This enables it to cut a deeper channel as it flows downstream. Downstream, the channel becomes wider as the gradient becomes more gentle leading to less vertical erosion. This is because a river tends to become deeper, wider and have a higher discharge the further downstream it moves.
In addition in the upper course the wetted perimeter of the river is higher in proportion to the area of the river than it is downstream. This increases friction on the water and reduces its speed. As a river flows downstream, its velocity increases. The larger mass of water causes wider and deeper water channels in order to allow water in the river to flow more freely.
Attrition — wearing down of the load as the rocks and pebbles hit the river bed and each other, breaking into smaller and more rounded pieces. Changing channel characteristics — cross profile, wetted perimeter, hydraulic radius etc Energy in a river Energy in a river is determined by three factors: mass of water; the height of the river above sea level; the gradient of the channel. Calculating the hydraulic radius of a river. Search for:. While you are here, please consider supporting A Level Geography.
Many thanks, Anthony. Drainage basin hydrological cycle Find out about the characteristics of the drainage basing hydrological cycle.
Storm Hydrograph Hydrographs can be used to illustrate discharge. The long profile of a river The long profile of a river shows changes in the height altitude of the course of a river from its source to its mouth.
Gaining streams are perennial streams: they flow year around. Losing streams are typically ephemeral streams: they do not flow year round. Some streams are gaining part of the year and losing part of the year or just in particular years, as the water table drops during an extended dry season. Streams have two sources of water: storm charge, from overland flow after rain events, and baseflow, supplied by groundwater.
Flood Erosion and Deposition: As flood waters rise, the slope of the stream as it flows to its base level e. Also, as stream depth increases, the hydraulic radius increases thereby making the stream more free flowing. Both of these factors lead to an increase in stream velocity. The increased velocity and the increased cross-sectional area mean that discharge increases. As discharge and velocity increase so do the stream's competence and capacity.
In the rising stages of a flood much sediment is dumped into streams by overland flow and gully wash. This can result in some aggradation or building up of sediments on the stream bed. However, after the flood peaks less sediment is carried and a great deal of bed scouring erosion occurs.
As the flood subsides and competence and capacity decline sediments are deposited and the stream bed aggrades again. Even though the stream bed may return to somewhat like its pre-flood state, huge quantities of sediments have been transported downstream. Much fine sediment has probably been deposited on the flood plain. Stream Patterns Meandering Streams: At a bend in a stream the water's momentum carries the mass of the water against the outer bank. Water piles up on the outer bank making it a little deeper and the inner bank a little shallower.
The greater depth on the outer side of the bend also leads to higher velocity at the outer bank. The greater velocity combined with the greater inertial force on the outer bank erodes a deepr channel. The deeper channel reinforces the velocity increase. The inner bank remains shallower, increasing friction, thereby reducing the velocity. Calculate Spearman's rank figures and draw scatter graphs for this river data. Calculate cross sectional area and Discharge in this exercise.
Analyse this bedload data for its spread or dispersion. Bags of river and stone data from to analyse. Width and depth are simple variables and generally increase downstream as more water is added from tributaries. Width can be derived either from the water surface width occupied channel width or from measuring from bank to bank, giving the bank full width.
We can calculate the stream order from source to mouth too, and this gives us an indication of the size and shape of river channels. The stream order is calculated as follows;. Stream order 1 streams have NO tributaries feeding into them, they are the original streams that start at springs up in the source. Stream order 2 streams occur where two stream order 1 rivers come together at a confluence.
Stream order 3 streams occur where two stream order 2 rivers come together at a confluence not a stream order 2 with a 1, it must be the SAME stream order meeting. The stream order continues like this.
Cross sectional area is another useful measure, and it shows in metres squared the surface area of a river is you could take a slice through and stop the water!
0コメント