flooding Flashcards
what is flooding
Flooding is where land that is not normally underwater becomes inundates.
when does a river flood occur
A river flood occurs when the discharge of a river is too high and the river channel can no linger hold the amount of water flowing in it. Water overtops the banks and floods the adjacent land, the floodplain.
how does lag time effect the chances of a flood occurring
The crucial factor in flooding is how long it takes for the rain to reach the river from where it falls on surrounding land and mountains. So therefore, the shorter the lag time the greater the chance of a flood
How might precipitation effect flooding
Sudden bursts of heavy rain mean the infiltration rate is too slow to allow rain to soak into the ground and so this increase surface run off.
how does impermeable and permeable rock effect flooding
impermeable rock means the water will just run off it and flow to the river ,however, permeable rock absorbs some of the water reducing the risk of flooding by alot
how does the gradient of the slope effect the risk of flooding
Steep slopes mean that the water runs straight down them by surface run on as the water hasn’t had time to infiltrate.
how does drainage density effect the risk of flooding
High drainage density means many tributary streams carry the water quickly to the main river making the risk of flooding greater
how does vegetation effect the risk of flooding
When there is little vegetation, less precipitation is intercepted and roots can no longer take water from the soil. The soil therefore gets saturated quickly and flooding is much more likely
how does deforestation effect flooding
When trees are deforested precipitation is no longer intercepted and roots can no longer take water from the soil. The soil therefore gets saturated quickly and the risk of flooding is much greater
how does farming effect flooding
Downhill ploughing instead of contour ploughing can increase the speed at which the water gets to the river. Cattle compacting the soil can also make the ground more impermeable. making the risk of flooding greater
How does urbanisation effect flooding
When infrastructure is built (roads, shopping centres and schools) the greater the area covered by impermeable services. This leads to precipitation not being able to infiltrate the ground and increasing surface run off making the risk of flooding greater
how does burning fossil fuels contribute to flooding
Burning fossil fuels is causing more melt from ice sheets and glaciers as well as more rainfall and storm events making it more likely to flood
