Mark Twain Lake Water Control Manual Update

1. Mark Twain Lake Water Control Manual Update Joan Stemler St. Louis District Water Control

2. 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

3. The Goal • Reduce pool elevations without increasing downstream flooding while enhancing other project purposes • Flood Control • Hydropower • Recreation • Fish and Wildlife • Water Supply

4. Process • Solicit inputfrom 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

5. Alternatives

6. 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

7. 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

8. Maximum Release Alternatives • For pool elevations above 630.0 release: • 14,000 • 24,000 • For pool elevations above 620.0 release 75% of inflow

9. 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

10. 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)

11. Fish Spawn Alternatives • Fish Spawn Pool Elevations: • 606 thru 620

12. 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

13. 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

14. Proposed Plan vs Current Plan

15. 1993 • Actual • Proposed

16. 2008 • Actual • Proposed

17. Deviation 2010 • Actual • WCM

18. NEPA National Environmental Policy Act

19. 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

20. 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

21. Questions or Comments about NEPA? • NEPA Contact Brandon 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 at http://www.mvs.usace.army.mil/pm/EAreports.html

22. 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.

23. ? ? ? Questions ? ? ?