California Takes Issue With Corps of Engineers' Levee Policy
A post-Katrina attempt by the Army Corps of Engineers to enforce a long-standing national policy in California raises questions about the role of vegetation on flood control levees.
Although not widely known outside California, the 700,000-acre Sacramento–San Joaquin Delta is critical to the state’s economy and a key component in its interrelated complex of natural resources. Once a natural estuary of freshwater and brackish tidal sloughs and marshes, the Delta, which produces the largest asparagus crop in the country, now supports an agricultural industry that grosses $500 million a year.
Located in the west-central part of the state immediately east of San Francisco Bay, the Delta receives runoff from 40% of California’s landmass, including almost the entire Sierra Nevada, the southern reaches of the Cascades, and the eastern flank of California’s coastal range, making it the collection point for a delivery system that provides drinking water to 20 million Californians, two-thirds of the state’s population.
Contrary interests have been squabbling over the Delta for decades, not the least because its remaining natural habitat is considered vital in a state that has lost over 90% of its riparian vegetation. The Delta is also a boating and fishing mecca served by over 600 marinas and recreational areas. A deep-water shipping channel connects San Francisco Bay with inland ports.
Historically, the banks of the Delta’s waterways were lined with low natural levees covered with woody vegetation. These natural landmasses were mostly tule marshes dominated by hardstem bulrushes (Scirpus acutus). In the last 150 years, however, more than 95% of the Delta’s tidal wetlands and up to 85% of its riparian habitat have been lost as the marshes have been reclaimed for agriculture and other human use. During the 20th century alone, the overall land-water interface was reduced up to 45%. Additionally, altered flow and sediment regimes, together with boat traffic, have increased shoreline erosion and led to consequent loss of tidal zone and riparian vegetation along many sloughs.
 |
Photo: Jeff Hart |
| Jeff Hart’s bioengineered approach to erosion control |
Though degraded, the Delta provides habitat for a number of special-status animals and plants, including spawning habitat for the Delta smelt (Hypomesus transpacificus) and rearing habitat for the smelt, juvenile Chinook salmon (Oncorhynchus tshawytscha), and steelhead trout (O. mykiss). Four special status plants—Suisun Marsh aster (Aster lentus), Mason’s lilaeopsis (Lilaeopsis masonii), mudwort (Limosella subulata), and Delta tule pea (Lathyrus jepsonii ssp. jeponii)—grow in the intertidal zone or adjoining riparian scrub of the Delta’s sloughs. Although maintaining and restoring natural vegetation along the sloughs is an important concern, it nevertheless remains that extensive bank erosion, along with contemporary repair and maintenance practices on the Central Valley’s 1,600 miles of levees, has reduced natural vegetation to a narrow strip of land on the water side of these manmade structures.
The Delta levees are an erratic patchwork that US Army Corps of Engineers Geotechnical and Materials Community of Practice Leader David Pezza has described as “a very fragile hodgepodge,” which not only is susceptible to erosion and potential breach but also would fail in a 6.5 magnitude earthquake. A portion of the levees was engineered and built as part of a federal flood control project authorized by Congress in 1917 (today referred to as project levees), but many more have been privately constructed either by local reclamation districts or by landowners. Besides the corps, a myriad of federal and state agencies maintain jurisdiction over the Delta, including the US Fish and Wildlife Service, the National Marine Fisheries Service, the California Board of Reclamation, and the state Department of Water Resources (DWR) and Department of Fish & Game.
Locals consider this disparate and irregular flood control system part of what makes this area of California unique. Not the least of the levees’ appeal is the oaks, cottonwoods, and sycamores that have grown up over the years and now shade public roads, bike trails, and private yards.
 |
Photo: Jeff Hart |
| Riprap being applied where the levee groundcover was sprayed with an herbicide |
“You walk away from the Delta for a year,’” says Bob Webber, manager of California reclamation District 999, “and it will decide what it will be. The tules and oaks will grow where they’re supposed to grow. Everything’s here. You don’t have to go fooling around spending a lot of money.”
The Delta’s levees are unique among other US flood control structures in both material and construction. Unlike levees along the Mississippi River, for example, California’s levees are built close to the water because they were originally designed to scour sediment washed into Central Valley streams and rivers from gold mining in the Sierras. The silt increased the annual flood risk, and the levees were built close to channels to keep water velocity high.
That the California levees were built without setbacks makes the issues of both erosion control and habitat preservation that much more critical. “The state has the responsibility for maintaining navigation,” says Webber. “Typically it would dredge the spoils out of the center of the river and throw them on the edge of the bank, where they would create a waterside berm. This created a lovely little habitat that protected the prism of the levee from boat wakes.” But according to Webber, the state hasn’t dredged for 30 years now, and erosion has reached levee prisms, making repair “way beyond the capacity of a reclamation district.”
The reclamation of the Sacramento–San Joaquin Delta was enabled by the 1855 Swamp and Overflow Land Act, which conveyed ownership of all swamp and overflow land, including the Delta marshes, from the federal government to the State of California. The early Delta levees were dug with Chinese immigrant labor and were a little over 3 feet tall with a base width of 12.5 feet. In the 1870s, steam-powered dredges moved large volumes of alluvial soils from the river channels to their banks, and by the end of World War I, the Delta had been transformed from a tidal marsh to a network of improved channels (now called sloughs) snaking between islands. The challenge, however, was that the fertile peat soils weren’t suitable for levees, which sank and developed deep cracks and fissures such that by 1974, reclamation costs for preservation of the Sherman Island levees totaled $500,000 ($6.2 million in today’s dollars), more than the assessed value of the property being protected.
Agriculture and wind erosion have also caused land in the central and eastern Delta to subside more than 15 feet below sea level. The loss of this heavily organic soil is also due in part to exposure to oxygen, which converts organic carbon solids to carbon dioxide and aqueous carbon. This land subsidence is a major concern in the contemporary Delta because it increases water pressure on the levees and enhances the probability of levee failure. More recently, development north of the Delta has removed land that naturally functioned for flood control, a trend that disturbs Steve Mello, manager of Reclamation District 563.
“Typically, the Sacramento Valley acted as a flood retention basin, allowing the water to percolate gradually into the Delta. Our little district submitted a protest to the rezoning and leveeing and pumping out of that ground, because instead of the 10,000 or so acres flooding a foot or 2 or 3 deep, with the water percolating into the groundwater table and slowly coming downstream, it’s now all roofed and paved and cemented, and we catch all that water lickety-split.”
Mello’s district is agricultural. Half of the 26 miles of levees he’s responsible for are project levees, the other half private. Mello himself is a second-generation farmer who grows corn, wheat, alfalfa, safflower, and pears on 2,500 acres. Most of the Delta’s lowlands are in fact protected by non-project levees, where improvements and maintenance can be a challenge, given the sometimes substandard construction and the reclamation districts’ limited resources. The 1973 Delta Levees Subvention Program was designed to reimburse non-project levees for a portion of their maintenance costs, and the 1988 Delta Flood Protection Act significantly increased reimbursements—not, however, without adding a significant environmental mandate that repairs and maintenance will result in no net long-term loss of habitat.
“There’s a limit to what we can do,” says Webber. “We spray the weeds. We try to control the vegetation to whatever standard they set, and we repair minor slips. But when it comes to doing a new design of a levee with rock, the kind of thing the corps is doing with their emergency repairs, that costs $7,000 a foot. My district has 33 miles of project levees and a total budget for both irrigation and levee maintenance of $500,000 a year.”
Given their origins, overlapping jurisdictions, and disparity in resources, the Delta’s levees experienced more than 150 failures over the last century. Three years ago, on June 3, 2004, a 350-foot section of levee 10 miles west of Stockton collapsed, flooding the 12,000-acre upper Jones tract. A year later, the corps identified 24 damaged levee sites that needed critical repair and restoration. Sustained high-water flows during the spring of the subsequent year caused significant damage to another nine sites. In September 2006, the corps and the California DWR identified 71 additional damaged levee sites needing repairs and designated 300 additional sites for deferred repairs.
Complicating an already complex and compartmentalized approach to levee maintenance, in February 2007 the Army Corps of Engineers released a national list of levees that failed the inspections ordered by Congress after Hurricane Katrina. According to a subsequently revised list, 32 California levees failed inspection, with vegetation being a primary culprit. The levee districts were given three months to come up with a plan that satisfied the corps, which specified nothing but grass on the land side of levees and nothing taller than 2 inches on the water side.
The corps justified its ordinance on the basis that it needed to maintain clear access to inspect and repair the levees as well as to flood-fight, and it gave the districts nine months to comply. Failure to meet the corps’s standards could mean decertification of the minimum requirement to provide 100-year flood protection, which could mean a loss of Federal Emergency Management Agency assistance in case of a catastrophic flood, as well as loss of the ability to purchase flood insurance at reduced rates through the National Flood Insurance Program. And the corps’s edict put the reclamation districts in a Catch-22 situation. If they complied with the corps and removed the offending vegetation to maintain their certification, they could face penalties from federal and state agencies for destroying habitat. The California DWR added fuel to the fire when a rough count during its spring 2007 inspection established that trees existed on 457 miles of Central Valley levees and shrubs and vegetation on 830 miles. (In 2007, literally thousands of trees were actually planted in more than 100 levee projects undertaken by the corps itself, according to its own operational guidelines, which called for planting vegetation—and installing irrigation systems—to provide shade and habitat.
Noting that most unsatisfactory levee ratings were due to the presence of vegetation, the US Fish and Wildlife Service suggested that a collaborative effort could produce projects that “meet the desired flood damage reduction condition with lesser impact on fish and wildlife species, especially those that are threatened or endangered, such that migratory birds would have the requisite nesting, foraging, and cover habitat, overhead cover and shade, moderation of water temperatures and energy input in river productivity.” Fish and Game suggested the corps develop “more local criteria for evaluating and maintaining levee systems.”
“After Katrina,” says Meegan Nagy, emergency manager for the corps’s Sacramento District, “we obviously realized the need to be better at our levee inspections, to tighten them up and be more rigorous. And obviously there has to be a certain standard to ensure that we can visibly see the levee and be able to access it. To be able to do that, the corps decided it had to implement its long-standing policy of no vegetation.”
“Because of what happened in New Orleans, the Army Corps is super-sensitive to anything that has to do with levees,” says Gary Hobgood, environmental scientist for the California Department of Fish and Game. “What Washington headquarters doesn’t understand is that we have a totally different climate here in California. We have different plant communities and different growth patterns. When you look at the things that could be wrong with levees, such as erosion, under seepage, and through seepage, vegetation is at the bottom of the list.
 |
Photo: Jeff Hart |
| Levee groundcover after application of herbicide |
“This is a great frustration to us in the resource agencies. The policy makes the reclamation districts spend the few dollars they have for levee maintenance removing vegetation. You can’t just cut the tree out, because then you’ve got roots inside the levee rotting. You have to take the levee apart and rebuild it and make it whole again. Then you have the vegetation mitigation costs. These little districts can’t afford to take the hit.”
The corps’s 34-page white paper reaffirming its no-vegetation policy drew more than 1,000 comments, reflecting the wide divergence of special interests in the Delta (and the lack of a centralized administrative body that could mitigate conflicts). “I can’t argue with some of the conclusions that vegetation can reinforce a levee,” says the corps’s Pezza, “but as an engineer, I wouldn’t depend on the random presence of vegetation to make that happen. A safe levee must be structurally stable and provide unobstructed access and meet minimum standards for maintenance and operation. The corps has long allowed vegetation on levees as long as the levees were designed to accommodate it through overbuilding or containment.”
But as one informed observer notes, “Some of the Delta levees are a century old, and they were not constructed to the standards they would be today, which means the corps is not certain what the problems are. But vegetation is readily identifiable.”
And as Hobgood points out, the science doesn’t support the corps’s unilateral directive. Douglas Shields, a hydraulic engineer for the US Department of Agriculture National Sedimentation Laboratory, studied a 35-mile stretch of the Sacramento River after 1986’s record-breaking flood and found that levees with trees suffered less damage. Shields subsequently suggested that levee vegetation may have increased soil strength by deflecting high-velocity water. Shields gave particular attention to a 10-kilometer stretch of the river where large oaks and cottonwoods grow and found no evidence the trees compromised levee strength or caused channeling of water along roots. Rather, he concluded that the roots tended to strengthen the levees by binding the soil. Growing downward rather than sideways, the shallow roots (which grew no deeper than 3 feet) helped strengthen the levees from within. Shields did note one danger: Large trees could be felled by high winds and damage a levee.
 |
Photo: US Fish and Wildlife Service |
| Levees reinforced with a combination of small rocks and vegetation |
Sacramento Bee reporter Matt Weiser, who followed the vegetation saga, also reported on research by University of California at Davis scientists that willows growing in a simulated floodway flattened against the ground surface as water velocity increased, offering little resistance to water flow. The bent shrubs also protected the soil from erosion and created a bottom layer of slower water where young Chinook salmon sought refuge among the flattened willows.
“We look at this from multiple viewpoints,” says Nagy, “from an inspection standpoint, a flood-fight standpoint, and an engineering stability standpoint.” Not so the reclamation districts, who like their trees and have commitments with resource agencies not to diminish the levee habitats. “Fish and Game carries a gun,” says Webber, “and the corps regulations have no teeth in them. So, if it comes down to ‘all they can do is yell,’ we’re fine with that.”
Webber is also among the reclamation district managers who have been working with Jeff Hart on a bioengineered approach to controlling erosion along the levees by establishing the missing setbacks that could help protect the levee core. “It’s well known,” says Hart, “that dense vegetation and biotechnical features can serve as areas of soil accretion by increasing the frictional resistance of the banks and decreasing flow velocities and shear stresses. It’s also been shown that intertidal fences reduced wave energy by 50% in the Mississippi Delta, and this resulted in sediment accretion and habitat development.”
Using plants grown in his native plant nursery in Walnut Grove, CA, and funded by the California Bay–Delta Authority, Hart successfully established 8,000 feet of native tules along Georgina Slough and the North Fork of the Mokelumne River using biotechnical brush boxes he designed, along with planting appropriate vegetation. The structures consisted of waterside coarse materials to allow some flow-through of water and sediment and, closer to the levee, brush bundles and coir biologs. After two years, 20% of treated sites accumulated woody debris as opposed to 10% of untreated sites. The cover of recruited plants was greater in treated sites, despite less available space due to the treatment structures, plantings, and a greater cover of woody debris. Installed and recruited plants covered more than 33% of the treated sites, and the soil surface was exposed in just 10% of the these sites, as opposed to 64% of those where nothing was done. Non-treated sites experienced more than 2 inches of erosion during the time period, while the treated sites had no significant erosion.
“This reversal of the erosional to depositional regime is the most noteworthy outcome of the project,” says Hart, “although not altogether unexpected.”
 |
Photo: California Department of Water Resources |
| An aerial view of the Delta |
Hart readily concludes that brush boxes won’t work in areas of extremely steep banks, narrow offshore shelves, or steeply inclined shorelines, and with his long experience on the river, Webber agrees. “In our district, we have areas on the Sacramento River where the levees are from 100 to 140 feet wide, which means there’s a lot of dirt which isn’t part of the levee that holds the water back. In these places, there’s a lot of opportunity to install these erosion control boxes. They’re creating silt behind them, and they’ve raised the level of the little waterside berms 18 inches to 2 feet in some places.
“But there are places in the river where the boxes won’t work. When the river changes direction 180 degrees, you have to have a lot of weight. Any vegetation or dirt you put over the top of the rock will be gone in the first big event. But there are other places where the river runs straight or, on the opposite side of where the river turns, where a little sandbar has built up that offer wonderful places to establish vegetation.
“On the river you have to use some rock but not the kind of rock the corps is putting down. What we use is the little rocks that prevent the boat wakes from tearing things up and then maybe a little rock up higher and maybe a little dirt on top of that. But we’re talking maybe a quarter of what the corps is using for miles. I was able to get them to do three of the four sites in our districts that needed repair. With the worst one of the four, we’re continuing our environmental fix. We think this provides us the opportunity to demonstrate the difference between how the corps does it and how it can be done environmentally.”
The white paper the Army Corps of Engineers issued caused such a ruckus among the various parties with an interest in levee sustainability that it led to a hastily convened symposium sponsored by the corps, the California Reclamation Board, the DWR, and the Sacramento Area Flood Control Agency in August 2007. More than 500 people from 21 states, representing more than 151 agencies--including federal, state, and local flood management; resource agencies; academic institutions; consulting engineers; and environmental firms--met for two days to explore the science, real-world experience, challenges, and policy solutions related to levee vegetation. Leslie Harder, California DWR deputy director, set the stage when he told participants in his opening remarks, “We need a levee vegetation management policy, and we have to focus on safety elements. But we need to be careful we don’t unnecessarily spend our very limited resources in areas that don’t significantly reduce risk. These resources must be carefully applied to the most critical things that affect public safety.”
Based in part on the symposium, the corps put its no-vegetation policy in California on hold, and Lieutenant General Robert Van Antwerp went on record that the corps’s engineers intended to create a flexible levee maintenance policy. Safety is job number one, said Van Antwerp, who also acknowledged that he recognizes California’s Central Valley levees are “multipurpose levees that provide important habitat for endangered species.”
Advertisement
But California is not taking any chances and intends to take advantage of a regional variance process the corps initiated in 2001. “If the new national policy were more lenient,” says Nagy from her office in Sacramento, “you wouldn’t need a variance. But we’re moving forward on the assumption that the national policy is probably going to be a lot stricter. We have a unique situation in the West, and we will need to regionalize the national policy to make sure it’s appropriate to our area. We don’t grow sod like the rest of the country, for example, and grass in the West doesn’t have the same strength. We have a very good relationship with the Department of Water Resources and work together with them during flood events. So obviously we’re concerned whether the levees are up to par. And our guidance is out there for the public to use as a guide to how to maintain levees in the rest of the system.”
The corps variance process that Nagy finds hopeful, however, has yet to be applied, and a regionalized approach to vegetation would be precedent setting. In the meantime, Webber says he’ll “keep his powder dry and wait for the next letter to come. Because it only takes one 8.5-inch sheet of paper with the right words on it to take you out.”
May 2008
California Takes Issue With Corps of Engineers' Levee Policy
A post-Katrina attempt by the Army Corps of Engineers to enforce a long-standing national policy in California raises questions about the role of vegetation on flood control levees.
Although not widely known outside California, the 700,000-acre Sacramento–San Joaquin Delta is critical to the state’s economy and a key component in its interrelated complex of natural resources. Once a natural estuary of freshwater and brackish tidal sloughs and marshes, the Delta, which produces the largest asparagus crop in the country, now supports an agricultural industry that grosses $500 million a year.
Located in the west-central part of the state immediately east of San Francisco Bay, the Delta receives runoff from 40% of California’s landmass, including almost the entire Sierra Nevada, the southern reaches of the Cascades, and the eastern flank of California’s coastal range, making it the collection point for a delivery system that provides drinking water to 20 million Californians, two-thirds of the state’s population.
Contrary interests have been squabbling over the Delta for decades, not the least because its remaining natural habitat is considered vital in a state that has lost over 90% of its riparian vegetation. The Delta is also a boating and fishing mecca served by over 600 marinas and recreational areas. A deep-water shipping channel connects San Francisco Bay with inland ports.
Historically, the banks of the Delta’s waterways were lined with low natural levees covered with woody vegetation. These natural landmasses were mostly tule marshes dominated by hardstem bulrushes (Scirpus acutus). In the last 150 years, however, more than 95% of the Delta’s tidal wetlands and up to 85% of its riparian habitat have been lost as the marshes have been reclaimed for agriculture and other human use. During the 20th century alone, the overall land-water interface was reduced up to 45%. Additionally, altered flow and sediment regimes, together with boat traffic, have increased shoreline erosion and led to consequent loss of tidal zone and riparian vegetation along many sloughs.
|
Photo: Jeff Hart |
| Jeff Hart’s bioengineered approach to erosion control |
Though degraded, the Delta provides habitat for a number of special-status animals and plants, including spawning habitat for the Delta smelt (Hypomesus transpacificus) and rearing habitat for the smelt, juvenile Chinook salmon (Oncorhynchus tshawytscha), and steelhead trout (O. mykiss). Four special status plants—Suisun Marsh aster (Aster lentus), Mason’s lilaeopsis (Lilaeopsis masonii), mudwort (Limosella subulata), and Delta tule pea (Lathyrus jepsonii ssp. jeponii)—grow in the intertidal zone or adjoining riparian scrub of the Delta’s sloughs. Although maintaining and restoring natural vegetation along the sloughs is an important concern, it nevertheless remains that extensive bank erosion, along with contemporary repair and maintenance practices on the Central Valley’s 1,600 miles of levees, has reduced natural vegetation to a narrow strip of land on the water side of these manmade structures.
The Delta levees are an erratic patchwork that US Army Corps of Engineers Geotechnical and Materials Community of Practice Leader David Pezza has described as “a very fragile hodgepodge,” which not only is susceptible to erosion and potential breach but also would fail in a 6.5 magnitude earthquake. A portion of the levees was engineered and built as part of a federal flood control project authorized by Congress in 1917 (today referred to as project levees), but many more have been privately constructed either by local reclamation districts or by landowners. Besides the corps, a myriad of federal and state agencies maintain jurisdiction over the Delta, including the US Fish and Wildlife Service, the National Marine Fisheries Service, the California Board of Reclamation, and the state Department of Water Resources (DWR) and Department of Fish & Game.
Locals consider this disparate and irregular flood control system part of what makes this area of California unique. Not the least of the levees’ appeal is the oaks, cottonwoods, and sycamores that have grown up over the years and now shade public roads, bike trails, and private yards.
|
Photo: Jeff Hart |
| Riprap being applied where the levee groundcover was sprayed with an herbicide |
“You walk away from the Delta for a year,’” says Bob Webber, manager of California reclamation District 999, “and it will decide what it will be. The tules and oaks will grow where they’re supposed to grow. Everything’s here. You don’t have to go fooling around spending a lot of money.”
The Delta’s levees are unique among other US flood control structures in both material and construction. Unlike levees along the Mississippi River, for example, California’s levees are built close to the water because they were originally designed to scour sediment washed into Central Valley streams and rivers from gold mining in the Sierras. The silt increased the annual flood risk, and the levees were built close to channels to keep water velocity high.
That the California levees were built without setbacks makes the issues of both erosion control and habitat preservation that much more critical. “The state has the responsibility for maintaining navigation,” says Webber. “Typically it would dredge the spoils out of the center of the river and throw them on the edge of the bank, where they would create a waterside berm. This created a lovely little habitat that protected the prism of the levee from boat wakes.” But according to Webber, the state hasn’t dredged for 30 years now, and erosion has reached levee prisms, making repair “way beyond the capacity of a reclamation district.”
The reclamation of the Sacramento–San Joaquin Delta was enabled by the 1855 Swamp and Overflow Land Act, which conveyed ownership of all swamp and overflow land, including the Delta marshes, from the federal government to the State of California. The early Delta levees were dug with Chinese immigrant labor and were a little over 3 feet tall with a base width of 12.5 feet. In the 1870s, steam-powered dredges moved large volumes of alluvial soils from the river channels to their banks, and by the end of World War I, the Delta had been transformed from a tidal marsh to a network of improved channels (now called sloughs) snaking between islands. The challenge, however, was that the fertile peat soils weren’t suitable for levees, which sank and developed deep cracks and fissures such that by 1974, reclamation costs for preservation of the Sherman Island levees totaled $500,000 ($6.2 million in today’s dollars), more than the assessed value of the property being protected.
Agriculture and wind erosion have also caused land in the central and eastern Delta to subside more than 15 feet below sea level. The loss of this heavily organic soil is also due in part to exposure to oxygen, which converts organic carbon solids to carbon dioxide and aqueous carbon. This land subsidence is a major concern in the contemporary Delta because it increases water pressure on the levees and enhances the probability of levee failure. More recently, development north of the Delta has removed land that naturally functioned for flood control, a trend that disturbs Steve Mello, manager of Reclamation District 563.
“Typically, the Sacramento Valley acted as a flood retention basin, allowing the water to percolate gradually into the Delta. Our little district submitted a protest to the rezoning and leveeing and pumping out of that ground, because instead of the 10,000 or so acres flooding a foot or 2 or 3 deep, with the water percolating into the groundwater table and slowly coming downstream, it’s now all roofed and paved and cemented, and we catch all that water lickety-split.”
Mello’s district is agricultural. Half of the 26 miles of levees he’s responsible for are project levees, the other half private. Mello himself is a second-generation farmer who grows corn, wheat, alfalfa, safflower, and pears on 2,500 acres. Most of the Delta’s lowlands are in fact protected by non-project levees, where improvements and maintenance can be a challenge, given the sometimes substandard construction and the reclamation districts’ limited resources. The 1973 Delta Levees Subvention Program was designed to reimburse non-project levees for a portion of their maintenance costs, and the 1988 Delta Flood Protection Act significantly increased reimbursements—not, however, without adding a significant environmental mandate that repairs and maintenance will result in no net long-term loss of habitat.
“There’s a limit to what we can do,” says Webber. “We spray the weeds. We try to control the vegetation to whatever standard they set, and we repair minor slips. But when it comes to doing a new design of a levee with rock, the kind of thing the corps is doing with their emergency repairs, that costs $7,000 a foot. My district has 33 miles of project levees and a total budget for both irrigation and levee maintenance of $500,000 a year.”
Given their origins, overlapping jurisdictions, and disparity in resources, the Delta’s levees experienced more than 150 failures over the last century. Three years ago, on June 3, 2004, a 350-foot section of levee 10 miles west of Stockton collapsed, flooding the 12,000-acre upper Jones tract. A year later, the corps identified 24 damaged levee sites that needed critical repair and restoration. Sustained high-water flows during the spring of the subsequent year caused significant damage to another nine sites. In September 2006, the corps and the California DWR identified 71 additional damaged levee sites needing repairs and designated 300 additional sites for deferred repairs.
Complicating an already complex and compartmentalized approach to levee maintenance, in February 2007 the Army Corps of Engineers released a national list of levees that failed the inspections ordered by Congress after Hurricane Katrina. According to a subsequently revised list, 32 California levees failed inspection, with vegetation being a primary culprit. The levee districts were given three months to come up with a plan that satisfied the corps, which specified nothing but grass on the land side of levees and nothing taller than 2 inches on the water side.
The corps justified its ordinance on the basis that it needed to maintain clear access to inspect and repair the levees as well as to flood-fight, and it gave the districts nine months to comply. Failure to meet the corps’s standards could mean decertification of the minimum requirement to provide 100-year flood protection, which could mean a loss of Federal Emergency Management Agency assistance in case of a catastrophic flood, as well as loss of the ability to purchase flood insurance at reduced rates through the National Flood Insurance Program. And the corps’s edict put the reclamation districts in a Catch-22 situation. If they complied with the corps and removed the offending vegetation to maintain their certification, they could face penalties from federal and state agencies for destroying habitat. The California DWR added fuel to the fire when a rough count during its spring 2007 inspection established that trees existed on 457 miles of Central Valley levees and shrubs and vegetation on 830 miles. (In 2007, literally thousands of trees were actually planted in more than 100 levee projects undertaken by the corps itself, according to its own operational guidelines, which called for planting vegetation—and installing irrigation systems—to provide shade and habitat.
Noting that most unsatisfactory levee ratings were due to the presence of vegetation, the US Fish and Wildlife Service suggested that a collaborative effort could produce projects that “meet the desired flood damage reduction condition with lesser impact on fish and wildlife species, especially those that are threatened or endangered, such that migratory birds would have the requisite nesting, foraging, and cover habitat, overhead cover and shade, moderation of water temperatures and energy input in river productivity.” Fish and Game suggested the corps develop “more local criteria for evaluating and maintaining levee systems.”
“After Katrina,” says Meegan Nagy, emergency manager for the corps’s Sacramento District, “we obviously realized the need to be better at our levee inspections, to tighten them up and be more rigorous. And obviously there has to be a certain standard to ensure that we can visibly see the levee and be able to access it. To be able to do that, the corps decided it had to implement its long-standing policy of no vegetation.”
“Because of what happened in New Orleans, the Army Corps is super-sensitive to anything that has to do with levees,” says Gary Hobgood, environmental scientist for the California Department of Fish and Game. “What Washington headquarters doesn’t understand is that we have a totally different climate here in California. We have different plant communities and different growth patterns. When you look at the things that could be wrong with levees, such as erosion, under seepage, and through seepage, vegetation is at the bottom of the list.
|
Photo: Jeff Hart |
| Levee groundcover after application of herbicide |
“This is a great frustration to us in the resource agencies. The policy makes the reclamation districts spend the few dollars they have for levee maintenance removing vegetation. You can’t just cut the tree out, because then you’ve got roots inside the levee rotting. You have to take the levee apart and rebuild it and make it whole again. Then you have the vegetation mitigation costs. These little districts can’t afford to take the hit.”
The corps’s 34-page white paper reaffirming its no-vegetation policy drew more than 1,000 comments, reflecting the wide divergence of special interests in the Delta (and the lack of a centralized administrative body that could mitigate conflicts). “I can’t argue with some of the conclusions that vegetation can reinforce a levee,” says the corps’s Pezza, “but as an engineer, I wouldn’t depend on the random presence of vegetation to make that happen. A safe levee must be structurally stable and provide unobstructed access and meet minimum standards for maintenance and operation. The corps has long allowed vegetation on levees as long as the levees were designed to accommodate it through overbuilding or containment.”
But as one informed observer notes, “Some of the Delta levees are a century old, and they were not constructed to the standards they would be today, which means the corps is not certain what the problems are. But vegetation is readily identifiable.”
And as Hobgood points out, the science doesn’t support the corps’s unilateral directive. Douglas Shields, a hydraulic engineer for the US Department of Agriculture National Sedimentation Laboratory, studied a 35-mile stretch of the Sacramento River after 1986’s record-breaking flood and found that levees with trees suffered less damage. Shields subsequently suggested that levee vegetation may have increased soil strength by deflecting high-velocity water. Shields gave particular attention to a 10-kilometer stretch of the river where large oaks and cottonwoods grow and found no evidence the trees compromised levee strength or caused channeling of water along roots. Rather, he concluded that the roots tended to strengthen the levees by binding the soil. Growing downward rather than sideways, the shallow roots (which grew no deeper than 3 feet) helped strengthen the levees from within. Shields did note one danger: Large trees could be felled by high winds and damage a levee.
|
Photo: US Fish and Wildlife Service |
| Levees reinforced with a combination of small rocks and vegetation |
Sacramento Bee reporter Matt Weiser, who followed the vegetation saga, also reported on research by University of California at Davis scientists that willows growing in a simulated floodway flattened against the ground surface as water velocity increased, offering little resistance to water flow. The bent shrubs also protected the soil from erosion and created a bottom layer of slower water where young Chinook salmon sought refuge among the flattened willows.
“We look at this from multiple viewpoints,” says Nagy, “from an inspection standpoint, a flood-fight standpoint, and an engineering stability standpoint.” Not so the reclamation districts, who like their trees and have commitments with resource agencies not to diminish the levee habitats. “Fish and Game carries a gun,” says Webber, “and the corps regulations have no teeth in them. So, if it comes down to ‘all they can do is yell,’ we’re fine with that.”
Webber is also among the reclamation district managers who have been working with Jeff Hart on a bioengineered approach to controlling erosion along the levees by establishing the missing setbacks that could help protect the levee core. “It’s well known,” says Hart, “that dense vegetation and biotechnical features can serve as areas of soil accretion by increasing the frictional resistance of the banks and decreasing flow velocities and shear stresses. It’s also been shown that intertidal fences reduced wave energy by 50% in the Mississippi Delta, and this resulted in sediment accretion and habitat development.”
Using plants grown in his native plant nursery in Walnut Grove, CA, and funded by the California Bay–Delta Authority, Hart successfully established 8,000 feet of native tules along Georgina Slough and the North Fork of the Mokelumne River using biotechnical brush boxes he designed, along with planting appropriate vegetation. The structures consisted of waterside coarse materials to allow some flow-through of water and sediment and, closer to the levee, brush bundles and coir biologs. After two years, 20% of treated sites accumulated woody debris as opposed to 10% of untreated sites. The cover of recruited plants was greater in treated sites, despite less available space due to the treatment structures, plantings, and a greater cover of woody debris. Installed and recruited plants covered more than 33% of the treated sites, and the soil surface was exposed in just 10% of the these sites, as opposed to 64% of those where nothing was done. Non-treated sites experienced more than 2 inches of erosion during the time period, while the treated sites had no significant erosion.
“This reversal of the erosional to depositional regime is the most noteworthy outcome of the project,” says Hart, “although not altogether unexpected.”
|
Photo: California Department of Water Resources |
| An aerial view of the Delta |
Hart readily concludes that brush boxes won’t work in areas of extremely steep banks, narrow offshore shelves, or steeply inclined shorelines, and with his long experience on the river, Webber agrees. “In our district, we have areas on the Sacramento River where the levees are from 100 to 140 feet wide, which means there’s a lot of dirt which isn’t part of the levee that holds the water back. In these places, there’s a lot of opportunity to install these erosion control boxes. They’re creating silt behind them, and they’ve raised the level of the little waterside berms 18 inches to 2 feet in some places.
“But there are places in the river where the boxes won’t work. When the river changes direction 180 degrees, you have to have a lot of weight. Any vegetation or dirt you put over the top of the rock will be gone in the first big event. But there are other places where the river runs straight or, on the opposite side of where the river turns, where a little sandbar has built up that offer wonderful places to establish vegetation.
“On the river you have to use some rock but not the kind of rock the corps is putting down. What we use is the little rocks that prevent the boat wakes from tearing things up and then maybe a little rock up higher and maybe a little dirt on top of that. But we’re talking maybe a quarter of what the corps is using for miles. I was able to get them to do three of the four sites in our districts that needed repair. With the worst one of the four, we’re continuing our environmental fix. We think this provides us the opportunity to demonstrate the difference between how the corps does it and how it can be done environmentally.”
The white paper the Army Corps of Engineers issued caused such a ruckus among the various parties with an interest in levee sustainability that it led to a hastily convened symposium sponsored by the corps, the California Reclamation Board, the DWR, and the Sacramento Area Flood Control Agency in August 2007. More than 500 people from 21 states, representing more than 151 agencies--including federal, state, and local flood management; resource agencies; academic institutions; consulting engineers; and environmental firms--met for two days to explore the science, real-world experience, challenges, and policy solutions related to levee vegetation. Leslie Harder, California DWR deputy director, set the stage when he told participants in his opening remarks, “We need a levee vegetation management policy, and we have to focus on safety elements. But we need to be careful we don’t unnecessarily spend our very limited resources in areas that don’t significantly reduce risk. These resources must be carefully applied to the most critical things that affect public safety.”
Based in part on the symposium, the corps put its no-vegetation policy in California on hold, and Lieutenant General Robert Van Antwerp went on record that the corps’s engineers intended to create a flexible levee maintenance policy. Safety is job number one, said Van Antwerp, who also acknowledged that he recognizes California’s Central Valley levees are “multipurpose levees that provide important habitat for endangered species.”
But California is not taking any chances and intends to take advantage of a regional variance process the corps initiated in 2001. “If the new national policy were more lenient,” says Nagy from her office in Sacramento, “you wouldn’t need a variance. But we’re moving forward on the assumption that the national policy is probably going to be a lot stricter. We have a unique situation in the West, and we will need to regionalize the national policy to make sure it’s appropriate to our area. We don’t grow sod like the rest of the country, for example, and grass in the West doesn’t have the same strength. We have a very good relationship with the Department of Water Resources and work together with them during flood events. So obviously we’re concerned whether the levees are up to par. And our guidance is out there for the public to use as a guide to how to maintain levees in the rest of the system.”
The corps variance process that Nagy finds hopeful, however, has yet to be applied, and a regionalized approach to vegetation would be precedent setting. In the meantime, Webber says he’ll “keep his powder dry and wait for the next letter to come. Because it only takes one 8.5-inch sheet of paper with the right words on it to take you out.”