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“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”
Kevin Landwehr, P.E., D.WRERock Island DistrictU.S. Army Corps of Engineers6 April 2017
DES MOINES RIVER RESERVOIRSWATER CONTROL PLAN UPDATES
IOWA ASCE WATER RESOURCES DESIGN CONFERENCE
1
• Purpose and Motivation For Updates • Overview of the Reservoir Projects and their
Congressionally Authorized Purposes• Current Water Control Plan Philosophy• Challenges and Concepts Being Evaluated• Study Timeline and Status
PRESENTATION OVERVIEW
• USACE has initiated an update of the Des Moines River Reservoir Regulation Manual which includes the Water Control Plans for Saylorville Lake and Lake Red Rock.
• Water control plans provide decision making guidance for water management of each individual reservoir or system of reservoirs and ensure the operations of reservoirs conform to laws and applicable USACE rules.
• Water control plans consist of operational parameters that define when, and how much, water is stored and released. These include a schedule of releases, conservation pool levels to be maintained during non-flood or drought conditions, and downstream water level constraints.
SCOPE OF STUDY
• Focus of the study is how to best manage water with the existing, authorized project.
Important to understand that:
• There will always be a residual risk of flooding. No alternative plan can prevent all flooding or drought (capacity of the reservoirs is limited), goal is to identify the water management strategy (plan) that allows us to best meet the Congressionally authorized project purposes. Continued risk communication is important!
• Changes in the water control plans that affect when reservoir storage is utilized (and associated release rates) generally involve trade-offs. Stakeholder input is critical to evaluating the benefits and impacts associated with alternative plans.
SCOPE OF STUDY (CONT.)
DES MOINES RIVER BASIN5
SAYLORVILLE LAKE
• Authorized by Congress - 3 July 1958
• Initial filling to conservation level in September 1977
• Modifications to Regulations:
► 1982 – Pool raised from 833 feet to 836 feet as part of the Water Supply Contract (Iowa)
► 1994 – Pneumatic Crest Gates installed on overflow spillway section
LAKE RED ROCK
• Authorized by Congress - 28 June 1938
• Construction completed in 1969
• Modifications to Regulations
► 1979 – Conservation Pool raised from 725 feet to 728 feet
► 1982 – Flash Flood Operation was Implemented (10.8 feet at Ottumwa)
► 1988 – Conservation Pool raised from 728 feet to 734 feet; Maximum growing season release raised to 22,000 cfs when pool exceeds 760 feet; Start of the growing season changed from 21 April to 01 May
► 1992 – Pool raised from 734 feet to 742 feet
CONGRESSIONALLY AUTHORIZED PURPOSES
Saylorville Lake and Lake Red Rock:• Flood Risk Management (Primary)
Des Moines and Upper Mississippi Rivers• Water Conservation/Low Flow Augmentation• Water Supply (Saylorville only)• Fish and Wildlife• Recreation*
Private Hydropower Development Currently Under Construction at Lake Red Rock
*Access and facilities are provided for recreation but water
is not controlled for this purpose.
WHY UPDATE THE WATER CONTROL PLANS?
Floods of 1993, 2008, 2010.
Conditions change over time and it is important to periodically review and update the water control plan to address current and anticipated future conditions.
What has changed?• Observed changes in the frequency and magnitude of flood
and drought events.• Changes in land use and flood risk management infrastructure
(e.g., levees within the City of Des Moines).• Impacts of Sedimentation.
9
ANNUAL PRECIPITATION – CENTRAL IOWA10
11
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 2015
Peak
30-
Day
Inflo
w (c
fs)
Saylorville Reservoir Peak 30-Day Inflow 1917-2016
12
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 2015
Peak
30-
Day
Inflo
w (c
fs)
Red Rock Reservoir Peak 30-Day Inflow 1917-2016
13
http://corpsmapu.usace.army.mil/cm_apex/f?p=313:2:0::NO:::
WHY UPDATE THE WATER CONTROL PLANS?
Floods of 1993, 2008, 2010
Conditions change over time and it is important to periodically review and update the water control plan to address current and anticipated future conditions.
What has changed?• Observed changes in the frequency and magnitude of flood and
drought events.• Changes in land use and flood risk management
infrastructure (e.g., levees within the City of Des Moines).• Impacts of Sedimentation.
14
IMPACTS OF SEDIMENTATION• Sedimentation was anticipated as part of original reservoir
design.• Greatest impact is to conservation storage, impacting:
drought management, natural resource management, and recreation.
15
Reduction in Flood Control Storage Since Impoundment• Saylorville – 1.3%• Red Rock – 16%• Coralville – 12.5%
Reduction in Conservation Storage Since Impoundment• Saylorville – 19%• Red Rock – 44%• Coralville – 64%
OVERVIEW OF CURRENT WATER CONTROL PLANS
• Water control plans consist of operational parameters that define how, and when, water is stored and released. These include a schedule of releases, conservation pool levels to be maintained during non-flood or drought conditions, and downstream water level constraints.
• Approved by Mississippi Valley Division Commander.
• Contain provisions for deviations from approved plans.– Subject to approval by Division Commander.
16
GENERAL PHILOSOPHY OF WATER CONTROL PLANS
• Saylorville Lake and Lake Red Rock are operated as a system.
• During non-flood or drought periods release reservoir inflow to maintain conservation pool.
• Normal Flood Operations - During flood events limit release to “safe” discharge, allowing for tributary inflows downstream of the reservoir; excess inflow is stored in the reservoir.
– Reservoir “Balancing” of flood storage
17
BUILDING STRONG®
!?
!?
!?!?
!?
!?
!?
Des Moines River Basin
Raccoon River Basin
Ottumwa, Iowa
Keosauqua, Iowa
Quincy, Illinois
Burlington, Iowa
Lake Red Rock Reservoir
Saylorville Lake Reservoir
SE 6th Street, Des Moines, Iowa
Des Moines River Reservoirs and Constraints
Operation of Lake Red RockSummer of 1998
690
700
710
720
730
740
750
760
770
1-Jun 8-Jun 15-Jun 22-Jun 29-Jun 6-Jul 13-Jul 20-Jul 27-Jul 3-Aug 10-Aug 17-Aug 24-Aug 31-Aug1998
Elev
atio
n (f
t. N
GVD
)
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
Flow
(cfs
)
Normal Conservation Pool Elevation 742.0 ft. NGVD
Reservoir Pool Elevation
Lake Red Rock Outflow
Lake Red Rock Inflow
Top of Full Flood Control PoolElevation 780.0 ft. NGVD
GENERAL PHILOSOPHY OF WATER CONTROL PLANS
• Saylorville Lake and Lake Red Rock are operated as a system.
• During non-flood or drought periods release reservoir inflow to maintain conservation pool.
• Normal Flood Operations - During flood events limit release to “safe” discharge, allowing for tributary inflows downstream of the reservoir; excess inflow is stored in the reservoir.
– Reservoir “Balancing” of flood storage
• Large Magnitude Flood Operations - If a significant portion of the reservoir storage has been utilized, begin releasing progressively higher flows. Downstream constraints are no longer in effect.
20
GENERAL PHILOSOPHY OF WATER CONTROL PLANS(CONT.)
• If the full flood control capacity is exceeded, outflows are increased further and focus of operations is on dam safety.
• Following flood events, outflows are managed to evacuate flood storage as quickly as possible, controlling the rate of fall within the reservoir.
• During periods of drought (inflow falls below minimum desired conservation flow), augment inflows with conservation storage to maintain desired conservation releases (coordinated with Iowa DNR).
If reservoir continues to fall, progressively scale back releases giving highest priority to water supply.
21
STATE OF IOWA WATER SUPPLY CONTRACT
• In 1982 Iowa purchased storage in Saylorville Lake for consumptive water supply – 18.86% of conservation storage
This storage was determined to provide a continuous flow of 75 cfs with 99% reliability
Reliability has reduced over time due to sedimentation in reservoir
• Conservation pool was raised 3 feet to accommodate the contract
• State has authority to withdraw water from the lake or to order releases through the outlet works
• Iowa has subcontracted 2/3 of the water to the Des Moines Water Works and 1/3 to Alliant Energy
CHALLENGES AND CONCEPTS• Managing flood volume vs. managing flood risk.
• Need for flexibility in plan.
File Name
23
Elevation 742 – Conservation Pool0 % Flood Control Storage Utilized
Elevation 76031 % Flood Control Storage Utilized
Elevation 780 – Full Flood Control Pool100 % Flood Control Storage Utilized
Elevation 775 – Start of Large Magnitude Flood Operation79 % Flood Control Storage Utilized
Lake Red Rock – Growing Season (May 1 – Dec 15) Water Control Plan
Current Plan Overview
• 18,000 cfs maximum release.• Reduce releases below maximum release as needed to maintain
Ottumwa and Keosauqua Gages below 7.5 and 17.6 feet, respectively (5,000 cfs minimum release).
• If Burlington or Quincy Gage on Upper Mississippi River is forecast to exceed 18.5 or 20.0 feet, respectively, reduce outflow to reduce peak on Mississippi to the extent possible (variable minimum release based on reservoir elevation).
• 22,000 cfs maximum release.• Reduce releases below maximum release as needed to maintain
Ottumwa and Keosauqua Gages below 8.7 and 18.4 feet, respectively (5,000 cfs minimum release).
• If Burlington or Quincy Gage on Upper Mississippi River is forecast to exceed 18.5 or 20.0 feet, respectively, reduce outflow to reduce peak on Mississippi to the extent possible (variable minimum release based on reservoir elevation).
• 30,000 – 60,000 cfs maximum release based on reservoir elevation.• No downstream constraints on release.
• 60,000 – 130,000 cfs maximum release based on pool elevation up to Elevation 785; uncontrolled (open spillway) release thereafter.
• No downstream constraints on release.
Top of DamElevation 797.0 feet
Flood Control Storage1,463,250 Acre-Feet*
Design Flood Surcharge Storage
Conservation Storage185,450 Acre-Feet
• Maintain 300 cfs minimum conservation release until reservoir falls to elevation 734.0. Progressively lower releases as reservoir continues to fall.
Elevation 744Seasonal (Fall) Conservation Pool Raise
* Storage values based upon 2011 survey.
CHALLENGES AND CONCEPTS• Managing flood volume vs. managing flood risk.
• Need for flexibility in plan.
• Increase water in the system and the need to evaluate tradeoffs in FRM benefits.
File Name
25
EVALUATION TOOLS• Leveraging modeling tools developed as part of USACE ational
modernization of Corps Water Management System (CWMS)• HEC-ResSim• HEC-RAS• HEC-FIA
File Name
26
CHALLENGES AND CONCEPTS• Managing flood volume vs. managing flood risk.
• Need for flexibility in plan.
• Increase water in the system and the need to evaluate tradeoffs in FRM benefits.
• Reservoir “balancing”.
File Name
27
CHALLENGES AND CONCEPTS• Managing flood volume vs. managing flood risk.
• Need for flexibility in plan.
• Increase water in the system and the need to evaluate tradeoffs in FRM benefits.
• Reservoir “balancing”.
• Future Sedimentation and Balancing Drought and Flood Storage Considerations.
File Name
28
OPPORTUNITY!
SUSTAINABLE RIVERS PROJECT• Partnership with The Nature Conservancy to achieve
more ecologically sustainable flows, while maintaining or enhancing project benefits.
• Currently working with natural resource agencies to identify alternative strategies that could be included in the water control plans to provide environmental benefits (habitat, improved water quality, etc.).
29
UPDATE STUDY TIMELINE• Began Planning Process Oct 2016• Public Scoping Meeting Jan/Feb 2017• Identify and Evaluate Alternatives Feb - Oct 2017• Draft Recommendation/Report Dec 2017• Agency and Public Review Feb - May 2018• Final Approved Manual Sep 2018
30
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