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'To what extent does the River Lyn conform to the Bradshaw model of River characteristics?'

Extracts from this document...

Introduction

Introduction. Aims of investigation + my key questions. The aim of my investigation is to see 'To what extent does the River Lyn conform to the Bradshaw model of River characteristics?' To help me answer this main question I have split it up into key questions. They are: 1. Does the size and speed of the River increase going downstream? And therefore does the discharge increase as you go downstream? 2. Does the gradient decrease as you go downstream? 3. Does the load particle size decrease as you go downstream? Background information. The River Lyn has two channels which meet about two thirds along the River Lyn, and carry on as one until it reaches the Bristol Channel at Lynmouth. They join at Watersmeet, and from Watersmeet to the mouth the length of the River Lyn is 2.5 miles and drops 110 metres. The gradient can be up to 1 in 63 at some parts of the River Lyn. Canoeing takes place November to February (on a restricted scale), and at other times fishing is allowed. The East and West Lyn rivers once flowed parallel to the coast eroding 660 ft deeply into the plateau, where it entered the sea at Lee Bay. With the breaching of the valley sides the East and West Lyn rivers cascaded to the shore at Lynmouth, and now there is a fossil filled Riverbed high above the active river. On the 15th August 1952 there was a huge flood, there was high rainfall levels and all the water in the Exmoor catchment went into the River. Above Lynmouth the catchment area of a total 39.2 square miles are of gentle sloping and flat toped moors. Large boulders and rocks were carried in the flow towards Lynmouth destroying houses, roads and bridges. Many lost their lives during the flood. Changes have been made nearer the mouth of the River Lyn due to this. ...read more.

Middle

0.740 m/s Cross sectional area (m2) Average width (m) x average depth (m) (then converted to m by multiplying by 4 and dividing by 10,000) 1 (19 x 4) � 10,000 0.008 m2 Average width (m) x average depth (m) (then converted to m by multiplying by 4 and dividing by 10,000) 2 (409 x 4) � 10,000 0.164m2 Average width (m) x average depth (m) (then converted to m by multiplying by 25 and dividing by 10,000) 3 (421 x 25) � 10,000 1.050m2 Hydraulic radius. Cross sectional area (m2) � wetted perimeter (m) 1 0.008 � 0.460 0.017 Cross sectional area (m2) � wetted perimeter (m) 2 0.1636 x 2.40 0.393 Cross sectional area (m2) � wetted perimeter (m) 3 1.050 x 9.750 10.238 Discharge. (m3/s) Velocity (m/s) x cross sectional area (m2) 1 0.198 x 0.008 0.002 m3/s Velocity (m/s) x cross sectional area (m2) 2 0.242 x 0.164 0.040m3/s Velocity (m/s) x cross sectional area (m2) 3 0.740 x 1.050 0.777m3/s Analysing the cross sectional diagrams. Site 1. The banks of site one look steep. The water depth is about 6cm, and the water width is about 17cm. The cross sectional area is about 0.008m2. The wetted perimeter is 0.46m. Site 2. The banks in contact with the water are steep, then on the right hand side the bank gradually flattens out, whereas on the left hand side, it stays quite steep. This could be for a variety of reasons, including because there is a meander, so the outermost side would have been eroded away, there is also a path to the river, maybe from animals drinking water, which could have made the River flatter on one side then the other. The water depth is about 22cm, and the width is about 92cm. The cross sectional area is 0.1636m2. The wetted perimeter is 2.4m. Site 3. The banks in contact with the water are quite flat, so therefore the River is quite shallow, it is only about 21cm in depth, but about 4m62cm wide. ...read more.

Conclusion

* The graphs were very helpful and helped create a visual picture of the trends as you move down the River Lyn. * All key questions were answered at the end so this is a good achievement. Weaknesses * There weren't many maps to draw a map of the River Lyn and its surrounding area from. * There was lots of information needed in the method about each of the measurements I would be collecting data on, so this made the word count considerably higher. * The statistical test to see if there is a relationship between velocity and distance downstream didn't really work very well because I didn't have enough readings from along the River Lyn. * There weren't many Internet sites to obtain secondary data about the River Lyn. Opportunities * If I did this experiment again I would use appropriate equipment to find out the load quantity. * If I did this experiment again I would use appropriate equipment to find out the channel bed roughness. * If I did this experiment again I would take readings at more sites along the River Lyn. Threats * There are obstacles along the River Lyn like there has been flood protection downstream because of the 1952 flood, so this could affect the readings. (See the picture below.) * The weather could make the level of the River rise, fall or even freeze which could affect the River and the results. Fig. 31 Overall. The River Lyn does follow the Bradshaw model of River characteristics very well, apart from the load particle size, which the form of data collection I used was not very accurate. Load quantity and channel bed roughness were not researched, and there was no secondary data suitable for using. Overall the whole enquiry went very well and I am very proud of what I've achieved. I was able to answer all the key questions and nearly answer the question, 'to what extent does the River Lyn conform to the Bradshaw model of River characteristics? Page of . ...read more.

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