01 - Water Body Overflow

Flood from rivers, lakes, etc. as well as surface runoff (due to rain) is included in this factor.

The number of flooding events that have occurred in the past give some indication of the event occurring in the future. Changing runoff and weather patterns also change the occurrence of floods. In mountainous areas, flooding was usually expected in late spring with the melting of snow. Other areas experience summer monsoons with heavy precipitation, or late fall / winter storms. However, a changing climate means events can coincide and create new flood seasons.


  • Water bodies such as rivers, streams, creeks, lakes, bays, seas, or even dry riverbeds are located nearby.
  • Site elevation above the water bodies nearby is relatively low.
  • Site or nearby area has experienced flooding in the past.
  • The area or the site has experienced overwhelming of gutters and drainage systems leading to surface flooding.
  • Increased development in the region since inception of the site. 


  • Presence of offsite fixed flood control features maintained and operated by local authorities. Natural or technical retention measures include but are not limited to natural, designated flood plains upstream, retention basins, river flood polders and reservoirs.
  • Other technical protection measures include spillways, spillway tunnels, flood bypasses, flood channels and retention lakes to reduce the peak flow.
  • Structural river protection features then include dams, levees, dikes, drainage works in former swamps, raised land above swamps or flood plains, river relocation, sediment management, etc.

Risk improvement ideas

  • Consider modification of site layout in terms of distribution of values within the site. For example, relocate high-value contents and important processes away from the source of flood or at higher levels in buildings.
  • When building a new site or constructing an extension to existing facilities, consider whether the construction itself will change water tables, flow patterns, or run-off from standing water on developed and built up areas. Examples include large storage or parking lots, large underground construction, culverts etc.
  • Drainage of yards and lots should consider the capacity of public drainage system to which the surface runoff will be drained.
  • Consider the site’s hazard and flood susceptibility in any site design modifications or extensions.
  • New development should be located outside flood-prone areas, ideally above the 1 in 500 year flood zone.



External Resources