Public Works, Flood Control Engineering

17.08.090 Replacement, new bridges
and culverts-Design criteria

A. Replacement and new bridges or culverts on the natural tributaries and open man-made channels, except irrigation canals, listed in Section 17.08.040, shall be sized for a frequency based on consideration of the benefits and costs derived from the improvements.

As a minimum all such bridges and culverts shall be designed to pass the greater of the one-hundred-year snowmelt runoff or the twenty-five-year cloudburst storm unless the director of the division of flood control and water quality shall deem such level of protection unwarranted. In any case, replacement culverts or bridges with an equivalent opening of sixty inches in diameter, or greater, shall be sized for at least the one-hundred-year snowmelt or twenty-five year cloudburst standard.

Bridges and culverts on Big and Little Cottonwood Creeks through the valley floor shall be designed for the greater of the one-hundred-year snowmelt or the one-hundred-year cloudburst storm for present development conditions. In addition to the design flow, consideration shall be given to the freeboard necessary to pass debris and accommodate bed load and bulking.

B. The phrase ""one-hundred-year snowmelt"" means that snowmelt runoff of the magnitude which is expected to occur on the average of a one-hundred-year frequency or has a one-percent chance of being equalled or exceeded during any one year.

C. The phrase ""twenty-five-year cloudburst storm"" means that cloudburst storm of the magnitude which is expected to occur on the average of a twenty-five-year frequency or has a four-percent chance of being equalled or exceeded during any one year. (Ord. 921 §§ 1, 1985: prior code §§ 7-2-9)