How does drainage density affect flooding

High drainage densities also mean a high bifurcation ratio. For hydrologists, drainage density is significant in that it plays an important role in surface-runoff processes, influencing the intensity of torrential floods, the concentration, the sediment load and even the water balance in a drainage basin. Granite is an impermeable rock and so there is a high drainage density , in other words, there are a lot of rivers and streams.

Granite is resistant to weathering so usually forms upland areas, Dartmoor is no exception. There is a lot of rainfall so there are peat bogs and areas of standing water on the surface. Drainage basins characterised by impermeable rock and soils tend to have higher drainage density due to the lack of infiltration and percolation.

This means that water enters a channel quickly, leading to an increase in discharge. Indented landscapes will collect water and reduce runoff rates, reducing the amount of water reaching the river channel. Heavy Storms: runoff will increase after soil field capacity is met which means water will reach the channel quicker. Vegetation and land use affect the amount of water reaching the river channel. Evaporation and transpiration from vegetation evapotranspiration return moisture to the atmosphere, while uptake of water and anchoring of soil by vegetation can reduce surface water runoff and erosion, respectively.

Human Activity Humans will normally cover soil in impermeable materials like tarmac or concrete which will increase surface run off and reduce the amount of water being stored, increasing the peak discharge and reducing the lag time. Drainage frequency and density are two most important aspects of a drainage basin, which affects the runoff capacity of a basin. Drainage frequency is the number of streams in per unit area.

It is associated with lithology, degree of slope, stages of fluvial cycle and amount of surface run-off. In comparison with other climates , however, such as the Marine West Coast Climate , it is possible that the less intense precipitation of a marine climate may result in lower runoff intensities and lower drainage densities, however the lower mean temperatures of such climates may develop soils of generally higher.

For a fixed return interval, as watershed size increases, the runoff per unit area decreases. This occurs primarily because average rainfall amount decreases with increasing area ; secondarily, increased travel time for runoff allows more infiltration and other losses.

Larger size also means a longer lag time as water has a longer distance to travel to reach the main river. An elongated basin will produce a lower peak flow and a longer lag time than a rounder basin. Basins with a higher drainage density number of tributary rivers collect rain water more quickly, therefore the lag time will be shorter. Flow can be faster down a steep slope, resulting in a steeper rising limb and a shorter lag time.

Permeable rocks mean rapid infiltration and little overland flow, resulting in a less steep rising limb. Impermeable rocks will lead to an increase in overland flow and a steep rising limb.

Neerja Indian. Zira US English. Oliver British. Wendy British. Fred US English. Tessa South African. Select another language:. Please enter your email address: Subscribe.

Notify me of new comments via email. Cancel Report. Create a new account. Log In. Powered by CITE. Don't keep it to yourself Submit Definition. The ASL fingerspelling provided here is most commonly used for proper names of people and places; it is also used in some languages for concepts for which no sign is available at that moment.

There are obviously specific signs for many words available in sign language that are more appropriate for daily usage.