2023-04-24-minutes-public-works-study-session

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walking through the culvert, taking measurements and photographs, but could also involve the use of machinery within the structure limits. Clearances above the minimums provided below are allowed and may be desirable based on an analysis of the project's contextual needs. WSDOT Hydraulics Manual (M23-03): 7-4.5.1 Freeboard The 100 -year design freeboard is the minimum dimension from the 100 -year water surface elevation to the minimum low chord that is necessary to pass all expected debris, water, and sediment expected over the life of a structure. The figures in the Standard Plans further illustrate the terms used here (WSDOT 2021d). A minimum of 3 feet of freeboard above the 100 -year water surface elevation is required on all structures greater than 20 feet long and on all bridge structures unless otherwise approved by the HQ Hydraulics Section. The stream designer shall also confirm that local ordinance requirements are met and any necessary permit conditions are satisfied. The 100 -year design Freeboard required on all buried structures unless otherwise approved by the HQ Hydraulics Section are listed in Table 7-2. Table 7-2 100 -Year Design Freeboard Requirements on Buried Structures Structure Bankfull Width Required Freeboard Less than 8 -foot BFW 1 foot above 100 -year flow event 8- to 15 -foot BFW 2 feet above 100 -year flow event Greater than 15 -foot BFW 3 feet above 100 -year flow event (bridge) In areas that are tidally influenced, the impacts of 2 feet of sea level rise shall be considered for the project. For all projects, the stream designer shall consider providing the clearances in Table 7-2 above the 100 -year projected 2080 water surface elevation. The required minimum 100 -year design freeboard shall be maintained across the entire minimum hydraulic opening, as shown in the SFZ figures in the Standard Plans (WSDOT 2021d). If aggradation is expected to occur, additional freeboard shall be given above the 100 -year design freeboard equal to the anticipated aggradation. If the 100 -year design freeboard requirements listed above cannot be met, a deviation will be required in the specialty report and approval from the HQ Hydraulics Section is required. At a minimum, the stream designer shall demonstrate the following: • The proposed freeboard will pass all expected debris, water, and sediment • There is no history of repetitive maintenance at the crossing location