Water Level Control and Tidal Flows

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The Master Plan: The Lake Merritt Master Plan (City of Oakland, 2002) also includes proposals that would improve water quality. In addition to the installation of storm White Paper on Tidal Flows October, 2002 Page 9 drain filters, the plan recommends:

Replacement of the narrow culverts at 12th Street with a bridge.

Operational Changes: Improvements could be made by changing operational patterns at the flood control structure, e.g. providing more manpower to fine tune gate closures and Lake levels. At present this multi-million dollar facility is being operated largely to provide flood control at minimal labor costs. If additional manpower were assigned to this county facility during the times when gate closures are implemented (typically only several weeks per year) it would be possible to significantly reduce the time when tidal flows are restricted.

Recommendations: To improve water quality by providing better tidal flushing, promote the health of wetlands that are expected to be built in 2003, minimize low oxygen conditions and increase opportunities for the passage of migratory fish, the following are recommended:

• Restrictive tidal structures at 12th and 10th Streets should be replaced with bridges
  
• The flood control facility at 7th-8th Streets should be re-designed and moved to 12th Street
  
• Decisions on tide gate closure should be made daily every 12 hours, and should be based on computer modeling (using a program such the Corps of Engineers, Hydrologic Engineering Center’s RAS model). Gates should not be kept closed for longer than 12 hours unless current conditions indicate a flood is possible if high tides are allowed to enter the Lake.
  
• Tide gate closure should be avoided except during imminent flood threat, 12 hour periods for seaweed harvesting and for occasional 12 hour boating events or maintenance efforts.
  
• Alameda county should make personnel available on an as-needed basis, 7 days a week, to modify tide gate operation. For example, if a boat race ends on Saturday or Sunday afternoon, the gates should be opened that night, not Monday morning. In like manner, when rain is not expected within 12 hours, the gates should remain open. A 12 hour window should be adequate to drain the Lake on a low tide and close the gates to keep out a high tide.
• Optimal operation of this very expensive capital improvement should not be hampered by the cost of labor needed to run it. The damage to Lake Merritt marine life, future wetlands and to oxygen levels from keeping tide gates closed more than absolutely necessary far outweighs the cost of overtime for 1-2 employees several weeks per year.

Consideration of Flood Control: These recommendations are not in any way meant to compromise flood control. Floods can cause serious property damage, cost millions of dollars, and may even be life threatening. The judgement of a professional operator is needed to determine when such factors as ground water saturation, runoff, weather, wind and tidal conditions warrant more severe controls on Lake level and tidal restriction. Under severe circumstances where floods are likely, flood control must be the higher priority.

Balance Between Flood Control and Lake Health: Decisions on flood control however, should be made based on the best and latest information on a daily basis. For example, if tide tables do not indicate high tides, if rain has not occurred in several weeks, soils are dry, and there is a low percentage chance of rain, flooding is unlikely and natural tidal flows could be maintained. But if the forecast changes and significant rain is likely, gates could then be closed to keep out high tides. In this way flood control can be better balanced with the health of the Lake. Next >>

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