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.
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| Access Updates | Background | |
Construction at the Chester Diversion Dam hydro project is ongoing through 2010
October 22, 2009 Update: Work continues at the Chester Dam Hydro Project. Access to the boat take-out above the dam, and the boat put-in below the dam, remains the same as it has been all summer. See the July 1 notes below. If you are driving up to the dam through Chester Wetlands on the west side of the river, be cautious of heavy equipment on this road. The
7/1//09 Update: Access to the boat launch below Chester Dam is the same but space is very tight. Please do not park near the boat launch as it may prevent others from launching. Please park your vehicles in the large parking lot at the boat take-out above Chester Dam. Please do not park along the access road.
Access to the boat take-out above Chester Dam is mostly the same, but the last 1/4 mile has been re-routed to a new temporary road. A new crossing has been constructed across the Crosscut Canal to access the upper boat take-out, and the old wooden bridge has been closed. Detour signs are in place to route anglers to the new access road. There will continue to be lots of heavy equipment activity both at and around the site, so be aware of additional traffic on the access road. Construction crews will be working Monday through Saturday. Few additional delays to recreational traffic are anticipated in the near future.
If you are planning to float the Vernon to Chester stretch of the Henry’s Fork, you’ll want to know whether or not to expect any delays. To help anglers stay apprised of the situation, the Henry’s Fork Foundation has added this page to the website where current information on anticipated Chester Boat Ramp access delays will be posted. We will update this page with information from the Chester Hydro Project Manager as needed.
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| This sign is posted near the Chester Dam road to inform visitors of construction. | Last Chance Canal diversion rebuild work. |
(article from HFF newsletter Summer 2008)
Chester Dam Update
by Steve Trafton
HFF Executive Director
In July, the Federal Energy Regulatory Commission (FERC) issued a license to hydropower developer Symbiotics of Rigby, Idaho, granting them permission to retrofit Chester Dam on the lower Henry’s Fork with a hydropower generating facility. The license was the final step in a negotiating process that lasted many years, one in which the Henry’s Fork Foundation played a leading role. The final license will, we believe, result in dramatic improvements for the fishery of the lower river (all species of fish). To understand why, the project must be understood in its full context. 
Chester Dam was constructed in 1938 to divert water for irrigation into two canals, the Cross Cut on the eastern bank of the river and the Last Chance on the west. The facility was part of an era that resulted in seven diversion dam structures for ten canals on the lower Henry’s Fork and nine diversion dams and canals on the Fall River (not to mention the irrigation storage reservoirs at Island Park and Grassy Lake, completed just a year later in 1939). These diversions and their attendant irrigation canals created a veritable fish passage obstacle course. Most of the diversion structures are either impediments or complete obstacles to upstream fish movement. None of the Henry’s Fork diversions and only two of the Fall River diversions are screened to prevent fish making a one-way trip into the irrigation canals.
Although our understanding of the full impact that these structures have on fish populations in the lower Henry’s Fork is incomplete, we do know that thousands of fish of all species are entrained into the canals each year. Virtually none of these fish return to the river. A few undoubtedly return to the river via overflow channels, and a few may persist in spots in canals that offer year round habitat, but the majority die when the canals are dewatered at the end of the irrigation season – if they have not previously ended up in the fields, or been killed by herbicide treatments. The effect that the loss of fish to the canals has on the numbers of fish in the river has not been specifically studied on the Henrys Fork. It is not surprising, however, that the number of trout estimated in the Henrys Fork below Chester Dam is about half of that in the reach above.
Thus, when the opportunity presented itself to screen two canals on the Henry’s Fork, and to provide fish passage at a hitherto impassable barrier to upstream fish movement, the Henry’s Fork Foundation worked hard to bring those improvements about. Chester Dam and its diversions are, with one minor exception, the farthest upstream diversions on the lower Henrys Fork, and the dam’s position immediately downstream of the Fall River confluence makes it all the more significant to fish passage, and the status quo all the more potentially damaging. With that in mind, the completed Chester Dam hydroelectric project will include the following features:
- Fish screens in both the Cross Cut and the Last Chance canals.
- A fish ladder to provide upstream passage to fish of all species.
- A screen on the hydropower turbine intake to prevent large fish from passing through. Fish small enough to pass through the screen and downstream through the turbines should do so with relatively low mortality.
- Permanent public river access, including improved boat launches above and below the dam and an expanded parking area, (it is worth noting here that public access is currently not guaranteed at Chester Dam, but is dependent on the Fremont-Madison Irrigation District, the owners of the dam).
The project has its critics. Chester Dam is, and will remain, a run-of-the-river dam (that is to say a dam that backs water up but passes flows at the same rate that flows enter). The backwater has traditionally expanded and contracted with the ebb and flow of the river. The hydro project will use inflatable bladders, fixed to the top of the existing concrete structure, to raise the height of the dam by three feet and hold the backwater at a constant level (approximately the same level that it currently achieves at high flows), in order to create sufficient head to generate electricity. This means that several hundred feet of what is currently riffle habitat at lower flows will be permanently inundated. Project critics have also raised the question of increased water temperatures in the backwater, although the changes projected by the applicant’s study are slight.
The project will also alter the character of the Henry’s Fork immediately below Chester Dam. Currently, flows are evenly distributed from bank to bank across the length of the dam. When the project is complete, flows will be concentrated on the east bank, where the hydro facility will be located. Although the volume of water passing the dam will not change, water going over the spillway will only occur during high flows in the spring, with water going entirely through the turbines or into the canals for the remainder of the year.
The Foundation believes that these changes are a small price to pay for two screened diversions and a fish ladder. It is hard to overstate the difficulties facing fish screening projects in Idaho, or to overstate the fishery losses sustained by rivers like the Henry’s Fork to unscreened diversions. The Chester Dam hydropower project licensing process offered what was, in all likelihood, a once in the lifetime of the dam opportunity to fix the dam’s inherent fish passage problems, permanently. There are times that the greatest service that the Henry’s Fork Foundation can provide is the ability to recognize opportunity in what might appear, at face value, to be a threat to the river. This was one of those times.
We were not alone in our efforts to mitigate the project proposal. Trout Unlimited and the Greater Yellowstone Coalition worked closely with the Foundation throughout the process, and deserve great credit for their contributions to the successful outcome. The Idaho Department of Fish and Game, US Forest Service, US Fish and Wildlife Service, and Idaho Department of Parks and Recreation all weighed in to make the final license the best product that it could be. Finally, Symbiotics should be recognized for its willingness to make its project not only a viable means of generating electricity, but also an improvement for the fishery.
The hydroelectric project license will be transferred from Symbiotics to the Fall River Rural Electric Cooperative, Inc., based in Ashton, Idaho. Construction of the project will be financed by Fall River Electric and subsequently, they will collect all the revenue generated by selling the power until the construction debt is repaid. After that, Fall River Electric and the Fremont-Madison Irrigation District will become equal partners in the project. Regardless of who owns the project, the FERC license and settlement agreement require the operation and maintenance of the fish passage and recreational improvements for the project. Upon construction, the project will be a benefit to the river and the fishery for many years thereafter. ◊
