This project will study the transition of the River Conwy as it flows downstream. It will concentrate on the following variables:
* Water Width
* Wetted Perimeter
* Flow Velocity
* Float Velocity
* Stone Roundness
* Stone Size
Another variable we could have measured is the pH value of the water in the river. This would have detected pollution levels as it goes downstream.
These 8 variables will provide us with the sufficient information.
The aims of the project are:
1. To investigate changes in the channel form and river processes at different sites downstream on the River Conwy.
2. To identify landforms associated with river processes
The following hypotheses were tested:
1. Downstream, the width will increase.
2. Downstream, the depth will increase
3. Downstream, the velocity will decrease
4. Downstream, the cross sectional area will increase
5. Downstream, the discharge will increase
6. Downstream, the gradient will decrease
7. Downstream, the wetted perimeter will increase
8. Downstream, the bed load size will decrease
9. Downstream, the bed load roundness will increase.
Site 1- (Nant-y-Brwyn) Ref- 792 450
Nant-y-Brwyn was the site highest above sea level and therefore the nearest to the source, which we studied. This site shows examples of interlocking spurs, a V-shaped valley and impermeable slates and quartz. The site is a tributary to the river Conwy. The rocks were impermeable and had a covering of peat, so there is no infiltration and the ground is flashy. The peat is saturated as high rainfall levels and cold conditions mean there is neither very little evaporation nor decaying here. The V-shaped valley is a result of vertical erosion. Here there is rough grazing for sheep, with natural vegetation of grass and moss. Trees would be too exposed to exist in this area.
Site 2 – Meanders (792 446)
The meander site is the second nearest to the source. It consists of consecutive meanders. The meander we studied and observed had a slip off slope that consisted mostly of slate rocks and quartz. This meander had a wide, flat valley that shows us that there is no vertical erosion and only lateral erosion evident. This is unusual for this type of location, and is due to solifluction. Solifluction begins in the ice age where the soil freezes, then later melts and slumps into a valley and it becomes shallow and so meanders form. There is turbulence in the water as the pools and riffles show. Still based in Upper Conwy, the vegetation is still mosses and grass with the addition of cotton grass because of the saturated peat.
Site 3- Ysbyty Ifan (842 488)
Ysbyty Ifan is a small village and was the lowest site downstream safe to measure but was the uppermost village on the Conwy. There is a large bridge on this site that creates an obstruction for the water and slows the river flow down. It slows it down enough for deposition to take place upstream from the bridge. This results in the river here being less efficient, and so flooding has a larger chance of occurring. Therefore flood defences have been inserted to protect the neighboring village.
First of all we:
1. Chose a 10 metre stretch of the river to work on.
2. Put ranging poles at ends
3. Mark out the halfway point (5 metres)
1. At the 5 metre point measure the width of the water surface in metres and record the results.
1. Undercut banks can cause problems
2. The velocity pulls the tape
3. Obstructions can get in the way
We did the width on each site to see if it gets bigger or smaller. If it gets bigger we know that there is more water in the river, and if this changes downstream.
1. With the width measurement, divide that measurement into 5 equal parts.
2. On these new 5 measurements, measure the depth of the river with a metre stick.
3. Record the results
1. Stones and rocks on the riverbed can make it hard to find the bottom and find the true result.
We do the depth to see if the river holds more water as it goes downstream. We also record this as it is a good variable and is liable to change.
1. On the 5 metre point of your 10 metre stretch, you must take a large chain and go to the other side of the river.
2. Place the chain’s end where the water meets the bank, but do not keep the chain tight. It must touch the bottom and sides of the riverbed and may go round obstacles.
3. When this is done, hold the end of the chain that has been in the water and measure it
4. Record the results.
1. Trying to keep the chain as straight as possible whilst keeping it in every curve on the riverbed.
2. The length of the wetted can be a problem if the chain is not long enough, or if the river is too wide.
Wetted perimeter is done so that a hydraulic radius can be found. This is a very good variable and changes during the course of the river.
1. On the 10 metre poles two people must hold a pole each on the surface of the water.
2. One person has an instrument that measures the angle of the gradient
3. Find a point on the pole that is in the same place on the other pole and measure the angle from that point to the other point.
1. Making sure your view is squared to the other post
2. Making sure the post is on the water surface
The gradient is important to measure because if the angle is higher upstream than it is downstream then there will be other changes downstream and that is what we are looking for.
1. One person must have a stopwatch, another must throw in the float and another must catch the float.
2. On the ends on the 10 metre segment a cork must be thrown.(From upstream to downstream)
3. The person catching the float must be downstream.
4. Once the float is thrown and reaches the first post the stopwatch must be started.
5. When the float reaches the other post downstream the stop watch must be stopped
6. Record the time
1. Cork gets stuck/ caught by certain obstructions
2. Wind can slow it down
This is done to find out how fast the water is travelling on the water surface, and is a good variable as this may change a lot. You can also reach an average if you do the method a few times.
1. On the points you used to measure the depth do the same thing for this except don’t measure the depth, put in a flowmeter two thirds into the water.
2. When the stopwatch starts, start the flowmeter
3. When 30 seconds is up stop the flowmeter
4. Record the data
1. Sometimes the instrument didn’t spin due to obstacles etc
This is done to measure how fast the water is moving under the surface of the water.
1. Use 30 random numbers between 0 metres and 10 metres
2. For each number go to the specific point, point your finger and put your finger onto the seabed.
3. The stone the finger touches must be picked up
4. The size and roundness must be recorded
1. You only choose a very small sample from what the river really holds
2. Some stones had two long sides.
3. It is never a definite reading because the angular opinion is subjective.
This must be done to see how each of the stones change in relation to each other at the different sites.
As seen on the graph the width changes from 2.6 metres at site 1 to 11.6 metres at site 3.This is because the channel has to become larger to accommodate the increased amount of water coming in from:
b) Ground water
The channel becomes wider as the increasing volume of water erodes more efficiently and effectively.
The depth increases a greater volume of water needs to be held. At site 3 the depth is larger upstream than it is downstream. This is due to the bridge. The water has to slow down to get through the narrow bridge. After going so slow through the bridge the river deposites its load causing deposition.
The speed increases in the water because there s less friction because attrition is breaking up the bed load to make smaller rocks which are smoother and there are less boulders.
This decreased which on other experiments had increased. This may have been a human error or may have been obstructed
Cross Sectional Area:
This gets bigger because the depth and width have increased to accommodate the increased amount of discharge and load.
This increases as the sides of the channels get bigger.
From the results we can see that the gradient has decreased. The profile of the Conwy River tells us this:
1. It starts off in the mountains
2. Vertical erosion upstream
3. Lateral erosion nearer the sea
The stone size gets smaller as we can see from the results. Except at site 3, in which the stones get bigger, because of the bridge slowing down the river and causing deposition.
We can tell this increase because the banks are wider and there is more water in the channel.
This is the relationship between the wetted perimeter and the cross sectional area. It’s a measurement of efficiency as the smaller the number of the hydraulic radius is, the more friction takes place and so is less efficient. The river gets more efficient.
Was my hypotheses right?
The R.Conwy is a very interesting river and I a river that I am glad to have done my project on. It contains many features during its course such as:
. Ox bow lake
. Interlocking spurs
. Slip off slope
. V-shaped valleys
. Pools and riffles
. Tributaries and many others
The climate change is also worth mentioning; on the 1st two sites the environment was moist, cold and wet as you get more downstream to site 3 the environment is much less wet and cold and the ground is not as saturated.
I feel that our fieldwork on this project has been a success but has been limited in some ways like our equipment. There is equipment that is of a higher quality than the equipment that we used.
We also were limited to the amount of experiments and readings we can carry out on the river.
We were limited to the amount of sites we went to due to health and safety reasons.
We were limited to how many times we saw the river. We only saw a snapshot of the river.
We could have improved the results by:
1. Going back every season to see if there are any key changes that have taken place.
2. Having more sites downstream
3. We could have made more measurements using a different set of equipment such as measuring the gradient with a dumpy level.
4. Take the pH reading of the river, this would have told us the pollution level of the water in the river.
5. We could have checked the river life with indicators such as small animals/insects that can only survive in very clean water, or can survive in all waters.
6. We also may have compared the Conwy to another river; perhaps the Roding would have been good as it is near and will be interesting to see how the different rocks and the different climate will affect the river.
My skills learnt:
I think my skills have developed enormously after going to the Conwy sites. I am now much more precise with my readings and my teamwork skills are much more effective now. I can now carry out an experiment on a river and will be confident that my results would be accurate.