The Willwood Dam was constructed in 1924; it is 70 feet high with a crest length of 476 feet and a base width of 41 feet, with a volume of 22,100 cubic yards. The dam was built with a penstock for an electrical generator but has never had …
After two weeks of nearly non-stop research, this is how I believe we arrived at the Willwood Dam/Shoshone River 200,000 cubic yard silt spill, ecological disaster and fish kill of 2016 — and how we might proceed.
The Willwood Dam was constructed in 1924; it is 70 feet high with a crest length of 476 feet and a base width of 41 feet, with a volume of 22,100 cubic yards. The dam was built with a penstock for an electrical generator but has never had one installed. The penstock is seen as a square opening (blocked with redwood planks) just below the two gates for the main Willwood irrigation canal on the face of the dam, when viewed from the upstream side. On the downstream side, the penstock is seen as an empty round hole above the downstream water pool. The dam also has three sluice gates located at the bottom of the dam, called the south, middle and north gates. These gates allow the control of the water level in the upper pool as well as providing for the sluicing of annual silt accumulations downstream or lowering the pool for service to the dam.
Recipe for disaster
The Bureau of Reclamation owns the dam; the Willwood Irrigation District operates the dam (the Bureau of Reclamation operated the dam until sometime in the 1950’s). The Department of Environmental Quality (DEQ) has regulated the dam’s downstream discharge since the department’s creation in the early 1970’s.
The dam appears to have operated without a significant buildup of silt until sometime in the 1960s. In the early ‘70s, two things changed: the south sluice gate became inoperable and the then-new DEQ started restricting the turbidity of the downstream discharge. As silt built up to 60 feet deep in front of the inoperable south gate, turbidity became an even greater problem. Sometime in the early ‘90s, the middle gate also became inoperable, believed to be stuck in the ever increasing silt building up behind the dam. (Todd Singbeil, a new employee at Willwood Irrigation District, would discover it was just a blown fuse when he went to work for Willwood some 18 years later.) With two gates out of commission, turbidity and increasing silt were an even greater problem, forcing DEQ to place even tougher turbidity restrictions on Willwood. All this, in turn, caused changes in the annual operating procedures of the dam from the original Bureau of Reclamation's plan.
Willwood Irrigation started looking into options to remove the ever-growing silt over 20 years ago. A barge-mounted suction dredge seemed to be the most likely method but the $5.6 million price tag was well out of reach of the 188-member district. According to the engineers, suction dredging is only effective down to 25 feet at the most. The material must also be very agitated and liquid (typically 10 percent solids) for the dredge to move it. Then, once moved, it must be contained in dikes until the water drains away and the material dries. High turbidity would certainly be an issue during the dredging.
As the Willwood dam nears 93 years old, there are an increasing number of mechanical and structural things that need maintained. With the ever-enlarging mass of silt above the dam, a 2007 gate malfunction that dumped silt and killed the fish below the dam to Eaglenest Creek and last year’s tire, silt and motorcycle mess, Willwood was definitely on the DEQ’s and Game and Fish’s radar. DEQ and G&F had been completely involved with the planning process for the present maintenance on the dam. Engineering firms had looked at the silt many times in the past. The process to get the permits for the repairs took over a year and a half. All parties thought if they let the water down slowly, an excessive silt spill could be avoided.
It was a tragic miscalculation. When the sluice gates were opened to lower the dam pool, the water cut a 10- to 12-foot-wide channel through the silt bed down to the stone river floor all the way to Buck Creek — close to one and a half miles upstream. It has been estimated that 200,000 cubic yards of silt have gone downstream at this time, wiping out the free stone riverbed clear to the Penrose Dam. What is more concerning is that Engineering Associates estimates there is still 530,000 cubic yards of silt left above the dam — more than enough to repeat the current silt spill twice over.
It should also be mentioned here that the sluice gates must be opened in the winter months to prevent ice from going over the dam and damaging the apron. Without removing the upstream silt, there is no guarantee that the silt will not continue to move through the dam in an excessive volume.
While this disaster has created a widespread awareness of the problem this dam faces, it has also created a rare and time-sensitive opportunity to mine the remaining 350,000 cubic yards of silt above the dam while the dam pool is empty. Mining would be far more cost effective and timely than dredging. It would be a truly fresh start for the river.
If this silt is left in the river channel and the pool level raised (which is scheduled to occur Wednesday at the recommendation of the DEQ), it will only be a matter of time before the Shoshone River is covered in silt yet again. The three sluice gates are scheduled to be changed out in just five years, which would again mean lowering the dam pool, resulting in yet another massive silt spill. Now is the time to come together and find the money to clean and restore our river, not to wait and see if it gets better and merely hope the next time we open the sluice gates, the silt will not come rushing out.
Moving forward, it would seem to be a conflict of interest for the irrigation district to maintain and operate the dam. District employees have little training and experience in river dam maintenance and operation, nor a vested interest in caring for a river and its ecosystem. The district does not have adequate funds to keep the dam in good repair and already relies heavily on state and government grants. It would seem a much better choice to treat the Willwood Dam like the Bureau of Reclamation-run Buffalo Bill and Yellowtail dams. The Bureau of Reclamation-operated dams are in tiptop shape; this cannot be said for the district’s dam.
The DEQ must also realize that an estimated 50,000 cubic yards of silt moves down the river annually, and this silt must keep moving or be abated before it gets into the river. DEQ must also see that filling the dam pool at this time is not an acceptable answer but merely, once again, hiding the problem rather than solving it.
New types of silt abatement and management must be part of the plan moving forward. This stretch of the river is said to be a blue ribbon fishery, however this is true only a very few weeks out of the year. The low visibility of the river through the summer months from irrigation tail watering keeps the river off most fishermen’s go-to list. The tail water also contains many farming chemicals that would be better left on the field than in the river. The Natural Resources Conservation Service says they have proven irrigation methods that can reduce soil erosion up to 70 percent, but they struggle to see these methods implemented, battling against the “this is the way we have always done it” mentality.
The BLM-owned McCullough Peaks contribute large amounts of silt to the river each year as well in the form of rain-driven runoff. Discussions about silt abatement management could be beneficial here as well.
Only better to come
To keep the river clear and clean is not just the right thing to do, it is also very good business. A Montana Fish, Wildlife and Parks spokesman said the Bighorn fishery at Fort Smith, Montana (just downstream) is worth $51 million annually. During my research, a Willwood farmer said, “We were here first, if you want a fishery, you pay for it. Why should the farmer bear the cost?” The taxpayer response could be, “We helped farmers get started with several very expensive dams and canals. We may decide a fishery would be a good use of taxpayer money as well…”
This can be a very polarizing issue, often resulting in the farmer on one side and the fishermen on the other. I would suggest it does not have to be farming or fishing, as it can be both, as evidenced by the Bighorn River fishery and the farming in the Big Horn Valley that co-exist. Farming started and built the Powell community and it should be part of our future, but not at the cost of doing what is right for the Shoshone River, the local economy, and a national water resource.
There is hope
A spokesman at the EPA’s region 8 water division said, “I do this for a living, and it always amazes me how fast a river comes back once the contaminant is removed.”
When we look to the west and see the pristine snow-capped mountains where the Shoshone River begins, it should break our hearts, that in just 70 miles the river is so polluted we would not want it in our toilets. Just think … it still has to travel all the way to Louisiana.
The Park County Commissioners are planning a meeting Nov. 15 at 5:30 p.m. at the Park County Fairgrounds to discuss this matter, and all the major players will be there. The only problem is that the most economical and timely manner of removing the silt will no longer be an option if the dam pool is filled with water on Wednesday. Once again the silt will be on the bottom of the river, posed to be washed downstream one more time, creating another ecological disaster. Please call the DEQ today 307-777-7937 to advocate for removing the silt now, before allowing the Willwood Dam pool to be filled.
Let us not hide this beneath the river once again.
(Royal Stukey owns and operates a small manufacturing company and lives on the East Willwood near the Shoshone River. He would like to thank all the individuals who contributed information for this column.)