Public Works, Flood Control Engineering

Construction Guidelines for Structures

1. Structural elements (i.e.; columns, footings, peers, fill, buildings, bridges, etc.) will not be permitted to encroach upon the Floodway as defined by FEMA. The Floodway is defined by the area of the 100-year flood plain which can be filled without increasing the existing flood elevation by 1 foot or more.
   1. If the FLOODWAY is undefined, the Applicant must perform calculations as required to establish the 100-year flood plain and the floodway, including water surface elevations.
   2. If the structure changes the 100-year flood zone, these changes must be documented.
2. Structural plans for bridges must be analyzed and certified by a licensed Structural Engineer.
3. Rebar used in abutments, culverts, wing walls and such must have a minimum cover of 3 in (7.6 cm) from the water contact surface, and a minimum cover of 2 in (5.1 cm) from the soil contact surface.
4. A minimum of 3 feet (92 cm) freeboard distance is to be maintained between the 100-year flood level and the lowest chord or stringer of bridges. When freeboard requirements can not be met, the engineer must simulate a blockage of 3 feet below the bottom chord of the structure and calculate new flood elevations for a distance of 100 feet upstream of the structure.
5. Flood elevations may be calculated using the County's master plan flood flows or quoted from FEMA Flood Maps or the current Flood Insurance Study (FIS).
6. Private bridges and decks must be designed so as to allow removal without significant structural damage to the flood control facility. Property owners must agree to remove decks upon request by Salt Lake County for maintenance and other purposes.
   1. Structures which do not meet this requirement must provide a minimum of 15 feet (4.6 m) clearance above the channel flowline or, provide access ramps so that heavy equipment may enter and exit the channel for maintenance purposes.
7. Abutment footings and retaining walls should be located at least 3 feet (92 cm) below the channel flowline.
   1. If this requirement can not be met, document and submit the reasons and provide for bank protection from channel scour up to the footing elevation or the 100-year flood level, which ever is highest.
8. The first course of riprap used to stabilize and protect banks must be buried to a depth of 3 feet (92 cm) at the toe of a slope, must be appropriately graded, and may be covered by vegetation.
   1. Bank Slopes should be no steeper than 2:1 (horizontal to vertical) although slopes of 1:1 may be permitted if justified. Terracing with gabion baskets may be used for steeper slopes.
   2. Rubble, broken concrete and other ?garbage? MAY NOT be used for bank stabilization.
9. Drainage outfalls should not be fitted with pipe end sections or outlet structures (except to accommodate water quality provisions), and must have riprap or other erosion control measures installed.
10. Easements, or other appropriate instruments should be recorded for affected parcels or properties to insure the perpetuation of the requirements and restrictions of the Flood Control permit.