Sec. 26.17.04.07. Changes in Stream Channels or Floodplains

A. In addition to the general requirements, as described in Regulation .04 of this chapter, the following special requirements shall apply to applications for changes in stream channels or floodplains. The following information shall be submitted with the application unless specifically waived by the Administration:

(1) Alternate proposal studies.

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

(3) Type and source 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 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 proposed project, showing location; land ownership; contours of presently existing ground and proposed fill or excavation; presently existing and proposed structures, buildings, roads, and drainage structures; the proposed additionally inundated area associated with the 100-year flood event; and all cross sections taken.

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

(c) Water surface profiles computed using an energy balancing method, showing the invert elevation of the stream bed, water surface elevations in feet above mean sea level, and water velocity, by segment, in feet per second, associated with the 2-year, 10-year, and 100-year frequency flood events, for both the presently existing and proposed conditions, at each cross section. Cross sections shall be taken at appropriate intervals to a point, both downstream and upstream of the proposed project, where the presently existing and proposed water surface profiles coincide.

(d) Cross section plots, showing stream and floodplain elevations as well as any proposed modifications and water surface elevations.

B. Design 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) Proposed floodplain encroachments may not increase the tractive force by more than 10 percent during the passage of the 2-year and 10-year frequency flood events unless it can be demonstrated that the channel will remain stable.

(4) Proposed floodplain encroachments may not reduce the natural meander width of the channel as measured from outside bank to outside bank.

(5) Proposed floodplain encroachments, except for roadways, culverts, and bridges, shall be designed to provide a minimum of 1 foot of freeboard above the elevation of the 100-year frequency flood event. In addition, the elevation of the lowest floor of all new or substantially improved residential, commercial, or industrial structures shall also be at least 1 foot above the elevation of the 100-year frequency flood event.

(6) Proposed unlined earth channels may not change the tractive force associated with the 2-year and the 10-year frequency flood events, by more than 10 percent, throughout their length unless it can be demonstrated that the stream channel will remain stable.

(7) Proposed lined channels may not change the tractive force associated with the 2-year and the 10-year frequency flood events, by more than 10 percent, at their downstream terminus unless it can be demonstrated that the stream channel will remain stable.

(8) An environmental study, which identifies existing natural resources as well as proposed mitigation measures to offset the impacts of the channelization, shall accompany a proposed channel change.

C. Repair. Before beginning the repair of any works permitted pursuant to this regulation, the owner shall apply for, in writing, and obtain a permit from the Administration for the proposed work. The application for a permit shall include 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:

(a) May make the minimum repairs necessary to safeguard life and property against imminent danger without prior written approval of the Administration;

(b) Shall notify promptly the Administration of the emergency repairs necessary and the extent of work underway;

(2) Work shall conform to any requirements specified by the Administration.

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

(4) In all cases, including emergencies described in §D(1)(a) of this regulation:

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

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