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Canyon Flooding: Next Steps

Canyon Flooding: Next Steps. Presented by Steve King, Public Works Director-Engineering. No. 1 Canyon Drainage Fifth Street on July 28th. Canyon Drainage Problems. Flooding and debris from higher up in the canyons (outside the city) Poorly maintained drainages on private property

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Canyon Flooding: Next Steps

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  1. Canyon Flooding: Next Steps Presented by Steve King, Public Works Director-Engineering

  2. No. 1 Canyon DrainageFifth Street on July 28th

  3. Canyon Drainage Problems • Flooding and debris from higher up in the canyons (outside the city) • Poorly maintained drainages on private property • Obstructions in the canyon drainages on private property

  4. No. 2 Canyon Drainage Blockage on No. 2 Canyon Drainage inlet with grass clippings and debris above Brandi Terrace on private property. Backyard of 1607 Brandi Terrace on 7/29/10

  5. Flood History

  6. Past Flood Hazard Studies • Army Corps of Engineers Study (1974) • Chelan County Public Works Study (1977) • Munson Engineers Wenatchee Area Flood Hazard Report (1980) • Northwest Hydraulics Flood Hazard Investigation of Alluvial Fans below Canyon No. 1, Canyon No. 2 and Dry Gulch (1996) • Hammond Collier Wade Livingstone Stormwater Management Plan for City of Wenatchee (2000)

  7. Summary of Flood Hazard Reports • Canyon No. 1 and No. 2 pose the highest risk of potential mud flows. • Risk factors • high hill slope gradient • high rainfall intensity (greater than 1.25 inches/hour) • lack of vegetation • land-use practices

  8. Recommended Structural Best Management Practices (BMPs) • Debris control dams and large concrete conveyance structures (Corps Study, 1974) • 10 to 20 acre flat, grassy areas at the mouths of the canyons (Chelan Co. Public Works, 1977) • Debris control dams and stilling basins (Munson Engineers, 1980) • Debris control dams and increase capacity of city stormwater conveyance system (HCWL, 2000)

  9. Zintel Canyon Dam, Kennewick Completed in 1992 Cost: $7,275,000

  10. What’s been done • 2010 Comprehensive Stormwater Plan Update • Grants for flood control measures in the city • Maintain right-of-way crossings • Respond to complaints • Existing City Code • In new subdivisions, developers are required to improve/preserve the existing drainage channels for Dry Gulch, No. 1 and No. 2 Canyons (WCC 11.24.080). • City can require a drainage easement (WCC 11.20.060). • Minimum lot sizes can be increased as slopes increase to avoid or mitigate drainage, siltation, and flood control problems (WCC 11.20.050). • Flood hazard controls are addressed for areas within the flood zone (WCC 2.02.010 et seq.).

  11. Possible Next Steps • Maintenance of Drainage channels under private ownership • Public Service Announcements • Develop city code regarding drainage channel maintenance

  12. Draft Code Language “Watercourse” shall mean a stream or established drainage for stormwater coming from outside the urban area WATERCOURSE PROTECTION. Every person owning property through which a watercourse passes, or such person's lessee, shall keep and maintain that part of the watercourse within the property free of trash, debris, excessive vegetation, and other obstacles that would pollute, contaminate, or significantly retard the flow of water through the watercourse. In addition, the owner or lessee shall maintain existing privately owned structures within or adjacent to a watercourse, so that such structures will not become a hazard to the use, function, or physical integrity of the watercourse. (This language is from the EPA Model Ordinance for Illicit Discharges).

  13. Next Steps continued… • Develop flood control measures through City stormwater utility • Debris & Detention ponds for the canyons • Flood Channel Development • Pursue formation of a Flood Control District • Regional flood control measures • Access to federal funding

  14. Cal Anderson Park, Seattle(vaulted stormwater park facility)

  15. Recreation Field, Vancouver, BC(above ground stormwater facility)

  16. Flood Control Zone DistrictRCW 86.15 • Quasi municipal corporation of the State of Washington Initiated by county legislative authority or by petition • General Powers • Plan, construct, acquire, repair, maintain, and operate all necessary equipment & facilities. • Take action necessary to protect life and property from flood water damage. • Control, conserve, retain, reclaim and remove flood water and stormwater. • Accept funds or property by loan, grant, gift or otherwise. • Remove debris, logs and other material which may impede the orderly flow of waters in streams and water courses • Fees Options include but are not limited to: Excess levy authorized by voters, assessments, annual property tax not to exceed fifty cents per $1000 assessed value, & stormwater fee charges.

  17. Regional Flood Control Examples • Greater East Wenatchee Stormwater Utility • Riverside Flood Control District (Okanogan County) • Yakima County Flood Control Zone District • Walla Walla County – 3 flood control districts

  18. Questions & Discussion

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