Sec. 26.17.04.06. Bridges and Culverts

A. In addition to the general requirements as described in Regulation .04 of this chapter, the following information shall be submitted with all applications for bridges and culverts unless specifically waived by the Administration:

(1) Alternate proposals studied.

(2) Geologic investigations and conclusions based upon geologic maps, surface investigations, seismic or other geophysical studies, or borings.

(3) Type and source (on-site or off-site) of borrow and fill materials to be used in construction.

(4) Estimated cost of the project and the length of time required for construction.

(5) Construction plans and specifications.

(6) Construction Schedule. The construction schedule shall include the following:

(a) The sequence of construction phases, such as channel and structure excavation, structure and embankment construction;

(b) Equipment stream crossings and storage areas;

(c) Means for diverting stream flow during construction;

(d) Means for controlling the dewatering discharges;

(e) Means for controlling runoff during the various construction phases.

(7) Map and measurement of the drainage area upstream of the proposed project.

(8) General plan of the proposed project, showing location; land ownership; contours of presently existing ground and proposed structures, buildings, roads and drainage structures; and the proposed additionally inundated area associated with the 100-year flood event.

(9) Design report, which shall at a minimum, include the following:

(a) Discharge-frequency curve, which shall include the discharge, in cubic feet per second, associated with the 2-year, 10-year, and 100-year frequency flood events;

(b) Stage-discharge curve, which shall include the water surface elevation, in feet above mean sea level, associated with the 2-year, 10-year, and 100-year frequency flood events, for both the presently existing and the proposed conditions;

(c) Slope, cross section, and capacity of the presently existing stream channel and average bankful velocity.

B. Designs and Specifications.

(1) References used by the designer shall be cited in the application submitted to the Administration, especially where unusual features are incorporated in the design.

(2) Specifications shall be written to assure that design criteria, with regard to the quality of the materials and methods of construction, will be met or exceeded.

(3) The length of culverts shall be limited to a maximum of 150 feet unless it can be demonstrated through an environmental study that any adverse impacts will be adequately mitigated.

(4) The proposed project shall be designed to safely withstand the hydrostatic and hydrodynamic forces associated with at least the 100-year frequency flood event throughout the project area.

(5) Adequate protection shall be provided in the design of all bridge piers, abutments, and culvert entrances and outlets to prevent damage due to scour. Protective measures may not prevent the passage of fish.

(6) Culverts shall have at least one cell placed at least 1 foot below the invert of the stream. In the case of bedrock foundations, culverts shall be designed without a concrete invert unless measures are incorporated into the design to ensure that fish habitat or migration patterns are not adversely affected.

(7) All bridges shall completely span stream channels which have a width from top-of-bank to top-of-bank of 80 feet or less, as measured along the centerline of the proposed roadway.

(8) The outlet velocity of culverts which is associated with the dominant discharge may not exceed the existing stream channel velocity associated with the dominant discharge. A higher than existing stream channel velocity may be allowed at a culvert outlet when or if measures are incorporated into the design to prevent increases in stream channel erosion.

(9) The maximum allowable Froude number, associated with the 100-year frequency flood event as calculated through the bridge opening or at the outlet of the culvert, shall be as follows:

(a) 0.9, if the presently existing Froude number is less than or equal to 0.9; or

(b) The presently existing Froude number, if the presently existing Froude number is greater than 0.9.

(10) The Froude number, Fr, shall be given by:

Fr=V divided by (gy)^0.5

when, V = average velocity, in feet per second;

g = acceleration of gravity, in feet per second per second;

y = depth, in feet.

C. Repair of Bridges and Culverts. Before commencing the repair of any bridge or culvert, the owner shall apply for, in writing, and obtain a permit from the Administration for the proposed work. The application for a permit shall give the name and address of the applicant, details of the proposed changes, referenced to the existing structure, and shall be accompanied by the necessary plans and specifications. If the proposed work may best be explained by description, this description shall be included as part of the application along with the proposed time of commencement and completion of construction, as well as other information the Administration may require.

D. Emergency Repairs.

(1) In an emergency, a person may make only the minimum repairs necessary to safeguard life and property against imminent danger without obtaining prior written approval of the Administration for the necessary emergency repairs.

(2) The person initiating repairs shall contact the Administration within 24 hours.

(3) To the extent possible, all work shall conform to the requirements specified by the Administration.

(4) If additional works, maintenance, or repairs not necessary to safeguard life and property against imminent danger are also considered by the owner, the owner shall obtain a permit in accordance with Regulation .02 of this chapter.

(5) Except as provided in §D(1) of this regulation:

(a) The Administration shall be notified before any motorized equipment enters the stream channel; and

(b) Approval from the Administration shall be obtained before any channel modifications are initiated in conjunction with emergency repairs.