Why are Middle Deschutes flows so low in the fall?

September 23, 2020
Why are Middle Deschutes flows so low in the fall?

You’ve probably noticed that flows in the Deschutes River are dropping above and below Bend. Flows in the Middle Deschutes have dropped substantially. This is the section of the river that runs downstream from Bend through Sawyer Park into Tumalo State Park and down to Lake Billy Chinook.

Why is this happening? It has to do with water rights and how they are constructed. Water rights give a person the ability to divert water from a water source to use in a way that has been designated as beneficial. Many of the Deschutes water rights do not allow consistent access to the same rate or volume of water throughout the irrigation season. Rather, they allow for less water in the spring and fall and more during the summer. These are shoulder and peak seasons, respectively.

In this way, water rights for the Deschutes have a tiered or stair stepped rate. Their lowest diversion period is in April and October (40-50%), they then step up a bit in the first half of May and in the last half of September (about 55-60%), with peak diversion rates occurring from the second half of May through the first half of September (100%). The peak rates correspond with plant needs and growing seasons.

Kind of like walking up and down a podium. Some districts have water stored in reservoirs to supplement their use, others rely completely on the natural available flow of the river (live flow), and some use a combination of the two. Live or natural flows, not supported with reservoir storage, are extremely low this year due to many years of lower than average and drought level precipitation.

Flows in the Middle Deschutes would drop to nearly nothing in the irrigation season if it weren’t for restored flows from water conservation projects, permanent instream water rights transfers and water rights leasing. The DRC’s Water Rights Leasing Program is available to some water rights holders who are not planning to use their water in a given season and would like for it to be protected instream. This source of restored flows makes up 25% of the water you see in the Middle Deschutes. So, during the lowest times of diversion, there is less leased water to augment flows. The Deschutes water protected instream follows the same podium shaped availability as the diverted water.

Many of the districts have already used the storage water available to them. This affects not only the districts, which are being hit hard by the drought and water supplies in 2020, but also affects the instream protected water. This is where junior and senior water rights come into play. Senior water rights are met first and junior water rights are met last. If a district is being cut back due to their more junior priority date and lack of water, the instream protected water with that same priority date will also be cut back proportionally. Luckily for the river, much of the instream protected water is senior, but even the senior water has been affected at times in 2020.

The Deschutes River Conservancy has been working for 25 years to find solutions to complex water issues in the Deschutes River Basin. When we first started our work, the Middle Deschutes would be reduced to a warm rivulet when irrigation season started. It was only a handshake agreement between irrigation districts that allowed for 30 cubic feet per second to stay instream. Flows in this reach have increased four-fold since then, but we still have a way to go before we get to a better-balanced flow rate. Projects currently underway in Central Oregon will help restore more flows to this critical reach which will help lower temperatures and improve habitat for native fish.

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