.com topographical default map (the “Geocaching” layer), identify the average elevation along the shoreline of the Fraser River - use the Derby Reach Park area as your sample.
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Let’s now assume that Campbell Valley Park and the 16th avenue corridor represent an edge of the larger floodplain. Using the same map, what is the average highest elevation in that area?
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Compare the elevation you took at waypoint #1 against these other two elevations. Explain in your own words where the Fraser Creek Floodplain sits (elevation-wise) in comparison to the larger flood plain, and how that might affect the movement of water and creation of smaller floodplains within the larger one.
Sources:
*(Goudie, A. S., 2004, Encyclopedia of Geomorphology, vol. 1. Routledge, New York. ISBN 0-415-32737-7)
Fraser Basin Council website
https://www.fraserbasin.bc.ca/water_flood_fraser.html