16.36.140 Floodways.
Located within the area of special flood hazard established in IMC 16.36.040 are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles, and erosion potential, the following provisions apply:
A. Prohibit encroachments, including fill, new construction, substantial improvements, and other development unless certification by a registered professional engineer is provided demonstrating through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that the proposed encroachment would not result in any increase in flood levels during the occurrence of the base flood discharge. New construction and substantial improvements meeting this standard shall comply with all applicable provisions of IMC 16.36.130.
B. Construction or reconstruction of residential structures is prohibited within designated floodways, except for (1) repairs, reconstruction, or improvements to a structure that do not increase the ground floor area; and (2) repairs, reconstruction, or improvements to a structure, the cost of which does not exceed 50 percent of the market value of the structure either (a) before the repair or reconstruction is started, or (b) if the structure has been damaged, and is being restored, before the damage occurred. Any project for improvement of a structure to correct existing violations of state or local health, sanitary, or safety code specifications that have been identified by the local code enforcement official and that are the minimum necessary to assure safe living conditions, or to structures identified as historic places, may be excluded in the 50 percent.
C. Agricultural uses, including crops, nursery stock, tree farming, stream improvements and all stream maintenance functions or operations of any government agencies, or private individuals, public works such as streets, bridges, water and sewer and other underground utility lines, and park and recreational facilities, excluding structures, may be permitted in the floodway when shown to be in conformance with the provisions of this chapter.
D. Substantially Damaged Residential Dwellings in Floodways Other Than Farmhouses. For all substantially damaged residential structures, other than farmhouses, located in a designated floodway, the Department of Ecology, at the request of the City, is authorized to assess the risk of harm to life and property posed by the specific conditions of the floodway. Based upon scientific analysis of depth, velocity, flood-related erosion and debris load potential, the Department of Ecology may exercise best professional judgment in recommending to the City repair, replacement or relocation of a substantially damaged structure consistent with WAC 173-158-076. The property owner shall be responsible for submitting to the City any information necessary to complete the assessment required by this section when such information is not otherwise available.
1. Recommendation to repair or replace a substantially damaged residential structure located in the regulatory floodway shall be based on the flood characteristics at the site. In areas of the floodway that are subject to shallow and low velocity flooding, low flood-related erosion potential, and adequate flood warning time to ensure evacuation, the Department of Ecology may recommend the replacement or repair of the damaged structure. Any substantially damaged residential structure located in the regulatory floodway in a high risk zone based on the flood characteristics will not be recommended to be repaired or replaced. Flood warning times must be 12 hours or greater, except if the local government demonstrates that it has a flood warning system and/or emergency plan in operation. For purposes of this subsection, flood characteristics must include:
a. Flood depths cannot exceed more than 3 feet; flood velocities cannot exceed more than 3 feet per second.
b. No Evidence of Flood-Related Erosion. Flood erosion will be determined by location of the project site in relationship to channel migration boundaries adopted by the City. Absent channel migration boundaries, flood erosion will be determined by evidence of existing overflow channels and bank erosion.
2. At the request of the City, the Department of Ecology will prepare a report of findings and recommendations for the City concurrence on repair or replacement of substantially damaged residential structures located in the regulatory floodway. Without a recommendation from the Department of Ecology for the repair or replacement of a substantially damaged residential structure located in the regulatory floodway, no repair or replacement is allowed per subsection B of this section.
3. Before the repair, replacement, or reconstruction is started, all other requirements of this chapter must be satisfied. In addition the following conditions must be met:
a. There is no potential safe building location for the replacement residential structure on the same property outside the regulatory floodway.
b. A replacement residential structure is a residential structure built as a substitute for a previously existing residential structure of equivalent use and size.
c. Repairs or reconstruction or replacement of a residential structure shall not increase the total square footage of floodway encroachment.
d. The elevation of the lowest floor of the substantially damaged or replacement residential structure is a minimum of 1 foot higher than the base flood elevation.
e. New and replacement water supply systems are designed to eliminate or minimize infiltration of floodwater into the system.
f. New and replacement sanitary sewerage systems are designed and located to eliminate or minimize infiltration of floodwater into the system and discharge from the system into the floodwaters.
g. All other utilities and connections to public utilities are designed, constructed, and located to eliminate or minimize flood damage.
E. All Other Building Standards Apply in the Floodway. If subsection (A) of this section is satisfied or construction is allowed pursuant to subsection (B) of this section, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of this chapter.
F. Livestock Sanctuary Areas. Elevated areas for the for the purpose of creating a flood sanctuary for livestock are allowed on farm units where livestock is allowed. Livestock flood sanctuaries shall be sized appropriately for the expected number of livestock and be elevated sufficiently to protect livestock. Proposals for livestock flood sanctuaries shall meet all procedural and substantive requirements of this chapter. (Ord. 2915 § 1 (Exh. A), 2020; Ord. 2775 § 1 (Exh. A), 2016; Ord. 2420 § 1, 2005; Ord. 2030 § 6, 1994; Ord. 1827 § 8, 1989; Ord. 1465 § 7(C), 1981).