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WSDOT Bridge Design Manual (M23-50): <br />2.3.3.0 Vertical Clearances <br />Water crossings structures shall provide vertical clearance for both freeboard, maintenance, hydraulic <br />and, where applicable, shall satisfy navigation clearance requirements. <br />Bridges over navigable waters shall satisfy the vertical clearances required by the Coast Guard. <br />Communication with the Coast Guard will be handled through the Coast Guard Liaison Engineer. The <br />actual minimum vertical clearance (to the nearest 0.1 foot) for the channel span shall be shown on the <br />Preliminary Plan. The approximate location of the minimum vertical clearance shall be noted in the <br />upper left margin of the plan. The clearance shall be shown to the water surface as required by the Coast <br />Guard criteria. <br />Minimum vertical clearances for the 100 -year design freeboard and Maintenance shall be determined <br />and documented in accordance with the WSDOT Design Manual M 22-01 Section 720.03(5)(b)(4) for <br />Water Crossing Structures. The roadway profile and the bridge superstructure depth shall accommodate <br />all minimum vertical clearances provided. <br />The actual minimum vertical clearance to the 100 -year flood shall be shown (to the nearest 0.1 foot) on <br />the Preliminary Plan, and the approximate location of the minimum vertical clearance shall be noted in <br />the upper left margin of the plan. <br />WSDOT Design Manual (M22-01) <br />720.03(5)(b)(iv) Water Crossing Structures <br />When determining the vertical clearance beneath a bridge or inside a buried structure, there are two <br />elements that must be considered. The first is 100 Year Design Freeboard (Freeboard), and the second is <br />Maintenance Clearance. <br />Freeboard is related to the hydraulic capacity of the structure and is required by state and federal <br />guidance. Typically, all bridges and buried structures are required to have a minimum of 1-3 feet of <br />Freeboard above the 100 -year water surface elevation (see WSDOT Hydraulics Manual). The State <br />Hydraulics Engineer determines the Freeboard, and it is documented in the Preliminary/Final Hydraulic <br />Design Report (PHD/FHD). Approval from the State Hydraulics Engineer is required for any vertical <br />clearance that is less than Freeboard. <br />Maintenance Clearance is the distance from the highest ground elevation within the horizontal limits of <br />the Hydraulic Width to the controlling top elevation. The State Hydraulics Engineer determines the <br />Hydraulic Width, and it is documented in the PHD/FHD. Providing Maintenance Clearance beyond the <br />minimum Freeboard is beneficial for required monitoring and inspections, as well as any maintenance <br />activities that may be required during the life of the structure. Generally, these activities include staff <br />