Excessive Rain | floodzee-informatics

Excessive rainfall Flooding -Excessive rainfall flooding is sometimes called pluvial flooding after the latin term for rain pluvius. It is usually the third most destructive form of flooding. It also is closely aligned with flash flooding due to its sudden onset. It can have very severe localized effects. It occurs as a result of very heavy rain and typically with rainfall amounts of over 25 or 30mm. It sometimes includes very severe incidences of rainfall with amounts of between 70 and 100mm.

Such heavy rain would typically cause instantaneous localized moderate to severe flooding. It would overwhelm small drains and gullies and even small streams and rivers. In overflowing it would typically take the shortest possible path to rivers and lakes. This could be through houses and built up areas.

These events are typically rare; however like all forms of flooding with the increase in population more people are now in harms way than before. Excessive rainfall flooding has the potential to overwhelm culverts and rise rapidly in underground structures. As a result there is a severe risk to life from excessive rainfall in particular in basements and underground buildings.

One particular risk with excessive rainfall in Ireland is where single large daily amounts occur at the end of a prolonged wet period lasting typically 2 to 3 weeks. These single daily events may be of only 25 to 35mm but the combined effect on top of the prolonged spell is to cause widespread local flooding. This would typically cut off many local roads and cause a multiplicity of small rivers and streams to overflow. Such events can also be associated with land and mud slides and even the destruction of bridges over rivers.

Another risk associated with excessive rain is where the rainfall washes dirt that has accumulated in underground channels and crevices. This washout then leads to an increase in dissolved and suspended solids in groundwater and this can cause significant difficulties in water treatment plants. Many plants are not capable of dealing with such loading. This can lead to problems with drinking water supplies. This is an issue which frequently occurs in the Autumn after the summer season. It can occur at any time however.