Less than 2″ of rain fell last night. I don’t know if that’s good or bad, only that it could have been worse. We did see the dam at Prairie Du Sac come up 2kcfs which wasn’t unexpected and I believe it’s now leveled off around 12kfs. To put that number in perspective, 15kcfs is where we start cancelling trips. [kCFS = Thousand Cubic Feet per Second of water, 1 CFS = 7.5 Gallons per second]
It’s always hard to know what exactly is going to happen with local rainfall. We have access to river gauges at Muscoda below us and Prairie Du Sac, Portage, and Wisconsin Dells above us plus a few other spots on larger tributaries (Baraboo, Lemonweir, Black Earth) but because the rains happen so close it doesn’t really have a chance to show up in the gauges at or above the Dells. That means our usual 2+ day notice on river levels gets fuzzy and I have to start doing mental math. For example, our current 4 day outlook is great. The most important dam at Castle Rock has been holding steady all week at ~5kcfs. That gives us enough room for 10kcfs more water between Castle Rock and Spring Green. Following down the river at Wisconsin Dells we’ve also been holding steady around 7kcfs which makes sense given the Lemonweir dumps into the Wisconsin above this gauge and adds just over 1kcfs plus the smaller streams and creeks. Coming another 12 hours downstream we hit Portage. There aren’t any major tributaries between the Dells and Portage so I’d expect to see very similar numbers – in fact right now they are separated by .2kcfs.
This is where it gets fuzzy. We’ve still got ~8kcfs of room to work with. The Baraboo River comes in below Portage and has a fairly large drainage area. This is also where we’re getting into all of the recent rainfall. The gauge near where the Baraboo drops into the Wisconsin is currently ~3.5kcfs. This will likely go up to 4 or 4.5kcfs but that’s still a long way from our 8kcfs of capacity. Now we come another 12 hours downstream to the Prairie Du Sac dam. This is where our longest overnight trips start and is just over 12 hours upstream of where all trips finish.
As mentioned above, the dam at Prairie Du Sac is now running at 12kcfs (5kcfs above Portage) which includes most of that 3.5k from the Baraboo River as well as the runoff from the immediate area that you’ll see immediately following a rainstorm. I expect the contributions from the smaller tributaries to fall off very quickly – the gauge at Black Earth creek is a good proxy for this given it’s close proximity to the river. Looking at Wednesday’s massive storm, the creek went from 60 to 600cfs in less than 12 hours. Less than a day later it was almost back to 100cfs. The Baraboo is going to move slower both going up and coming down but for the most part, I believe that will be a pretty close match with the small tributaries falling off in time with the rise in the Baraboo. All of this makes me pretty confident our 3kcfs of remaining capacity is enough to ensure we won’t have any issues losing sandbars tonight.
Going forward it gets a little more difficult. There’s a chance that all of the small local streams combined with the Baraboo River could continue rising up to that 15kcfs cap on Monday or Tuesday. I’m still waiting to see the latest prediction out of the Portage gauge later this morning, and especially this evening, to see where the real professionals believe the river will crest. There’s just too much variability to make any kind of prediction for midweek. That said, my feeling is that we’ll be okay if the amount kicking out of Castle Rock holds steady (and I think it will based on their lack of rainfall).