Logging Requirements:
THE QUESTIONS:
1.) Looking to the bend in the river, is the side of the river you are standing on the inner or the outer side of the meander bend? Give your reasons.
2.) On which side of the river does the water appear to be moving slowest? What effect is this having?
3.) What colour is the water? Why is it this colour?
4.) Then post a photo of you at the location with your log, (please do not show the subject of the questions in your photo). Of course, if you do not want to appear in the photo, a personal item in the photo is enough proof of your presence.
You may log the cache as soon as you submit your answers to us via messenger.
Logs without accompanying answers sent or without a photo uploaded may be deleted without notice.
Sending the answers is a requirement not a request.
Please note, answering the logging tasks is based on your observations at the site and using your understanding of content of the cache page, there’s no need to do any further research.
THE LESSON:
Here at Picnic Point Reserve we are standing on the edge of the Tarago River. It is a 49-kilometer perennial river (perennial meaning it flows continuously all year). Over its 49km it descends roughly 320 meters.
Rivers form when water moves from a higher elevation to a lower elevation, all due to gravity. When rain falls on the land, it either seeps into the ground or becomes runoff, which flows downhill into rivers and lakes, on its journey towards the seas. River landforms are caused by the processes of erosion, transportation and deposition. The main landforms created by a river can be found in 3 main areas; those found in the upper valley which is referred to as the upper course and those found in the lower valley, the middle course and the lower course.
Image: 3 stages of a river.
The Upper course of the Tarago River originates in the Bunyip State Forest, flowing in a SE direction through the Strzelecki Ranges at an elevation of around 350 meters. The Middle Course of the Tarago river slows as the gradient becomes flatter. It flows into the Tarago Reservoir near Neerim South. Below the dam wall, the river winds through rural landscapes. It is joined by a couple of minor tributaries. The Lower Course part of the river is the slowest, it loses energy and drops sediments. The Tarago river’s course ends when it joins the Bunyip River at Longwarry North.
At the Picnic Point Reserve the Tarago River is in transition from middle to lower course where meanders become less prevalent. Here you can see quite clearly on this meander bend the river is experiencing both erosion and deposition because water flows at different speeds across the channel.
The deepest part of a river channel is on the outside of the bend, water flows faster in deeper sections. As water moves downstream and around a bend, it moves in a spiral fashion. The helicoidal flow 'corkscrews' the water towards the outside of the bend at a greater velocity. This greater speed gives the river more energy, causing it to erode and undercut the outer bank and gouge the river bed using hydraulic action and abrasion. The outside bank is therefore becomes concave & steep and is called a river cliff or cut bank. The river also gains depth.
This process repeats over and over at each meander bend as the water flows downstream.
Much of that eroded material is carried downstream toward the opposite or inside bank, where the water slows. The water’s velocity and energy is reduced because of friction between water and the river bed & banks. As a result, the water no longer has the energy required to carry its load of sediments and deposits the sand, gravel, and other sediment it is carrying. This deposition creates a gentle slope known as a slip-off slope or point bar, (most of us would call it a beach). The river bank on the inner side becomes convex.
As you can see in the above diagram, the concave and convex sides in a meander gives the channel an asymmetrical shape. It is shallow on one side and deep on the other. Over time, erosion on the outside of the bend and deposition on the inside cause the bend to become larger and more pronounced. This process contributes to the development of meanders in a river.
Summary:
- Outside of bend: Fast flow → more energy → erosion → river cliff.
- Inside of bend: Slow flow → less energy → deposition → slip-off slope.
Resources:
https://en.wikipedia.org/wiki/Tarago_River
https://www.geo41.com/rivers-matu#river-processes-swiss-maturity
https://www.youtube.com/watch?v=MQCL9GX0PYw
https://www.internetgeography.net/flashcard/draw-a-simple-diagram-to-show-the-main-features-of-a-meander/