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Flash Floods and Why They Happen

Flash Floods and Why They Happen

The flash floods in Arizona claimed the lives of nine people this past weekend. SBSA is saddened by this news and send our condolences to the families of the victims, as well as our praise to the responders. This form of catastrophe also gives us reason to reflect on the causes of flooding and how we can try to minimize the impacts they cause. We hope the following information will help others evaluate their situations and provide some insight to the myriad of issues that can arise. Descriptions of flood types are:

Riverine Flooding

When water levels rise above the tops of river banks, this is due to excessive rainfall within a watershed. Thunderstorms which linger over the same area for extended periods of time, combined rainfall and snowmelt, or ice jams cause the capacities of the watercourses to be exceeded.


Coastal Flooding

This occurs when greater than average high tides develop, and becomes aggravated by heavy rainfall and onshore winds.

Coastal Flooding

Storm Surge

This is caused by an abnormal rise in water level in coastal areas, much higher than in regular tides, caused by severe storm winds, waves and low atmospheric pressure.

Storm Surge Hurricane Ganzalo

Inland Flooding

Develops due to moderate precipitation accumulating over several days, intense precipitation falling over a short period, or a river overflowing because of ice or debris jam, also dam or levee failure. In this case the water has no where to go and surrounding low lying areas are inundated.

Inland flooding in Galveston, Texas

Flash Flooding

Heavy or excessive rain falls over a brief period of time (generally less than six hours) will produce flash flooding results in the higher portions of the watershed. The accumulated rainfall runoff in the upper regions collects in the upstream reaches of rivers and other watercourse, and flows downstream at very high speeds as walls of water rip through river beds, streets, or mountain canyons sweeping everything before them. Flash floods can happen within minutes or hours after extreme rainfall develops. Areas damaged by wildfires or locations where vegetation has been removed increase these conditions of flash flooding since the lack of ground cover escalates both the rate and quantity of water runoff. Further, when a levee or dam fails, or following a sudden release of water when a debris or ice suddenly bursts in the upstream of a river.

Colorado Flash Flooding


Insurance Response

SBSA’s personnel possess a diversity of knowledge ranging from the ground to the roofing system.  This allows us to review your claim with a determination of the integration of the systems and how each interplays in relation to the others.  From ground water to building envelopes and the interaction of the components that create the building systems, SBSA understands this relationship and their impact on your claim.

When evaluating your claim, SBSA will provide timely reports, with clearly written analyses and conclusions that include:

  • Claim review
  • Scope of damages
  • Cause(s) of damages
  • Repair solutions (when requested)

For claims that require forensic engineering or analysis in a litigation setting, SBSA has expert witnesses experienced in insurance-based matters.

During the numerous wind, seismic, hurricane and other natural events of the 2000 to 2016 time frame SBSA staff was on site to review, analyze and determine the causation of damages from flood, surge, wind and rain, and other associated causes of damages.

SBSA staff has conducted hundreds of observations and analyzed many structures due to the impacts of wind, rain, tornados, snow and other weather related events allowing our expertise to aid you in determination of the cause and results of your claims.