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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.

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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.).

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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

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