Skills Investigation

Seite 1

Aim: to investigate if the Lightwater Stream at Carding Mill Valley, Shropshire displays the changes in channel characteristics downstream as outlined in the Bradshaw Model

Our Hypothesises:

Hydraulic Radius increases downstream

Channel Velocity increases downstream

Channel Gradient decreases downstream

Bedload becomes smaller and more rounded downstream

Hydraulic Radius Methodology

Take a and hold it across the width of the bank. Take a measurement from bank to bank in cm. Keep the tape measure in place and at every 5cm interval across the width take metre stick and measure the depth in mm. Repeat this every 5cm across the channel. Once this has been done, place the chain on the river bed up until the surface of the water. Place the chain on bank and measure the distance of it to find the wetted perimeter. A metre stick should be used in cm. Record results

Velocity Methodology

Take two range poles and put them 5m apart by using a tape measure to accurately measure this distance. Then drop a cork into the river at the range pole which is most upstream and simultaneously start the stop clock. When the cork reaches the second range pole stop the stop clock and collect the cork. Record results.

Gradient Methodology

Place two range poles 5m apart by using a tape measure. Take a clinometer and from a level point on the range pole point the clinometer at the same stripe on the other range pole. Pull the trigger on the range pole and release once the wheel stops spinning. Repeat this from the other range pole and record results.

Bed-load Methodology

Use random sampling to select 10 rocks from the river bed. For each of these measure the longest axis using a 30cm ruler. Record your result. Then decide on what category the rock falls into on our power scale: very angular, angular, sub angular, sub rounded, rounded, well rounded.

Results/Conclusions

In our investigation, velocity slightly increased shown by a weak positive correlation on spearman's rank, however by using degrees of freedom we found that there was a 5% chance that the it occurred by chance and so the hypothesis must be rejected- probably because we only investigated the upper/middle course. As distance downstream increased we found hydraulic radius in some cases increased - due to only investigating upper/middle course and lack of water in the stream due to dry weather conditions in August and September. The gradient in our study generally stays the same (UC investigation). However, National Trust say that the gradient of the light water stream does actually decrease but they only investigated 4 sites across Upper, Middle and Lower Course. Bedload did become smaller and more rounded with a weak positive correlation when using standard deviation with a dispersion of 19.2 showing a weak correlation which is therefore a rejected hypothesis.

Overall, the Lightwater Stream did not show the changing channel characteristics of the Bradshaw Model as all hypothesis had to be rejected as there was either no correlation or a weak positive one.

Evaluation

Low discharge due to dry weather in August and September - cork didn't flow efficiently and so, instead we could have used a flowmeter (also may not be deep enough). Velocity generally good method - except human error in starting stop clock

Grass overhang made it difficult to measure width.

Gradient, good accurate method

Random sampling often uses human subconsciousness to pick rocks and so should have used systematic sampling with a quadrat. Smoothness was personal judgement should have taken a vote within fieldwork group.

We only took samples in UC so should have investigated more sites with a larger spread between to see if it concurred with Bradshaw.

Risk Assessment

Tripping/Falling - wear suitable footwear, be careful where you step, free hand for balance

Drowning - keep away from deep water, be sensible in the stream

Hurting yourself or other with equipment - carry it sensibly and safely, point range poles to the ground

Ill from faeces - avoid touching your face, don't touch eyes (blind), wash your hands

Getting run over - be aware of vehicles on site