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1 Flood/Stormwater Flood/Stormwater Education, Prevention, Education, Prevention, and Response Update and Response Update March 3, 2009 March 3, 2009 ---PAGE BREAK--- 2 Tonight Tonight’s Presentation s Presentation Flood Causes Flood Causes Preventive Options Preventive Options Responses to Flooding Responses to Flooding ---PAGE BREAK--- 3 Flooding Causes Flooding Causes There are two primary mechanisms There are two primary mechanisms associated with flooding within the City: associated with flooding within the City: - First, major storm events within the City Limits. First, major storm events within the City Limits. - Secondly, major storm events within the Secondly, major storm events within the Puyallup River Watershed. Puyallup River Watershed. ---PAGE BREAK--- 4 Flooding Causes Cont Flooding Causes Cont’d Secondary Causes: Secondary Causes: - Shallow groundwater elevation. Shallow groundwater elevation. - Low surface gradients (slopes) on the valley Low surface gradients (slopes) on the valley floor. floor. - Saturated soil conditions. Saturated soil conditions. ---PAGE BREAK--- 5 Flood Causes Cont Flood Causes Cont When there is a major storm event within When there is a major storm event within the City, the storm system may be the City, the storm system may be overwhelmed by surface runoff resulting in overwhelmed by surface runoff resulting in flooding. flooding. However, flooding within the City will also However, flooding within the City will also occur when the Puyallup River is above occur when the Puyallup River is above normal flow, regardless of a storm event normal flow, regardless of a storm event within the City. within the City. ---PAGE BREAK--- 6 Flood Causes Cont'd Flood Causes Cont'd There are two major There are two major “pathways pathways” for water from the river to for water from the river to flow into the City, Clarks Creek and Deer Creek. (Consider flow into the City, Clarks Creek and Deer Creek. (Consider these these “pathways pathways” as breaches through the levee). as breaches through the levee). As a result, the high river water does not allow the creeks As a result, the high river water does not allow the creeks and City storm system to drain. This is called the and City storm system to drain. This is called the Backwater Affect. Backwater Affect. Bottom Line Bottom Line – Any increase in river surface elevations and Any increase in river surface elevations and the resultant backwater affect can have serious the resultant backwater affect can have serious consequences on our community, i.e., higher levees or consequences on our community, i.e., higher levees or sediment buildup. sediment buildup. ---PAGE BREAK--- 7 Flood Causes Cont'd Flood Causes Cont'd As the water rises during a flood event, the creek level also rises until it can find an outlet in a low lying area. ---PAGE BREAK--- 8 Flood Causes Cont'd Flood Causes Cont'd ---PAGE BREAK--- 9 Flood Causes Cont'd Flood Causes Cont'd Also, flood elevations are relative. Also, flood elevations are relative. The USGS Gage Station near the City is at River Mile 6.6, The USGS Gage Station near the City is at River Mile 6.6, just upstream of the confluence with Clarks Creek. just upstream of the confluence with Clarks Creek. The 1% Chance Flood, or 100 The 1% Chance Flood, or 100-year event, flood level at the year event, flood level at the Puyallup Gage Station is elevation 30.0 feet. Puyallup Gage Station is elevation 30.0 feet. When the Gage Station is at flood stage, areas within the When the Gage Station is at flood stage, areas within the City at higher elevations may be flooded due to the slope City at higher elevations may be flooded due to the slope (gradient) of the river. (gradient) of the river. ---PAGE BREAK--- 10 10 Flood Causes Cont'd Flood Causes Cont'd ---PAGE BREAK--- 11 11 Preventive Options Preventive Options To mitigate the negative impacts of the To mitigate the negative impacts of the Puyallup River backwater on Clarks Creek Puyallup River backwater on Clarks Creek and/or Deer Creek, a flood gate and/or Deer Creek, a flood gate-pump pump station would be required at the respective station would be required at the respective confluences with the river. confluences with the river. Extremely unlikely due to ESA, permitting, Extremely unlikely due to ESA, permitting, and costs. and costs. ---PAGE BREAK--- 12 12 Preventive Options Preventive Options Other methods to mitigate the backwater Other methods to mitigate the backwater affect within the City is to lower the river affect within the City is to lower the river water surface elevations. This can be water surface elevations. This can be accomplished by: accomplished by: - Sediment reduction (very controversial). Sediment reduction (very controversial). - Setback levees (costly) Setback levees (costly) - Controlled flows (dams) Controlled flows (dams) ---PAGE BREAK--- 13 13 Preventive Options Preventive Options Due to the extreme sediment loading of the Due to the extreme sediment loading of the river, continuous sediment reduction river, continuous sediment reduction projects can never be the end projects can never be the end-all solution . all solution . Also, sediment reduction projects on Clarks Also, sediment reduction projects on Clarks Creek and/or Deer Creek will provide only Creek and/or Deer Creek will provide only localized relief and will not alleviate the localized relief and will not alleviate the flooding associated with the Puyallup River flooding associated with the Puyallup River backwater. backwater. ---PAGE BREAK--- 14 14 Preventive Options Preventive Options City City’s Approach to Flood Protection s Approach to Flood Protection - Enforce current City standards and regulations in an Enforce current City standards and regulations in an effort to not make flooding worse and improve effort to not make flooding worse and improve conditions where possible. conditions where possible. - Undertake capital improvements to convey flows as best Undertake capital improvements to convey flows as best as possible: as possible: - Construction of the 15 Construction of the 15th th Street NW Trunk Line Street NW Trunk Line - Replacement of the failing 14 Replacement of the failing 14th th Street SW storm system with a new Street SW storm system with a new box culvert box culvert - Future conveyance of Deer Creek through a 72 Future conveyance of Deer Creek through a 72-inch diameter inch diameter culvert, replacing an existing undersized 36 culvert, replacing an existing undersized 36-inch culvert inch culvert - Basin planning Basin planning - Strategic property purchases Strategic property purchases ---PAGE BREAK--- 15 15 Preventive Options Preventive Options Before (Dec ‘07) After (Jan ’09) ---PAGE BREAK--- 16 16 Responses to Flooding Responses to Flooding Citizens can, and should, prepare themselves Citizens can, and should, prepare themselves prior to flood events by: prior to flood events by: - Maintaining storm drains, ditches, and creeks located on Maintaining storm drains, ditches, and creeks located on private property. private property. - Getting emergency contact information organized. Getting emergency contact information organized. - Preparing a family disaster Preparing a family disaster-communication plan communication plan including rendezvous locations. including rendezvous locations. - Assemble disaster preparedness kits. Assemble disaster preparedness kits. Additional resource information may be obtained Additional resource information may be obtained from the Department of Emergency Management. from the Department of Emergency Management. ---PAGE BREAK--- 17 17 Responses to Flooding Responses to Flooding In emergency situations, the City In emergency situations, the City’s Emergency s Emergency Management Team works closely with regional Management Team works closely with regional safety personnel as well as the staff of Public safety personnel as well as the staff of Public Works to mitigate hazards to life and property. Works to mitigate hazards to life and property. - The Emergency Management Team is activated and The Emergency Management Team is activated and determines the level of event risk. determines the level of event risk. - Public Works crews mobilize equipment and materials Public Works crews mobilize equipment and materials to known areas of concern prior to flooding. to known areas of concern prior to flooding. ---PAGE BREAK--- 18 18 Responses to Flooding Responses to Flooding Depending on the level of risk: Depending on the level of risk: - Citizen advisories are issued via the City Citizen advisories are issued via the City’s s website, Reverse 911 calls, and/or in person. website, Reverse 911 calls, and/or in person. - Emergency shelters are opened. Emergency shelters are opened. - Evacuation procedures and routes are Evacuation procedures and routes are determined. determined. ---PAGE BREAK--- 19 19 Responses to Flooding Responses to Flooding In conclusion, the City is at risk of flooding In conclusion, the City is at risk of flooding whenever the Puyallup River exceeds whenever the Puyallup River exceeds “normal normal” flows. flows. City staff and the Department of Emergency City staff and the Department of Emergency Management will continue to coordinate their Management will continue to coordinate their emergency response efforts, improve upon emergency response efforts, improve upon previous performance by building upon lessons previous performance by building upon lessons learned, and educate our community on safety learned, and educate our community on safety preparedness and what it means to live in or near preparedness and what it means to live in or near a floodplain. a floodplain.