River Investigation. Aim: To investigate downstream changes along Glenderaterra Beck

Transcription

1 River Investigation Aim: To investigate downstream changes along Glenderaterra Beck N Site 2 GR. NY Site 1 GR. NY Site 3 GR. NY Glenderaterra Beck is a tributary of the River Greta, found in the Northern part of the Lake District National Park in Cumbria. Course of River: Sinen Gill (source grid ref: NY , altitude 601m)- Glenderaterra Beck (confluence grid ref: NY , altitude 327m) - River Greta (confluence grid ref: NY , altitude 127m) - River Derwent Bassenthwaite Lake Catchment Area: Glenderaterra Beck 11Km² Drainage Density: 5.7 Geology: Skiddaw Slates, glacial moraine Climate: High levels of precipitation that vary widely throughout the valley due to the effects of orographic rainfall. Average yearly rainfall is around 1499mm. Average maximum temperature of 12.8 o C and an average minimum temperature of 6.0 o C (from centre records). Land Use: Predominantly grass moorland with areas of bog, heather moorland and small areas of woodland. Pasture used for sheep farming. More info on water quality, 1 km Learning objectives All students must: Describe how 3 characteristics change downstream Describe the aim and state 2 hypotheses Describe how data was collected to ensure accuracy for 1 hypothesis Most students should: Justify a statistical strategy for analysing data Explain the strengths and weaknesses of 3 methods of collecting data, and their sampling strategy Explain why cross sectional area and wetted perimeter are used to calculate the hydraulic radius Some students could: Explain the strengths and weaknesses of one means of representing data Justify to what extent the aim has been achieved

2 Rivers Calculations These are the calculations that the computers work out when collating the rivers data. Cross sectional area (m 2 ) = width x average depth Velocity (m/s) = Average time * This formula for velocity works only for the hydroprop used at this centre. Hydraulic radius = cross sectional area wetted perimeter Discharge (m 3 /s or CUMECS) = cross sectional area x velocity Mannings n = hydraulic radius 2/3 x slope 1/2 Velocity

3 Name of sampling strategy Method Justification of sampling strategy Limitations & improvements to sampling strategy Measurement (equipment) Method (how) Justification (why collect this data and why use this method) Limitations & improvements (problems & solutions) Wet width (tape measure) Wet depth (tape measure and metre stick) Velocity (Hydroprop and stop watch)

4 Measurement (equipment) Method (how) Justification (why collect this data and why use this method) Limitations & improvements (problems & solutions) Wetted perimeter (chain and tape measure) Gradient (clinometer and tape measure) Bedload size and shape (ruler and power s roundness index)

5 Spearman s Rank Correlation Coefficient Spearman s rank correlation coefficient is testing for a significant relationship between two variables. Null hypothesis: Alternative hypothesis: Write your independent variable data in the value x column, and the dependent variable data in the value y column. Then rank the two sets separately, the lowest value gets the lowest rank. Equal values get the same rank (calculate an average rank). D = the difference between the ranks = sum of (the total) x R y Obs (n) Value (x) Rank (R x ) Value (y) Rank (R y ) D (R x R y ) D Check that your rankings are correct; D should equal zero.

6 Spearman s Rank correlation coefficient is calculated by the following equation; R s = 1 - ( 6 D 2 n ) 3 -n D 2 = 6 D2 = n = n 3 = n 3 -n = R s = 1 - ( 6 D 2 ) 1 - ( ) R s = 1 - n 3 -n R s = To see if your result is significant you will need to compare your test value (R s ) with a table of critical values. We usually work to a 95% confidence level. This means that we are 95% confident that we have significant correlation. If your test value is equal to or greater than the critical value you can reject you null hypothesis. NB You do not need to worry about the +/- value. It is there to tell you the nature of the relationship (positive or negative) Confidence Level Number of pairs (n) 90% 95% 98% 99% R s = n = Confidence level = % Critical Value = Therefore we can accept / reject the null hypothesis Got any questions about your fieldwork? Ask at Facebook.com/blencathrafsc or