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AS and A Level: Hydrology & Fluvial Geomorphology
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Five things you need to understand about hydrology and fluvial geomorphology
- 1 Make sure you understand the concept of systems, and the difference between a closed system (the global hydrological cycle) and an open system (the drainage basin)
- 2 Learn the correct definitions of all the specialist terms (eg percolation, throughflow, hydraulic radius, etc.
- 3 Learn a case study which shows how the theory relates to an actual example of a real river basin.
- 4 Remember that rivers are not static – they are affected in the short term by weather patterns and human activity and in the long term by changes in climate, tectonic processes and sea levels.
- 5 Pay attention to scale: for example British rivers (and British floods) are tiny compared to the great rivers (and great floods) experienced in other parts of the world.
Common errors in hydrology and fluvial geomorphology essays
- 1 Although rivers near their source often look like they are flowing quickly, and rivers near their mouth look like they are flowing slowly, river velocity increases downstream. This is because there is more turbulence upstream (due to friction) and rivers flow more efficiently as they get further downstream (as friction reduces).
- 2 Infiltration is the movement of water into the soil. Percolation is the movement of water into the underlying rock. Students often confuse these two terms.
- 3 Landforms are often referred to as landforms of erosion (eg waterfalls) or landforms of deposition (eg deltas). However, it is important to remember that other processes (erosion, weathering, transportation, deposition, mass movement) also contribute to the formation of these features.
- 4 River valleys and river channels are not the same thing.
- 5 Remember that flooding can bring benefits as well as costs.
Top facts to use in your essay answers
- 1 Water covers approximately 71% of the Earth's surface
- 2 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air.
- 3 Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere.
- 4 The Amazon river is by far the largest in the world in terms of discharge (which is greater than the next seven largest rivers combined), and it has the world’s largest drainage basin. The Nile is generally recognised as the world’s longest river (approximately 6550 km).
- 5 River flooding has been the cause of some of the world’s worst environmental disasters. For example, the 1931 Yangtze floods in China may have killed up to 4 million people.
- Marked by Teachers essays 4
- Peer Reviewed essays 1
and get smaller and more rounded downstream. 2. The change in the bed load will be partly due to an increase in velocity downstream, which will increase hydraulic action on the bed load, eroding it in size and angularity. A higher velocity downstream will also increase the process of attrition, which occurs when the rocks knock into one another, which causes them to erode. It will be interesting to compare my results to the Bradshaw model. This model shows the characteristics that rivers usually follow from source to mouth, based on data from rivers from all over the world.
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Key questions: * Is there a gradual increase or decrease in the velocity downstream in the River Holford? * Is there a gradual increase or decrease in the hydraulic radius downstream in the River Holford? * Is there a gradual increase or decrease in the average depth downstream in the River Holford? * Is the velocity affected by the change in hydraulic radius across the River Holford? * Is average depth affecting the velocity at each separate interval within the River Holford?
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Temperature also needs to be considered because if temperatures are higher it will increase the rates of evapotranspiration, resulting in less water flowing into the river. The landscape can include the relief of the land (is it flat / mountains / steep or gentle slopes?) and the geology, both of which can affect the river regime. For example, permeable rocks will allow some water to flow through them, meaning there is less water flowing in the river channel while impermeable rocks will increase the amount of water in the river, as water cannot sink through them to travel as groundwater.
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Technique Data Collected Purpose Method Limitations Suggestions on expanding data Date Photographic Evidence Photographs taken at 12 sites of river. To show size and shape of river at each site. Also to show management. Photographs were taken at best angle using a digital camera if each site. Weather and foliage may have affected quality of photographs. Only one photo taken at each site. More photographs taken. 10/10/07 Velocity Survey 10 speed measurements measured in seconds To work out the average speed of the river down stream Dog biscuits were thrown into river and timed how long it took to float just below the surface over 10 metres.
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Also we plan to look at all the different processes operating within the river from its source to mouth; this data will be presented in graphical form. Hypotheses 1. Width, depth and cross-sectional area will increase from source to mouth. 2. The velocity and discharge of a river will increase from source to mouth. 3. Bed load becomes smaller and more rounded from source to mouth. Location Our study is of the Glendun River. The map below shows part of Northern Ireland and where the river is positioned.
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* Only takes one person The problems of this test is that: * You have to make sure the can is in the ground properly so the water doesn't escape and therefore wasting water. Pupil with the equipment 1. Water 2. Tin can 3. Stopwatch Soil Auger Test This test will tell us how deep the soil is in a section of the ground. The list of equipment needed is: * Soil Auger * Soil to Auger * Meter Stick To do this test start to screw the auger into the ground in a clockwise direction.
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To assess whether the modified channel of the river ash is effective in reducing the risk of flooding to local homes.
This causes a large amount of surface run-off when water simply lies on the surface of the ground. This surface run-off can initiate flooding. In Britain flooding often occurs in summer. After large periods of dry hot weather the ground becomes hard and dry and hard to infiltrate. A heavy rainstorm can often follow this where the surface run-offs caused by poor infiltration results in a rapid rise in water level, or a flash flood. Heavy snowfall means that large amounts of water are held in storage. If there is a slight rise in temperature the water melts and is released.
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To what extent the flood alleviation scheme has had on the environment and people of Swanage and to find out weather the scheme has been successful.
The headlands of Swanage are quite obvious and easy to notice. Both the chalk and Purbeck bed are hard rock which is found to the north and south of Swanage. The soft rock has been severely eroded in comparison to the other rock, especially the chalk found at Studland Bay. This is where the famous 'Old Harry' stands. This site receives a lot of tourism and still has been eroded less than the Swanage area. Question 2 In any place there is obvious causes of flooding, the most common cause of flooding is heavy rainfall over a long periods of time, often lasting many days, thunderstorms being the most severe of these.
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My hypotheses are:The character of the course of the River Bollin will change along its course to the mouth. The bed load will decrease and angularity of the materials found in the river will be reduced. The velocity
This was also a good way of reinforcing our knowledge of the hydrological cycle, as we could physically see the precipitation further up the hill, and how it trickled down to create streams. We planned to go to the highest and furthest site first, this was a perfect example of the beginnings of a river, or it's Source. This site was found in the "Macclesfield forest", and so we shall refer to the site as Site 1, Macclesfield forest. This site showed the characteristics of a V shaped valley, and formed truncated or "interlocking" spurs.
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So when two 3rd order streams meet at a confluence a 4th order stream is created. Predictions and hypotheses With my knowledge of river basics I have made the following predictions on how the channel parameters will change downstream. Measurement Predicted changes downstream Reason / theory for prediction Width Increase - bigger increase when river order increases These parameters increase because the river is going to get bigger downstream. Wetted perimeter Increase Depth Increase Cross sectional area Increase Hydraulic radius Increase As the river gets bigger it should have less of a wetted perimeter to water ratio meaning the hydraulic radius increases.
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I expect to find this because as the river flows downstream there will be a larger volume of water. This is because as the river travels downstream more water will accumulate in the channel as the water enters the river from the drainage basin. 6. The bed load size will decrease with distance downstream. This is because I expect the velocity of the river to increase and so there will be more erosion of the rocks. This type of erosion is attrition and as the rocks collide because of this they will break up and become smaller. 7. The bed load shape (roundness and smoothness)
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Site 3 - Llanychaer Site 3 was situated next to a small village. The river was a lot wider and deeper than in site 2. The riverbanks were not steep but there was a (large) overhang in some parts. Bed load was less frequent than in site 2 but there was some more large and angular rocks. Site 4 - Lower Fishguard This is in the middle of a residential area with access to ferries. It is at the mouth of the river and is a lot wider than any of the other sites.
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I chose three sites on the river Caerfanell, to perform my methods. Site 1 � Blaen - y- Glynn Site 2 � Pont blaen y Glyn - The Valley Site 3 �By the Talybont reservoir. These sites are situated on the location maps later in my project. My main focus of these coursework is to answer the following question... "Is there a correlation between velocity, gradient, and channel shape?" I intend to answer this question through a series of key questions.
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decreases GRADIENT decreases TURBULENCE decreases HYDRAULIC RADIUS increases HYDRAULIC RADIUS - cross sectional area Wetted perimeter Explains how energy is loss in the river through its friction with the bed and the banks. High values show efficiency (closer to the semi-circular shape.) low values show a poor efficiency. RIVER LANDFORMS POTHOLES - the eddy currents formed in a river can result in particles being trapped in them. As they move in a circular motion they begin to wear in depression to the bed, these are called potholes.
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These hillsides are known as interlocking spurs and they restrict the view up or down the valley. The river is now entering its middle course. The midd le course of the river Rhymney is located in Ystrad Mynach. During the Middle course of the river, the river is eroding laterally as well as vertically. During it's Middle course the river begins to Meander slightly at Trethomas. When a river reaches a Meander most water is directed towards the outer bend. This will reduce friction and increase the velocity of the river at this point. The river will therefore have more energy to transport material in suspension.
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Changes have been made nearer the mouth of the River Lyn due to this. The Bradshaw model of River characteristics. This is what I will be comparing the River Lyn with to see, 'to what extent does the River Lyn conform with the Bradshaw model of River characteristics?' Fig. 1 Annotated sketch maps of location. Hypothesis Fig. 4 River channel characteristics Hypothesis. As you go down stream it will... Water depth (and channel depth) Increase, due to erosion, surface runoff into River, through flow Occupied channel (And water) width Increase, due to erosion, tributaries joining on to it, surface runoff into River, through flow Wetted perimeter Increase, due to erosion, tributaries joining on to
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In times of flood or when the river is at bankfull is when this form of erosion is at its most effective. The appearance of the river tends to be brown in colour due to the large amount of load that the river is carrying and is a signal that corrasion is at its peak. When the river is in low flow, the river transports a smaller load, therefore the water will appear clearer, and its at these times when corrasion is at its lowest.
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Study the river Cray and see whether the river actually follows a natural path of a conventional river which is in a text book.
It then flow downhill toward lower and lower places until eventually reaching the lowest position possible, the ocean. This is a Simple Model of a River Valley from the beginning of the river to the end I will explain it in more detail. The place where a river starts is called its source. The rivers source always begins in high places as we can see in the first part of the diagram. Position 1 of this diagram is the rivers source.
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Geography investigation - The River Skirfare located in the Littondale region in the Yorkshire Dales National Park.
The River Skirfare is located in the Littondale region in the Yorkshire Dales National Park. The two locations which will be sampled for a range of data will be Arncliffe (Downstream) and Halton Gill (upstream). These can be seen in the area Littondale on Fig.2.1, and individually in Fig.2.2 and Fig.2.3 on the next page; From this map of Littondale we can see the locations of both Halton Gill and Arncliffe. It also shows me many other factors that will affect the hypotheses. One of these factors is the relief of Littondale. If the relief is steep from Halton Gill to Arncliffe then this will have a profound effect on the velocity of the river, hence will be extremely useful when analysing the velocity as required by the third hypothesis.
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More water undoubtedly meant a great amount of erosion and transportation. This also meant there was a great deal of surface run-off. Our survey was taken so as to give a better understanding of the rivers characteristic (i.e. its dimensions, depth and speed). Measurements of the wetted perimeter, the depth and the height were taken down. The average depth, cross-sectional area and channel width, for each stage of the river was worked out. (Fig. ) The map below shows the location of Epping Forest in relation to neighbouring cities.
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SEQUENCE OF INVESTIGATION I am investigating how efficiency and sediment change with distance downstream. I need information about the river with a detailed map of the area. This enables me to locate the different site I will investigate. My key questions are stated above; I need to measure the depth, pebble size, width, velocity, gradient, and bank full and low flow measurement of the river to answer my questions. I will collect the data as explained in my data collection.
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In river A the ratio between cross sectional area and wetted perimeter is very low which means the river flows slowly. In river B the ratio is much greater which means the river flows faster. In general the larger the cross sectional area in comparison to the wetted perimeter the faster the river flows. This ratio is usually greater the further you go downstream and so the river flows faster. Discharge is the volume of water flowing in a river at a given point and is measured in cubic metres per second (cumecs).
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Ilkley lies in the heart of the Yorkshire dales which in turn is in West Yorkshire. The follow on of maps from the original map of Britain shows where the two sites are in relation to other places in Britain. The purpose this serves is to give a precise location of each site and an exact idea of how far away from each other they are. Appendix 4 locates the two sites of Backstone Beck and the River Wharfe and where they are in relation to height. Appendix 3 shows the catchment area of the River Wharfe and its approximated area.
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The aims of our study were to measure and analyse the changing characteristics of a river as it travels downstream, and to obtain "primary data".
The state of the river i.e. if it was feasible for us to obtain the results we needed, depending on the height of the river and velocity. 3) How many people there were to visit and take measurements at each site. We decided that we needed to visit six sites with varied stream orders to enable us to provide a significant range of results and therefore accurate representation of the River Ballymully's characteristics. 7. How many recordings/samplings will you take?
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I am going to study the characteristics of rivers and how they change as stream order changes. I will do this in Epping Forest to the North East of London.
* As stream order, increases pebble size will decrease: This will occur due to the effects of attrition, abrasion and hydraulic action and because the river will have insufficient energy to carry the biggest pebbles far downstream. * As stream order, increases pebble shape will become more rounded: I believe that as meanders develop and the force of the river increases around the outside bends hydraulic action will take place and it will smoothen and round the pebbles. * As stream order, increases cross-sectional area will increase: Erosion is increased as stream order changes and as a result, the cross-sectional area is also increased.
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