Lower Henry's Fork Doomed?

**neckdeep** · 12-09-2009, 12:54 PM

Those of you who have fished the Henry's Fork tailwater below Ashton Dam know it can be one of the West's finest pieces of water. Few places have this many fish of large size, incredible insect hatches plus relatively easy access for waders and boaters alike. Sadly, the power company that owns the dam just announced a major overhaul that will probably kill off all fish and insects below the dam for a generation of anglers. 40,000 cubic yards of fill above the dam will be removed and replaced. Not to forget, this will disturb and release untold amounts of natural sediment accumulated over a 98 year period. Ashton res will be drawn down to a shallow pond and, according to the power company, a coffer dam downstream of Ashton dam will trap released sediment. Of course, their claim that they can keep damaging levels of mud out of the river is pretty much contradicted by the results of every previous dam overhaul ever to happen and the company press release itself is basically fatalistic and apologetic about what is going to happen....so....this next season may be your last opportunity to enjoy this fishery before it is lost for decades...

Work is planned to begin in the upcoming summer, probably after runoff ends and the coffer dam (the first step to disturb the river) will begin in September. The owners plan that the project will be completed in two years and say the repair is inevitable and, in our zone of seismic activity, a mandatory upgrade to an old failing structure.

Well.....shit. Spring fishing will not be the same, as this is about the best early season water to be found in the region.

**PROVO** · 12-09-2009, 05:07 PM

This is a bummer! you see, I've never fished the henry's fork but I have always wanted to and had planned on it this fall but that fell through.

Will I be able to experience it in all its glory before they start this project? If you could make a suggestion of when to go before they fuck it all up I would appreciate it!

thanks for the heads up.

**RootSkier** · 12-09-2009, 05:24 PM

40,000 ain't shit. They have taken 2 million+ cubic yards out of the Clark Fork above Milltown dam which has since been bypassed and is being removed. And all this sediment is toxic.

Sure it will hurt the fishing for a few years...but for a whole generation? I am skeptical.

**plugboots** · 12-09-2009, 11:59 PM

This last summer the Clark Fork sucked, but in the end it will absolutely help the river. I'm with rootskier, a couple seasons at most, and it'll be better.

**neckdeep** · 12-10-2009, 09:51 AM

Uh....I did not want to argue about it but I think you are overlooking some key differences between the situations,

1. This is not a dam removal but a massive repair. At its conclusion, the river will not be free flowing and will not have the same ability to purge itself.

2. This river is not big and drains a fairly low elevation basin. The runoff on the Henry's is small, it is a giant spring creek/little tailwater. The lower sections in question are among the river's slowest and it is already a very weedy area. The many long slow holes will become sediment traps. If they fill in, the trout's winter habitat is gone. A 5000 cfs peak in runoff is huge down there; 1000-3000 is the normal flow. It will take time to clean out. 4 miles downstream is the Chester lowhead dam that creates a half mile irrigation impoundment that will become a settling pond.

3. With all respect to the Clark fork, it doesn't have the incredible diversity of insect life that this area of river does. This is a world famous section, an entymologist wet dream. If the Clark is known for being covered with bugs of multiple species from dawn to dark, I've not heard it. A average may-june day on the lower Hank might see a dozen hatches or more. Thats why its famous and a destination fishery for those two months. The invertebrate biodiversity may take a long time to recover both in terms of species composition and volume. Maybe decades.

4. This happened before in 1992 at the Island Park dam. Loads of sediment got through and the fishing in the Box Canyon and Harriman State Park collapsed for years. Senior guides will tell you that the Box(which is rapids) has rebounded but it took a full decade and the slow flowing waters of the world famous state park, while good fishing, still have not seen a full return to the glory days that made it famous. And because of that loss, the Ashton-Chester section had come to be regarded as the river's best hatch factory. I think other local anglers on the forum will agree that this section is a jewel in the crown, so to speak. Loosing this part as well will really hurt the river's rep and its ability to bring in visitors.

So, no, I don't think I am overstating how sad this will be. Check the place out for yourself. Good fishing starts in March, anglers begin to show up for the mother's day caddis hatch at the end of April, crowds show 2-3 weeks later for stoneflys, fishing peaks around the 4th of July and goes into the doldrums by August.

**steved** · 12-10-2009, 06:34 PM

Thanks for posting neckdeep,
You know...shit nevers ends eh'..y/n? Will try to get out there prior...but hoping for the best.. Power company project supervisors..having regard only to finishing a project "below budget".

**ak_powder_monkey** · 12-11-2009, 02:48 AM

so what else are they gonna do with all the sediment?

**steved** · 12-11-2009, 08:37 AM

Rocky Mountain Power...
Snippet from online headliner(News 8)...
>A company V.P. says their evaluation will take time to complete.
>Then Rocky Mountain Power will develop and implement a maintenance and repair plan
>for the Ashton Dam.

Would be nice if they were to talk to/with local enviro chapters and people...with ongoing plans...or am I dreaming..y/n?

**neckdeep** · 12-11-2009, 01:30 PM

The press release I read indicated that they already have their plan and timetable. The coffer dam is scheduled to begin next fall. Based on what happened at IP dam, the concern is that the exposed lake sediment will wash into the river during rains and runoff season's high flow. What can you do about that? Can't hold back a river, just slow it down is all. At best, a coffer dam can stop sand. Fine particulate(suffocating silt) stays in suspension. Tailwater fisheries are Faustian bargains and now its time for the good Doktor to take a final ride with Mephistopheles.

**Woolly the Mammoth** · 12-11-2009, 08:07 PM

I've been trying to find information about this but I'm not having any luck. Can you direct me to anything?

**neckdeep** · 12-12-2009, 10:21 AM

I googled it and got articles from the local papers and flyfishing forums like Westfly. I got one key thing wrong I should correct. The coffer dam goes UPSTREAM of the site to reroute water through a bypass tunnel. There isn't a sediment trap below the site. I don't know how PacificCorp plans to deal with lake sediment washed into the river during summer rains or from normal streamside erosion. Pray for drought, I guess. The plan is to prevent the worst of it by refilling the lake during runoff season to prevent exposed lake bed sediment from being washed out by a flooding river. I fully expect that once the lake is drained the river will start cutting into collected sediment until it finds the resistance of its original channel. The temporary "banks" of the river in the exposed lake bed will just be unstable mud and will not stop meandering that adds even more muck. That initial unstoppable process may dump enough silt through the bypass to ruin things. There's probably a good deal of mud in there as that lake holds the byproduct of decades of intense clearcut logging that dominated the region up through the 1980's.

**sunpower** · 12-12-2009, 06:34 PM

A friend of mine sent me this link of Pacific Corps plan http://www.uvsj.com/articles/2009/12/04/news/26.txt

**neckdeep** · 08-18-2012, 09:20 AM

Bad news for east Idaho's best spring fishery. The coffer dam upstream of the construction site has been leaking and if this problem continues to defy repair attempts at current water level, PacificCorp will draw down Ashton reservoir another five feet. That would expose large mud flats to river flow and put a potential 10,000 tons of lake bottom sediment through the bypass and into the lower river. According to modeling done by PacificCorp, this will be equivalent to approximately an entire year of sediment flow ( i.e. what flows naturally down the river above the reservoir) but it will be released over a short period and will impact insect and spawning habitat below the dam.

**skifishbum** · 08-18-2012, 01:21 PM

Well that blows i myself dig that stretch better than the fabled ranch.

couldn't above get that link to work
but this one seems to say it was federally mandated and the sediment release will be 10%of the ip damn project in 92
How long did it take for the box and down stream to recover back then?
granted thats a much steeper gradient and I'm sure ip damn has a much greater cfs capability. but 90%????
A bit skeptical on the doomed for a generation scenario and that the epa tu hff and other watchdog orgs wouldn't step in