Flows in the Bighorn River will be significantly reduced over a five-day period during October to facilitate the measurement of springs below Yellowtail Dam. Releases from the Yellowtail Afterbay Dam will be reduced in increments beginning at 7:00 am on October 17, so that by early in the morning of October 21 a flow rate of 400 cubic feet per second (cfs) will be obtained. A flow of 400 cfs will result in a drop in river stage of approximately three feet from the current level. The 400 cfs flow rate will be maintained for approximately five and one half hours while the springs that flow into the Afterbay Reservoir are measured. At approximately 12:30 pm on October 21, releases from the Afterbay Dam to the Bighorn River will be incrementally increased until a flow rate of approximately 3,000 cfs is reestablished. Measuring the flow from the springs is a necessary and critical part of inspections we perform at Yellowtail on a three year cycle. Unfortunately, we have to evacuate the Afterbay Reservoir to take the measurements, and that means there is a period of time when flows in the Bighorn River are very low, said Tom Tauscher, Reclamations Yellowtail Facility Manager. Tauscher added, I wish we had some other way to perform the measurements, but we simply dont have that luxury. We have however, worked closely with Montana Fish, Wildlife Parks both on the timing of the tests and on the increments of our flow fluctuations, to minimize impacts to the river fishery. Fishermen and other recreationists using the river are cautioned that low flows during this period may make it difficult to float the river.
Just a few minutes ago, Bighorn Lake dropped below the flood pool. The average lake elevation for September 22nd is 3,626ft, or 14 feet lower than today’s elevation.From this point forward, any drop in lake elevation will be subtracted from Dan’s 20 foot window, and we all know what that means for the river.
Since the equipment malfunction a couple of months back, Reclamation is back to measuring river stage with the old equipment, which works very similar to the float valve in your toilet. Stage is the elevation of the surface of the river. The stage of the river can fluctuate for two primary reasons on the Bighorn River: 1) river releases from the Afterbay or 2) algae. Its obvious how river releases affect stage, so let’s talk about algae for a moment. As algae grows, it displaces water. For example, if you fill your bathtub half full of water and drop a brick in the tub, the water level (stage) rises, although there isn’t actually any more water in the tub than before you dropped in the brick.What happens on the Bighorn is the algae grows and displaces water causing the stage of the river to rise. The float in the gaging station right below the Afterbay detects the rise and tells the valves in the Afterbay to close. Since the stage has risen, it doesn’t always look like we’re losing water in the river, but we most definitely are, and sometimes it can be as high as 200 or 300cfs. I’m sure you’re wondering Isn’t somebody monitoring this?. Well, someone is monitoring this, but not always who you’d think. Often its Western Area Power Administration that notices a decrease in power generation and not Reclamation.Just such an occurence came to light today. We were told river releases for the first two weeks in September were 3,100cfs, but in actuality, they were more like 2,900cfs. Will the new gaging equipment help? It should, and we anxiously await its return to service.