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Ashton & Chester Dam Updates
Disclaimer: This information is provided as a courtesy by the Henry's Fork Foundation. Every effort will be made to make sure the information is accurate and timely. Please contact the Foundation if you have questions or concerns.
January 23, 2013
The Ashton Dam Remediation Project has drawn to a close after two years of construction. PacifiCorp finished filling the Ashton Reservoir at the end of December and the dam has since returned to run-of-river operation. This means the amount of water flowing in the reservoir is released below the dam. From the project's inception, the Henry's Fork Foundation and regulatory agencies have stressed the importance of the fisheries on the lower river. Though construction caused increased turbidity and limited access for much of the 2011 fishing season, the long-term impacts are likely to be minimal.
This project was required to address dam safety concerns that could have impacted downstream properties and fisheries. In 2009, PacifiCorp engaged federal and state agencies, the Henry's Fork Foundation and the Henry's Fork Watershed Council in consultation about the project. The Henry's Fork Watershed Council continued to serve as an important forum during the project.
September 21, 2012
HFF received news this week that PacifiCorp will begin refilling Ashton Reservoir in November. This refill is currently planned to take 46 days. Updates will be provided by PacifiCorp if this plan changes. The project is moving along on schedule and should finish this year. Reports from the river are that turbidity has been low, but that there is some sediment in slow, slackwater areas. As with any project of this nature, turbidity and overall river conditions can change daily without notice. HFF will continue to monitor the progress of the project.
August 21, 2012
HFF received good news Tuesday when PacifiCorp announced they would not have to draw down the Ashton Reservoir in order to fix leakage problems with the coffer dam. PacifiCorp discovered that a concrete cut-off wall underneath the existing dam could be used to allow the project to proceed without the need to more drastically protect the existing coffer dam.
Early last week, PacifiCorp was considering an option to draw the reservoir down by up to five feet in order to fix the coffer dam. The reservoir has already been drawn down to a level below which it was not supposed to drop further. Another drawdown could have flushed an annual supply of sediment through river below the dam over the course of a much shorter time period. The Henry’s Fork Foundation and others voiced concern about the impacts such a drawdown would have on the fisheries, associated fishing industry, and recreation, and had asked PacifiCorp to look at other alternatives.
August 16, 2012
The federally required Ashton Dam Remediation Project has hit unanticipated problems with seepage through the coffer dam that holds back the reservoir while the almost century old dam's upstream face is repaired. PacifiCorp (the dam owner) has proposed dropping the level of Ashton Reservoir down by up to five additional feet. This is one of several alternatives or packages of alternatives being considered to remedy the situation. A drawdown could mean that sediment would move downstream out of the reservoir and potentially disturb the fisheries below the dam. The amount of sediment would be approximately that which accumulates in the reservoir in a year. With the proposed drawdown, it could come through in a much shorter time frame.
The sediment released from Ashton Dam would be about a tenth of the amount released from Island Park Reservoir in 1992, but sediment-laden waters would almost certainly affect trout spawning gravels and the key food source for fish. We will keep you posted as information becomes available. You can also download HFF's letter to PacifiCorp about the possible drawdown.
July 24, 2012
Unrelated to work being done at Ashton Dam -- Ashton Reservoir Boat Take-out will be closed Thursday, July 26. This to allow the parking lot and access road to be seal-coated as part of the overall boat ramp improvement project.
July 13, 2012
The scheduled work to seal the upstream coffer dam was completed as planned on July 9. Ashton Dam continues to be a very busy place with the major excavation of the old dam fill running full bore. The photo shows this work several days ago.
July 6, 2012
Pacificorp has informed us that additional work is needed to seal off the upstream coffer dam. The work is scheduled for Monday, July 9. This requires sending divers down near the dam bypass tunnel. For safety reasons, water flows through the tunnel must be reduced while the divers are down. However, due to high irrigation demands they must continue to pass high volumes of water to the Henry's Fork below Ashton Dam. This means river flows below Ashton Dam will fluctuate significantly and frequently on Monday. The current run-of-the-river flow is 2200 cfs. On Monday, flows will vary from 1000 cfs to 2800 cfs. We suggest you avoid fishing the Henry's Fork below Ashton Dam on Monday. They expect to complete the work in one day.
June 12, 2012
The river below Ashton Dam continues to clear up, flows have stabilized, and reports are that it is fishing well. Meanwhile, some issues have arisen at Chester Dam regarding angler access. Please park vehicles with boat trailers in the upper parking lot. This is now accessed via the road between the powerhouse and the chain-link fence, then cross the new bridge over the canal (see photo below). More importantly, please slow down when driving to the boat ramps. There have been a number of near accidents recently and Fall River Electric is concerned about people driving too fast through the project area. A little common courtesy and respect for private property will help protect angler access to Chester Dam in the future.
June 6, 2012
River flows below Ashton Dam were briefly reduced today as some work was completed on the upstream coffer dam. Heavy rains over Memorial Day weekend, followed by hot weather last weekend, have much of the Henry's Fork and tributaries running off-color, somewhat normal for this time of year. The turbidity levels in the Henry's Fork below Ashton Dam continue dropping. From a high of 32 NTU's the last day of the drawdown two weeks ago, they are now down to about 7 NTU's.
May 23, 2012
Good news - the Ashton Reservoir drawdown has been completed. PacifiCorp completed the drawdown to the 5130-foot level this morning. The reservoir will stay at this level and operate in run-of the river mode until November. As expected, the water clarity was somewhat impacted during the final stages of the drawdown. However turbidity levels have already begun dropping today and water clarity is improving. When the Henry's Fork opens for fishing between Ashton Dam and Vernon Bridge this Saturday, the water will likely still be somewhat off color, but improving. Please remember the area around Ashton Dam remains closed to the public for safety reasons. This includes the steep road down to the base of Ashton Dam.
May 17, 2012
The Ashton Reservoir drawdown is about half complete. PacifiCorp anticipates completing the drawdown May 24. So far the river has stayed clear downstream of the dam, but we expect there will be some discoloration in the river when the last few feet of the drawdown occurs next week.
May 11, 2012
The Ashton Dam bypass tunnel was opened this morning and the Ashton Reservoir drawdown is now in progress.
May 10, 2012
The temporary coffer dam was removed Thursday morning in preparation for the drawdown.
May 9, 2012
The drawdown of Ashton Reservoir was delayed slightly while PacifiCorp awaited final approval from the Federal Energy Regulatory Commission. However that approval was granted about 4:00 pm today. PacifiCorp plans to remove the downstream coffer dam on Thursday, and begin the reservoir drawdown on Friday, May 11. The drawdown is expected to take two weeks to complete.
May 2, 2012
PacifiCorp has announced they are planning to begin the drawdown of Ashton Reservoir on May 9. The reservoir will be lowered to the same level it was at last fall, 5130 feet. They anticipate it will take two weeks to complete the drawdown. We expect the water to be off-color again during the drawdown and immediately afterwards. We do not anticipate the water will be as sediment-laden as it was last September when considerable rock excavation was being completed in front of the bypass tunnel during the drawdown. The reservoir drawdown in September 2011 was the first major drawdown in nearly 100 years. Unconsolidated sediment in the reservoir most likely moved out of the reservoir last fall. It is unlikely a significant amount of new sediment has accumulated since last December, thus we do not think the Henry's Fork below Ashton Dam will be as discolored during this drawdown.
Ashton Dam Reconstruction Re-cap
If you haven’t been in the area for the last few years, you may be wondering what the talk of Ashton Dam is all about. Here is a re-cap. Ashton Dam is owned and operated by PacifiCorp Energy, an investor-owned utility. Problems have plagued the earthen dam for years, including water leakage through the earthen fill, presenting a threat to the safety of downstream residents as well as the fisheries of the lower Henry’s Fork. HFF has maintained close communication with PacifiCorp about these concerns for several years.
In 2009, the Federal Energy Regulatory Commission ordered PacifiCorp to fix the dam to address the safety issues. This requires removing the old earthen fill on the upstream side of the dam and replacing it with better material. To do this work the reservoir level needed to be lowered nearly 20 feet. At the lower water level, the river can’t pass through the spillway or through the turbines, so the first phase of the project was to build a new bypass tunnel, completed in 2011.
Sometime in mid-to-late May 2012, PacifiCorp will lower the reservoir again, running the entire river flow through the bypass tunnel. The river will likely appear off-color immediately after the reservoir drawdown. Many anglers have expressed concern about the timing of the drawdown and its impact on water quality and recreational fishing.
There are many reasons for the timing of the drawdown. The drawdown occurs right after peak spring runoff to ensure a large amount of sediment is not moved out of the reservoir and into the river with impacts to downstream fisheries. Furthermore, PacifiCorp needs every possible day this summer and fall to finish the project on schedule by late 2012. To postpone the drawdown, as some have suggested, would push the work into next year, requiring yet another drawdown.
After the drawdown, PacifiCorp will replace the earthen fill on the upstream side of the dam. The project is currently on schedule to be completed by the end of 2012. HFF supports the project as planned and has worked with PacifiCorp since the early stages to minimize potential impacts to downstream fisheries. We have been impressed by PacifiCorp’s willingness to revise construction plans to ensure the legendary Henry’s Fork trout fisheries are protected during the dam’s reconstruction. Contact Kim Ragotzkie to find out more information.
Work on the Ashton Dam powerhouse will be completed in April.
March 22, 2012
The Ashton Dam remediation project continues on schedule. The photos below show the concrete work being done on the powerhouse, and the spillway through which the entire Henry's Fork is currently flowing. The next reservoir drawdown is scheduled for late May or early June of this year. The entire project is anticipated to be complete by late 2012.
February 23, 2012
Workers at Ashton Dam continue preparing the powerhouse for some new concrete. The small pool of water in the photo is where thousands of trout were living when the main river flow was blocked out of the work area. Idaho Fish and Game and PacifiCorp moved over 1,500 of the trout to the main river two weeks ago, and plan to move the remaining fish in the next few days. Fresh water feeds the pond due to seepage under the dam and powerhouse.
The photo below shows the spillway and temporary coffer dam.
February 6, 2012
Work on Ashton Dam has started again. The bypass tunnel has been closed and the entire Henry's Fork is now flowing through the spillway. Much of the riverbed downstream of the dam and powerhouse has been dewatered to allow workers and equipment access to the powerhouse for needed maintenance. A temporary steel and rubber coffer dam is keeping the river out of this area. Fish that may have been trapped during the dewatering are concentrated in the reimaining deep pool which is being monitored for dissolved oxygen levels. Ashton Reservoir will remain at or near current levels during this phase of the project which is expected to take three months.
PacifiCorp Ashton Dam Fact Sheet Click for PDF
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