Sediment Solutions

Tony Michaelsen - noemail@earthwormjobs.com — Sun, 14 Mar 2010 04:00:00 GMT

When wildfires strike southern California—and they strike often—two things are likely. First, news crews take to the airwaves to describe the latest devastation. Second, behind the scenes, it is often Michael Harding preparing for what comes next.

“The secondary disaster is always the ash and sediment that comes down and injures people. That’s where I get involved, trying to prevent that,” says Harding, CPESC, of Great Circle International and former president of the International Erosion Control Association.

“We can do that, in a number of different ways. Our focus is generally on source control, where we try to get up on the burned slopes to protect them from erosion with some sort of mulch. But this takes time, particularly on the size acreages we’re dealing with, so we simultaneously install diversions or catchment systems around people’s homes to protect them from mudflows until stabilizing vegetation is reestablished.

“I generally teach that for most types of projects, you try to work from the top down using erosion control BMPs [best management practices]. You first try to control sediment by keeping it in place before it gets mobilized. But in fire work, it’s sort of the opposite. The first thing we do is try to protect houses and people’s structures and roads. We’ll assign work crews from the California Conservation Corps to go out behind people’s homes, businesses, and critical evacuation roads to install k-rails [lane dividers] or sand or gravel bags to try and divert the mud around the homes, because we know it’s going to come with the first rains. These efforts are focused on high-priority sites where lives and property are at stake. That’s generally a subset of the overall burn area that’s referred to as the ‘urban interface.’ For example, in the San Diego County fire in 2007, we had 435,000 acres that burned. For economic as well as practical environmental reasons, we typically treat between 1% and 2% of that overall total. These treatments can range from hydraulic applications to straw wattles to gravel bags and k-rails.

Photo: Hamilton Manufacturing
Aerial application of mulch after a California fire

“Typically, after a fire incident, we spend the first few days and weeks conducting assessments to determine which areas are at greatest risk. I say ‘we’ because this is a coordinated team effort between the local sponsoring governmental agency—in 2003 and 2007 it was San Diego city and county—and the federal agencies such as FEMA and the NRCS Emergency Watershed Program, the groups who eventually provide the funds for remediation. I’ve been real fortunate to be included as part of the Geosyntec Consultants’ team in 2003 and 2007, and we work right alongside the local, state, and federal folks to get the assessments done rapidly and secure the necessary funds to pay for all the upcoming work. That’s important, because the big-ticket BMPs don’t proceed until assessments are completed, agreement is reached among the team on treatments, and the money is dedicated.

“While that work is being completed, we send out the California Conservation Corps crews to install the exigency measures, such as sand and gravel bags, which can sometimes appear backward from what you would do on a regular job, where you do the source control first. We also have the CCC install wattles on the slopes in advance of hydraulic applications, which takes some coordination to make sure the activities of diverse groups of contractors and CCC crews are phased properly. That’s where the county inspectors and Geosyntec field engineers really prove their worth. And then there’s my partner Chuck Austin and his son, David, who coordinated the activities of the hydraulic contractors in 2003 and 2007. Enough credit cannot be given for their efforts.

“Once we get the hydraulic mulching on the slopes, it pretty much stops all the sediment delivery and makes our sediment control even more efficient.”

Harding laments the fact that often people knowingly or unwittingly put themselves in harm’s way by virtue of where they live or build their homes. “It’s hard to control development in California. My wife Carol used to say, ‘People buy airspace.’ They buy small plots of land, in areas where it is difficult to protect them from fire, and they build upwards. Berkeley, in 1991, was a great example. People built along old logging roads in the East Bay hills. Their homes had a small footprint that caused them to cantilever their houses out over the steep hillsides. When the fire started, it raced up the hills, right up underneath them. You’d see a lot of burnt-out cars down in the canyons because even the garages were cantilevered over the edges.

“If you really want to protect people from fire incidents, you don’t let them build in areas where they can’t be protected,” he adds. “But I don’t know that that’s possible in California or on the front range of the Rockies. People are going to build where they can afford to build. Land use planning really gets to the issue, but I think in many areas in California it’s probably a little bit late for that.”

He notes that since the 1930s, many communities, such as areas in Pasadena and Glendale, CA, have built large debris basins at the base of large hills. This can be an effective measure, he says, “but communities have to have the funds to do that.” In places where homes are backed by a wilderness area or where homes are built at the toe of the slopes, these large debris catchments could provide some protection: “These devices act as a containment buffer behind homes for mud and debris flows. I think a lot of the structures that can collect runoff and divert it around people’s homes should be designed and built as part of the community itself, but they’re not. To go back in and retrofit communities with this type of protection is very costly, and the federal government doesn’t use its disaster remediation money to pay for that.” Next Page >

13-Mar-10 10:00 PM

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Sediment Solutions