Temporary Use of Sediment Pool for Emergency Water Supply at Falls Lake

Transcription

1 Temporary Use of Sediment Pool for Emergency Water Supply at Falls Lake Tony Young, P.E. Water Management Chief Wilmington District USACE Water Supply Workshop Savannah, GA 1 2 June 2011 US Army Corps of Engineers Wilmington District

2 Aerial View of Falls Lake Project

3 Project Location ~ Neuse River Basin North Carolina

4 Falls Lake Project Authorized Operating Purposes Flood Control Water Supply Water Quality Recreation Fish/Wildlife PL

5 BUILDING STRONG

6 BUILDING STRONG

7 Water Supply Primary water supply for City of Raleigh, NC City of Raleigh owns the total water. supply storage in Falls Lake as an original project sponsor POR safe yield is currently estimated to be about 63 mgd City withdraws water directly from lake

8 Drought Conditions ~ Dec 2007 Record-setting extreme drought with forecast to completely deplete conservation pool in early 2008 Less than 100 days of WS storage remaining 24% WS storage remaining 16% WQ storage remaining All non-essential water uses banned No readily available, adequate alternative water supplies (purchases, GW, etc)

9 Alternative Courses of Action No Action Continue normal operation depleting conservation pool storage resulting in zero water supply withdrawals by the City of Raleigh and provide minimum 7Q10 release of 27 cfs downstream with whatever sediment pool storage remained (Not realistic) Variations of the No Action alternative (still not realistic) Dredging (expensive, time-consuming, still no more water) Use Section 6 authority to temporarily reallocate 20,000 AF of remaining sediment pool storage to water supply for the State of North Carolina (selected)

10 Sediment Pool...why an option? Resurveys indicate very little sedimentation, due in large part to development of several upstream reservoirs. City has a river intake that predates the reservoir, so they would still have withdrawal capability.

11 Agreement Basics Temporary Sediment Pool reallocation would be to the State of NC, not to City of Raleigh State would determine how much water would go to Raleigh for WS, versus being released for downstream WS needs. Temporary agreement for a period not to exceed 5 years (1 yr initial with up to 4 annual renewals). Letter report (completed) required as attachment, includes: summary of need and alternatives considered review of potential impacts EA/FONSI Cost determinations (updated cost of storage) Delegate signature authority to District Commander for implementation when needed

12 Early Schedule (prepared in mid-dec 07 assuming depletion of conservation pool on April 1 st )

13 3 years later... Current Status Thankfully Falls bottomed out Christmas Day 2007, but it also took away the urgency. SAW has continued to coordinate with SAD and HQUSACE, but it s been fairly slow-paced...couple of remaining issues: Format of agreement Pricing policy...likely pursuing policy waiver (annual lease w/out interest vs 30-yr amortization) Meanwhile, Raleigh has added two supplemental water supply sources and continues work to acquire additional water supply: New Water Supply Reservoir on downstream trib Permanent reallocation of excess sediment storage Reallocation of WQ storage to WS storage WS Reallocation from Kerr Reservoir (IBT & Interstate issues)

14 QUESTIONS? CONTACT: Michael A (Tony) Young michael.a.young@usace.army.mil

15 Incidental Water Supply Storage Permits for Residential Irrigation at John H. Kerr Reservoir Tony Young, P.E. Water Management Chief Wilmington District USACE Water Supply Workshop Savannah, GA 1 2 June 2011 US Army Corps of Engineers Wilmington District

16 ISSUE: 200+ adjacent property owners already withdrawing water from reservoir for lawn irrigation under Shoreline Use Permits no M&I water supply storage in Kerr, except what has been reallocated from power pool under 58 WSA authority continued irrigation demands APPROACH: formalized, consistent district policy quantify acceptable cumulative irrigation withdrawals that won t impact other project purposes still allow minor conditional irrigation

17 AUTHORITY: ER , MODIFICATIONS TO COMPLETED PROJECTS Paragraph 8.d, Modification under Existing Authority, Multiple Purpose Projects, Addition of Water Supply Pursuant to the Water Supply Act of 1958, reallocation of reservoir storage to add water supply (as a purpose) to a completed project may be undertaken under the Chief's discretionary authority when it will have no significant effect on other authorized purposes and will involve no major structure or operational change. In addition, local interests and adjacent or nearby property owners may be allowed under license, granted for an administrative charge, to install facilities across project lands to withdraw minor amounts of water for which storage is not required and which does not affect project purposes. (This does not constitute a water supply "purpose.") Policies concerning the modification of a project to serve water supply functions are described in ER (Chapter 7).

18 SOLUTION: limited number of conditional-use permits (Incidental WS Storage Permits) for local, adjacent residential property owners granted for an administrative charge commensurate with the value of such privilege and cost of real estate processing (reviewed and adjusted at least every 5 years) Permission to withdraw minor amounts of water for residential irrigation without a formal storage agreement. Formalized in SAW Commander s Policy Memorandum No. 40

19 RATIONALE FOR MINOR AMOUNT: limited to an inconsequential fraction of the incremental storage between the top of the power pool (elev 300.0) and the seasonal drawdown level (elev 295.5), or approx 210,700 AF chose a fraction of 0.4% of this incremental storage, which should be computationally insignificant for daily accounting and have minuscule lake level impacts (< 0.02 ft)

20 COMPUTATIONS: Max Available Storage: x 210,700 AF = AF Annual Water Use: AF/user/yr 1 per week irrigation 22 wks per year approx 1 ac lots Number of Permits Allowed: 483 (currently 200+ users) Permit Cost: $ updated cost of storage: $404 per AF access is restricted to upper 47% of storage (adjustment factor applied)

21 PERMIT RESTRICTIONS/CONDITIONS: Single 2 diameter water line Minimum intake elevation for water line: feet, msl 4 ft below our summer pool / 4.5 ft below top of power pool Limits access/impacts during serious droughts ~80% of power pool still remaining below Limited number of permits available: 483 Location and elevation of lines and pumps clearly documented Permit can be revoked at anytime

22 QUESTIONS? CONTACT: Michael A (Tony) Young michael.a.young@usace.army.mil