US Army Corps of Engineers BUILDING STRONG ® Mark Twain Lake Water Control Manual Update Joan Stemler St. Louis District Water Control.

US Army Corps of Engineers

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Mark Twain Lake Water Control Manual Update

Joan Stemler

St. Louis District Water Control

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2008 Event Overview Record flood event in July/August

►Pool = 640.4 NGVD►Outflow = 54,000 cfs

Funding was provided to update the Water Control Manual (WCM)►WCM was over due to be updated

Additional items funded►Updated Tailwater Rating Curve►Inundation Mapping for various flow scenarios►Updated Hydrology

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The Goal Reduce pool elevations without increasing

downstream flooding while enhancing other project purposes►Flood Control►Hydropower►Recreation►Fish and Wildlife►Water Supply

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Process Solicit input from the stakeholders, emergency

responders, and the public (6 meetings) Present alternatives to be analyzed (5 meetings) Analyze the alternatives (>150 alternatives) Present findings and propose a preferred operating

plan and take comments (9 meetings) Respond to comments and concerns (7 meetings) “Official” 30 day comment period Send draft WCM for Division approval

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Alternatives

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Crop Season Release Alternatives Change Crop Release Restriction to (Max releases are

based on downstream conditions):► 8,000 ► 10,000► 12,000

Graduated Scales► Max release: 8,000 at elevation 618.0 and is increased as

elevation increases to max 14,000 at elevation 638.0 (No Miss River restriction)

► When Miss River in flood, max 2,000 at <609.0 increasing to equivalent 24-hr generation at 621.0 (approximately 8,000). Max releases are based on downstream conditions

► When Miss River is not in flood and in crop season, sliding scale for max discharge 6,000 at <606.0 and 12,000 at 624.8. Max releases are based on downstream conditions

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Mississippi River Release Alternatives Release ahead of the Mississippi River crest and cut

24 hours prior to the crest Remove the Mississippi River restrictions Change the pool elevation where the Mississippi

River is no longer operated for from 624.8 to:► 615.0► 618.0► 620.0

Change the Mississippi River release restriction from 2,000 to 6,000

Raise the Mississippi River stage restriction:► Plus 5 feet► Plus 3 feet

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Maximum Release Alternatives

For pool elevations above 630.0 release:►14,000►24,000

For pool elevations above 620.0 release 75% of inflow

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Surcharge Regulation If pool elevation is forecasted to reach

surcharge (water on the ground), the max discharge may be preempted increased to discharge called for on the surcharge curve for that given elevation and inflow.

Recession side of Surcharge - Target 1 to 2 foot fall per day not to exceed previous max event release until pool elevation:

► 630.0► 620.0► 615.0

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Winter Drawdown and/or Guide Curve Change

Season Guide Curve Nov thru March►600.0

Other Alternatives Analyzed►Season Guide Curve Nov thru March

• 520.0 (Bottom of Reservoir)

►Year Round Guide Curve• 589.0 (Bottom of Hydropower Pool is 592.0)

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Fish Spawn Alternatives

Fish Spawn Pool Elevations:►606 thru 620

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Summary of Proposed Changes

Crop Release Restriction►Increased from 6,000 to 10,000

• Releases are based upon downstream conditions

Mississippi River Release Restrictions:►Max Release – when Louisiana or St. Louis is at or

forecasted to be at or above flood stage and not on the recession side of the hydrograph:• Pool Elevation lowered from 624.8 to 615.0• Increased from 2,000 to 6,000• Cut to 2,000 24hr prior to crest• Releases are based upon downstream conditions

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Summary of Proposed Changes

Surcharge►Max Release:

• If pool elevation is forecasted to reach surcharge (water on the ground), the max discharge may be preempted increased to discharge called for on the surcharge curve for that given elevation and inflow.

• Recession side of Surcharge - Target 1 to 2 foot fall per day not to exceed previous max event release until pool elevation 620.0

Fish Spawn►Start date changed from May 1st to April 23rd ►Pool Elevation at or below 610.0

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Proposed Plan vs Current Plan

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1993ActualProposed

Elev Diff (ft)

Actual 636.8 -

Proposed 629.6 -7.2

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2008ActualProposed

Elev Diff (ft) Flow Diff (cfs)

Actual 640.4 - 54,000 -

Proposed 638.7 -1.7 25,910 -28,090

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Deviation 2010

ActualWCM

Elev Diff (ft)

WCM 636.0 -

Actual 630.2 -6.2

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NEPA National Environmental Policy Act

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30 Day NEPA Review Period

The EA will be distributed to all interested parties►Includes all attendees of public meetings that

provided an address All interested parties are given 30 days to

review the environmental assessment and provide comments

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30 Day Review Period Continued

All comments received will be addressed on an individual basis, including any new or ongoing concerns

Such comments will be incorporated into the Environmental Assessment

A “Finding of No Significant Impact”, signed by the St. Louis District’s Commander, concludes the NEPA process assuming the public review results in a determination of no significant impact to the human environment

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Questions or Comments about NEPA?

NEPA ContactBrandon M. Schneider

Environmental Compliance Section

Planning and Environmental Branch (CEMVS-PD-E)

St. Louis District, U.S. Army Corps of Engineers

1222 Spruce Street

St. Louis, Mo 63103-2833

PH: 314-331-8496

Brandon.Schneider@usace.army.mil

EA will be posted athttp://www.mvs.usace.army.mil/pm/EAreports.html

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Approval Process for Revision of Water Control Plan

“Finding of No Significant Impact” from NEPA process is required

Review and approval of plan from Mississippi Valley Division (Vicksburg, MS) is required.

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? ? ? Questions ? ? ?