Why does Beaver Lake Dam have Interim Risk Reduction Measures?

All USACE dams with similar or higher risk classifications as Beaver Dam are required to have a risk reduction plan.  An interim plan is implemented while more research is done to determine the best ways to reduce the risk at a dam.

What is an Interim Risk Reduction Measures Plan (IRRMP)?

An interim risk reduction measures plan is a series of measures put in place to reduce the risks of a catastrophic event at a USACE project.  The plan is considered interim because the measures may or may not be part of the long-term risk buy-down once the issues have been studied more closely for best solutions.

What is an Interim Risk Reduction Measure (IRRM)?

An interim risk reduction measure is an action to reduce a known risk.  The action is considered interim because the measure may or may not be part of the long-term buy-down once the issue has been studied more closely for best solutions.​

What does DSAC mean?

DSAC stands for Dam Safety Action Classification.​

How is risk evaluated for a USACE project?

What has been the history of the White River Water Management Plan?​

Beaver Lake began to fill in December 1963.  From 1963 until 1998, the upper four lakes of the White River sub-system used a seasonal guide curve at Newport where the regulating stages were 21 feet, 18 feet, and 14 feet. Greers Ferry used a seasonal guide curve at Georgetown where the regulating stages were 21 feet, 19 feet, and 16 feet. During the 1960’s into the early 1990’s the agriculture industry requested annual deviations from the Water Control Plan (WCP) for a lower regulating stage at Newport. Due to the regular, reoccurring deviation requests, in the spring of 1993, Southwest Division (SWD) directed Little Rock District (SWL) to form an Ad Hoc group of the various stakeholders within the White River Basin and allow them to investigate possible changes to the WCP. A recommended plan was unanimously endorsed by the Group as the best possible compromise plan. SWL evaluated the Group's recommended changes and were satisfied that they were both technically sound and within our authority to implement, without Congressional action.

The resulting action was the 1998 WCP plan. Since 2008, according to NOAA precipitation data, the White River Basin is receiving an average additional 10+ inches of rain annually. The increased annual rainfall has resulted in an increased duration of perched pools. Prior to 2008 Beaver had 6 surcharges releases less than 40,000 cfs and one surcharge greater than 40,000 cfs. Since 2008 Beaver has surcharged 18 additional times, four of which were greater than 40,000 cfs. The proposed interim plan which adjusts seasonal guide curves at Newport and Georgetown reduces the risk of the frequency and magnitude of surcharges for the entire system. The proposed plan attempts to encompass the flexibility of the 1963 and the 1998 Water Control Plans to reduce risk to the dams while operating to stages that are familiar to downstream stakeholders. Targeting higher seasonal regulating stages allows for higher flood risk management releases during months most likely to receive runoff producing rainfall and provides more storage

How many IRRMs are being implemented at Beaver Lake Dam?​

There are approximately 15 non-operational IRRMs for Beaver Lake Dam and three operational IRRMs (how water is managed at the dam).​

What are the non-operational IRRMs for Beaver Lake Dam?

• Emergency action plan

• Communication plan

• Emergency exercises

• Stakeholder meetings

• Emergency communications

• Seasonal testing of remote gate operations

• Public education

• Inundation maps

• Lake release probability frequency analyses

• Downstream warning system

• Emergency flood barriers (inside dam)

• Increased monitoring plan for seepage

• Gate equipment waterproofing

• Hoist and catwalk door waterproofing

• Added sensors for remote operation​

What are the three operational IRRMs for Beaver Lake Dam?​

• Double flood risk management minimum release after floods.​

• Deeper Drawdown After Surcharge (release to prevent gates from overtopping).​

• Revised Guide Curves at Newport and Georgetown.​

What risk is being decreased by the operational IRRMs for Beaver Lake Dam?

The IRRMs are designed to reduce the risk that the machines that lift and lower the gates are inundated by high water.  Reducing the risk of losing the gates also reduces the risk of overtopping the dam or the gates being stuck in a position that allows large releases. See Figure 2 through Figure 4 for pictures of machinery, top of gates, and high pool proximity to the machinery.

Figure 2. Machine Deck is at elevation 1133.5 feet.

Figure 3. 2015 flood event, two days after the flood peak at 1132.04

Figure 4. May 10, 2018, elevation 1128.5', catwalk (middle), top of gates (left), and machine platform (lower left).

Why is USACE implementing operational changes for Beaver Lake Dam and the White River system?

The operational changes reduce:

1. the population at risk by about 1000 people per day,

2. the number of days at Beaver Lake Dam the flood pool is full or nearly full,

       and the frequency that Beaver Lake reaches the elevations near the machinery.​

What temporary operational changes will USACE be making to decrease risk at Beaver Lake?

Three operational changes are being made at Beaver Lake Dam.

How long are the IRRMs expected to last?

The plan is to follow the IRRMs for three years.  This time might be shortened if ongoing analyses reveal a better way to reduce risks at Beaver Lake Dam.​

I like the operational IRRMs, could they be made permanent?

The IRRMs cannot be made permanent without a careful study of ways to best address the risk.  Even if the IRRMs are shown to be the best long-term solution, the IRRMs are subject to National Environmental Policy Act (NEPA) evaluation.  Additional study may discover better alternatives than the IRRMs.​

What sort of differences might I see at Beaver Lake due to the operational IRRMs?

The lake is expected to spend more time near top of conservation pool instead of top of flood pool.  

The lake levels are not expected to change much during the winter but should see a reduction the fraction of time the lake is high during late spring, summer, and fall. The releases will shift, there will be less days with releases near 1,000 cfs (approximately firm power release) and more days with releases near 2000 cfs (approximately double firm power release) because the minimum flood release is doubled.​

What sort of differences might I see at Bull Shoals Lake due to the operational IRRMs?

Bull Shoals Lake will not be affected as much as Beaver Lake; however, Bull Shoals Lake may experience fewer days near the top of its flood pool during summer months.  Bull Shoals Dam releases are not expected to change much.​

What sort of differences might I see at Greers Ferry Lake due to the operational IRRMs?

Greers Ferry Lake is the least impacted lake from the IRRMs.  It may see a few more days near top of conservation pool, days of releases at 3,000 cfs should decrease, and the occasional 10,000 cfs release might begin sooner after a large flood event.​

How might farming downstream of the lakes (near Newport, AR) be impacted by the operational IRRMs?

The impacts are expected to be mixed depending on where the farming is occurring and what agricultural practices are being used.​ Holding a stage near 21 to 24 feet is expected to be more likely in late April, but not other times during the growing season. ​

The time the river is calculated to be near 14 feet is not expected to change much between the current plan and the IRRM during the summer and fall.​ The time the river is at 12 feet is expected to noticeably decrease for both wet and dry years during the summer and fall.​

How might farming downstream of the lakes (near Georgetown, AR) be impacted by the operational IRRMs?

Expecting similar results as Newport.​

What sort of differences might I see at Norfork Lake do the operational IRRMs?

Norfork Lake will not be affected as much as Beaver Lake; however, Norfork Lake may experience fewer days near the top of its flood pool in the summer.  Norfork Lake releases are not expected to change much.​

What sort of differences might I see at Table Rock Lake do the operational IRRMs?

Table Rock Lake will not be affected as much as Beaver Lake; however, Table Rock Lake may experience fewer days near the top of its flood pool in the summer.  Table Rock may see a small decrease in the time it makes flood releases.