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Town Lake Dam Replacement Technology Choices


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This slideshow gives information about the variety of options studied by Gannett Fleming on the dam technology choices for Tempe Town Lake. More information can be found at and click on Dam Replacement in the blue box in the upper right hand corner of the webpage.

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Town Lake Dam Replacement Technology Choices

  1. 1. Tempe Town Lake Downstream Dam ReplacementALTERNATIVES EVALUATION UPDATE<br />IRS Tempe City Council September 22, 2011<br />
  2. 2. Timeline<br /><ul><li>Alternatives Evaluation – June thru November
  3. 3. Project Update with Council – September 22
  4. 4. Phase 1 Validate Concept & Select Dam Technology – November
  5. 5. Phase 2 Design New Dam – August 2012
  6. 6. Acquire Permits – July 2013
  7. 7. Bid and Procure Construction Contract – October 2013
  8. 8. Fabricate New Dam – November 2014
  9. 9. Construction Complete – December 28, 2015*</li></ul>* Per current agreement with Bridgestone.<br />
  10. 10. Town Lake: Part of a River System<br />Granite Reef Dam Watershed Map<br />
  11. 11. Town Lake: Part of a River System<br />Salt River Watershed Schematic Diagram<br />Tempe Town Lake Dam<br />
  12. 12. Current Level of Flood Protection<br />Designed to maintain or improve current levels of flood protection <br />– 210,000 cubic feet per second (cfs.) <br />This is consistent with the rest of the river system.<br />
  13. 13. Dam Must<br /><ul><li>Maintain Waters of Town Lake
  14. 14. Handle Flows from Storms, Regular Water Sources
  15. 15. Return Lake to Normal After Floods
  16. 16. Handle Water from Extreme Flood Events Smaller Than 210,000 cfs
  17. 17. Meet Regulatory Requirements
  18. 18. Be Safe</li></li></ul><li>Dam Design Criteria<br />Maintain or Improve Current Level of Flood Protection <br />Maintain Full Lake Quickly After Flood Event<br />Raise, Lower and Operate Reliably at Normal Lake Levels <br />Be Cost Efficient – Capital, Lifespan, O&M <br />Have Parts Easily Available <br />Be Compatible with Pedestrian Bridge, Existing Structures<br />Meet Regulatory Requirements<br />Perform Well in this Climate<br />
  19. 19. Regulatory Conditions<br />
  20. 20. Flood Control Criteria<br />Flood Control District <br />of Maricopa County:<br /><ul><li>Use 200-Year Discharge for Design as it’s Close to Capacity of Area Bridges (like Mill Ave, Rural Rd)
  21. 21. West Dam 200-Year Discharge: 204,000 cfs
  22. 22. East Dam 200-Year Discharge: 207,000 cfs
  23. 23. Tempe Town Lake Capacity Discharge: 210,000 cfs</li></li></ul><li>Current Alternatives Evaluation<br />About 20 Dam Options Studied:<br /><ul><li>Radial (tainter) Gates
  24. 24. Bascule or Bottom-Hinged Leaf Gates
  25. 25. Inflatable Rubber Dams (water and air-filled)
  26. 26. Ogee Crest Weirs
  27. 27. Labyrinth Weirs
  28. 28. Many Styles of Fuse Plugs
  29. 29. Several Styles of Pneumatically-Operated Hinged Crest Gates (Obermeyer)
  30. 30. Hydraulic Hinged Crest Gates
  31. 31. Dyrhoff Rubber Dams (Sumitomo)
  32. 32. Vertical Lift Gates
  33. 33. Swing Gates
  34. 34. Fusegates (Hydroplus)
  35. 35. Earth Embankment/Fuseplug
  36. 36. Several Styles of Mixed-type Spans
  37. 37. Cable-Operated Hinged Crest Gate
  38. 38. Others</li></li></ul><li>Mixed Type Alternatives:Concrete Sections and Gates<br />Gate Section<br />Concrete Section<br />Gate Section<br />Concrete Section<br />Gate Section<br />Concrete Section<br />Gate Section<br />Concrete Section<br />Gate Section<br />Concrete Section<br />Gate Section<br />Concrete Section<br /><ul><li>Different technologies in the different spans between the existing piers
  39. 39. Concrete dams in outer spans and gates in inner spans
  40. 40. Gate section atop concrete section each span</li></li></ul><li>Results of Restricted Flow<br />Results of alternative that requires additional piers<br />
  41. 41. Results of Restricted Flow<br />Results of Mixed Type Alternative that Impedes Two Spans<br />
  42. 42. Earthen (Fuseplug) Embankment<br /><ul><li>Typically located within an auxiliary spillway channel.
  43. 43. Zoned earth and rockfill embankment with a sloping impervious core
  44. 44. Designed to wash out in a predictable and controlled manner.</li></li></ul><li>Earthen (Fuseplug) Embankment<br />Alternative not carried forward due to uncertain performance, potential to increase upstream flooding, inability to maintain lake after storm and permitting issues<br />
  45. 45. Alternatives Carried Forward<br />Obermeyer Crest Gates<br />Fusegates<br />Hinged Crest Gates<br />Inflatable Rubber Dams<br />1<br />2<br />4<br />3<br />
  46. 46. Inflatable Rubber Dams<br /><ul><li>Rubber body fixed to a reinforced concrete foundation
  47. 47. Inflated by pumping air or water until height is reached
  48. 48. Deflated by allowing the air or water inside the rubber body to escape</li></li></ul><li>Inflatable Rubber Dams<br />
  49. 49. Fusegates (Hydroplus)<br /><ul><li>Consists of a bucket, a base, and an intake well connected to a chamber in the base
  50. 50. Designed to breach and wash out when overtopped</li></li></ul><li>Fusegates (Hydroplus)<br />
  51. 51. Obermeyer Crest Gates<br /><ul><li>Steel gate panels supported on their downstream side by inflatable air bladders
  52. 52. Water elevation maintained by controlling the pressure in the bladders </li></li></ul><li>Obermeyer Crest Gates<br />
  53. 53. Hinged Crest Gates (Hydraulic Operation)<br /><ul><li>Steel gate panels hinged at the bottom
  54. 54. Operated with overhead pier-mounted hydraulic cylinders</li></li></ul><li>Hinged Crest Gates (Hydraulic Operation)<br />
  55. 55. Hinged Crest Gates (Electric Operation)<br /><ul><li>Steel gate panels hinged at the bottom
  56. 56. Operated with wire rope electric motor hoist</li></li></ul><li>Hinged Crest Gates <br />(Electric Operation)<br />
  57. 57. Dam Budget<br />Minus $367,000 Gannett Fleming Contract for Dam Technology Analysis<br />
  58. 58. Dam Financing<br /><ul><li>Preliminary Capital Cost Estimates: $25 - $35 Million
  59. 59. Includes Design, Materials, Construction
  60. 60. Does Not Include East Dam or Pump System
  61. 61. Finance Options Include:</li></ul>Use Remaining $3,633,000<br />Seek Voter Approval for Bond Authorization for Dam Replacement Capital Costs<br />Sale of City Properties<br />Combinations<br />
  62. 62. Next Steps<br /><ul><li>Public Meeting on Oct. 17, 6 p.m. Tempe Center for the Arts
  63. 63. Failure Modes and Effects Analysis
  64. 64. Third Party Review
  65. 65. Gannett Fleming, Staff Will Recommend Dam Technology
  66. 66. Review Financing Options
  67. 67. Bring Selected Dam System to Council in November</li></li></ul><li>Want more information? <br />Visit and<br />Click on Town Lake Dam Replacement in the Blue Box<br />