Updated 6/21/2022 The next 36 hours are going to be dicey for Montana water managers, and the National Weather Service (NWS) as they monitor and assess flood conditions occurring on many rivers and streams in southwestern and southeastern Montana. Many of the state’s rivers, including the Stillwater, Rock Creek, East Rosebud, are roaring into the Yellowstone River at record high levels due to high rainfall accumulations and late season snowpack runoff. The combination of those two factors has caused Yellowstone National Park to close temporarily due to flooding, rockslides, and mudslides on roadsides and numerous statewide fishing access sites to close. In Billings, record high Yellowstone River levels has caused the city water plant to shut down. It has also caused one of our own BHRA employees (who lives on Rock Creek) to leave work early due to bridge closures. If those bridges fail, she and her family will need to evacuate their home.
Until now, the Bighorn Basin has absorbed the shock of increased inflows, with storage availability made possible by Buffalo Bill, Boysen and Bighorn reservoirs - reservoirs that up to a month ago, were in question of even filling to full capacity. However, with the combination of high precipitation received over Memorial Day weekend, delayed runoff timing, and high weekend heat forthcoming, the upstream dams are scheduled to start increasing releases with Buffalo Bill increasing to 4000cfs on 6/15, and Boysen Reservoir increasing to 4800cfs on 6/14.
The Montana section of the Bighorn River (downstream from Yellowtail dam) is the largest tributary to the Yellowstone River. Under the June Yellowtail Operations plan, Bighorn River releases were scheduled to increase Monday (6/13), but due to the high volume of water entering the Yellowstone from upstream tributaries and the terrible flooding occurring within communities on/around the Yellowstone River, the Army Corp of Engineers has instructed the USBR Montana Area office to hold off on increases until the gage at Miles City reaches peak, later this week. This order, combined with the increases from the Wyoming dams means that Yellowtail dam will be entering the exclusive flood pool to help alleviate infrastructure and community flooding on the Yellowstone. Currently, the Yellowstone River in Billings is anticipated to crest (reach peak flow) on Wednesday, after which the NWS predicts it should drop 2 feet.
After the Yellowstone crests, Bighorn River water managers flows will start evacuating storage space from the flood pool starting Thursday by increasing Bighorn River flows 1,000cfs a day (500cfs AM increase; 500cfs PM increase) until Bighorn River flows reach 7,000cfs on Saturday. As with rivers and streams throughout the state, conditions, stage, and peaks are changing rapidly, so please check back frequently throughout the next few weeks.