Hard and soft engineering techniques Learning Objectives: To compare the advantages and disadvantages of river defence techniques To consolidate our knowledge of river landscapes, river processes and river flooding

Flood Engineering Techniques Hard engineering is a method of river flood management which involves major construction work Soft engineering is a method of river flood management which works or attempts to work with natural river processes. It does not tend to involve major construction work e.g. Floodplain zoning

HARD ENGINEERING These are structures built by engineers, with the help of geographers and hydrologists. They are expensive and often not an option in LICs. They often have a negative impact on the environment and can even cause more flooding further down the river’s course. Use a full page and write the following headings along the top of the page: Method Description Comment Write notes on each technique as we go through the following slides.

Flood banks These are raised 1) Can be used as a path 1) The banks are   banks along the river, so it can hold more water. for pedestrians beside often not built the river. high enough 2) Concrete embankments 2) Concrete are effective at stopping embankments bank erosion. are ugly and 3) Earth embankments spoil the view. provide habitat for plants and animals.

Channelisation (straightening and deepening of the river) The river channel may 1) Effectively protects 1) Altering the   be widened and immediate area because river channel may deepened allowing it water is moved away lead to greater to carry more water. A quickly. risk of flooding river channel may be 2) Long lasting downstream, as straightened so that the water is water can travel faster carried there along the course faster. 2) Unnatural and visually intrusive.

Los Angeles channelisation

Flood relief The channel course 1) Makes the people who 1) They require a channels of the river can be live close to the main large amount of   altered, diverting river safer as the flood land which might floodwaters away water is diverted into be difficult to from settlements. the relief channel. purchase 2) Can be used for water particularly if it is sports. productive farmland. 2) Extremely expensive.

Construction of a flood relief channel

Dams and reservoirs Dams are often built 1) Water is usually stored 1) Building a dam is   along the course of a in a reservoir behind the very expensive. river in order to control dam. This water can then 2) Sediment is often the amount of discharge. be used to generate trapped behind the Water is held back by the hydroelectric power or wall of the dam, dam and is released in a for recreation purposes. leading to erosion controlled way. further downstream. 3) Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.

The Three Gorges Dam in China Use the resource sheet to complete a fact file on this example of a hard engineering scheme. Write your fact file around the map of China. Include: Its main features, Why it was built? The impact : social, economic, environmental. Extension work – How to get the A/A* Use the booklet to add more detail to your case study: 1. The history of flood events on the Yangtze (table 2), 2. Why can the 3 gorges be described as a multi-purpose scheme? 3. What does displacement mean and how have people been re-settled? 4. What have the impacts on the Yangtze ecosystems been like? 5. Add the detail from figure 1 to your map. 6. What hazards has the dam created? Do you think it should have been built? Do the benefits outweigh the costs?

Flood walls   A vertical barrier usually made from prefabricated concrete. 1) Can be used in areas where space is limited. 2) Easily and quickly erected in pre-constructed sections. 1) They have to be assembled very well so that water doesn't get through joints.

Flood wall on the River Moskva, in Moscow

Storage areas   A large depression close to the river that will fill with water if the river overflows and therefore protecting the surrounding land. 1) Natural looking 2) Does the damage the environment. 1) Need a large area of land that is not being used. 2) Only come into use when the river has flooded.

Barriers, such as the Thames Barrier. The barrier is raised when a high tide or flood is forecast.

SOFT ENGINEERING These do not involve expensive structures, but instead uses the natural features of the drainage basin to control flooding. It involves planning the land use in the drainage basin. Forecasting and warning systems are also important

Floodplain zoning   Local authorities and the national government introduce policies to control urban development close to or on the flood plain. 1) A very cheap way of reducing the risk of damage to property. 2) It is sustainable because it reduces the impact of flooding and building damage is limited. 3) Also because the flood- plain has not been built on, surface runoff is less likely to cause flooding. 1) There can be resistance to restricting developments in areas where there is a shortage of housing. 2) Enforcing planning regulations and controls may be harder in LICs.

Washlands   The river is allowed to flood naturally into wasteland areas, to prevent flooding in other areas, for example, near settlements. 1) Very cost effective as nothing is built. 2) Provides potential wetland sites for birds and plants. 3) The deposited silt may enrich the soil, turning the area into agricultural land. 1) Large areas of land are taken over and cannot be built on. 2) Productive land can be turned into marshland.

Warning systems   A network of sirens which give people early warning of possible flooding. The Environment Agency uses TV, radio, email, fax, text and phone messages to keep people informed. 1) A very cheap system. 2) Electronic communication is a very effective way of informing people. 3) Because the people have warning of floods they can move valuable belongings to safer places. 1) The sirens could be vandalized, so they are tested annually. 2) There might not be enough time for residents to prepare.

Afforestation or Flood abatement Trees are planted in the 1) This is a relatively low 1) It is often conifers that   catchment area of the river cost option. are planted which can to intercept the rainfall and 2) It improves the qulaity of make the soil acidic. slow down the flow of water the environment. 2) Dense tree plantations to the river. 3) Soil erosion is avoided as spoil the natural look of trees prevent rapid runoff the landscape. after heavy rainfall. 3) It increases fire risks 4) Very sustainable. because of leaisure activities in the forest.

How can we manage the Cumbria Floods? Use the map to help you suggest and explain which management techniques you would put in place. Hard or soft engineering? Where? Why?

Flood proofing This is where buildings are either designed or altered to make them less at risk of flooding. Do you recognise this place?

ACTIVITY: 1. Use the photo of Skipton, you have been given, to annotate with evidence of flood management. Try to identify evidence of the different types of hard and soft engineering. 2. Draw 2 spider diagrams, one for soft and one for hard engineering schemes and include their advantages and disadvantages. The Environment Agency manage floods in England and Wales.

Your task: You work for the Cumbrian Flood Action Group. You have a brief to report to the Environment Agency and the Cumbrian County Council your views on the flood. Go back to the previous page where you have already: 1. Stuck the OS map of the area in to the centre of a double page, 2. Around the edge of the map included details on why it happened, it’s impacts (social, economic and environmental) and the responses to the event.( Put these in neat boxes with headings) NOW: 3. On the same map label your ideas on which hard and soft engineering techniques should be used to protect Cockermouth against a future flood event of this magnitude. Outline the benefits and problems of each around your base map. You must also state your reasons for the choices you made (weighing up the balance between social, economic and environmental benefits). Be prepared to present this to the rest of the class! Resources available to you: You have been given a resources pack to help you produce your report, as well as a base map of the area to detail your ideas for your flood alleviation plan. Use your notes on methods of flood protection looked at in lessons.

What decisions have the Environment Agency made? Open the sealed envelope to find out! Cumbrian Floods of 2009 What are the proposals for flood alleviation? Flood defence works begin! Innovative developments in Cockermouth.

Plenary: Name and describe each method of flood management. Relief channels Washlands Floodwalls d. Flood warnings g. e. f. Channelisation Afforestation Floodplain zoning

HARD SOFT Engineering Engineering Floodwalls Flood warnings Channelisation Floodplain zoning Flood relief channels Washlands Afforestation Flood relief channels Floodplain zoning Afforestation Channelisation Washlands Flood warnings Floodwalls