Stepping Stones River Flooding PI0122

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1 Stepping Stones River Flooding Resource Description Just what is a flood? Why do floods occur and what problems do they create? Flood prevention work is explained. National Curriculum Key Stage 2/Year 3/Citizenship 1a,2a,2j. Key Stage 2/Year 3/PSHE 1a,2a,2j. Key Stage 2/Year 4/Citizenship 1a,2a,2j. Key Stage 2/Year 4/PSHE 1a,2a,2j. Key Stage 2/Year 5/Citizenship 1a,2a,2j. Key Stage 2/Year 5/Geography 4b. Key Stage 2/Year 5/PSHE 1a,2a,2j. Key Stage 2/Year 6/Citizenship 1a,2a,2j. Key Stage 2/Year 6/Geography 4b. Key Stage 2/Year 6/PSHE 1a,2a,2j. QCA Key Stage 2/Geography/Unit 11 Water Key Stage 2/Geography/Unit 14 Investigating Rivers

2 Key Issues: What is a Flood? Why do they Occur? Problems of Flooding Flood Prevention and the Work of the Environment Agency 1. What is a Flood? A flood is a natural event that can have far reaching effects on people and the environment. It is caused by a combination of factors, not just heavy rainfall. Rainfall might drain from the land, creating streams and rivers, or sink into the ground to refill aquifers (natural underground reservoirs). 2. Why do Floods Occur? Human Factors Concrete surfaces Farming methods Flood plain development Physical Factors Impermeable rock Heavy rainfall Lack of vegetation Flooding of River Nene near Wisbech Aquifers are layers of porous rock, such as chalk, with many small holes or pores that can fill with water, forming underground reservoirs. When heavy rain occurs, there may be too much water for the porous rock to absorb, so it will lie on the surface. Water will also lie on the surface if it is impermeable (it does not allow water to pass through). Clay is an example of an impermeable rock. As the natural landscape is developed, it is covered by buildings and roads, which are impermeable surfaces. Rainwater cannot easily soak into the ground in developed areas which can lead to an increased risk of flooding during heavy rain. The Anglian Region of the Environment Agency is at particular risk of flooding since much of the underlying rock is impermeable clay. This is made worse by the fact that 4,700 square kilometers is actually below sea level and in recent years there have been many examples of severe flooding.

3 3. Problems of Flooding Floodwater can be very dangerous - people have been swept away and killed as well as many farm animals. It can cause great damage to property and its contents, and can severely disrupt transport and communications links. If the flooding occurs in an important commercial area, such as a town centre, trade can be badly affected. 4. Flood Prevention and the Work of the Environment Agency One of the aims of the Agency is to protect people and their property from flooding. In the Anglian Region, the Agency provides effective defence against flooding for 5.7 million people and their property. Each year approximately 52 million is spent on flood defences in the region, of which half is for new works and half is for maintenance of existing flood defences. The region s Flood Defence Department has the responsibility for maintaining 5,775 km of river defences. Its function can be broken down into the following areas: Flooding affects people s homes A weedboat Prevention - advice on controlling developments that may increase the danger of flooding or be in areas prone to flooding. Defence - building flood protection structures. Operations - maintaining and operating flood defences and the monitoring of river flow. Warning - forecasting and issuing flood warnings. Prevention The population of the region is increasing, leading to more severe pressure on the environment. The Agency aims to protect the environment from possible damage from new developments, to protect any of these developments from flooding and to reduce flood risk for existing property. In order to avoid new flooding problems the Agency is consulted by local planning authorities before permission is given for any new development. These include the construction of new buildings and roads. Each year the Anglian Region of the Agency is consulted on approximately 13,000 planning applications. The Agency would generally resist any new development on areas liable to flooding, such as homes being built on flood plains (areas of flat land next to a river). They would also resist any development that would greatly affect the natural water cycle. These include bridges and weirs, as they prevent the natural flow of water in a river, and large car parks that stop rainwater sinking into the ground.

4 Flooding was welcomed in the past since it allowed fertile alluvium and silt to be deposited on the land, but then some farmers built drainage channels to prevent flooding, so increasing the amount of land able to be farmed. Unfortunately, this stopped the soil from receiving the nutrients in the alluvium and forced the farmer to use artificial fertilizers. Pumping stations were also used to either pump water directly into the sea or back up into the higher reaches of a river. However in recent years, there has been a move towards stopping this practice, as flooding is encouraged in some areas. This allows the land to revert to its natural environment, such as on the Ouse Washes. Did you know? Most of the world s population lives on flood plains. The Environment Agency has a target for those affected to be warned, where practicable, two hours before flooding occurs. The Agency issues information on what action to take in the event of a flood. Defence Although flooding can never be totally prevented, the Agency continues to develop new schemes to reduce the risk of flooding by, for example, regulating the flow of rivers - when there is too much water, the Agency will seek to reduce the flow. This can be done in several ways, including: Flood storage reservoirs. During heavy rainfall, the extra water will be held back in temporary lakes behind dams (artificial barriers) whenever the flow exceeds the channel capacity. This water can then be released at a controlled rate in order to prevent flooding (eg near Milton Keynes on the River Ouse). Relief channels. In effect, another river channel is built, able to take excess water when the main channel is full (eg the Great Ouse relief channel between Denver and King s Lynn). Dredging. This causes the shape of the river channel to be changed. It is made deeper and/or wider. This takes place in most rivers in the region in an environmentally sensitive way. New works are needed because of increased urbanisation, which leads to more rapid runoff, meaning that previously acceptable channels have needed further improvement. Dredging in operation

5 Operations Environment Agency staff work constantly measuring the amount of water flowing in the river. This is done automatically at gauging stations and by staff in times of emergency (such as extreme heavy rainfall or during flooding), so that warnings can be issued and action taken to reduce damage from flooding. Maintenance of existing flood defences is essential. Activities include weed cutting which helps to ensure water is able to flow uninterrupted through the river channel, so reducing the risk of flooding. Agency staff also work, where necessary, to maintain raised river banks, keeping the river in a defined channel. In the event of river floods occurring, Agency staff will take emergency action. This may include using sandbags to raise the riverbank and contain the excess water in the channel, clearing blockages in river channels, or opening sluice gates (to enable floodwater to drain away quickly). If the river breaches the riverbank, they may also build emergency dams to contain the water. Warning The Agency uses information, such as that from measuring, to assist the operation of the flood warning system. Flood defence staff constantly monitor weather conditions, in particular rainfall figures, river flow data and tidal levels to determine where floods may occur, the severity of the flood and the extent of areas that may be affected. Information is gathered using data from the Meteorological Office weather radar stations, gauging stations and other sources. This information is sent to the Area offices, where staff decide the level of risk and, if necessary, issue flood warnings. There are also automatic sensors that will alert Agency staff of exceptionally high levels of water in the river channel. The Agency issues the following warnings to the Emergency Services, local authorities and the public: Flooding possible. Be aware! Be prepared! Watch out! Flooding expected affecting homes, businesses and main roads. Act now! Severe flooding expected. Imminent danger to life and property. Act now! All Clear. There are no Flood Watches or Warnings in force. Water levels receding. Check all is safe to return. Seek advice.

6 Activities How would you illustrate each of the flood warnings? Draw a set of diagrams which you think people will understand. Describe what you would do at home if you heard there was a severe flood warning. Write a letter to your local newspaper about a flooding incident near your home or school. How has this affected your home and your local community? Have you seen the web site? Questions What are the natural and human causes of flooding? What can we do to reduce the human causes?

Flash Flood Science. Chapter 2. What Is in This Chapter? Flash Flood Processes

Flash Flood Science. Chapter 2. What Is in This Chapter? Flash Flood Processes Chapter 2 Flash Flood Science A flash flood is generally defined as a rapid onset flood of short duration with a relatively high peak discharge (World Meteorological Organization). The American Meteorological