In last week’s article, I gave our readers the flooding library.
We looked at how to keep track of our streamflows, and how to look at the short and long-term forecasts of what’s going to happen with critical rivers and creeks in our region. We also looked at how to look at the underlying conditions, like snowpack and soil moisture levels, that impact flooding. It was all cool stuff.
If that last article was a library, this one is a bulletin. Instead of telling you how to find the information, I’m just going to tell you about what’s forecasted — at this moment, anyway. Here are the latest forecasts from our flooding researchers at the National Weather Service.
When and how likely is it that each Salt Lake County creek will flood?
The forecasters at the Colorado River Basin Forecast Center issue daily forecasts, using historical data and the underlying snowpack to predict how high Utah’s various rivers and creeks will peak. But forecasting these things is difficult in the long term without knowing exactly how the weather will unfold — instead, we have to consider them in terms of probabilities.
Of course, flooding can also happen in other ways than the rivers simply flowing too quickly, too high. Debris can get caught, unexpected washouts can happen and so forth.
But for the seven major inflowing creeks on Salt Lake County’s east side, here’s the amount of water flow (in cubic feet per second) that would almost certainly cause flooding, along with the CRBFC’s current projected chances it reaches that height.
Unfortunately, the CRBFC didn’t have a forecast for Parley’s Creek — the one that flows through Sugarhouse and Liberty Parks — at press time. But for the others, you can see their model’s odds that the rivers flow high enough to cause some flooding.
Farther south in the valley, Big Cottonwood Creek could easily go either way — flood or not flood. . We would have to get relatively unlucky with our warming cycle to see significant flooding at the other creeks moving forward.
Flows are modeled to peak at their highest points for Red Butte Creek and Emigration Creek quite soon, because those creeks are sourced from lower-elevation mountains. In particular, there’s a good chance we’ve already seen highest flows at Emigration Creek, where peak flows reached 155 cubic feet per second two weeks ago. At Red Butte Creek, models show less than a 1% chance at reaching the 100 cubic feet per second level needed to flood.
Also note the dates in the table above. Those creeks with a higher chance of flooding aren’t likely to peak until the end of May or beginning of June. As with peak water amounts, the date at which peak flow is expected is also some guesswork — the absolute earliest that the model could see City Creek peaking, for example, isn’t until May 16, while the latest is June 11. The most likely outcomes see peak flow right in the middle of that date.
In short, there certainly is time to prepare — and to keep watching these forecasts.
What are the consequences of that flooding?
Tribune reader J. Alan Crittenden sent along a tool that wasn’t included in last week’s article: the National Weather Service Advanced Hydrologic Prediction Service website. The most helpful information on that site beyond what we already had elsewhere was information on what river flow levels would cause what impacts.
Let’s zoom in on City Creek, for example. The NWS says that:
• When City Creek reaches 210 cubic feet per second flow, minor flooding will occur to areas near North Temple and 400 West. Water will upwell from underground culverts along this area through manhole covers.
• At 300 cubic feet per second flow, moderate flooding will occur to areas near North Temple and 300 and 400 West. Upwelling water will pond in these areas and move into regions near 200 South.
• At 400 cubic feet per second flow, major flooding will occur along North Temple near 2nd West and areas west. Additionally, 200 South will receive major flooding in the form of ponding throughout the area.
Interestingly, Salt Lake City Public Utilities says that they can handle even higher water flows through City Creek than the 210 cubic feet per second level. They say 220 feet per second is the level they can handle without intervention — but then the water managers have various tricks to handle more flow if need be. More information on that will come in a future article.
As we get closer to peak flood time, we’ll keep you updated on other potential impacts in the valley. Check out the NWS website link above if you’d like to know more information for your specific nearest creek before then.
Elsewhere in the state
At press time, we have other Utah rivers and creeks forecasted to flood in the next 10 days, all up north.
In particular, the Weber River near Plain City is already higher than it’s ever been in recorded history. Measured at a height of 25 feet on Thursday, the previous recorded high was 24.7 feet on April 18, 2006. However, it’s projected to get even higher in the coming days, and to reach heights of 28.5 feet around May 3.
Should the river indeed exceed 28 feet, the NWS says that flooding will occur along the levee system near Plain City, which would affect local farmland adjacent to the river. Perhaps of more concern, homes adjacent to the Weber River near Plain City are projected to receive flood damage at that 28-foot level.
If the river were to exceed 29 feet, the levee system could receive damage, NWS says, potentially leading to “major flooding (that) will affect homes and structures in and around Plain City.”
Farther south at the Weber River, the forecast near Hill Air Force Base anticipates the river will rise to a height of 17.2 feet next week, just above the 17-foot projected flooding mark. As a result, the NWS says “near minor flooding (could) affect homes in the town of Uintah just outside of Weber Canyon.”
Flooding is also projected in the south fork of the Ogden River near Huntsville. Projected to reach 5.5 feet around May 3, minor to moderate flooding is projected in the “low lying areas near the banks of the South Fork of the Ogden River below Causey Reservoir through the town of Huntsville,” the NWS says.
Six other Utah river and creek monitoring stations project river flows that are in the “near flood stage” over the next week — the point at which the NWS recommends taking precautions to prevent the flooding that would result should the forecast change. Those are:
• the Bear River near Corinne
• the Little Bear River in Paradise
• the Blacksmith Fork River near Hyrum
• Silver Creek near Silver Creek Junction
• the Ogden River below Pineview Reservoir
• the Sevier River near Hatch
Editor’s note • This story is available to Salt Lake Tribune subscribers only. Thank you for supporting local journalism.
Editor’s note • This story has been updated. When it was posted, the National Weather Service’s website had an out-of-date number for the flooding capacity of City Creek in Salt Lake City. That reported number has since been updated, showing a significantly reduced likelihood of flooding from that creek in particular. Our updated story reflects this change.