FLH PDDM Chapter 9 - Eastern Federal Lands Highway Division

9.4.E. Drainage Design.E. Drainage Design. Drainage facilities convey both normal surface and subsurface waters (and withinreasonable limits, expected flood and storm waters) across along, or away from a highway. The designerconsiders the most cost efficient and practical manner to do this without undue damage to the highway, thedrainage facility, or adjacent stream channels and property. Various types of drainage methods will accomplishthis, including the use of open channels, riprap and channel lining, bridges, culverts, storm drains, underdrains,and related appurtenances. Some installations require provisions for fish passage.Chapter 7, Hydrology/Hydraulics, contains information, references and methods for designing drainagefacilities.The designer shall include all of the drainage facilities in the contract plans and make certain the specificationscontain provisions for these facilities.The designer is responsible for the design of drainage facilities and for submitting requests and data to thehydraulics engineer, the bridge unit, and the geotechnical unit. The designer normally designs all minordrainage structures and appurtenances, such as small culverts (1200 millimeters and smaller), end sections,catch basins, and inlets as well as minor drainage channels and ditches.Large culverts and channels are usually sized by the hydraulic engineer or by the designer with the assistanceof the hydraulic engineer.Bridge design (layout, minimum opening under bridge, pier placement, etc.) is the co-responsibility of thebridge unit and the hydraulics engineer.The geotechnical unit is responsible for specialized design of underdrains, horizontal drains, drainage blankets,and subdrainage systems using geotextile fabrics. They are also responsible for obtaining pH values of soilsand waters and for determining foundation materials for bridges and large culvert installations.Refer to Chapter 7, Section 7.1 to determine responsibilities of drainage design.The designer shall furnish lines, grades, cross sections, detail maps, and vicinity maps to the hydraulicsengineer and the bridge and geotechnical unit for design.The designer often adjusts grades (and lines) to provide adequate cover for culverts, minimum clearance underbridges, or for other constraints imposed by drainage facility designs performed by others.Early in the design process, the designer should consult with the hydraulics engineer, the bridge unit, and thegeotechnical unit where any special needs are foreseen. Also, early in the design process, the designer shoulddiscuss the need for various Federal, State, and local permits and approvals with the hydraulics engineer.The designer must review the environmental documents and correspondence with fish and wildlife agenciesand review all permits to ensure that all drainage requirements are in the contract.The hydraulics engineer or the bridge unit designs the larger and more complicated drainage facilities.However, the designer must have familiarity with the design principles and methods to supply adequateinformation so others can design these facilities. The designer should know the minimum vertical dimensionsof structures to adjust the highway grade, and should be aware of alternative designs that could affect the lineand grade of a highway.9 - 89