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Coastal Management Study - Swanage

Day two of our geography fieldtrip to Dorset
by

Harriet Clark

on 24 April 2014

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Transcript of Coastal Management Study - Swanage

Background photo by t.shigesa
Data presentation
Methodology
Swanage
Beach profile
land use
We wanted to find out what coastal management is in place at Swanage Bay and why.

To answer this we will look at three hypotheses that are:
1. Longshore drift occurs in Swanage Bay
2. Land value in Swanage affects the choice of management scheme of the coastline
3. Beach nourishment is an effective form of coastal defence in Swanage Bay

Swanage Bay Coastal Management Objectives:
•Protect the economic viability of Swanage
•Protect the core values and character of the centre of Swanage
•Reduce flood risk to Swanage
•Maintain beach widths and beach use
•Manage risk to properties due to erosion and flooding where sustainable
•Maintain geological exposures in relation to World Heritage Site and SSSI status
•Maintain the outstanding landscape and the views and appreciation of the varied coastal environment
•Support adaptability of coastal communities
•Reduce reliance on defences

We will have to do beach profiles and field sketches at each of the three sites, and we will have to do a groyne profile of 4 groynes at the third location, Shep's Hollow. We also will have to do a land use map of Swanage finding out what the land is specifically used for.
Coastal Management study
Sub aerial processes - a process which contributes to cliff erosion. They are natural weathering processes such as the wind and rain.
Terminal groyne - Is the end groyne of a series of groynes.
Terminal groyne syndrome - This is the starvation of the beach after the terminal groyne. The beach becomes more vulnerable to the waves and erosion.
Key words
Groyne profile
Photo annotation
Land use mapping
Field sketching
At 3 locations along the Swanage coast, we completed a beach profile. To complete this beach profile we first had to take a tape measure and use it to measure the width of the beach in metres, this meant the distance from the shoreline to wither the sea wall or the cliff face. We then stuck one ranging pole at the shoreline end of the tape measure and the second ranging pole at the first pole along the tape measure at which we thought the gradient of the beach had changed, we then use a clinometer to measure the depth change between the two poles. This meant we had to line the clinometer up with the point where the top red and white bands meets, looking through the clinometer in order to look at the same point on the second pole, however this time you HAVE to record the angle to the right inside the clinometer in degrees in order to calculate the change in the gradient of the sand.
To complete a groyne profile we first had to take a tape measure and use it to measure the width of the beach in metres, this meant the distance from the last groyne spine to the sea. We then took the ranging pole and dug it into the ground just before each of the spines of each of the 4 different groynes. Using the pole in this position, using the metre rule we measured the height of the highest horizontal timber plank and recorded the data.
For this we had an aerial photo of the area of Swanage and were asked to label anything that we felt was geologically important and could be a reason for why the Swanage council would build groynes and sea walls, e.g. tourist attractions and high wealth homes.
We also drew a dotted line as a prediction of where we felt the shoreline would be in 20 years if there was a do nothing approach to the coastline.
For this we printed out a sheet showing the local town Swanage divided up into equal sized squares. We then created a key, giving each type of land use a letter (for example residential – owned, was A), this letter was also marked with a number from 1 to 4 (1 meaning the area had no tourism influence, where as 4 meant the area was heavily based around tourism). To complete the land use map, we had to walk through each square on the map and decide what was the dominant land use and then write down the letter and it’s number according to the key.
At 3 locations along the Swanage coast we stopped to take a quick sketch, this involved having to quickly sketch all of the land use that we felt was geographically important e.g. car parks, Peveril Point, tourist rides, sea wall, groynes, cliffs and the beach to name a few.
Groyne profile
Beach profile
Location 1 – Southern end of Swanage beach, hold the line but minimum approach. The only hard engineering along this area is a sea wall. The reason for this is the existence of a natural defence – Peveril point.
Location 2 – Swanage bay, hold the line with an active approach. The reason for this approach is because of the high value residential land, as well as a major road behind the defences, if not defended the loss of this land will cause extreme disruption. The physical processes also mean this area is more susceptible to erosion. Long shore drift and easterly blowing storms are causing the loss of sediment from the bay.
Location 3 – Shep’s hollow, no active intervention. The reasons for this is the area behind is low value farmland, the area is belonging to the national trust and this area is part of the Jurassic coastline. The Jurassic coastline is geological important, the fossils themselves are higher value than the land they are embedded in.
We found from the field sketch of site three that where the cliffs have slipped due to recent mass movement or rain/flooding there is no vegetation growing on these areas so we can tell that they have slipped recently. We also found out that the cliff at this section of coast consists of chalk which is a form of hard rock and sandstones/clays which are forms of soft rock. The longshore drift is moving sediment to the north and the last groyne (terminal groyne) is in this area which leads to terminal groyne syndrome past the last groyne.
The groyne profiles showed that they are doing their job; reducing the movement of sand and keeping a nice beach but sub aerial processes are still affecting these areas such as rain causing slumps of parts of the cliff.
It could be seen that the management techniques that have be put into place are relatively effective because they have helped to reduce the rate of erosion but the area is still being affected and eroded by sub aerial processes e.g. rain and wind.
We found what type of management scheme has been put into place at each of the three sites, site one being under hold the line (minimum defences) which only had a sea wall, site two also being under hold the line (more defences) which had groynes, a sea wall and replenishment of sediment, and site three being under do nothing (no active intervention). We found out that site two had the most defences because it was a residential area that if wasn’t protected from coastal erosion could result in houses/gardens becoming swallowed by the sea. We found out that site three was do nothing (no active intervention) because it is low value farm land that is mainly owned by the National Trust (land ownership) and that as it is a section of the Jurassic coast geologically important fossils are found in the cliffs and are of higher value than the land it sits in.
Conclusion
We found out from the aerial pictures and the field sketches that we drew ourselves that perveril point acts as a natural defence against easterly storms and therefore protects site one, Swanage Bay. We also found that the sea wall is built up in front of the tourist attractions to protect the building e.g. arcade from erosion and flooding. This is good because the tourist area attracts the most amount of income from people visiting.
We can also see from the field sketch of site two that the area needs more protection against flooding and erosion as it has main infrastructure such as main roads that if damaged or destroyed could cause mass disruption. The field sketch of site two shows us that there was a through-flow gate allowing longshore drift but that also reduces flooding in the area. We also found out that this section of the beach had been replenished with sediment dredged from the Poole Harbour. There was no natural defence against storms in this section of the coast/beach but there were three types of human defences, these were beach nourishment/replenishment, timber groynes and the through-flow gate. We found that there was more because it is a residential area that includes houses/flats, arcades, shops, restaurants and Swanage beach gardens.
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