Blencathra fieldwork questions
Aim : To investigate and observe the downstream changes in the Glenderaterra Beck near the Blencathra Field Study Centre in the Lake District National Park. Hypothesis 1: as you go further downstream the higher the velocity will be as the higher capacity of the river will mean it has more energy so will travel faster and the channel will be wider and deeper leading to less friction and a higher hydraulic radius Hypothesis 2: As you go further downstream the bedload size will become smaller and rounder as attrition will have worn away the bedload making them decrease in size.
Hypothesis 1: As you go further downstream, more tribrituaries, precipitation and potentially snowmelt will increase the capacity of the river. This increased capacity will increase the energy of the river, further eroding the beds and banks of the river and increasing it’s cross sectional area. As the beds and banks will have eroded, they will be much smoother hence decreasing friction and increasing the river’s efficiency. Hypothesis 2: As stream order and distance downstream increase, the bedload found at these areas would be expected to be much rounder and smoother than bedload found upstream on an earlier stream order. This is due to the bedload further downstream being eroded over time, by processes of abrasion and attrition, which reduces the smoothness and size of the bedload. Upstream, the bedload in the channel is still large and angular because the river has had neither the time or the power to erode the bedload.
The selection of our sites allowed us to take samplings and observe downstream changes at 3 different locations down the river and at 3 different stream orders, the fact we took 5 sets of data from 3 different stream orders allowed us to observe the changes downstream using both stratified sampling ( 1st,2nd,3rd(X2 with one being further downstream) order streams) and systematic sampling (5 10meter intervals). We chose our sites in such a way that it allowed us to compare channel characteristics at different points in the river. Our choice of where to obtain data from was determined by health and safety and accessibility of the site. The sites we chose were close to the center and footpaths made it easy for us to carry our equipment b)
We could’ve used a random sampling method i.e. random number tables to plot the points along the river from which data was obtained . An advantage of our method was that we were able to look at a 1st, 2nd and 3rd order stream which best allowed us to obtain the data we needed to observe downstream change. c)
In order to calculate hydraulic radius at each site, it was necessary to measure channel width, average depth and wetted perimeter. Measurements were collected for both current and “bankfull” levels. Channel width was measured using a tape measure held taut across the channel. From the total distance (in metres), the width was divided into tenths and the depth in centimetres was measured using a metre rule at each of these points across the channel. An average depth was calculated from these measurements in order to account for the variation in depth. The wetted perimeter was measured by carefully laying a chain along the bed and banks of the channel. The length of the submerged section of the chain was then measured using the tape measure. Once we had all three measurements (width, average depth and wetted perimeter), we could then calculate the cross-sectional area and hydraulic radius for each of our 15 sites. Average velocity was measured at each site using a hydroprop and an impellor. Recordings were taken next to each bank and then at a quarter of the way, halfway and three quarters of the way across the channel. The impellor was held at 3/5 of the depth of the channel (point of fastest flow) and the time taken for the impellor to move from one end of the hydroprop to the other was recorded in seconds. The time taken...
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