Describe and explain the changes that occur in a river channel as it moves from source to mouth.
All rivers have an upper, middle and lower course. The long profile of a river is basically the changes in gradient at these different stages in the river, every river is trying to achieve a smooth, concave, long profile.
The river begging in the upper course, normally in the hills and mountains. Here the river is smaller, the flow is fast and load and water volume are slow. The river erodes a v-shaped valley. At this stage the channel is inefficient as it has a large channel surface compared with channel surface area. There will be more friction as more water touches the river bed. A steep gradient is needed to maintain the rivers energy levels. The path of the river is fairly straight.
A river can erode the soil and rocks which form its channel banks. They erode in four ways Abrasion, Corrosion, Attrition and Hydraulic action. The main erosion processes that take place in the upper reaches are:
Abrasion or corrasion-This is when rocks in the sediment load which is being carried along by the river hit the rock materials on the bed and banks of the river. This is most effective if the river is flowing at high velocities like the upper course. This is the main process that causes vertical erosion.
Hydraulic action- This is the force of moving water. Loose sediment is most susceptible to hydraulic action. This happens at high velocities.
Corrosion-This is the chemical weathering of minerals in rocks in contact with the river water. The minerals in the rocks are slowly dissolved, eventually causes them to break apart. This process is most effective where there is fast flowing water and the river is not already saturated with minerals again this will therefore be more effective in the upper course.
Attrition-this is the process where the rocks in the sediment load erode by colliding with each other as they are carried along the river. The result is that the sediment load becomes more rounded and smaller in size. Even though this process takes place in the upper course the sediment tends to be larger and more angular here as attrition has not been acting on them for very long, however Sediment can be added anywhere along the rivers course.
Yes this feature is the result of erosion and depositional processes however, it is not associated with the current water course. This feature may be the result of a Gilbert type delta that once occupied this area. Gilbert type deltas have three main components; topsets, foresets and bottomsets. Topsets are fluvial sediments (primarily sandur deposits) that were deposited on the subaerial delta surface. Erosive events occurring on the upper forslope can result in downslope channels and chutes. These features are then eroded by either strong currents or by debris flow resulting in these channels and chutes to become filled. Foresets are a combination of sand and gravel facies. The are deposited by gravitational processes on the delta foreslope and the grains tend to become finer and more angular downslope. Bottomsets consist of fine grained silts and clay and are deposited at the foot of the delta front.
Sedimentary rock from the older Silurian Period is further from the river banks (Geological map of Victoria, 1973). Mudstone, inter-bedded shale and greywacke depositions indicate the Maribyrnong River may have previously taken a different shape, and younger sediments have replaced the older sediments in more recent geological periods.
As can be seen from the photo( Image 1), looking downstream, there were steep sections of bank where it appeared the erosive forces of the river when high have cause part of the bank to fall away leaving steep about 1m high drops on the bank with exposed rocky soil visible. The phenomenon also illustrate that it is an alluvial landforms, which will find erosional feature from fluvial
The forecast calls for rain. The erosion of the Le Sueur River has been an ongoing problem for a while. The rain has caused the river to rise, and make residence, and wildlife flee to a safer area. A plan is in store to make this area a quality, safe, and useful area again.
Removing vegetation removes the root systems, which help hold soil in place. Running water can now more easily wash soil and rock away, increasing erosion.
...ansportation in the natural direction of the littoral drift. This particular jetty is responsible for the accretion of sediment immediately adjacent to the South Jetty (Kraus).
Wentworth, C.K. (1922) A scale of grade and class terms for clastic sediments. Journal of Geology, 30, 377–392.
How does the smooth mountain rock surface type affect the amount of runoff? Speculate why this happens.
My first view of the river makes me breathless. Shallow water washes over the road’s cement pavement. Men, women, and kids break the river’s flow; some sit in fold-up chairs and read a book, but most
Bridge scour is one of the three main causes of bridge failure (the others being collision and overloading). It has been estimated that 60% of all bridge failures result from scour and other hydraulic-related causes. Major damage to bridges at river crossings occurs during flood. Damage is caused for various reasons, the main reason being riverbed scour at bridge foundations, namely piers and abutments.
The sediments on the Arrastre wash were deposited in the alluvial environment, in other words, by a river that passed through the region during the Cretaceous. Moreover, they were initially horizontal, but stresses, which could be caused by the increase in pressure and temperature or even the movement of the tectonic plates, forced the layers to fold. In addition to the folds, it was possible to observe the ripple marks on the floor of the Ripple Wash, which gives the direction in which the river was flowing, and joints on certain
We traveled to the west coast of Wales to find out how a river changes
during normal conditions. Dam-like ridges form along the banks of rivers on flood plains and under normal conditions keep the river in its channel. During floods rivers flow over the tops of levees and flood the flood plains that lie adjacent to the river channel. Man has constructed channel walls to "beef up" the natural levees to protect the flood plains. However, all of New Orleans and the flood plain beyond the city is constantly threatened by flooding of the Mississippi River (Madsi, July 99).
The river velocity is the speed of water flowing along or through it. A rivers velocity can change during different courses of the river. This can be determined by the rivers gradient (how steep it is), the shape of the river, how much friction there is created by the river bed and the volume of water. Velocity is measured in meters per second.
Hydraulic Action, when waves hit the cliff, air is forced into cracks, and then as the wave retreats this air expands explosively. Over time the cracks enlarge, weakening the base of the cliff causing erosion.