The Art of Testing
Putting stormwater, erosion, and sediment control BMPs through their paces
There are those who would argue that the science of
keeping stormwater runoff free of sediment, dirt, and pollution is
boring, like eating dry toast without butter.
These people have never met Jett McFalls.
True, his name is cool, but that’s not the only interesting thing
about McFalls. He’s the manager of the Hydraulics, Sedimentation, and
Erosion Control Laboratory operated by the Texas Transportation
Institute and Texas Department of Transportation. This means that he
oversees a 19-acre funhouse of flumes, indoor waterfalls, and
McFalls isn’t running a waterpark. His facility, and all the
equipment in it, exists to make sure that officials with the Texas
Department of Transportation use erosion and sediment control products
that actually work.
So McFalls and his fellow engineers pour gallons of simulated
rainwater over erosion control blankets to make sure they hug the soil
even in fierce storm conditions. They send raging rivers of water down a
30-foot channel flume and dare liner materials to stay not only in
place but also in one piece. They stretch, bend, and crush sediment and
erosion control products to make sure they can take whatever punishment
nature can give them.
Does that sound like a dry-toast kind of job?
“Oh, we do have fun here,” McFalls says. “We are doing a job, an
important one, but at the same time this is a fun place to work. People
always say that erosion control is not an interesting topic, not an
exciting topic to study. Well, they’ve never been here.”
McFalls isn’t alone. Labs designed to test stormwater and erosion
control products dot the country. Some, like McFalls’s lab, work mainly
for one state, testing materials; then, if the products pass, they get
put on the state’s list of approved best management practices (BMPs).
Others run tests not associated with state agencies, trying to discover,
for instance, if wattles filled with recycled palm fronds perform as
well as those filled with straw or other materials. (By the way,
according to preliminary data from the San Diego State University Soil
Erosion Research Laboratory, they do just fine.)
The research labs are an important element of the stormwater and
erosion control industries. They provide key information about how
different products work and in what environments and situations they
work best. And they do this without the bias that a manufacturer, no
matter how scrupulous, has when testing its own products.
But how do these labs operate? What equipment do they use? What tests
do they put products through? And how do they decide what gets tested?
Stormwater decided to find out. To do so, we spoke with the
researchers at four of the busiest testing labs in the country. What’d
we find? The testing industry is a fascinating one, and one that
deserves a little press now and again.
Photo: Jett McFalls
|Test beds under a rainfall simulator. Clay and sand soils are tested.
Paving the Way for Palms
The engineers at the San Diego State University Soil Erosion
Research Laboratory are busy. The lab tests sediment and erosion control
products for local, county, state, and federal agencies. The engineers
also test products for private companies who are either developing new
ways of keeping stormwater runoff clean or are preparing to go to market
with a product.
There is never a shortage of work here.
“We have two things going on here all the time: research and
development,” says Ed Beighley, co-director of the laboratory. “We are
always trying to get a better understanding of how the different devices
work. When we work for private companies, they will have a particular
product and they want to know how well it works. We’ll run the tests and
then give them the data and tell them how well their products performed
under our conditions.”
To do this, the laboratory relies on a tilting soil bed, portable
overhead rainfall simulators, and a water treatment and storage system.
The soil bed is 3 meters wide and 10 meters long, occupying a total of
323 square feet. The bed can accommodate soil up to a foot deep.
When testing products, the researchers here compare them to a bare
soil run. This allows them to determine how well the particular sediment
or erosion control device performs against a soil bed that is graced
with no BMPs. The engineers then know how much runoff and sediment
displacement they’d get with no stormwater products in place.
They then test again, this time with the BMPs installed, and make a
comparison. This gives a picture of how specific stormwater products
perform in certain conditions during a certain type of rainfall.
Photo: Jett McFalls
|Testing in an outdoor flume
City officials in San Diego often turn to the
laboratory, which recently tested wattles filled with recycled palm
fronds. The goal? To see if the fronds are as effective a filler
material as are the more traditional ones such as straw.
The lab’s engineers finished testing the palm fronds in September of
last year. That doesn’t mean the project, though, is complete. Beighley
and others with the lab are still conducting their own independent
research. Beighley is also preparing the lab’s results for publication.
The results are important for the city. San Diego, after all, has no shortage of palm fronds.
“Palm fronds are abundant here, and they are a product that no one
uses,” Beighley says. “They have to go to the landfills. But if we could
find a use for them, if we could use them in wattles, that would be a
good solution of what to do with these products.”
The testing process lasted about nine months, Beighley says. The lab
tested the palm-frond-filled wattles much the same way it tests other
stormwater and erosion control materials, comparing against a bare soil
bed with no BMPs installed. The results were solid. The palm fronds
worked just as well as any other wattle material, Beighley says.
The lab is now testing the palm fronds to see how they work for
blanket-type settings. Lab researchers are in the middle of these new
tests, mixing the palm fronds with other materials to see how effective
they are in preventing sediment in water runoff. The tests will probably
continue through mid- or late 2007, Beighley says.
Testing the Separators
St. Anthony Falls Laboratory, run by the University of Minnesota, is
a rarity: It’s the only fluid-mechanics laboratory that uses a natural
waterfall as its primary source of water. It’s situated on an island in
the Mississippi River.
But most unusual of all might be the research that the lab tackles.
The dozen University of Minnesota faculty members who work at the lab
conduct both applied and basic research. Currently, the lab is running
more than $1 million worth of projects with state agencies, testing
different stormwater BMPs.
The lab is currently testing the effectiveness of a variety of
underground hydrodynamic separation devices in removing suspended
sediments and other pollutants.
“We realized that there are many who are building these devices,”
says Omid Mohseni, associate director of applied research with St.
Anthony Falls. “But no one knows how they really perform. They only way
to evaluate them is through monitoring, and there are a lot of problems
The biggest problem with monitoring, Mohseni says, is that most
observers only monitor a system’s performance for one year or, at the
most, two summers. The underground separator may for this limited time
period perform extremely well or do a terrible job, depending on the
amount of rainfall an area sees during these months. Thus, underground
separators rarely receive an accurate portrayal of how they perform
during specific types of rainfall conditions. This is important: The
devices may work well in one area that sees a certain amount of
rainfall—and a certain number of severe storms—in a given year but fail
in another area that suffers from significantly higher rainfall.
Municipal officials also generally rely on automatic samplers to
monitor their underground devices. This is a mistake, Mohseni says,
because such samplers are not designed to analyze suspended sediments.
Automatic samplers work well only for dissolved materials, he says.
Researchers at St. Anthony Falls decided that it was time to put the
popular underground hydrodynamic separators to the test. The lab would
test four of the most commonly used separators, but the tests wouldn’t
be run in simulated laboratory conditions. Instead, researchers would go
out into the field, testing separators that were currently operating in
municipalities in the Minneapolis–St. Paul area.
To do this, researchers mapped 150 of the underground devices from
the different manufacturers that were currently in use in the Twin
Cities area. In the end, the lab found four different brands of
separators to test, in four different locations. Researchers chose
separators that were located close to fire hydrants that had
sufficiently powerful water flows.
Lab officials also made sure that their researchers would be able to
run their field tests safely. That meant not testing separators that
would require testing crews to stand alongside heavy traffic. It also
meant not testing devices located in the middle of busy streets.
In the summer of 2006, crews from the laboratory subjected the
underground separators to 12 different water-flow tests, using the water
from nearby fire hydrants to conduct their work. Researchers fed known
amounts of sediments into the underground separators and then analyzed
just how much of these sediments the separators removed.
Researchers subjected the devices to a wide variety of water-flow
levels to see how they handle heavier and lighter rainfalls. They also
fed varying sediment sizes—80 microns to 400 microns—into the devices.
The results? Not surprisingly, they depend on the severity of the
water flow and the size of the sediments fed into the devices. If the
sediment was heavy and the flow rate slow, the devices were able to
remove 100% of the sediment particles, Mohseni says. But as the flow’s
force increased and the sediment size dropped, the effectiveness of the
underground separators dropped, too, he says.
Photo: Jett McFalls
|Testing at Texas’s Hydraulics, Sedimentation, and Erosion Control Lab
Researchers at St. Anthony Falls were preparing their
final analysis of the data as this article was being written. Their
final report will include a series of performance curves for the four
separators that show how each performed depending on flow rates and
“Our testing is probably the most robust done on these devices,”
Mohseni says. “Now different agencies can use the data we produce for
evaluating these four products, no matter where they are being
installed. In Washington or Vermont or down in Louisiana, anywhere they
go, these results will be valuable. The only thing they need to know is
what kind of sediment size they have in their stormwater runoff. If they
don’t have that piece of information, then these performance curves
will not be that valuable. They’ll have to assume something. They’ll
have to assume what they think the sediment size will be instead of
knowing exactly what it is.”
The Need for Testing
James Mailloux, engineer with Holden, MA–based Alden Research Laboratory, is a busy man.
Photo: Jett McFalls
|A typical test flow
Then again, so are all the researchers at Alden, the
oldest continuously operating hydraulic laboratory in the United States.
This lab never has any shortage of stormwater-treatment devices to
This is no surprise. Alden is one of the most respected, and largest,
hydraulic labs in the country. The Alden campus occupies 32 acres of
hilly land, though Mailloux does much of his work in a 70- by 120-foot
building designated exclusively for stormwater-related testing. A
5-foot-deep sump at one end holds 50,000 gallons of water.
A 50-horsepower vertical pump produces the water flow that Mailloux
and his fellow researchers rely on to test separator units, filter
units, or whatever other product they happen to be analyzing. A second
50-horespower pump sits alongside the first, just in case they need an
even more powerful flow of water.
Of course, this is just the start of the equipment that Alden relies
on to test sediment removal products. Mailloux has five calibrated flow
meters at his disposal, ranging from the 2-inch to the 12-inch variety.
“Depending on what we are testing, what size unit, and what size flow
we need that day, we select one of these meters to run the flow
through,” Mailloux says. “We then have full documentation of the flow,
averaged every five seconds, during the duration of the test. It gives
us an excellent record of what the flow was during the entire test. We
get all types of useful information.”
Researchers then inject sediment into the flow. Alden uses both a
flurry system and a dry-injection system, though researchers here
typically reserve the dry-injection method for testing larger sediment
The tests Alden runs are important, Mailloux says, in part because
manufacturers are constantly developing new products to treat stormwater
runoff. As federal regulations regarding sediment control become more
stringent, these products have to do a better job than ever at removing
sediment, oil, trash, and debris from water runoff.
Without independent testing labs such as Alden, government agencies
and local municipalities would have to rely too much on test results
provided by the manufacturers themselves. Not all manufacturers test
their products using the same test parameters, and some potential buyers
trust third-party testing over the manufacturers’ own results.
Photo: Jett McFalls
|Vegetated flume test trays in the greenhouse
The goal at Alden, Mailloux says, is to establish
accurate removal rates for the sediment control devices that its
researchers test. That way, municipalities can install those devices
that have been proven to work well under the type of actual weather
conditions that they’d be expected to face in the field.
Most of Alden’s testing requests come directly from the companies
that manufacture stormwater-related devices. “They come to us and ask if
we can write a proposal to test to a specific protocol, whether it be
for Washington state or New Jersey,” Mailloux says. “We’ll find out what
is required by that particular municipality, write a proposal to do the
work, and, if they decide they want to go ahead, we’ll work up a
Mailloux, though, doesn’t want to know ahead of testing what specific
results—as far as sediment removal goes—his clients want to achieve.
“I don’t want to know anything about what the clients expect,”
Mailloux says. “I don’t want to go into testing with any predetermined
ideas. I don’t want to be biased on what I can expect to see. Then we
can run the tests and, after we’re done testing, get feedback from the
Sometimes testing will prove that a manufacturer was dead accurate in
its predictions of how a particular product will work. Other times, the
results may surprise a company. Perhaps the product removed even
greater levels of sediment at more powerful flows than the manufacturers
Other times the surprise isn’t as pleasant: The product may perform less ably than its makers anticipated.
“But we don’t like to have the information on what the clients
expect,” Mailloux says. “I don’t want that at all before we start
running our tests.”
Those who run the independent testing labs across the country feel
the same way. It’s important not to perform a test with biases—even
unconscious ones. It helps no one, after all, to give a product a better
performance evaluation than it deserves.
It’s not just highway department officials, contractors, builders,
and municipal officials who rely on the labs for impartial product
evaluation. The labs are sort of the Consumer Reports of the stormwater
industry. Manufacturers, too, then, rely on the labs to help them
develop the best products they can.
It is these products that work the best that will attract the most attention, and most business, from clients.
“We’ve been at this since 1990,” says McFalls in Texas. “I think we’ll be running these tests for a long time.”
Author's Bio: Dan Rafter is a technical writer and frequent contributor.