For all non-critical streets, the 100-year return frequency storm runoff can be contained within the street right-of-way. Non-critical streets are streets that are not thoroughfares. All bridges, culverts, underpasses, and open ditches shall be designed for a 100-year return frequency storm based on ultimate upstream development conditions. All piped storm drainage shall be designed such that at least one lane of any thoroughfare is open during a 100-year event, and such that any overflow due to a 100-year event storm is contained within the street right-of-way for non-thoroughfare streets or within the easement or right-of-way of non-street areas.
The intensity and duration of the rainfall shall be based on the Texas Department of Transportation formula and TxDOT coefficients for Tarrant County for areas less than 1000 acres. Technical Paper No. 40 of the Weather Bureau of the United States Department of Commerce, or other methods approved by the City Engineer, shall be used for larger areas. Flow in streams which have been studied by the U.S. Army Corps of Engineers and which have been studied and mapped by FEMA, shall use Corps data as an initial basis.