'How does the risk of flooding vary along the course of the River Eea?'

Site One was at Ayside Tarn (see fig. 2).  It was near the source of the River Eea.  It was very rural, with just one road running past and it was very hilly.  The rock type here is limestone.  The river was very small here set in a very steep valley.  This would mean a very rapid run-off from rain water as it would flow down the side of the valley very quickly because it would have very little time to be soaked into the soil or rocks underneath.  This could cause a risk of flooding, as the river may not be able to carry the increased capacity of water.  There were quite a lot of trees and vegetation so that would intercept the rain and the roots would absorb the moisture in the soil while keeping the soil together.  The land was covered in vegetation, mainly ferns, which would usually increase the lag time after periods of rain.

At this part of the river there was very few settlements, just a few farmhouses.  The land was used for agriculture on one side of the road, and on the other vegetation was left to grow.  There have been no attempts to manage this part of the river, as there is nothing here that is in need of flood protection.  The gradient of the river here is 9°.  The velocity, width and depth are in the following table:

Here is the channel profile for site 1:

The wetted area for this site is 0.14m2.  The wetted area is the area of the channel that is occupied by water.  This tells you the amount of water in the channel.  The wetted perimeter is how much of the bank is in contact with the water.  For this location it is 1.1m.  The hydraulic radius is calculated by dividing the wetted area by the wetted perimeter.  The higher the number, the more efficient the channel is.  Here it is 0.127.  You can work out discharge by multiplying the wetted area and velocity.  Here it is 3.08m3/sec

This table will take the main factors of flooding, score them on a scale of 1 – 5 and then find a score for site out of 25.  This will make it quite easy to compare the risk of flooding by just looking at the total score.

Site Two is at High Cark Bridge (see fig. 3).  The land here has been altered by man so it can be used for agriculture.  Farmer’s cattle graze on improved farmland.  The farming here is extensive rather than intensive meaning the land more land is needed to support fewer cattle or crops than in more fertile regions like the Southeast of England.  There are very few crops grown here, as the soil won’t support them.  Little vegetation grows here apart from along the river channel.  The river channel has been straightened and a wall has been either side of the river to channel the water and stop erosion of the farmland and to protect the farm houses.  It channels the water off the land quicker to prevent flooding.  This form of flood defence is low maintenance but doesn’t solve the problem of flooding, it just moves it further on downstream.  It looks natural as there is vegetation growing on each wall either side of the river.  Here, at High Cark Bridge, the river had a gradient of 4° and width, depth and velocity as follows:

*Here there was a large rock one metre across the river.  It stuck out of the water so here our reading for depth is 0cm.

        Here is the channel profile for site 2:

        

The wetted area for this site is 0.4m2.

For this site the wetted perimeter is 1.2m.

        The hydraulic radius here is 0.333.

        Discharge at this site is 7.84m3/sec

        

Cartmel Centre is Site three (see fig. 4).  Here the River Eea runs through the town of Cartmel.  This area is a large settlement; therefore it needs protecting from the risk of flooding.  There are lots of houses here along with a range of recreational activities including pubs, shops, playing fields and a horse racing track.  The river has been straightened and widened to increase the velocity of the river running through it, as it will then help prevent the flooding of Cartmel.  Small walls have been built on either side of the Eea to help cope with an increased volume of water running down it.  The land north and south of Cartmel is arable land used for growing crops. There is also some more improved grazing land just south of Cartmel.  The gradient at Cartmel Centre is 2°.  The width, depth and velocity of the River Eea is as follows:

The depths at the various intervals are all very similar because this part of the river as been almost completely man made.

        This is the channel profile for site 3:

        

The wetted area for this site is 1.7m2.

For this site the wetted perimeter is 1.1m.

        The hydraulic radius here is 1.545m

        This site has a discharge of 23.8m3/sec

Site four is at Cark farm, near the mouth of the River Eea (See Fig. 5).  The River Eea’s mouth is in Morecambe Bay.  The land here is residential and flooding could cause lots of damage to the shops or houses around this part of the River Eea.  A lot has been done here to help prevent flooding, the river has been straightened to increase the speed of the water flowing through it and high walls have been built either side of the river to try to stop it flooding.  A marker has been placed in the river so that the resident can tell when the river is about to burst its banks.   Each of the three houses along one side of the river has used a different form of flood prevention to try to protect their homes.  The first of the three houses has had high stone walls built around their garden to prevent the water from getting in.  This method doesn’t look too out of place the walls are built from local stone.  It is quite low maintenance, as the walls don’t need to be looked after very much, just repaired once in a while, as the stones will erode.  The second house has used metal flood/storm gates to keep the flood water out of the house.  These look slightly unattractive but are quite small so they don’t really stand out.  The flood/storm gates are high maintenance and need to be well looked after to prevent rust and gaps appearing in them.  The third and final house of the three has used a different method again, they have sand bags to stop the water coming through the doors, and they also have had their first floor windows built a lot higher than usual to keep the water out of the house.  This method will need no maintenance, the sand bags will just need replacing.  At Cark Farm the River Eea has a gradient of just 1°.  The width, depth and velocity of the river here are as follows:

This is the channel profile for site 4:

The wetted area for this site is 1.8m2.

For this site the wetted perimeter is 1.3m.

        The hydraulic radius is 1.823m

        For this site discharge is 13.14m3/sec

        

From studying these four sites I have seen that the extent of flooding along the River Eea greatly varies at each of the four different sites.  This is shown by a high total score near the source of the river, and low ones near the mouth.  Graph 4 illustrates this.  Near the source the potential for flooding is high because a lot of rain over a very short time may be too much for the river to contain near the source, as it is still very small there.  This may mean that the river will end up flooding.  But near the source there is nothing apart from rough grazing or improved grazing around this part of the river.  At site two a lot has been done to reduce the risk of flooding, the farmers here are trying to protect their farmland so the river channel has been almost completely man made.  Depending on the factors of flooding that you choose to look at, the risk of flooding will vary greatly.  From Graph 1 you can see that the velocity decreases as it gets further from the source, which would increase the risk of flooding near the mouth.  Graph 2 shows that the further from the source of the river, the more efficient the channel becomes.  This could cause flooding near the source.  Discharge changes all the time along the course of the river.  From Graph 3 you can see that discharge tends to increase nearer to the mouth of the river.  This is due to smaller rivers or steams, tributaries, join the river.  So by combining all these factors you will be able to get an overview of where the risk of flooding is greatest, Graph 4.

After combing these factors and drawing a graph of the total scores I can see that as you get further from the source, the risk of flooding is reduced.

        There were a few limitations that I have come across while carrying out my investigation.  These included:

• The level of accuracy, as the results that I got may not have been very accurate.  For example, when measuring the gradient, I used a clinometer.  This was to be accurate to 1°, and only if you had a steady hand and something or someone the same height as you to aim it at.  
• It was also difficult to get an accurate reading on the velocity as the velocity of the river changed throughout the width of it.  
• The reliability of the scoring system, as it may not of been constant for each site as there was no set value to compare them with and it did not include every factor that could contribute to flooding.
• Other factors that could cause flooding, there are other factors such as the geology of the land and the amount of vegetation etc, that I have not collected which could alter my investigation.

To try to improve my investigation I could of visited more than four sites.  This would then allow me to take more readings.  Or if given more time I could visit more than just the one river.  I would then be able to see if this pattern was just a one-off, or if it is the same for most rivers.  This piece of work only looked at one river system out of hundreds around Great Britain, although they all have similarities between them all, each one will be individual and have different qualities.