Ponding (Drainage) Flood

Unique identifier / Notation

MH0010

Synonyms

Drainage flood,

Surface retention.

A ponding flood is a flood which results from rainwater ponding at or near the point where it falls because it is falling faster than the drainage system (natural or man-made) can carry it away (WMO, 2006).

Primary reference(s)

WMO, 2006. Technical Regulations Volume III: Hydrology. WMO-No. 49. Page IX. World Meteorological Organization (WMO).

Additional scientific description

A ponding flood is that part of the precipitation which remains on the ground surface, without running off or infiltrating, until it evaporates or transpires (Flood Site, 2008). Metrics and numeric limits Not identified.

Metrics and numeric limits

Not identified.

Key relevant UN convention / multilateral treaty

Not identified.

Examples of drivers, outcomes and risk management

Floods are one of the most common hazards. The effects of flooding on health are extensive and significant, ranging from mortality and injuries resulting from trauma and drowning to infectious diseases and mental health problems (acute and longterm). While some of these outcomes are relatively easy to track, ascertaining the human impact of floods is still weak. For example, it has been reported that two-thirds of deaths associated with flooding are from drowning, with the other third from physical trauma, heart attacks, electrocution, carbon monoxide poisoning and fire. Often, only immediate traumatic deaths from flooding are recorded (WHO, 2013).

Morbidity associated with floods is usually due to injuries, infections, chemical hazards and mental health effects (acute as well as delayed) (WHO, 2013). Hypothermia may also be a problem, particularly in children, if trapped in floodwaters for lengthy periods (WHO, no date). There may also be an increased risk of respiratory tract infections due to exposure (loss of shelter, exposure to flood waters and rain). Power cuts related to floods may disrupt water treatment and supply plants thereby increasing the risk of water-borne diseases as well as affecting proper functioning of health facilities, including cold chain (WHO, no date). Floods can potentially increase the transmission of the following communicable diseases: water-borne diseases (such as typhoid fever, cholera, leptospirosis and hepatitis A) and vector-borne diseases (such as malaria, dengue and dengue haemorrhagic fever, yellow fever, and West Nile Fever) (WHO, no date).

The longer-term health effects associated with a flood are less easily identified. They include effects due to displacement, destruction of homes, delayed recovery and water shortages (WHO, 2013).