It’s still the middle of winter and lots more snow needs to pile up in the mountains, but early indications are the snowpack is average or better, but more importantly there is A LOT of water in Anderson Ranch Reservoir. And it’s got to come downstream at some point in 2011.
So for our first update for 2011 we present a state of the river report, looking at the coming water year. Long time South Fork Boise aficionados recall the normal flow regime is 300 cfs in the winter (Oct through March), followed by the 600 cfs for the shoulder season, usually a period in September but also importantly in April and May for the mainstem river spawning. Then during the summer it’s around 1,800 cfs in a steady push of water for downstream irrigation and salmon water budget contributions.
This year looks like it will be different because the water is stacking up, more than in recent years. Here’s what we know so far…
Check out this graph showing water content in the reservoir through the first four months of the water year:
It’s the end of January 2011 and there is nearly 300,000 acre feet in Anderson pool. Last year the reservoir the contents are shown by the green line. The AVERAGE is the red line. And on average during the winter the pool is supposed to be emptying as the 300 cfs minimum flow normally exceeds that coming in. There is a 50,000 acre feet surplus between today’s total and the average.
And just so you don’t think we are seeing some manifestation of water being managed differently between the storage pools in the Boise River Basin, here’s the graph of total system storage:
Total storage this year is running ahead of last year and well ahead of the average storage at this time of year. And this additional storage as we near the end of January is more remarkable given that Idaho Power rented some water and the Boise River ran higher for a couple of weeks in January.
Finally, the amount of snow in the mountains is running ahead of the past couple of years. Check out this comparison of snow water equivalent piled up at Trinity Mountain one month into 2011 compared to 2009 and 2010.
So people, you better start planning for some pretty high flows from Anderson Ranch Dam this spring. It may mean the season opener Memorial Day weekend we may see those high flows well above the 1800 cfs.
For the river itself maybe we will see some high flows that tumble the rocks around and rearrange the substrate, creating some new habitat and moving some silt downstream.
We’ll check in with our friends at the Bureau of Reclamation and see if they are thinking this far down the road. Things can still change. The snow could quit falling and we could end up in a below normal precipitation situation (drought) by this spring, but that is not likely. Still, it makes sense to plan your spring and summer on the South Fork Boise keeping in mind what is going on upstream of Anderson Ranch Dam.
