Eyot is that? EarthCache

What have we here? This lesson will have you looking at the Credit River from Riverrun Park and both sides of the Main Street overpass - or alternatively and optionally - this can be done from on the river (but you need photos from topside, so bear that in mind). We'll be looking at river flow patterns and sedimentation, and confluences.

You will need to visit 2 locations to understand the full picture of the river flow in this area, and to compare and contrast upstream and downstream areas. A car is best, although as mentioned, you could try and float between locations in the summer months. The D & T ratings reflect the travel required. Start at the posted coordinates.

Please ensure that each person completing this EC submits their own responses and posts their own qualifying photos. Using the messaging service is vastly preferred.

Thanks!

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An ait or eyot is a small island. It is especially used to refer to river islands found on the River Thames and its tributaries in England. Aits are typically formed by the deposit of sediment in the water, which accumulates. An ait is characteristically long and narrow, and may become a permanent island should it become secured and protected by growing vegetation.

A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid islands/bars or aits/eyots resulting from the erosion of the depositional environment with the resulting sediment deposited downstream. 

Braided streams tend to occur in rivers with high sediment loads and/or coarse grain sizes, and in rivers with steeper slopes than typical rivers with straight or meandering channel patterns. They are also associated with rivers with rapid and frequent variation in the amount of water they carry, i.e., with "flashy" rivers, and with rivers with weak banks. Braided channels are found in a variety of environments all over the world, including gravelly mountain streams, sand bed rivers, on alluvial fans on river deltas, and across depositional plains.

  This is an example of an eyot in the Thames, London - Chiswick Eyot. 

 This is an example of a braided river. 

  This is an example of a braid bar.

A confluence occurs when two or more flowing bodies of water join together to form a single channel. Confluences occur where a tributary joins a larger river, where two rivers join to create a third or, where two separated channels of a river, having formed an island, rejoin downstream.

On the other hand... we can have meandering rivers.

A meander is one of a series of regular sinuous curves, bends, loops, turns, or windings in the channel of a river, stream, or other watercourse. It is produced by a stream or river swinging from side to side as it flows across its floodplain or shifts its channel within a valley. A meander is produced by a stream or river as it erodes the sediments comprising an outer, concave bank (cut bank) and deposits this and other sediment downstream on an inner, convex bank which is typically a point bar. The result of sediments being eroded from the outside concave bank and their deposition on an inside convex bank is the formation of a sinuous course as a channel migrates back and forth across the down-valley axis of a floodplain. The zone within which a meandering stream shifts its channel across either its floodplain or valley floor from time to time is known as a meander belt. It typically ranges from 15 to 18 times the width of the channel. Over time, meanders migrate downstream, sometimes in such a short time as to create civil engineering problems for local municipalities attempting to maintain stable roads and bridges.

The degree of meandering of the channel of a river, stream, or other watercourse is measured by its sinuosity. The sinuosity of a watercourse is the ratio of the length of the channel to the straight line down-valley distance. Streams or rivers with a single channel and sinuosities of 1.5 or more are defined as meandering streams or rivers.

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Questions to answer - each person, please submit your own work.

1. At the posted cache coordinates, make your way down to the banks of the Credit River and look north toward Saluit Island. Describe what you see - include approximate length & width & depth (in metres) of the Credit River and any associated depositional environments. 

2. Is this an example of an eyot, braided channel, braided bar or none of the above? If none of the above, what would you call it?

TAKE A PHOTO of you/your GPS in front of the triple parking signs (in the parking lot) and post it with your log.

DRIVE/MAKE YOUR WAY TO WP2

3. At the posted coordinates from the Main Street overpass (WP2), look south & down, name and describe what you see - include approximate length & width & depth (in metres) of the Credit River and any associated depositional environments.

4. Is this an example of an eyot, braided channel, braided bar or none of the above? If none of the above, what would you call it?

5. Explain how you think your answer to Q4 was formed in this particular location.

6. In conclusion, and based on your observations from both stages of this EC, would you describe the Credit River as more of a confluence or a meander?

7. Finally, to demonstrate you were on site at WP2, take & post a photo of you/your GPS in front of the Timothy Street Park sign which is located near the NE end of the overpass. Don't forget your photo from WP1.

Thanks for visiting; I hope you learned something new. Please submit your responses via the messaging service prior to posting a find (a note is requested if there will be a delay in sending answers). I'll read and reply to all responses. Logged finds without complete and/or corresponding answers will be deleted.