New definition for the 100-year storm?

An article in the Houston Chronicle by Mahir Zaveri dated November 28, 2017 is entitled:

"NOAA may reclassify 100-year storm definition because Houston storms have been so bad"
The subtitle is "the results could spur sweeping changes to maps, development regulations"

It states that the National Oceanic and Atmospheric Association (NOAA) has conducted an update of rainfall data analysis that shows that the 100-year storm has risen by three to five inches across Harris County. The last study of this type was in 2001.  The results of the new study will be released in May 2018 following peer-review.

The 100-year floodplain is a crucial standard because it is the basis for regulations regarding new development, drawing of floodplain maps, and the design of detention basins and flood control projects.  

The floodplain maps are built using models of rainfall spilling out of bayous, creeks, and ditches during a 100-year storm.  If the standard is revised to include more rainfall then the mapped floodplains would expand.  This would result in higher insurance rates for structures newly included in floodplains and new regulations for development.

According to the Clear Lake City Water Authority (CLCWA) as of February 2013 there had been 10 100-year and greater rainfall events in the Clear Lake City area since 1979.  Adding the 2015 Memorial Day, 2016 Tax Day, and 2017 Harvey events the total is 13 events in 38 years.

According to CLCWA the 100-year event equates to 13.5 inches of rain within a 24 hour period. A 500-year event equates to 19 inches of rain within a 24 hour period.   With the new NOAA standards mentioned in the Chronicle, those definitions would increase by 3 to 5 inches.

The attached map shows a possible net effect for Clear Lake City.  The 100-year floodplain (green), could expand to a size between the current extent and the area of the 500-year floodplain (yellow).

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