Flood Event

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Flood Event by Mind Map: Flood Event

1. Causes

1.1. human

1.1.1. Concrete Concrete will decrease the lag time because the water will flow directly into a drainage system and into a river. This is because the water does not get absorbed by the concrete therefore causing it to flow into a drain, and into a river.

1.1.2. Roof Roofs have almost no infiltration due to the solid concrete surface. Water will not stay there long, it will be washed off very quickly into drainage system and therefore fill up a river system faster, thus increasing the chance of flooding. The larger the surface of the roof the more water gets washed off.

1.1.3. Drainage sytems Drainage systems are going to prevent flooding in urban centres, but increase the probability of flooding of a river. The drainage system will have an efficient "U shaped" pipe that will bring water to the drainage basin. Inefficient urban drainage system - In Kampala, Uganda there are small inefficient ditches around parts of the city that : are poorly constructed, not fully made by concrete, and are normally in an awkward concave shape that reduces the hydraulic radius and contributes to large amounts of surface stores on the poorly constructed "roads." (Observation)

1.1.4. Gradients The gradients will decrease lag time. The reason for that is the fact that the gravity pushes water downstream, while on flat surface the gravity will push water into the soil.

1.1.5. Ground cover Gravel Gravel will decrease the lag time as it is quite a hard surface therefore precipitation will run -off it faster and reach drainage systems quickly. However, compared to concrete it is slightly more permeable. Synthetic grass Synthetic grass absorbs some of the water and by doing so the lag time is higher. Concrete Grass paving permeable paving consists of both grass and pavement and it allows stormwater to flow through the surface and also traps suspended solids and filters pollutants from the water

1.2. Natural

1.2.1. Tree Trees increase the lag time when water is travelling to a river. This is because plants such as trees absorb water and hold the soil together. When it rains the soil will absorb the water more easily because of the tree. Trees are often added around urban areas to increase the otherwise very fast lag time.

1.2.2. Bamboo The bamboo acts as interception and increases the lag time of water flowing to a river. The dead leaves, small wood pellets and soil absorbs rainwater and holds the soil together. The slope in which the bamboo faces is downwards and forces the water to flow in this direction and ultimately increases flow time.

1.2.3. Grass Grass increases interception and regulates absorption of water in the soil. Grass is a necessity in urban areas as they prevent flash floods from taking place in areas where slopes and tarmac concrete would not allowed water to get infiltrated. Grass would increase the lag time of the river. The roots of grass networks that reduce soild erosion

1.2.4. Soiil Soil water capacity Dry Soil Water logged soil

1.2.5. Storm Intensity

1.2.6. jet-stream location and force if the force of the jet-streams increases, than the wind increases. This creates a big waves which causing the flood.

2. Consequences

2.1. Economical

2.2. Political

2.3. Social

2.4. Environmental

2.4.1. Soil degradation

2.4.2. Salinization

3. Management/prevention

4. Timeline of events

5. Location