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Field investigation around the hypothesis: The River Piddles bed load will become smaller and rounder downstream.

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Introduction

Hypothesis: "The River Piddle's bed load will become smaller and rounder downstream." The aim of my study is to investigate the bed load of the River Piddle, in particular the size and texture of the rocks and gravel in the river. I will compose this from various different points along the river, from places near to the source going down to the mouth of the river. I aim to discover: 1. Does the size of the bed load change from upstream to downstream? 2. Does the calibre of the bed load change from upstream to downstream? 3. Does the velocity of the river affect the size of the bed load? 4. Does the cross sectional area affect the calibre of the bed load? 5. Does the cross sectional area affect the size of the bed load? The River Piddle (See fig 1.0) is a small rural river in Dorset. It is roughly 25.8km long, and runs from its source at Alton Pancras church to its mouth in Poole Harbour. I investigated at eight different sites along the river - Athelhampton, Affpuddle A, Affpuddle B, Throop A, Throop B, Warren Road, Wareham A and Wareham B (listed in order from source to mouth). I predict that as the river moves further from the source, the bed load will get smoother, as this has been proved in various other studies before, and has been illustrated in the Bradshaw Model (see fig 1.1). The Bradshaw model states that various factors of the river change as the river flows downstream. It shows that on average, the bed load of the river becomes less rough in relation to the distance downstream. This could be because the further the bed load travels, the more abrasion and erosion it is subjected to, and so it is far more likely to become smooth after a longer period in the river - meaning the bed load closer to the mouth of the river would almost certainly be smoother and more rounded than that found closer to the source. ...read more.

Middle

Water Depth Number cm m cm 0 0 1 53 0 -20 2 166 0 -28 3 159 0 -45 4 212 0 -50 5 265 0 -52 6 318 0 -52 7 361 0 -47 8 424 0 -42 9 477 0 -25 10 530 0 -20 0 Average -38.1 Cross-s-a 2.0193 Wetted P 6.062 H-R 0.333107885 Bed Load Number Size Shape length width A SA R SR 1 29 18.5 1 2 11 10 1 3 10.5 4.5 1 4 8 7.5 1 5 25 15 1 6 10 8 1 7 12.5 10.5 1 8 9 5 1 9 9 8 1 10 12 8 1 11 9.5 6 1 12 9.5 9 1 13 13 10 1 14 8.5 1 15 10 9 1 16 15 12 1 17 10 8 1 18 8 6 1 19 15 9.5 1 20 8 5 1 Average 12.125 8.525 6 5 5 3 Velocity Distance Reading Time 0(s Speed 1 26.6 0.37593985 2 31.6 0.316455696 3 36.2 0.276243094 4 28.5 0.350877193 5 26 0.384615385 Average 0.340826243 Discharge 0.688230433 Throop A: Width m Depth Distance from Bank Water Depth Number cm m cm 0 0 1 60 0 19 2 120 0 28.5 3 180 0 47 4 240 0 58 5 300 0 60 6 360 0 57 7 420 0 50.5 8 480 0 49 9 540 0 35 10 600 0 0 0 Average 40.4 Cross-s-a 2.424 Wetted P 6.808 H-R 0.356051704 Bed Load Number Size Shape length width A SA R SR 1 5 1.5 1 2 4 1 1 3 3.5 2 1 4 3 1.5 1 5 2 2 1 6 2.5 1 1 7 2.5 1.5 1 8 2 1 1 9 2.5 1 1 10 2 1 1 11 2 2 1 12 2 1.5 1 13 2 1 1 14 2 1 1 15 2.5 1.5 1 16 1.5 1 1 17 1.5 1 1 18 2 1 1 19 2.5 1 1 20 ...read more.

Conclusion

2. Does the calibre of the bed load change from upstream to downstream? From these results, it is possible to see that the bed load calibre does change greatly from source to mouth. The number of angular samples is highest at Athelhampton, the site closest to the mouth, and that number then decreases as they move further downstream towards the mouth of the river. The sub-angular samples peak closer to the mouth, at Warren Road and Wareham A, where before they were constantly quite low, not increasing past 30%. The sub-rounded and rounded samples gradually increase as they move closer to the mouth of the river. As the bed load usually found at the source of the river has not been subjected to much erosion, it is suggested on the Bradshaw Model that it will be more angular, and will become smoother and rounder as it moves towards the mouth of the river. This means the Bradshaw Model predicts that there are more angular samples at the source, and more rounded samples at the mouth. This has been roughly proved in my results, and so I come to the conclusion that the calibre of the bed load does change from upstream to downstream. 3. Does the velocity of the river affect the size of the bed load? When comparing the length of the bed load and the river velocity, it is possible to see a rough correlation between the two. The length and velocity remain relatively low until Throop B, where the length peaks at 6cm. The width does not have any correlation with the velocity however, as it peaks at Affpuddle B whereas the velocity peaks at Warren Road. From my results, it is possible to see a very slight correlation between the length and the velocity, but it is doubtful to see whether this is by chance or whether they have affected one another. My conclusion would be that the velocity of the river does not affect the size of the bed load. ?? ?? ?? ?? Edith MacLean ...read more.

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