Heavy rains test Lab erosion control systems

Goal is to prevent contamination from flowing toward Rio Grande

Stormwater flowing from left to right eroded soil next to this structure in Pueblo Canyon.

August 19, 2010—Inspections since the heavy rains on Sunday and Monday are revealing damage to some important parts of LANL’s erosion and sediment control systems, said the Lab’s stormwater program manager.

“It’s kind of a crazy time,” said Steve Veenis of the Lab's Environmental Programs. “When it rains hard on consecutive days we have a lot of work to do. This is out of the ordinary to have multiple intense rain events.”

Seven LANL gauges recorded more than an inch of rain on Sunday, including one gauge that logged 2.12 inches—and 1.14 inches in just 30 minutes. The rain saturated the ground so that Monday’s big rain event caused flows well above normal to travel down many of Los Alamos’ canyons rather than soak into the usually porous soils.

Surveying the damage

Rain events send field crews into action. They must inspect erosion control measures, including straw tubes, rock structures aimed at lessening the force of runoff, rain gauges, and numerous structures in Pueblo, Los Alamos, and DP Canyons.

Major improvements to onsite stabilization controls have been effective in keeping sediments on Laboratory property. But inspections Tuesday showed damage at a new grade control structure in Pueblo Canyon and a storm water gauging station downstream of Los Alamos and Pueblo Canyons.

In one case, runoff washed away soils abutting the Pueblo Canyon structure. In the other case, the water washed tons of sediment into the gauging station, plugging the flow measurement equipment.

Early indications show that a majority of this sediment came from local non-laboratory sources near Totavi and Guaje Canyon. Engineering studies are now under way to look at repairs.

Crews will also collect any samples taken by automated water sampling stations and send them off for analysis. It’s too early to tell if the samplers detected elevated concentrations of contaminants in the samples collected during recent storm events.

Preventing sediment migration

The reason for the concern? Storm runoff flowing down hillsides or canyon bottoms can stir up sediments and carry contaminants toward the Rio Grande. It’s the focus of a major Lab sediment control project over the last several years.

Lab and independent studies have shown minimal impacts from LANL contaminants in the Rio, and the sediment control project is aimed at keeping it that way.

Supporting Santa Fe water

The project comes just as Santa Fe’s new Buckman water project is being constructed—which will divert water from the Rio Grande for homes and businesses.

Three elements of the Lab’s system are automated gauges at key points in the canyon system. The gauges will detect water flow levels, take samples, and send a wireless signal to Buckman controllers—who can shut off the intakes if they choose.

The Department of Energy and the Buckman Board have a memorandum of understanding outlining additional monitoring and analysis. The water diversion project is scheduled to go online in the spring of 2011.

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At its peak, water was flowing over the banks at this gauging station. Note the size of the rocks carried downstream.

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After heavy rains, crews must collect samples from LANL's automatic water samplers.