Baker County’s biggest reservoir won’t shrink as much this year as it did last, but some boat ramps, including ones on the Baker County shore of Brownlee Reservoir, could be left dry at times in late winter and early spring.

The 53-mile-long reservoir on the Snake River forms the border between Oregon and Idaho from near Huntington north to near Richland, where Baker County operates Hewitt and Holcomb parks, each with a boat ramp, on the north shore of the reservoir’s Powder River arm.

Brownlee is a popular reservoir for fishing, with populations of crappie, smallmouth bass, channel and flathead catfish and other species. Boaters also congregate at the reservoir, which is accessible from both Oregon and Idaho.

The reservoir’s level during late winter and spring depends on two main factors, said Jen Cuhaciyan, senior engineer for Idaho Power Company, which owns and operates Brownlee Dam and its two smaller downriver neighbors, Oxbow and Hells Canyon.

The first factor is the flood control requirement that the U.S. Army Corps of Engineers imposes on Idaho Power.

That federal agency regulates reservoir levels on the Snake and Columbia rivers with a goal of avoiding flooding on the Columbia in the Portland area, Cuhaciyan said on Wednesday, Feb. 26.

In years with unusually deep snowpacks, which create a glut of water when the snow melts, the Corps of Engineers requires Idaho Power to lower Brownlee by more than 50 feet to create room to store the torrents of snowmelt.

Because Oxbow and Hells Canyon reservoirs are much smaller and lack storage capacity, Brownlee is a key reservoir in the flood control system, Cuhaciyan said.

The second factor is also related to snowpack.

Cuhaciyan said Idaho Power officials strive to leave room in Brownlee to avoid having to spill large volumes of water into the Snake River below Hells Canyon Dam to comply with flood control targets.

Some of the water is diverted through the turbines that generate electricity at Brownlee Dam.

But there’s a limit on how much water can be sent through the turbines, and the rest pours through the dam’s spillways. The resulting turbulence increases the concentration of dissolved oxygen and nitrogen in the water, which can kill fish, Cuhaciyan said.

The difference between Brownlee’s actual level, and the federal flood control requirements, can be significant some years.

The main reason is that the flood control targets are based on snowpack for not only the Snake River basin but also the Columbia River basin, Cuhaciyan said.

This winter, for instance, the snowpack in the Columbia basin is slightly below average, which is reflected in the relatively modest flood control targets for Brownlee.

But because the snowpack is above average in much of the Snake basin — 33% above in the Weiser basin, 30% in the Payette and 65% in the Malheur as of Feb. 27, for instance — Idaho Power probably will keep the reservoir lower than the flood control targets, Cuhaciyan said.

The Corps of Engineers requires Idaho Power to have the reservoir at least 32.5 feet below full by Feb. 28, she said.

As of Feb. 27 the reservoir was 37 feet below full.

(When full, Brownlee’s surface is 2,077 feet above sea level. As of Feb. 27 the surface was 2040 feet.)

The flood control requirement for March 31 is 28 feet below full, Cuhaciyan said.

But based on the snowpack, and the potential for a significant rise in tributary rivers, she expects Idaho Power will keep Brownlee well below the target — probably between 37 and 47 feet below full — during March.

The reservoir likely will start slowly refilling in April and continuing through the spring, Cuhaciyan said.

The current flood control targets — which could change depending on the snowpack — are 19.5 feet below full for April 15, and 11.5 feet for April 30.

Actual reservoir levels will depend on weather, and particularly on mountain snowfall. March can be one of the snowier months at high elevations, and Cuhaciyan said heavy snow could affect both the flood control targets and Idaho Power’s decisions about Brownlee’s level.

Generally speaking, more snow means a lower reservoir level.

Based on Cuhaciyan’s projections of the reservoir being between 37 and 47 feet below full, the boat ramps at Hewitt and Holcomb Park might not be accessible at times during March

Holcomb’s ramp is usable, depending on the size of the boat, down to about 30 feet below full, while Hewitt’s ramp can be used down to about 39 feet below full.

Minimum levels for other ramps on the Oregon side, according to Idaho Power:

• Spring Recreation Site (near Huntington): 22 feet below full

• Farewell Bend State Park: 40 feet

• Moonshine Mine (south of Richland): 57 feet

The ramp at Idaho Power’s Woodhead Park, on the Idaho side of the reservoir, is accessible down to 53 feet.