High flow test shows reconstruction of the Silver Bullet Rapid may have smoothed things out

Silver Bullet Rapid via The Mountain Mail
Silver Bullet Rapid via The Mountain Mail

From The Mountain Mail (Maisie Ramsay):

The problematic Buena Vista-area rapid that disrupted commercial rafting last summer is showing improvement. A pulse of high water used to assess changes at the Silver Bullet Rapid last week indicates an overpowering hydraulic has been smoothed out.

“It looks like we took a step in the right direction,” said Rob White, park manager for Arkansas Headwaters Recreation Area. “Hopefully, it will continue to perform well when water comes up in the spring.”
Flows reached 1,200 cubic feet per second during the Nov. 26 evaluation. The real test won’t come until spring runoff, when dramatically higher flows will create more powerful currents.

“We still need to see how it performs at 1,500 cfs, 3,500 cfs,” White said.

The Silver Bullet Rapid was reworked last winter to have three drops instead of one drop. Those changes proved troublesome last May when they created a “massive recirculating wave that’s tending to hold boats and potentially cause a flip,” White said at the time.

The hydraulic was so dangerous AHRA closed Silver Bullet Rapid to rafters for 3 weeks.

The early-season closure created logistical headaches for local outfitters, who had to disrupt, shorten and revise trips.

“It hurt quality and cost money,” Wilderness Aware Rafting co-owner Joe Greiner said.
Even after the closure was lifted, AHRA still required all rafts to portage around the Silver Bullet Rapid and the adjacent Helena Diversion structure.

The issue prompted AHRA to embark on a reconstruction project in fall, splitting the cost with the engineering firm responsible for last winter’s redesign of the Silver Bullet Rapid boat chute, Recreation Engineering and Planning of Boulder.

The final cost of the most recent redesign has not been determined. Last year’s work cost roughly $400,000.
The most recent work included filling a hole in the riverbed with concrete, extending the rapid’s third drop about 20 feet and installing “reflectors … to create a flushing ‘V’ versus a standing wave,” White said.
The mid-river island was lowered to lessen the force of water in the boat chute, and the portage trail was extended to better avoid a downstream eddy. Additional rock will be added to the portage trail in spring so it won’t wash out at high water, White said.

At Wilderness Aware Rafting, Greiner is skeptical that a complete fix has been achieved for Silver Bullet Rapid.

“It’s still channeled into pretty much all one spot,” Greiner said. “I’m not a hydrologist, but my gut feeling is there’s going to be a pretty big wave at high flows.”

How the rapid pans out won’t be known until spring, but Greiner is braced for possible problems at high flows.

“I hope the powers that be are on standby if it does cause a problem and are prepared to keep going until we get it right,” Greiner said. “I think we’ll be okay for most of the year, might just be a couple weeks where it causes a problem.”

Wilderness Aware Rafting was one of many Arkansas River rafting outfitters affected by the Silver Bullet Rapid closure and subsequent portage requirement.

“It affected us greatly,” said Mike Kissack, president of the Arkansas River Outfitters Association. “It’s an excellent stretch of river from the Numbers into Buena Vista to Johnson Village. It’s important that everyone have access to that – having that rapid function properly is important to all of us.”

More whitewater coverage here.

The latest ENSO diagnostic discussion is hot off the presses — ENSO neutral now, 65% chance of emergence over the winter

Mid-November 2014 plume of ENSO predictions via the Climate Prediction Cenber
Mid-November 2014 plume of ENSO predictions via the Climate Prediction Cenber

Click here to read the discussion. Here’s an excerpt:

Synopsis: There is an approximately 65% chance that El Niño conditions will be present during the Northern Hemisphere winter and last into the Northern Hemisphere spring 2015.

During November 2014, sea surface temperature (SST) anomalies increased across the central and eastern equatorial Pacific. At the end of the month, the weekly Niño indices ranged from +0.4°C in the Niño-1+2 region to +1.0°C in the Niño-3.4 region. The subsurface heat content anomalies (averaged between 180o-100oW) also increased during November as a downwelling oceanic Kelvin wave increased subsurface temperatures in the central and eastern Pacific. However, the overall atmospheric circulation has yet to show a clear coupling to the anomalously warm waters. The monthly equatorial low-level winds were largely near average, although weak anomalous westerlies appeared in a portion of the eastern tropical Pacific. Upper level easterly anomalies emerged in the central and eastern tropical Pacific during the month. The Southern Oscillation Index has been somewhat negative, but the equatorial Southern Oscillation Index has been near zero. Also, rainfall continued to be below average near the Date Line and over Indonesia, and near average east of the Date Line. Although the SST anomalies alone might imply weak El Niño conditions, the patterns of wind and rainfall anomalies generally do not clearly indicate a coupling of the atmosphere to the ocean. Therefore, despite movement toward El Niño from one month ago, the combined atmospheric and oceanic state remains ENSO-neutral.

Similar to last month, most models predict SST anomalies to be at weak El Niño levels during November-January 2014-15 and to continue above the El Niño threshold into early 2015. Assuming that El Niño fully emerges, the forecaster consensus favors a weak event. In summary, there is an approximately 65% chance of El Niño conditions during the Northern Hemisphere winter, which are expected to last into the Northern Hemisphere spring 2015 (click CPC/IRI consensus forecast for the chance of each outcome).