6 Flood Proofing Flood-proofing includes raising homes and Flood-proofing commercial buildings within the 100-year floodplain. These structures are then protected in a 100-year event reducing structure, content, and inventory damages as well as some cleanup costs. Raising buildings reduces flood damages related to the structures; however, no other damage categories are affected. For example, flood waters might still surround a home or business such that households would need to be relocated or businesses would need to close. Flood-proofing consists of the following:
Raising residential buildings to avoid damages from a 100-year event. The cost is based on $35 per square foot plus permitting, contractor fees, and incidental costs of 20%. Flood-proofing commercial and industrial buildings to avoid 100-year flood event damages. The cost of Floodproofing is based on costs published by the Federal Emergency Management Agency (FEMA)7 including building floodwalls, interior drainage, and closures. The costs amount to $4.67/square foot of flood wall surface plus $10,000 per building for permitting, backflow prevention, and contingencies.8 Flood-proofing and structure raising costs are limited by the value of the structure plus the land. If the structure plus land value is less than the cost to flood proof, the property would be purchased instead.
7 Flood Proofing Achievability The Flood-proofing component of the Project Alternatives includes raising all residential homes within the 100year floodplain. If the cost to raise a home is greater than the value of the structure plus land, the value of the structure plus land is included in the cost for Flood-proofing. Essentially, these homes and properties would be acquired. For other buildings (commercial, industrial, government, schools) the expected case assumes that only 25% of the buildings within the 100-year floodplain are flood proofed. This lower achievability rate was selected based on conversations with commercial property owners. While some buildings, regardless of flood level, would be flood proofed, some building owners would not flood proof based on one or more of the following factors: 1. Flood-proofing is not cost-effective. The cost of Flood-proofing is too high compared with the perceived risk. 2. Flood-proofing is not feasible. The property or business is not conducive to Flood-proofing measures such as walls, berms, or levees due to lack of space or business function. 3. Other location specific factors. The cost for commercial Flood-proofing is based on 25% of the total cost to flood proof all commercial buildings. Note that a cost-effectiveness evaluation for each building is not part of the study scope. The 25% achievability rate is the best approximation for achievability, cost, and impacts. In addition to the expected case, low and high achievability rates are analyzed. A low achievability rate of 10% is selected and a high rate of 50% is also analyzed. This range is based on conversations with local building owners regarding the applicability of Floodproofing. The high value represents a high achievability rate given the issues raised by building owners. The selected range of achievability reflects the uncertainty related to how many commercial building owners would implement Flood-proofing if provided with the opportunity. The results with low and high achievability rates are presented as part of the uncertainty analysis. 7
Southern Tier Central Regional Planning and Development Board. Selecting Floodproofing Techniques – Financial Considerations. FEMA. Floodproofing Info #10. 8
Floodproofing costs developed by Larry Karpack, Watershed Science & Engineering. Email dated March 5, 2014.
Chehalis Basin Strategy: Reducing Flood Damage and Enhancing Aquatic Species — Project Alternative Costs
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