WSDOT policy regarding design storm frequency for hydraulic structures has been established so the PEO does not have to perform a risk analysis for each structure on each project. The design storm frequency is referred to in terms of mean recurrence interval (MRI) of precipitation. A more detailed discussion of MRI can be found in Chapter 2. New hydraulic structures shall also consider climate resilience for final design size by evaluating higher storm events. Consult the RHE and the State Hydraulics Office early for discussion and concurrence climate-resilient designs.
For design of hydraulic features, the PEO shall review Section 1-3.2.3 for required design tools and software. The PEO shall work with the RHE to verify that the required design tools and software are used for design of hydraulic features.
If the PEO wants to use a design tool or hydraulic software that has not been approved by the State Hydraulics Office, the PEO shall provide a side-by-side comparison analysis showing the differences between the approved design tool or approved software and the proposed design tool or proposed software. The analysis shall be submitted to the RHE for review and approval. The approval of using an alternative design tool or alternative software shall be obtained before the intermediate hydraulic report can be submitted. Contact the RHE for additional guidance.
Table 1-2 presents a design reference chart and approved software.
