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#5485
Pat Stout
Moderator

This is a timely article to post as it elucidates the spectrum of adverse conditions that our watersheds must endure. That is not to say that these adverse effects can be generalized for all watersheds as each are different, from topography to longitude/latitude to altitude to seasonal weather and so on. And, to say it is “all climate change related” is more than a little disingenuous as it excludes other drivers of poor water quality.

As for the Snake River, the region is abnormally dry this year, although we are seeing some seasonal rains and the pastures look good. The flows are around 17-18 cfs which indicates a wetter riparian zone. In a drought year, you might see it as low as 12-13 cfs. Of course, the writers act as if this is the first drought in history when in fact, this area has had one in 2002 and 2012, the latter exceptionally severe. The 2012 drought has been followed by years of wetter than normal years until 2020-2021.

The greatest threat to the Snake River below Merritt Reservoir is the operational hydrology. The building of the Merritt dam and its structural characteristics resulted in an exceptional wild trout fishery, what with sediment reduction and enhanced thermal regime. Those same attributes can be adversely altered depending on how the dam is run. Remember, this is an irrigation project. Period. For the first 40 years or so, it was run like a dam, largely irrespective of aquatic life in the lake and river or even neighbors. With Rod Imm assuming the manager position and the negative effects of the 2002 drought, attitudes began to change for the better. And the renewal of the dam lease in 2006 fostered even better discussion. With this lease, the Ainsworth irrigation District was restricted to around 85,000 acre feet. Prior to that, it was unlimited and had, in one instance used upwards of 94,000 acre feet. Some of the “enhancements’ that were negotiated were as follows.

Ramp Rates:
No formal regulations existed on how fast the AID could ramp up or ramp down water releases from the dam. The fish kill in 2000 was due to the AID allowing a cattle crossing during high summer temperatures around 100F +/-, dropping the water well over 200 cfs and 3 hours later, dumping the same amount in one turn of the wheel. This was associated with high thermal temps from the lake water and an ongoing blue algae blue killing large numbers of fish. Now, the AID has established a ramp rate of 50 cfs, up or down, over 6 hours. This is also highly beneficial for maintaining the integrity of the banks and minimizing slumping.

Timing of Releases:
If one studies each water year after the dam was built, you will notice the 1st 45 years were consistently inconsistent on flow releases. In particular, the spring and fall flows were helter-skelter. Or like in the fall, the water was turned off way more than on. The timing was potentially damaging as it coincided with rainbow (spring) and brown (fall) spawns. In 2012, the Bureau of Reclamation turned off the dam in late March for a week to do an inspection. An inspection that had been scheduled in September of 2011 and forgotten. The damage, particularly above the falls was irreparable in what already is limited spawning. Now, during March-April-May, the AID will not go below 100 cfs. In the fall, the flows from the dam will start on October 15th. A caveat here, is that these are guidelines during normal dam operations. In cases of adverse events or emergencies, the AID has to comply with the federal rules they work under. After all, it is only an irrigation project.

Adjustment of Summer Releases:
For many years, but not consistently, the summer dam release was ~ 50 cfs. It was apparently based on some Habitat Suitability Index (HIS) that nobody knew where to find. By the Memorandum of Agreement between the NGPC, AID and Reclamation, summer releases were decreased from 4000 acre ft to 2000 acre ft. A political action, but with no scientific basis. You must understand that even though we own the land below Merritt dam, we have no legal standing when it comes to the water. Based on scientific data, the SRPG/SFSC agreed to release the summer flow (total 20 days) for consistent fall flows. This happened in 2015. It was followed by wildly speculative claims of harm and devastation that are still embraced today. Once the irrigation begins in earnest, usually late June or early July, the dam release is shut off. With exceptions like 2018, where Noah-like precipitation occurred. While 17-18 cfs is low, it is sufficient for trout. However, the low flows come with a highly favorable diel thermal regime (DTR), while flow from the dam in June, July, August and even September have a greatly diminished DTR. With dam flows, we have documented maximum temps in the 75-80F range and DTRs so small that this river may stay in the 69-70-71 temperature around the clock. At spring flows, the DTR may vary as much as 16F over 24 hours. Why? Because the area is semi-arid and has cool nights and the river temps are influenced, up to 72%, by atmospheric condition, not so much the springs.