18S.40.060 Flood Hazard Management

18S.40.060 Flood Hazard Management.

The intent of the Flood Hazard Management policies and regulations is to minimize public and private losses due to flood conditions in flood hazard areas.

A. Applicability. This Section applies to actions taken to reduce flood damage or hazard. Flood hazard reduction measures subject to the requirements of this Section may consist of nonstructural measures such as setbacks, wetland restoration, levee or revetment removal, use relocation and bioengineered measures, gravel removal (scalping or dredging), and of structural measures such as levees, revetments, setback levees and setback revetments, floodwalls, channel realignment, and elevation of structures.

1. These regulations are in addition to those in Chapter 18E.70 PCC, Flood Hazard Areas.

2. This Section does not apply to mining; instead refer to PCC 18S.40.080, Mining.

1. Demonstrate avoidance of adverse impacts to shoreline uses, resources, and values, including shoreline geomorphic processes, water quality, fish and wildlife habitat, commercial aquaculture, scenic resources, and bank erosion.

2. Give preference to flood hazard reduction measures that consist of nonstructural measures such as setbacks, land use controls, wetland restoration, dike removal, impervious surface reduction, use relocation, vegetation retention, biotechnical measures, and stormwater management programs.

3. Flood hazard reduction measures may include structural measures such as dikes, levees, revetments, floodwalls, channel realignment, and elevation of structures.

4. Limit development, flood control structures, and other shoreline modifications that may adversely impact property or public improvements, or result in a net loss of ecological functions associated with rivers and streams, by interfering with channel migration processes.

5. Return river and stream corridors to more natural hydrological conditions, recognizing that seasonal flooding is an essential natural process.

6. Consider the removal or relocation of structures in flood hazard areas when evaluating alternate flood control measures.

7. Allow flood hazard management structures only when the following can be demonstrated:

a. They are necessary to protect development;

b. Nonstructural measures are not feasible; and

c. Appropriate vegetation conservation actions are undertaken.

8. Give preference to placing new flood hazard reduction structures landward of wetlands and associated buffers.

1. Proposals for flood hazard management measures shall demonstrate, by engineering and scientific evaluation, the following:

a. Measures are necessary to protect health, safety, or existing legally established development;

b. Measures are consistent with an adopted flood hazard management plan that evaluates cumulative impacts to the watershed system; and

c. Benefits of the flood hazard project outweigh the anticipated environmental impacts.

2. Removal of gravel for flood management purposes shall be consistent with an adopted flood hazard reduction plan and shall be allowed only after a biological study and geomorphologic study show that extraction has a benefit to flood hazard management, does not result in a net loss of ecological functions, and is part of a comprehensive flood management solution.

3. Removing material from rivers and streams for the sole purpose of flood control may be permitted under the following conditions:

a. The location and quantities of sand and gravel or other materials to be removed are specified;

b. Extraction amounts, rates, timing and locations are based on a scientifically determined sediment budget adjusted periodically according to data provided by a regular monitoring plan;

c. The development will not adversely affect the natural processes of gravel transportation for the river or stream system as a whole. Specific studies prepared by a hydrogeologist and included with the application shall demonstrate that any adverse flood, erosion, or other environmental impacts occurring either upstream or downstream of extraction sites are mitigated; and

d. The development shall be limited to work that occurs out of the water unless the project is adopted by a governmental agency or approved comprehensive flood hazard management plan.

4. Accessory aggregate processing (crushing, washing, screening, stockpiling, and staging areas) may occur on site on a temporary basis after review of potential impacts.

5. Riprapping and other bank stabilization measures shall be located, designed and constructed to protect the natural character of the waterway.

6. Levees, revetments, berms and similar flood control structures shall be shaped and planted with vegetation suitable for wildlife habitat when feasible.

7. Regulated Channel Migration Zones (CMZ) are identified in PCC 18E.10.140 H.4.a. For regulated CMZs that have not yet had a study adopted by Pierce County, the default CMZ shall be the regulated FEMA floodway area. For more information regarding Channel Migration Zones, please refer to Chapter 18E.70 PCC, Flood Hazard Areas.

1. New structural flood hazard reduction measures shall be:

a. Permitted only in those circumstances in which nonstructural flood hazard reduction measures will not achieve the intended flood hazard reduction; and

b. Constructed and maintained in a manner that does not degrade water quality.

2. Groundwater movement and surface water runoff shall be considered in the design and operation of new structural flood hazard reduction measures.