Dear Tumalo Irrigation District Patron:
Tumalo Irrigation District (TID) would like to take this opportunity to update you on TID’s water supply outlook to help you in your crop planning decisions for next season.
First the good news. TID will not run out of water this season. The drought is severe and Tumalo Creek flow has been far lower than I have seen it since the early nineties. But TID’s demand has also dropped as we complete piping projects. Savings from these piping projects have lowered our average summer demands from 178 cfs to less than 125 cfs in just the last five years alone. This means that we are lowering our demand on Crescent Lake storage, which in turn means the water in Crescent lasts longer and we can survive a longer and more severe drought before the water runs out. I will not go into the environmental benefits here, but I assure you those benefits are just as impressive.
The bad news is the drought is not over, and we are seeing a shortage on the horizon. A lot could change between now and next season but let’s talk about what happens if the drought continues!
At our current usage we will end the irrigation season with about 19,000 AF left in Crescent Lake. If this winter mirrors the previous winters, next spring we could see as little as 24,000 AF of storage in Crescent Lake. Of that, the last ~10,000 AF cannot be withdrawn at a rate sufficient enough in outflow to support the District’s needs.
This year we will have used ~30,000 AF, over twice as much as we may have access to next year. This means when Tumalo Creek snow melt is gone, we will have two choices. One, continue at 70% deliveries – as we have been doing this season – until we run out, probably in mid-August. Two, start a rotation when the Tumalo Creek snow melt runs out. Under a rotation schedule, we could deliver 70% to patrons every other week and attempt to stretch the supply until the end of the season.
As the District Manager, I will recommend we start the rotation as soon as the supply in Tumalo Creek is insufficient to supply TID’s needs and we are required to turn on Crescent Lake storage. Next spring when we know what the 2021 snowpack looks like, your board members will be making the final call and will be looking for your input. I do not envy the decisions they have to make.
By planning ahead and working together we can get through a challenging season with the greatest benefit to our patrons.
District Manager/ Secretary to the Board
You can skip the next few paragraphs if you already know how our system functions.
This is a very hi-level overview of our supply and volumes of detail are left out for your reading pleasure.
TID’s obtains most of its water supply from just a few natural sources. Our primary supply comes from Tumalo Creek. When Tumalo Creek runs low, a supplemental supply comes from Crescent Lake, ~80 miles south of Bend. Every year when Tumalo Creek snow melt runs out sometime between Memorial Day and the end of July, we switch from Tumalo Creek water to storage water from Crescent Lake.
Tumalo Creek is fully dependent on the past year’s snowpack. There is some spring fed base flow, but most of the water comes from freshly melting snow. There are no controls allowed on the creek. When the snow is melting, it flows. When the snow melt runs out, the flows drop to a small base flow. Not only is there a seasonal flow pattern, there is a diurnal fluctuation that can happen very rapidly, so Tumalo Creek earns its flashy reputation. In addition to the irrigation right, we have the right to capture water in Tumalo Reservoir when the flows in Tumalo Creek are high enough. Tumalo Reservoir leaks – a lot, therefore the water must be used within a few weeks or it will all seep into the ground.
Crescent Lake is a large natural lake with a relatively small drainage area. Crescent Lake Dam increased the level of the lake and TID can store water in that increased area. We have no rights to the natural lake under the increased level from the dam. Because of the relatively small drainage area around Crescent Lake, the lake is slow to fill and is mostly filled with spring runoff from the snowpack. Crescent Lake leaks a relatively small amount so for the most part, what we do not use will still be in the lake for use the following year.
Deschutes River TID also has a small portion of live flow from the Deschutes River of ~9.5 cubic foot per second. Although this source is small, we very much count on this flow as it is a year-round flow, and we can store the off-season portion in Crescent Lake.