AROUND OREGON: Phillips Reservoir dwindles to level not seen since 1988

This image taken from a drone on Tuesday, Aug. 17, shows Mason Dam at lower right, and the water intake structure, center right near the shore, at Phillips Reservoir. (JAYSON JACOBY/Baker City Herald)

There’s a strip of moist ground in Baker County that’s being exposed to the air after more than three decades under the water.

And if things keep on as they have been, a bit more land might emerge for the first time in better than half a century.

These patches form the shoreline of Phillips Reservoir, along the Powder River in Sumpter Valley, about 17 miles southwest of Baker City.

The reservoir, created by the completion of Mason Dam in 1968 and designed to store water for irrigation and flood control, has been depleted by drought to its lowest level since late October 1988.

And if the reservoir recedes slightly farther, ground will be revealed that has been covered by water since 1968, the year the dam began to impound the Powder River.

George Chandler, a Baker Valley rancher and longtime board member for the Baker Valley Irrigation District, which manages the reservoir, said the fall of 1988 is the only time he’s seen Phillips so low.

That’s also the only other time Chandler recalls that the intake, the concrete structure near the dam where water drains to flow through the dam and into the river below, was exposed.

Numbers illustrate the severity of the drawdown.

As of Wednesday Aug. 18, the reservoir’s “active storage” volume was 479 acre-feet, which is less than 1% of its storage capacity. That’s the lowest volume since the fall of 1988, when the reservoir reached a minimum of 449 acre-feet on Nov. 1.

There is, however, more water in the reservoir.

The active storage figure is the amount of water potentially available for irrigation. The reservoir’s official capacity for irrigation is 73,570 acre-feet, according to the U.S. Bureau of Reclamation, which built Mason Dam.

The reservoir can hold another 17,000 acre-feet — up to a total of 90,570 — for flood control.

The ‘dead storage’ factor

But the reservoir was also designed with what’s known as “dead storage.” That’s water that won’t drain from the reservoir by gravity. The dead storage for Phillips is 5,000 acre-feet, and that water is the reason the reservoir still looks like, well, a reservoir.

Chandler said that although the dead storage capacity has likely been reduced some by silt accumulation over the past 53 years, that water, since it won’t drain by gravity, means the reservoir’s level can’t drop much farther.

On Tuesday, the main source of water entering the reservoir — the Powder River — was flowing at a rate of 39 cubic feet per second.

Some reservoirs, including Thief Valley along the lower Powder River near North Powder, have no dead storage, so when they’re drained — as Thief Valley has been most years in the past decade — all that’s left is the river in its original channel.

But dead storage capacity in Phillips isn’t available to nourish crops.

And that means irrigation from the reservoir, with the exception of small volumes for livestock, is over for the year, and a meager year it was, said Mark Ward, a Baker Valley farmer and, like Chandler, one of the Baker Valley Irrigation District’s five directors.

When water is plentiful — a rarity over the past 15 years, Ward said — Phillips can supply 3.5 acre-feet of water for each of the more than 30,000 acres of land, mostly in Baker Valley, with rights to stored water.

(One acre-foot of water would cover one acre of flat ground to a depth of one foot. The measurement is equal to almost 326,000 gallons.)

But in 2021 the reservoir provided just 0.4 of an acre-foot per acre, Ward said.

“That’s the lowest allocation we’ve ever had,” he said.

The previous record was 0.5 of an acre-foot, about 15 years ago, Ward said.

Although Ward said farmers who grow higher-value crops such as potatoes typically have wells for irrigation rather than relying solely on reservoirs, the paltry supply from Phillips trimmed yields from some of his family’s crops, including peppermint.

Ward said they used “the bare minimum” of irrigation water on their mint, which contributed to a lower-than-usual yield of mint oil — the most valuable part of the crop.

(He said they also made hay from mint.)

The bigger culprit in the low oil yield, though, was not a lack of water but rather an abundance of another element — heat.

“We learned that mint does not like 100-degree heat in June,” Ward said, referring to the record-setting heat wave in that month’s final week, when the temperature topped out at 103 degrees at the Baker City Airport.

Although Chandler also laments the scant amount of irrigation water this year, he also remembers the era before Mason Dam was built.

Chandler, who graduated from Baker High School in 1965, recalls a summer when the Powder River ceased flowing through Baker City.

Complex causes

Both Chandler and Ward blame a combination of factors, which happened to coincide over the past year, for the possibly unprecedented depletion of the reservoir.

The trouble started almost a year ago.

In the fall of 2020, Phillips dropped to about 5,500 acre-feet in November, so there was a lot of space to fill.

The biggest source of water to refill the reservoir isn’t water at all — it’s snow.

Winter snowpack in the mountains is the largest reservoir in the region. As that snow melts in the spring it flows into the streams and rivers that replenish reservoirs.

The snowpack was actually about average in the upper Powder River basin, the headwaters for its namesake river and other streams that feed Phillips Reservoir.

The problem, Chandler and Ward agree, is that most of that melted snow soaked into the ground rather than trickling into the reservoir.

“The creeks never ran like they normally do,” Chandler said.

He and Ward attribute this in part to cold nights that predominated this spring, which slowed the snowmelt and allowed much of the water to leach into the soil.

Another factor was the lack of significant rainstorms. Heavy rain, especially when coupled with relatively mild temperatures, can cause a rapid, albeit temporary, glut of meltwater that flows into rivers.

Their anecdotes are corroborated by statistics.

Phillips Reservoir reached a maximum active storage volume this spring (not including the 5,000 acre-feet of dead storage) of just 16,632 acre-feet, on April 26.

In many years the reservoir holds more than 40,000 acre-feet in late April. Even in 1988, when the reservoir’s level plummeted in the fall, it was holding about 26,000 acre-feet the final week of April.

“It doesn’t take long to get rid of that” amount of water, Chandler said, and that was indeed the case in 2021.

Worse still, farmers needed reservoir water earlier than usual due to the aforementioned lack of spring rain, and persistent wind that leached much of the sparse moisture from the topsoil.

Rainfall at the Baker City Airport for the first six months of the year — a period that includes what are statistically the two wettest, May and June — totaled 2.44 inches. That’s 43% of average.

“We just don’t seem to get the rains like we used to,” Ward said.

Then came the June heat wave.

“It was the perfect storm,” Ward said — although in this case it was the absence of storms that caused the problems.

With much more water flowing through Mason Dam than was coming in from the Powder River, the reservoir receded rapidly, dipping below 10,000 acre-feet by June 29, which happened to be the 103-degree day at the airport.

By the end of July the reservoir’s active storage volume was below 3,000 acre-feet.

In that bellwether year 1988, the reservoir didn’t drop below that threshold until Sept. 6.

Banking on blizzards

With the reservoir so diminished, even a bountiful snowpack this coming winter probably won’t be sufficient to refill Phillips.

But a skimpy snowpack could make for even more dire conditions in 2022.

“I don’t like cold weather but I hope we get a lot of snow,” Chandler said. “I’ll plow snow every day if I have to.”

Ward also wouldn’t complain about a repeat of the 2016-17 winter, when snow depths topped two feet in Baker City and the temperature at the airport plummeted to 24 below zero in early January.

But he’d like to see heavy rain fall in October or November, before snow starts piling up.

That would start refilling the reservoir, making for a smaller hole to fill come the spring of 2022.

NOTE: This story is published with the permission as part of a collaborative of news organizations in Oregon sharing news content. The Malheur Enterprise is part of the arrangement.

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