• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

A study into the bed load of the River Lemon

Extracts from this document...

Introduction

A study into the bed load of the River Lemon Rivers dominate the landscape all over the world, producing widespread changes and affecting human and physical environments in many ways. Rivers are hugely variable because of factors such as climate, geology and human influences, but most follow similar patterns and have similar processes. Understanding these processes is essential for humans to live in harmony with rivers, and knowing how best to use and manage them. To understand these processes we can study river variables, such as velocity, efficiency and discharge, and how they change along the river's course. In this investigation I will try to find out how river variables change downstream in relation to the bed load. The bed load of a river is the material that sits at the bottom of the channel. The bed load is composed of material that is too heavy for the river to entrain and carry along the channel, this is mostly rocks. The bed load originates from two sources: 90% is exogenetic, coming from weathering and mass movement of slopes near the river. 10% is endogenetic, coming from the river's own channel. Understanding the bed load is important as it affects the characteristics of the river as a whole and therefore the management of the river. For my investigation I have studied five sites along the course of the River Lemon in South Devon. I have two key questions to guide my investigation: 1. In what ways does the bed load change downstream? 2. Is there a correlation between river velocity and the size and angularity of the bed load? The velocity of a river is a measure of the speed at which the water travels along the channel. My predictions for my key questions are that: 1. The bed load will start off large and angular at the source (this may be due to the river vertically eroding to reach equilibrium, which leads to the degradation of slopes from weathering and mass movement causing rocks to fall into the channel) ...read more.

Middle

Although a correlation does appear to exist, a way to see how reliable the correlation is to do Spearman's rank correlation test. This is an equation to find out if the null hypothesis can be rejected (in this case the null hypothesis being that bedload size does not decrease downstream). The equation to do this test is: n diameter rank site rank d d� 1 6.7583 5 1 1 4 16 2 6.7116 4 2 2 2 4 3 5.7383 3 3 3 0 0 4 4.523 2 4 4 -2 4 5 4.13 1 5 5 -4 16 This table is used to calculate the equation. n is the number of pairs. First the data for bedload diameter is put down and ranked from the smallest to the largest. The same is done for the sites (distance from source). d is the subtraction of the bedload diameter's rank number from the site's rank number for each row. This is then squared. Next, the sum of the numbers in the d� column is calculated and multiplied by six (6?d� =240). Then the n number is cubed, and the n number is subtracted from that (n�-n = 120). 6?d� is divided by (n�-n), and the result taken away from 1 (1-2= -1). This gives the answer (rs) which is compared to the significance table. n 10% significance level 5% 2% 1% 5 0.9 1 1 10 0.564 0.648 0.746 0.794 20 0.377 0.45 0.534 0.591 If rs is greater than or equal to the critical value for each number of pairs, then the null hypothesis can be rejected. At the 10% significance level, it means there is a 90% probability the results did not come about by chance. At 1% significance level there is a 99% probability the results did not come about by chance. In this case the rs value is -1. The fact that is a minus can be ignored when comparing it to the table. ...read more.

Conclusion

Although, because there were only five pairs, the result was not very accurate, it was the same rs value for both correlations. In the future I could have used more data points and a trend might be clearer. The flowmeter was a good way to measure velocity, but at site one, the channel was so small that the flow could not be measured very accurately. If I were to redesign the project I would change certain aspects. I would sample the bedload by taking it out with a shovel, and find the median rock size, as I think this would be more representative of the overall trend at each site. I would use data from more sites on the river, maybe seven or eight. I would have the sites be equally spaced out along the river, the first site being at the source, and the last site being at the mouth. In my investigation, the last site was not very near the mouth of the river, and therefore does not show the extent to which the bedload changes. Overall I think my investigation has been only partially successful. I aimed to show that velocity increased downstream which reduces the size and angularity of the bedload. What I found was that the correlation between velocity and bedload was not as strong as I thought it would be. The bedload is an important aspect of the river as it affects both the velocity and efficiency of it. The river Lemon does have some problems with flooding, and these problems stem from Dartmoor, where there is a large bedload of hard granite. One possible way to reduce the flood risk is to dredge the channel of sediment, making it deeper and therefore having a larger carrying capacity to cope with flooding, and so reducing the flood risk to settlements downstream like Newton Abbot. Dredging makes rivers more efficient and is cheap, but requires regular maintenance and can have a negative impact on any species living there. Studying rivers is important for humans to understand them and live in harmony with them. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Hydrology & Fluvial Geomorphology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Hydrology & Fluvial Geomorphology essays

  1. Investigating the river Caerfanell

    Also the overall result may have been largely influenced by the inside of the meander readings where sediment deposits are high and energy levels at there lowest. Also at this site a lot of water was flowing beneath the streambed, which could not have been measured.

  2. 'To what extent does the River Lyn conform to the Bradshaw model of River ...

    Data collected Equipment needed Purpose Method Limitations Date 5, 20, A, B, C Water + channel depth Metre rules To see if it conforms to the Bradshaw model At equal distances across the River the depth was measured with a measuring rule.

  1. The Amazon River: Case Study

    Rivers flow through V-shaped valleys in their upper course. V-shaped valleys are usually found in the mountains and hills. They are so called because they often have very steep sides. V-shaped valleys are formed by erosion. The river carries stones and rocks in its water. The force of the water and the grinding of rocks and stones cut down into the river-bed to carve out a valley.

  2. How does the Efficiency and Cross-Sectional Area of a River Change Down Stream?

    Rs = 1 - 6 x 18 12 (12� - 1) Rs = 1 - 108 1716 Rs = 1 - 0.062937 Rs = 0.937063 The correlation between the cross-sectional area and hydraulic radius is 0.937063. This is a near perfect positive correlation, showing graph 4 (see page 10)

  1. Geograpgy glendun river

    Also at this part of the river the route is almost like a horse shoe and eventually, it can get cut off to form an ox-bow lake. At the middle course a flood plain begins to form on the valley floor.

  2. As a group we have decided to look at the changes in a river ...

    As the amount of fresh water and vapour is restricted, it is continuously recycled because no water is being lost or added to the cycle it is termed as a closed system. Rivers would be non-existent without water. The water cycle can also be called the hydrological cycle.

  1. Case Study on The Three Gorges Dam in China

    The map on the following page indicates this loss of land to the reservoir. Tourism River cruises on the Yangtze have become ever more popular through the scenic area of the Three Gorges as the Chinese tourism industry has grown in recent years.

  2. To assess whether the modified channel of the river ash is effective in reducing ...

    Instead of trying to prevent flooding, it is simply preventing the damage that comes with it. Straightening rivers can be a huge job but a very effective way of reducing flood risk. Meanders in rivers slow down the velocity and so the speed at which the river can flow away from the settlement areas.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work