Wednesday, June 25, 2008

2008: A Good Water Year, But Can the Big Hole Watershed Committee Find Success?

2008 has been a good water year in the Big Hole River watershed, so far.

The question is, will the Big Hole Watershed Committee succeed even in this wet year?

It's doubtful. Very doubtful.

Here is the hydrograph for this year (2008), from 01 May through 24 June:

Note that there have been several peaks well over 1,000 cfs, though flows never exceeded 2,000 cubic feet per second (cfs). Currently, end-of-June flows are running 300 to 400 cfs.

Now, here is the hydrograph for 1997, from 01 May through 30 July:

Note that there was a sustained flow for several weeks that exceeded 2,000 cfs and even approached 4,000 cfs. 1997 was a MUCH bigger spring run-off year than 2008!

And yet, even with all that water in 1997, the Big Hole Watershed Committee could barely sustain survival flows over 60 cfs. Remember that 60 cfs is the "lower wetted perimeter" -- the minimum level for reasonable fish survival. Below this point, the carrying capacity of the stream diminishes rapidly, and thus the fish population plummets. Standing crop -- i.e. the number of living fish -- is maximized at the upper wetted perimeter. For the Wisdom reach of the Big Hole River, that means that the optimal flow is 160 cfs or higher.

Here is the hydrograph for 1997, 01 July through 30 Sept:

Note that in late August flows rapidly dipped below the upper wetted perimeter of 160 cfs, and hovered between 60 and 100 cfs for many weeks. Not bad, but not enough to optimize the recovery of fluvial Arctic grayling.

What does this portend for 2008? Well, considering that 1997 spring flows were about double the flows we have seen this year, we can probably expect late summer flows to decline sooner and go lower.

In other words, I hope that the Big Hole Watershed Committee is not falling into complacency merely because we have had a more-or-less long term average year in terms of spring flows. Sadly, I expect the Watershed Committee will fail to maintain flows at the 60 cfs minimum survival level. As usual, the committee's efforts will be too little, too late; a day late and a dollar short; and full of excuses about why grayling just have to die and creep ever closer toward extinction.

Big Hole Watershed Committee, please prove me wrong!

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