Duty to yourself #30 EarthCache
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Billabong in the making
Make sure you check out the 2001 Grandfather Cache very nearby here, WWWWandering GC613
Feel free to submit find before CO approval, but will be deleted if inadequate.
A billabong ('bill-a-bong') (/ˈbɪləbɒŋ/, BIL-ə-bong) is a body of water, an isolated pond or wetland left behind after a river changes course.
Then, after a big rain or wet season, the billabong fills again and sometimes re-connects with the river.
The etymology of the word "billabong" is disputed. The word is most likely derived from the indigenous Wiradjuri ('weir-add-jeer-ee') term "bilabaŋ", which means "a watercourse that runs only after rain" and is derived from "bila", meaning "river",and possibly "bong" or "bung", meaning "dead"
FORMATION OF A BILLABONG
When a river reaches a low-lying plain, it meanders widely.
Over time the river's meandering leads to erosion of the banks through hydraulic action, abrasion and corrosion.
Eventually the meander becomes very curved, and eventually the neck of the meander will become narrower and the river will cut through the neck taking a short cut downstream.
This cuts off the meander and forms an isolated wetland, (called an 'oxbow lake' internationally for the distinctive curved shape, named after part of a yoke for oxen) or Billabong depending how often it is capable of refilling.
FEATURES
In the vicinity of a river bend, debris deposition normally will occur on the convex bank (the bank with the smaller radius). In contrast, both lateral erosion and undercutting occur on the cut bank or concave bank (the bank with the greater radius.)
Continuous deposition on the convex bank and erosion of the concave bank of a meandering river cause the formation of a very pronounced meander with two concave banks getting closer.
The narrow neck of land between the two neighboring concave banks is finally cut through, either by lateral erosion of the two concave banks or by the strong currents of a flood. When this happens, a new straighter river channel is created and an abandoned meander loop, called a cutoff, is formed.
When deposition of sediment finally seals off the cutoff from the river channel, a billabong is formed. This process can occur over a time scale from a few years to several decades and may sometimes become essentially static.
Gathering of erosion products near the concave bank and transporting them to the convex bank is the work of the secondary flow across the floor of the river in the vicinity of a river bend.
The curved path of a river around a bend causes the surface of the water to be slightly higher on the outside of the river bend than on the inside. As a result, at any elevation within the river the water pressure is slightly greater near the outside of the river bend than on the inside.
As it flows along the floor of the river, it sweeps loose material toward the convex bank.
At this location in the middle of the bridge we can observe one aspect of the slow process of forming a new billabong. No need to get down to the river bank. Only in times of extreme flooding or drought will the answers be unavailable to obtain.
To get credit for this earthcache email me the answers to the following questions:
1. The name of this earthcache, your caching name and any other caching names who will be logging your answers as a find (if correct)
2. The number of cachers in your group.
3. From where you are standing where is the area of most water turbulence (as a compass bearing or stream direction) and why do you think it is located there?
4. Normally at the concave side of the curve we would see an undercut or active erosive process, what geological features can you see looking east that would slow this erosion?
5. Looking Easterly again but at the convex (inner) side of the curve why do you think there is very little 'beach'?
6. How far into the process of creating a billabong is this meander?
7. BONUS POINTS (non compulsory optional geo-karma): take a picture of the river at the posted coordinates of yourself and team, and post it with your found log (when approved) 8. Describe the highlight of any experience while hunting the caches in this series, and what GPSR you used.
While here you MUST visit WWWandering, GC613 one of Melbournes OLDEST caches 2001 just a literal stones throw away.
Additional Hints
(Decrypt)
rznvy gb QeYhxr@zr.pbz
Treasures
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