UWE lectures

I realise that many of you were not as fornuate as me and able to attend the two sessions yesterday afternoon run by two lecturers from UWE and, because they were so good, I thought I would share with you some of the things that were discussed.......

Climate Change and River Management:

What is climate change?
Before you can understand the impacts climate change is expected to have on rivers, a basic understanding of what climate change is, is required. Climate change refers to any long-term change in the statistical distribution of weather patterns over periods of time that can range from decades to millions of years; although it is most commonly used in reference to the increase in the average surface temperature of the earth over the recent decades and that which is predicted in the foreseeable future. Much of the work on climate change and its impacts on rivers is based on estimates as it is very hard to predict the future climate as it is dependent on a wide variety of things - although most importantly carbon dioxide emissions. Despite this uncertainity, central estimates have been produced for  changes that are expected to occur within the UK, within the next 30 years.....

• Increase in  the average summer temperatures of 3-5 degrees Celcius
• 10-30% increase in the average levels of precipitation experienced during the winter

There will be spatial variations though, from these intermediate values. For example, some areas of the UK are likely to experience a decrease in the mean winter precipitation level whilst others are expected to experience a 50% increase.

What is River Management?
River management is any action that includes intentional intervention by humans into the way that river systems funtion. This includes:
- Managing the quantity of water flowing through the channel ---> flooding, droughts, freshwater supply, reservoirs and flow regime modification
- Managing the stability of river channels ---> rivers are unstable and constantly change due to the processes of erosion and deposition and this threatens to cause major, and very costly damage, to infrastructure
- Managing water quality ---> pollution from littering, industry, sewage, sediment and agriculture (eutrophication)
- Managing the physical quality of the river ---> management of ecosystems to maintain and maximise biodiversity

Although managing water quality and biodiversity etc are considered when it comes to river management, its primary aim is to reduce the flood risk. Reducing the flood risk is a big problem for England and Wales as around 4 million people and £200 billion worth of infrastructure are a risk of flooding. At present, even though we spend roughly £800 milliom per year on flood and coastal defences, we experience £1,400 million of damage. Worryingly, this is the damage caused and the costs associated with current sea levels, temperatures and precipitation levels and so the impacts of climate change are likely to provoke a sharp increase in those at risk and the costs involved with reacting to the risks. It has been estimated that, due to the expected increase in the recurrence and magnitude of floods, that the costs of damage done by them could rise from £1,400 million a year to anything up to £20,500 million over the next 70 years if no further action is taken.

So, how is climate change likely to affect the flood risk........
Flood risk is the balance between the conveyance capacity and the amount of water that is actually trying to move through the channel and it is this balance that climate change threatens to disrupt, thereby increasing the flood risk.

Conveyance capacity is, in very simple terms, the amount of water that can fit in the channel and so when this level is exceeded by the actual amount of water trying to fit in the channel, flooding occurs. Due to increased precipitation levels, climate change is predicted to increase the flow. This means that there is more water trying to pass through the river and so a higher probability that this volume will exceed conveyance capacity and therefore result in flooding. A study carried out on a small section of the River Wharfe in Yorkshire, which was based on this idea, concluded that increased flows by 2050, provoked by climate change, would result in a 12.2% rise in the area flooded by a 1 in 0.5 year return flood.   

An increase in flow would provoke an increase in sediment and the relationship between the two can be descirbed as being non - linear (for exmaple, in the River Eden, in Cumbria, an increase of 4.2% in precipitation would lead to a 90% increase in the amount of sediment transported). The amount of sediment within a river is further being increased by urbanization. Although urbanization means that there is less bare surfaces, like soil, for sediment to be sourced from; because urbanization produces flashier rivers, as the increase in impermeable surfaces means the water enters the channel quicker; when the water reaches the channel it has more energy and so a greater erosive ability - which results in excess erosion and so therefore more sediment in the river. This decreases the conveyance capacity of the river and so the volume of water that can flow through the channel, before it reaches and exceeds bankfull capacity, is reduced. This relationship between sediment and flow was also tested on the River Wharfe and it concluded that a reduction in the size of the channel, caused by sediment deposition over two years would increase the flood risk by 5.7%.

Rivers are not stable and constantly change which makes it increasingly hard to make predictions in sediment dynamics and how rivers will change in the future due to climate change. To aid the development of rough predictions, cellular catchment evolution models have been created, like CAESAR (Cellular Automaton Evolutionary Slope and River model). CAESAR works by dividing drainage basins into 10m by 10m grid cells and then uses the height above base level and basic information on the river channel and whether or not one is present, to generate a virtual model of the landscape.  CAESAR can then simulate the morphological changes in river catchments, on a flood by flood basis, over periods up to several thousands of years. This was used on the River Eden and clearly showed that the predicted increase in flows would increase the sediment yield and this would directly increase the amount of sediment deposited thereby result in a significant increase in the flood risk. So, for example, for the town of the Carlise this means that increased deposition reduces the conveyance capacity and so increases the flood risk.

Climate change will also affect rivers in other ways too:

• More fine sediment will be depoisted in the river beds and thereby smother the natural environment used by fish for spawning
• Increased sediment flow will block out the sunlight and lead to the death of many organisms
• Increase in water temperatures will reduce the concentration of dissolved oxygen in the water and so will kill of many organisms. Also, the warmer conditions will encourage the growth of tropical species which will result in many of our native species being outcompeted

All of this just takes into account the impacts of climate change on rivers, but urbanization too, imparticular with reference to landuse change, will alter the flows into a river. As populations continue to grow this is going to become more of an issue - especially in areas like Bangladesh whose flood risk is affected by the deforestation in Nepal for fuelwood or in areas like India who are likely to see rapid urbanization over the coming decades.

There are solutions to these problems that we are likely to face, like strategic tree planting in the form of tree belts which can be planted to specific places in drainage basins to trap sediment, increase the interception store and therefore reduce the amount of water entering channel and increase the time taken for water to enter the channel. This example of soft engineering is very sustainable as it will continue to work even if climate change provokes increases in flows into a river.

So, in conclusion, climate change is likely to increase the flood risk by increasing the flow and thereby the sediment yield of the river whilst causing degradation of the physical habitat and water quality. This means that more needs to be done, and perhaps a different approach taken, to try and reduce the flood risk - so, if you are interested in a career related to river management and flood control there are likely to be lots of available jobs, in this field, in the near future!

Coastal Management in Bridgewater Bay:

What is the coast?
The coast is the region of mutual interaction between terrestial and marine environments and is extremely valuable in terms of as a defence, a habitat and a resource (industry and tourism). 50% of the worlds population live within 2km of the coast mainly due to the above reasons, its historical importance, for trade, climate, food and the flat and fertile land associated with it and so coasts are therefore important to manage and with rising sea levels and growing populations, the need to do so is only increasing.

Sea level rise is not a new thing though and has happened throughout history......

• 18,000 years ago the last glacier was at its maximum extent and so sea level was 140m lower than at present
• Initially the melting of the ice was rapid and so sea level rose rapidly but it gradually started to slow
• 4000 years ago sea level reached its present day level

This melting of ice has had significant impacts on coastal processes and landforms but its hasnt been until recently that people are becoming increasingly concerned by centimetre rises in sea level - why is this? Perhaps the biggest reason is us ourselves. People are now living closer and closer to the coast and as populations grow further in the developing world, more and more are going to be forced to live on marginal lands. Also, the building of infrastructure has restricted the migration of landforms in response to changes in sea level and therefore reduced the development of natural defences like salt marshes and sand dunes.

In terms of the South West, we are very prone to coastal flooding as much of the land lies below sea level already (and I think, that this area will increase not only due to rise in sea level but also isostatic readjustment in Scotland which is causing this part of the world to sink slightly). This means that coastal management is required to ensure that those living here are protected.

The question; would you rather live behind a sea wall or a sand dunes system was asked - you can make your own mind up on which you would prefer - but the class I was in was split. Many said that they would rather be protected by a sea wall but were they wrong........

Firstly, lets go over the basics of sand dunes and beaches. Beaches and dunes are linked and wind energy can modify beaches to create specific landforms like sand dunes which are created by aeolian sediment transport.
Different factors are required for the formation of sand dunes including:

• an area to accomodate them
• vegetation
• onshore winds
• sediment supply
• shallow sloping beach
• high tidal range

The sediment needed for dunes is transported via saltation which is when the sand is picked up and moved forward by the wind and then pushed further back by the land. This sand is transported from the intertidal zone unitl the saltating sediment reaches the back of the beach.

Sand dunes are such a good coastal defence as, unlike a sea wall, they are not a static sea defence (although due to human influences provoking coastal squeeze they are being forced to be more static than they would like) and so change to new conditions. New such conditions can occur due to storm surges. Storm surges are generated by tropical storms as the low pressure system and winds associated with them, provoke a large, but temporary, rise in sea level. This is why they have the capacity to cause extensive flooding over coastal lowlands. The average storm surge in the UK, adds an additional 1.45metres in height to that of the high tide and therefore much of the UK, especially around this part of the country, is suseptible to flooding. If you then factor in the possilbe impacts of climate change on sea levels and the frequency and severity of storms, this is likely to become more and more of a prominant issue in the not too distant future.

In relation to sea level rise, the IPCC predict a :-

• 0.10m - 0.30m rise by 2030
• 0.50m rise by 2050

In terms of protecting against storm surges, sea walls will be able to cope to a certain extent, but it is both too costly, unsightly and unsustainable to keep raising the height of sea walls to keep up with rising sea levels. Sea walls are clearly a static form of defence that cannot adapt to changing conditions but beaches can - which is one of the reasons they can form such a good, natural, sea defence. Beaches can change shape in response to changing conditions and so do sand dunes. Beaches will adjust to accomodate for larger than normal waves. High energy conditions flatten the beach and so give it a dissipative profile that provokes waves to break earlier and disperses their energy. This means that less of the waves intitial energy reaches the back of the beach and so its erosive ability is reduced. High energy conditions do not last forever and so beaches and sand dunes, during low energy conditions, are able to rebuild and readjust themselves. This process involves the increase in the onshore transportation of sediment which causes the beach to build up and adopt a reflective profile. 

Beaches and sand dunes, imparticular, are crucial for the protection of the of coasts over the next 100 years and are by far the most sustainable option. Not only do they cost alot less than many hard engineering options, they create rare and vital habitats that provide a home for a diverse range of species, both plants and animals, but they are also, and perhaps most importantly, able to adapt to changes in conditions that we are going to face in the not too distant future. The development of dune systems sometimes needs a helping hand. For example, in Bridgewater Bay, the beach is becoming very muddy and consists of very fine grain which is not ideal for sand dunes and so beach nourishment is required to feed the dunes. However this is significantly less costly than building a huge sea wall. What option for coastal management further in the future than the next 100 years is best is unclear. Urbanization, the encroachment of developments onto the coastline and our attempts to fix sand dunes into there location means that sand dunes will not offer a sustainable and effective coastal defence option for ever. Depsite the fact that they can adapt to changes in the energy levels and height of the sea/waves, they are unable to adapt to us changing surfaces and restricting their movement. Coastal squeeze is one of the largest threats to sand dunes and their development as the building of housing developments and sea walls etc is preventing sand dunes from migrating, which allows them to adapt to new conditions. Instead anthropogenic influences on the sand dunes have the potential to turn the dunes into an almost static form of defence which threatens to halt their development and lead to their destruction. This is why land use management is more crucial than ever (this implies to rivers aswell). With the risks of coastal flooding and extensive erosion being so high, is it really a good idea to be building new developments right along the coast or by waterways. For example, think about Hinkley Point.........

............ with the predicted rises in sea levels generating a higher flood risk; is it really a good idea to further develop nuclear power here??? This is of course not the only example....... people love to live on floodplains or near the coasts which are the areas most prone to flooding and not only does this increase and worsen the secondary impacts of flooding but it also increases the chance of flooding happening in the first place. Therefore, in the near future, greater consideration into landuse management is going to be needed to help reduce the risks of coastal flooding.

So, in conclusion, opting for natural sea defences like sand dunes are by far the most sustainable option in the near future as they are able to adapt and cope with changing conditions but this approach needs to be accompanied by landuse management to further reduce the risk of flooding and lengthen the time for which sand dune systems can offer a sustainable and effective method of managing and reducing the risk of coastal flooding.

This is just a summary of what we got taught and so only really covers the basics and is no way near as good as actually participating in the lectures yourself - but unfortunately many of you were unable to attend and so you will have to put up with my explanation instead..........

I hope the revision is going well - if there is anything I can do to help, via this blog, please don't be afraid ask. I have had lots of requests surrounding the topic of rejuvenation in rivers and, as it is a tricky topic which took me a long time to get my head around, I am going to try and write a summary post about either later tonight or tomorrow...........

Buoyant Bangladesh

Do you read National Geographic? Well, if you don't, I would strongly recommed that you do but if you struggle to find the time, I definetly recommend you read the latest article in the year long special series, 7 billion people as it links very closely to not only the population module but also the last section of the coasts module, rising sea levels, that we finished off last week.

http://ngm.nationalgeographic.com/2011/05/bangladesh/belt-text

Bangladesh is one of the most densely populated countries in the world and is 'a place where one person, in a nation of 164 million, is mathematically incapable of being truly alone'. Despite a sharp drop in it's CBR, the population is expected to grow to 220 million by 2050 and, due to trends in sea level, much of the landmass would be permanently underwater - further increasing the population density of this region. Sea level rise is not just something that will affect those in poor, low lying countries like Bangladesh as more than a third of the worlds population live within 62 miles of the sea. It has been predicted that by 2100 there could be as many as 250 climate refugees (related http://geography-student.blogspot.com/2011/02/do-developed-countries-have-moral.html), the majority of which displaced by rising sea levels and as many as 30 million coming from the coast of Bangladesh.

Click on the link to see the full interactive version

Where are these people supposed to go? That is a question being asked by many at present............. India is building a six foot barrier of barbed wire and concrete along its 2,500 mile border with Bangladesh to prevent immigration from Bangladesh. With this option being taking away from those displaced by the encroaching sea, many choose to move to the urban areas further inland which is causing huge problems for cities like the capital Dhaka. It has been predicted that by 2030, 41% of the population will live in urban areas with only 52% having access to sanitation. This predicted scenairo is the perfect breeding ground for disease and crime and would further hold back Bangladesh's development.

However, climate change not only threatens the coast but also the inland communties as, like neighbouring India, the main rivers in Bangladesh are fed by the Tibetan Plateau snowfall and the monsoon rains - both of which have been disrupted by changes to the climate. Although some may consider monsoons to hamper economic progress, my personal experience of them in India made me realise how much people rely on them and plan their year around then - even right down to day to day lives. When I was in India the monsoon arrived late (although when it did finally appear, its presence was definetly felt!) and this uncertainity to when it was going to arrive caused a lot of distruption and worry to the local people who explained that, over recent years the timing of the monsoons has never been as predicted. Adapting to these changes is not easy but, in Bangladesh, many new ideas have been implemented to help people cope with the rising sea levels. These include altering farming practices to enable them to farm on floating gardens and therefore still grow the crops required to survive. Many farmers have totally altered what they grow. Rising sea levels have increased the salinity of farm land and rivers to such levels that rice can't grow, whilst other fields remain flooded for most of the year. Therefore many farmers have changed from growing rice to growing crabs and shrimps in the ponds that have been created and then vegetables on the embankments. Solar-powered school boats have also been introduced so that kids can attend schools even if it floods whilst limiting the potential damage to infrastruture.

So, can the developed world learn from anything from Bangladesh? The attitude that many of the Bangladesh people share towards the problems they face is admirable - they don't complain but just shape their lives around the frequently changing conditions, with many saying they have moved more than 40 times within their life times. I am unsure if as many people in the developed world would be as resilient as many of those affected in Bangladesh have been. They have utilised their limited resources to the best of their ability but this problem is not likely to go away. In the near future, it is likely that Bangladesh will recieve more international aid to help it deal with the effects of climate change because due to the target set, by the developed nations in the Copenhagen conference of 2009, to provide $100 billion a year by 2020 for poor countries who face many problems which they played only a minimal role in creating. However, this is clearly not an problem that can be remedied by money.

Before I end up re-writing the whole article in my own words I had better stop - I have just picked out the main points but the article is honestly a really good thing to read as part of your revision. Although this is after our summer exam keep your eyes open for the July article related to this series which will discuss what it will take to feed 9 billion people in 2045.



Coastal landforms

There are many different landforms that are present along our coastline and they are all formed in slightly different ways and, as there are quite a few different ones, I am going to try and summarise the key points for each.

HEADLANDS AND BAYS:
- They form in areas of alternating resistant and less resistant rocks. The less resistant rocks, such as sand and clay, erode a lot faster than the more resistant rocks, like chalk, and  this differential erosion often results in sections of land jutting out into the sea, known as headlands. Due to refraction, the headlands recieve the highest energy waves and are most vulnerable to the forces of erosion. The shallower areas around the headland provoke the waves to start to break earlier and so, as they refract around the headland, lower energy waves are experienced in the bays which leads to the accumulation of sediment.

- Coastlines can either be described as being concordant or discordant. In concordant coastlines the alternating stratas of soft and hard rock run parallel to the coastline whereas in discordant coastlines they run perpendicular to the coastline. Where the rocks run parallel with the coast (concordant) it is possible for continued erosion to break through the more resistant rocks on the coast and begin to attack the less resistant rock strata behind. When this occurs a cave is formed which is then only enlarged by further erosion - Lulworth Cove is possibly the best local example of this.

WAVE CUT NOTCHES AND PLATFORMS:
- When high and steep waves break at the foot of a cliff they concentrate their erosive capabilities into only a smaal area of the rock face, This concentration eventually leads to the cliff being undercut, forming a wave cut notch. Contiuned activity at this point increases the stress on the cliff and after some time, it collapses. This causes the cliff to retreat and when the overhang is undercut a platform forms. The platform continues to grow and, as it does, the waves break further out to sea and have to travel across more of the platform before reaching the cliff. This leads to greater dissipatation of wave energy which reduces the rate of erosion on the headland and thereby slowing down the growth of the platform.
- Hydraulic action and abraision, accompanied by water layer weathering and some of the other weathering processes, lead to the formation of wave cut notches and platforms.

So in short......
1) Weathering weakens the top of the cliff
2)The sea attacks the base of the cliff, forming a wave cut notch
3) The notch increases in size, causing the cliff to retreat
4) The backwash carries the rubble towards the sea, forming a wave cut platform
5) The process repeats and the cliff continues to retreat

CAVES, ARCHES, STACKS,STUMPS, BLOWHOLES AND GEOS:
- If the cliff is undercut a cave can be formed, usually from a combination of marine processes including hydraulic action, abraison and solution. If erosion continues upwards, it is possible for the cave to be extended to the top of the cliff where a blowhole will form. If the cave extends backwards, to meet another, an arch will form. As the dliff retreats and a wave cut platform forms, the arch will collapse and create a stack. In time, the sea will exploit the wave cut notch at the base of the stack and cause it to collapse, forming an stump. It is important to remember that caves, arches, stacks and stumps occur in a sequence, one after another

- A geo is a narrow steep sided inlet which is created along a joint that is exposed to the sea. A combination of hydraulic action and the other marine processes widens joints to form geos.

BARRIER ISLANDS:
- Barrier islands are a series of sandy islands totally detached from, but running almost parallel to, the mainland. Between the idlands and the mainland is a tidal lagoon. Although they are relatively uncommon in the UK, they are widespread globally (lots in the USA, west of Africa, northern Netherlands and in Australia) and account for 13% of the worlds coastline. While their orgin is unknown, they do tend to develop on coasts with relatively high energy waves but a low tidal range. One theory suggests that they formed, below the low tide mark, as offshore bars of sand that have moved progressively landwards. Another thoery is that rises in post-glacial sea level have partly submerged older beach ridges.

TOMBOLO:
- A tombolo is a depositional feature that connects an island to the mainland. They are often temporary features and so should not be built on.
- waves refract around the island and as they meet, before meeting the coastline, they cancel each other out and so sediment is deposited.

SPITS:
- Spits are another depositional feature that are predominantly caused by longshore drift and they form whenever you get a change in the direction of the coastline.
The spit curves at the end (into a hook) due to winds that blow in a different direction to the prevailing wind.
- Mudflats, brackish lagoons and salt marshes form behind the spit and these areas are important for migratory birds. Spits are also important as they protect the area behind from the most powerful waves and so create the perfect conditions for the development of a port.
- The rivers flow often prevents the spit from connecting to the other side of the estuary but, if there is no significant flow from the river and it does connect to the opposite side, a bar is formed.

1) Longshore drift moves material along the coastline
2) A spit forms when material is deposited
3) Over time the spit grows and develops a hook, if the wind direction changes
4) Waves cannot get past the spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form

The last landform is a beach but, when I find the time, I am going to write a seperate post on them and try to explain in a bit of detail the beach profile as there are a few key words to learn and I sometimes seem to get a bit mixed up when trying to use them to describe the profile of a beach. Hopefully I will managed to write this in the next few days but if not definetly over half term.

Shoreline Management Plans (SMP's)

 A Shoreline Management Plan is designed to try and decide upon the most suitable scheme for each individual sediment cell. Although each sediment cell has its own SMP, often each sediment cell is split up into sub-sinks (normally beaches or other sedimentary features) which then often have a slightly altered SMP. DEFRA (Department for Environment, Food and Rural Affairs) oversee and partially fund coastal protection, amognst other things, and produce SMP's. They recognise that processes operating within the coastline occur within distinct lengths of coastline - hence why they split it up into sediment cells. They also recognise that the promotion of cooperation between all the other interested authorites is key and that they should all be involved with the development of an SMP. The development of a shoreline management plan is split into two stages.........

STAGE 1 - identify all those with an interest in the area and collate and analyse data on the key issues. Then, using this as the foundations, set management objectives and a plan for the area.
STAGE 2 - define the management units, decide on the objectives and then, before procuding the plan, consult on the preferred strategies of defence.

When considering coastal management, there are four options............
DO NOTHING - carry out no defence works except for those required for safety
HOLD THE LINE - maintain or upgrade the level of protection provided by the existing defences or build new defences along the coastline
ADVANCE THE LINE - build new defences seawards of the existing position
MANAGED RETREAT - adopt a more landward defence postion

There is one more option, that is only considered in areas where there has not been enough research and the processes at work have not yet be understood........
OBSERVE AND MONITOR - undertake a period of detailed examination of the shoreline and then decide on one of the previous options

When deciding on what option to take and what should be including on the SMP, it is often difficult to find a comprimise as, often, all the parties involved have conflicting interests. For example, property owners want protection, tourists want access and for the area to remain aesthetically pleasing, businiesses want to maintain their coastal industries whilst environmentalists want to protect rare natural habitats and environments. A lot of this often dictates whether or not hard or soft engineering is used or, in fact, a bit of both.

HARD ENGINEERING:

Groynes:
- Aim to build up sediment by preventing longshore drift from moving it along the coast. They are built at right angles to the coastline and are usually spaced between 50 - 100m apart. As they build up nice beaches they are popular with tourists and the way in which they divide the beach into sections is often welcomed by locals as well as it means that tourists can occupy one end whilst the locals the other. This is evident at Lyme Regis where the groynes seperate the shingle beach, which is quieter, from the sandy beach which is very popular with the tourists in the summer.
- They can be made from wood, concrete or blocks of stone and often need maintaince as, especially if made from wood, can be easily damaged by the marine processes
- In terms of cost they cost around £60 per metre but this can vary depending on the material used

- Although groynes help to build up the beach in the area they are implemented they can cause severe problems at stretches of the coastline downdrift (think about the impacts the groynes at Mappleton have had on Cowden and even the groynes at Lyme have impacted on Charmouth) like terminal groynes syndrome, also known as sediment starvation,  which results in increases in the rate of erosion

Sea Walls (curved):

- Aim is to reflect wave energy back out to sea and reduce the risk of flooding but, because they fail to reduce wave energy or cause waves to break early, scouring (excessive erosion causing removal of sediment at the base) often occurs. This means that, in conjunction with the construction of a sea wall, beach nourishment or, like at Lyme Regis, rip rap is placed at the base to reduce this and extend the life of the sea wall.

- This adds to the costs involved. ontop of the frequent maintainence that is required. Sea walls, alone, cost anything between £800 and £5000 per metre and are not expected to last any longer than 30 years.

Revetments:

- Aim to protect the shoreline behind them by provoking the waves to break early and so reducing the energy of the waves as they reach the beach and hit the base of the cliff.
- Like groynes, they can be made of blocks, wooden slats or concrete but ar positioned parallel to the coastline. They are often placed infront of a sea wall to increase the life of the sea wall by reducing scouring
- Average cost per metre is £1000 but constant maintainence is required
- The biggest issue is the fact that, because it reduces the erosion of the cliff, there is no fresh sediment entering the system and so it reduces the amount of sediment downdrift. This means that, in conjunction with the building of a revetment, beach nourishment is needed.

Rip Rap:
- Aim is to dissipate wave energy NOT to provide defence against coastal flooding. They are large boulders that are placed towards the back of the beach, often at the base of a sea wall. They can be made from native rocks but, in areas like Lyme Regis, this is not possible as the rocks are not resistant enough. Instead a hard crystalline, igneous rock named labradorite ( I think that is how it is spelt???) is imported from Norway
- They cost around £300 per metre but don't have a very long life span (10-15 years)
- Not ideal in honeyspot sites as they are unsightly and tourists seem to like to clamber on them, despite the number of health risks they pose

Gabions: - Aim to absorb wave energy and encourage sediment deposition by reducing the strength of the backwash.
- They are wire cages filled with stones that are either placed in front of areas prone to erosion or underneath sand dunes
- They are a cheap solution (with an average cost of £ll per metre) but they are unsightly and so are often not a popular choice in honeypot sites

Offshore Breakwaters: - Aim to reduce the power of the waves before they hit the coastline, by provoking them to break earlier, and thereby widen the beach, due to the fact it blocks longshore drift
- They are unsighly and can be obstruct as by reducing wave energy and causing them to break early it restricts what water sports, imparticular, can take place in that area
- They can be quite costly at around £1950 per metre but can cost a lot more if constructed in deep water

SOFT ENGINEERING: 
Soft engineering is a more sustainable form of engineering as it uses the natural environment and processes to protect the area. It often involves one of the following:
                       - Beach nourishment (???is neither really hard or soft engineering)
                       - Salt marsh growth
                       - Sand dune stabilization
                       - Planting of sea grass
                       - Reef building

Beach nourishment:
- This is the placing of sand, similar to that naturally found in the area, on the beach to build up the beach and protect the coastline. This is often done in conjunction with the construction of groynes or a sea wall.
- Sourcing the sand can be an issue as it needs to be taken from a source which will not damage the coastline. Unchecked dredging has increased the erosion rates in the Bahamas and the effects that dredging has had on Hallsands has been disastrous. I don't know if any of you have visited Hallsands, but I have, and you can now only view it from a platform and the pictures really show the extent of the damage......

This is the village before the impacts of the dredging could really be seen, apart from the shrinking of the beach.

And this is what it presently looks like....... if I can find the time I will write a post about what caused this, in more detail, why dredging was taking place and how this has effected the approach to coastal manangement at Beesands, a beach just down the coast from Hallsands.

- Beach nourishment needs constant replacement if it is to have the desired effect as it only lasts from 1 - 10 years before major recharge is required. This means that it can often become costly (anything from £5000 to £200 000 per metre).

Sand Dune Stabilisation:

- Sand dunes provide a natural sea defence and so vegetation is often encouraged to grow on them to stabilise them. Marram grass is often chosen as it is long roots bind the soil and it is tolerant of the salty conditions.

- There are a few disadvantages of this method though. The sand dunes take a long time to build up and they require constant maintainence and monitoring. To tourists they provide a perfect slope to slide down but this kills the vegetation and thereby destroys the sand dunes and so keeping people off of the sand dunes is a crucial part of their management.

- On average, the vegetation costs around £2o per metre to plant but this does not include the monitoring and maintainence costs.

Managed Retreat:

- Managed retreat can involve allowing the area to turn back to salt marshes. In 2008, in the first move of its kind in the UK, the Environment Agency decided to turn the Cuckmere Valley in East Sussex into a salt marsh nature reserve rather than continually building ever bigger flood defences.

- There are not really any fixed costs with this option and the main costs are those spent on purchasing the land from residents and paying for the dismantling expenses. This means that, sometimes, this is a costly option.

As we have learnt in previous lessons, sub-aerial weathering is also a problem from coastlines, especially those consisting of unconsolidated and unresistant rocks. This means that there are some sub-defence methods that can be implemented, most of which aim to reduce the water in the cliffs to reduce teh risk of mass movement

- Drainage of the cliff

- Stabilisation through the planting of vegetation

- Run off channels

- Grouting

- Rock bolts

- Planning constraints on land use

Okay, so this is the bare bones of our lesson on shoreline management plans and so there is more detail for each point but hopefully it will be useful to some........

Tides.....

We spent Friday afternoon's lesson learning about tides and how they form and there seemed to be lots of things that we needed to know about them. The extent of my knowledge of tides previous to Friday's lesson stretched as far as the fact that they are created by the moon. So, in an effort to try and consolidate what we got taught, I am going to try and summarise some of the key points....

The tide is the cyclic rise and fall of the ocean surface and it is caused by  the moon and the sun exerting force on the earth.  This gravitional force has the strength to alter both the depth of the ocean and the oscillating currents. The moon has the greatest influence on tides as it is significantly closer to us than the sun and so water is dragged to the point where the moon is directly ahead. However, the sun also has the gravitational pull to affect tides and this force complicates the lunar tide cycle as the alignment of the moon and the sun influences the amplitude of tides.

The location of the moon, in relation to the sun, determines whether or not we experience Spring Tides or Neap Tides. Spring Tides are the tides with the biggest difference between high and low tides. They occur twice a month (Day 1 and day 14) when the earth, moon and sun are aligned. This alignment puts an extra gravitational pull on the tidal bulge which results in an extra high tide.

Neap Tides are the tides with the smallest difference between high and low tides. Neap Tides occur when the moon and the sun are at right angles to each other (1st quarter = Day 7 and 3rd quarter = Day 21). A smaller tidal range is produced because the lunar high tide coincides with the solar low tide and they partly cancel each other out.

- It takes 28 days for the moon to orbit the earth and it takes roughly twelve and a half hours for a tidal cycle to occur.
- The time between high and low tides when the water is falling is called the ebb and when it is rising it is known as the flow.
- Most places experience two high tides and two low tides a day (semi-diurnal) but some only experience one high and one low tide a day (diurnal).
- Tides do have their benefits which include the fact that they have enabled for the development of ports, maintain the mudflats which migratory birds are dependent on, create currents and transport sediment - these are just some of them and there are plenty more!
- Some areas, like the Mediterranean Sea (experiences a tide of approx 11 inches), do not experience tides and this is because it is not a big enough body of water to feel the gravitational pull of the moon and it is restricted by land.
- However, other areas experience very large tidal ranges. The Bay of Fundy, Canada, has the highest tidal range in the world and one of the main reasons that they experience such high tides is because the water is funnelled through a narrowing channel.

The River Severn has a tidal range which is almost equal to that of the Bay of Fundy and at the time of the highest spring tides, the funnelling effect of the wide estuary, sends a wave several miles up the river against the current. This wave is known as a tidal bore and occurs when  the force of the incoming tide is strong enough to force the flow of the river back on itself, thus creating a wave. These tidal bores generally occur around the time of the spring and autumn equinoxes (when the moon is directly above the equator - usually late March abd late September).

The Qiantang River in China experiences possibly the largest tidal bores in the world (9 metres!) and is known locally as the Black Dragon.

Well I think this is the majority of the key points and I actually think that I have managed to consoldiate what I learnt quite well - I hope this will be useful for others of you out there. However, I still have a few questions and I would be very greatful if anyone could shed some light on them .......... so firstly, what determines whether or not an area experiences a semi-diurnal or a diurnal tide? And secondly, if the time between high tides is equal, how come low tides do not occur half way between them?

Waves - the basics

We have just started our final module of AS Geography - Coastal Environments - and started off by looking at waves and how they form. I have got a feeling that waves are going to be an important part of this module as the characteristic of a wave will determine whether or not erosion or deposition occurs and these processes contribute greatly to the shaping of the coastline.

So, how do waves form? There seemed to be a bit of confusion as to how excatly waves form. Waves are created by the transfer of energy from the wind to the water - not anything to do with the moon! The wind blowing over the surface of the sea creates friction between the two and this causes the water to begin to move in a circular orbit. When the wave reaches shallow waters, friction with the seabed begins to slow the speed at the base of the wave whilst the top of the wave stays the same. This causes the wave to become higher and steeper until it eventually breaks. If you are more of a visual learner the short clip mentioned in the module book is well worth watching - Understanding wave formation . The characteristics of waves differ and waves are often described as either being constructive or destructive......

Constructive Waves: Constructive waves are often created in calmer weather and have less energy than destructive waves. Constructive waves tend to be lower waves with a low frequency but long wave length. As the wave approaches the beach it gets steeper and so when it breaks it gives a gentle spill on to the beach. As the water percolates through the beach material the swash loses energy but remains stronger the backwash. The backwash is often very weak and has insufficient force to pull sediment off the beach. This results in material being slowly, but constantly, moved up the beach which leads to the formation of berms (berms mark the location of the spring high tide)

Destructive waves: Destructive waves are often created in stormy conditions and are a lot more powerful than constructive waves. Destructive waves are high, steep waves with a high frequency but short wave length. As a destructive wave approaches the beach it gets steeper and therefore, when it breaks, it plunges down with quite a bit of force. Due to the fact that there is little swash (forward movement of water up the beach) the backwash becomes dominant and is often very strong. This results is little material being moved up the beach as, instead, it is pulled away. Sometimes destructive waves are known as erosional waves and are often associated with steeper beach profiles. If the force of the wave is great enough it may well project some shingle and other material towards the rear of the beach and this can result in the formation of large ridges known as the storm beach.

Swell Waves: Swell waves are formed by distant storms. These waves travel long distances and are less steep whilst having both a longer wave length (the horizontal difference between successive crests or successive troughs) and wave period (wave period = the time between one crest passing and the next). Swell waves are usually constructive waves.
Sea Waves: Sea waves are formed by local winds and are effectively the opposite to swell waves. Sea waves do not travel very far and whilst being steeper have both a shorter wave length and wave period compared to swell waves. Sea waves are usually destructive waves.

As well as knowing the key characteristcs of waves there also seems quite a few key terms to learn. Most of them seem quite self-explanatory but after I discovered the definition of wave steepness last lesson (the ratio of wave height to wave length) I was quite interested in understanding why this cannot exceed 1:7. So, because I clearly didn't have anything better to do this afternoon and because the prospect of doing a bit of extra Geography seemed so much more interesting than my maths homework, I decided to try and find out why. As waves approach landmasses they get steeper and change shape. This is because the friction that occurs between the seabed and the water causes the circular orbital motion to slow at the base of the wave whilst, at the top of the wave, it continues at its orginial speed. This causes the wave to get steeper as it begins to lean forward. When it reaches the point that its wave steepness is at 1:7 the wave becomes unstable and so collapses on top of itself which forms a breaker. As far as I know, I think that there are two forms of breakers - spilling and plunging. A spilling breaker is a rolling wave that travels gradually up often sloping sandy beaches. The long incline drains that wave of its energy and I am guessing (this is just a gut feeling and so I wouldn't trust me on this) that spilling breakers are therefore most commonly associated with constructive waves as, as the water percolates through the beach material the swash loses energy. A plunging breaker is most commonly found approaching a steeper beach and forms a curling crest, due to the fact that the curling water is travelling faster, which travels over a pocket of air. Again this is a total guess, but I think perhaps plunging breakers are  more associated with destructive waves.

Unfortunately I really should get back to my maths homework and so this will have to be it from me tonight - I hope this is useful for some of you. I am going to try really hard over the next few weeks to primilarily write about what I learn in lessons and not get too distracted by other geographical things in the news that interest me - should be interesting to see how long this lasts!!!