However and wherever our water travels, it should do so without taking harmful baggage with it.
“Even the weariest river winds somewhere safe to sea,” wrote Algernon Swinburne in the 19th century. Most of us have stood or sat by the bank of a river, wondering at its peaceful beauty or awed by the power of its rapids and waterfalls, bemused by the gentle sounds of its ripples and eddies. Many of us have been annoyed when a noisy motorboat speeds past, disturbing the fish, upsetting the quiet of a picnic, and helping erode the riverbanks with its wake.
Water has always fascinated people, and it has been people wanting to be close to it who have accelerated (often unwittingly) the problems of the channel’s safe progress. From talking to professionals across the country I am convinced that the harm caused by we the people over the last many decades can be stopped, and even remedied. Erosion on bank and bed that carries danger to our water channels and their proficiency can be controlled.
Before the widespread laying of impervious surfaces, it was the responsibility of local vegetation to take care of erosion and channel problems, and nature performed the job well. Only unusual floods or high waters tended to overload the vegetation. Some of today’s solutions still rely on cooperation with vegetation to do the permanent work; that is their attraction for many landowners and municipalities.
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Photo:
Armortec
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| The same A-Jacks interlocking blocks you see by the bank can be used on the bed and around piers of bridges. |
Local and Natural Assistance
“Local conditions” are mentioned frequently when professionals discuss channel protection. Experts in local soil and vegetation should certainly be consulted before a community commits to any style of natural protection or synthetic barrier. Introducing new, non-native vegetation to an area is not necessarily a good idea just because it has worked somewhere else; it may not prosper in your soil and moisture conditions. This point is well illustrated by a quotation from the Tennessee Valley Authority: “Are you interested in ways to reduce erosion, improve water quality, provide habitat for wildlife, and enhance aesthetics? If so, you need look no further than the hardy and attractive trees, shrubs, and grasses that are native to our region, and well suited to life at the water’s edge. Once native plants are established, they require little or no maintenance, saving time and expense. Native shrubs, trees and grasses produce fruits and berries that are used by our native wildlife. Additionally, it’s refreshing to think that native varieties help provide regional context. They just ‘look right’ in this part of the country, and help to preserve the botanical heritage of the Tennessee Valley.” You could say the same about different locations in Florida, California, Montana, Iowa, Arizona, Minnesota, Pennsylvania, and every other state.
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Photo:
Armortec
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| Engineered blocks in mesh offer advantages over riprap for channel protection. |
Willow trees, for example, have been successful in places as far apart and different as Mississippi and Illinois for controlling streambank erosion. They also give cover over the channel, helping lower water temperatures, and their foliage can lower floodwater speeds. The willows (in their dormant stage) are planted as “posts” and allowed to grow. There are well-proven rules for willow size and placement, with much of the success due to work by Don Roberson, 20 years ago, with the Illinois State Water Survey. Your local expert will know which vegetation grows well by the river or stream; your local solution may be trees, shrubs, or grasses. One significant advantage of using vegetation to help you solve your channel protection problems is that it can be less expensive than synthetic solutions, especially when you compare installation and maintenance costs. Some of the products mentioned in this article work together with natural vegetation and that combination of natural and manmade technologies appeals to many communities. “What we can afford” is a common answer from communities when they are asked about their choice of infrastructure solutions, and inexpensive natural helpers are always welcome.
In the course of research for this article we found many excellent sources of information about channel protection, and about the possible results of poor protection. Individual states’ Web sites contain interesting and helpful information about these topics and examples, not only appropriate for the residents of one particular state but also generally applicable. Illinois, in particular, addresses streambank stabilization, describing five stages in the evolution of natural streambank erosion, with photos to show the conditions. It also names some results of streambank erosion: degraded water quality, unstable structures, and increased flood risks that can affect landowners, communities, and watersheds in both economical and environmental aspects. If this erosion is left untreated, it can “cause loss or damage to buildings, roads, farmland, wildlife habitat, and other property.” Roads? Yes, other public agencies which have addressed channel protection successfully are state departments of transportation. We were impressed by the amount of planning that preceded many major road construction projects nationwide.
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Photo: HESCO Bastion |
| Installation of Concertainer units in
Kivalina, AK |
Not All Armor Is the Same
Ask any mediaeval knight dinged by the latest mace. Armor comes in varying qualities. If the stresses in your community’s channels could be described as severe (whether mechanical or hydraulic), the solution may be poured concrete. It’s one solution in the “armoring” group, and it can involve complicated construction that feeds on time and dollars. Armoring is not new; most coastal communities have seen it used for several decades. Like many solutions to natural problems, the armor can have negative as well as positive effects. It depends on the site and the volume of the armor used. (Those local conditions again.) The coast of California has seen a steady increase in armor to protect new property developments and to delay erosion, and studies have shown that there are different results in different locations. In some places, coastal habitats have been changed or damaged. In others, some beaches neighboring the armored spot have lost sand and accelerated erosion has occurred. Public access and safety are other considerations.
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Photo: Black & Veatch |
| Perhaps the most common channels are small and meander through today's attractive neighborhoods. |
Erosion control specialists often distinguish between “hard armor” solutions like concrete and “soft armor,” often involving geosynthetic materials, such as turf reinforcement mats, and vegetation. Cellular confinement systems, such as Presto’s Geoweb, developed in cooperation with the US Army Corps of Engineers, can serve for armoring. The cells of the honeycomb-like structure are filled with soil or aggregate to form a stable structure. The cell walls may be perforated or not, with perforated being the usual choice when vegetation is to be encouraged, because the perforations permit lateral drainage. Generally, the perforated style is also chosen for concrete or aggregate infill and the non-perforated for finer-grain infill. Integral to the complete system are anchors, tendons, fasteners, and items such as turf reinforcement mats and geocomposite drainage materials, depending on the needs of the location for channel protection. This type of system can be much less expensive than concrete armoring, not least because the thickness of the sections can be uniform and defined specifically for the channel they protect. Another saving is that the compacted granular bedding layers, usually placed beneath concrete slabs for armoring, can be omitted. This is still an engineered, highly technical form of armoring and in-depth consultation with manufacturers is recommended before proceeding with remediation work.
How strong are artificial or synthetic defenses? A product called Concertainer from HESCO Bastion USA survived the battering of Hurricane Katrina where many other fortifications failed. Concertainer is a prefabricated, multi-cellular defense wall system, fabricated from galvanized steel Weldmesh and lined with non-woven polypropylene geotextile. It acts like a concertina to hold infill instead of music. “It is becoming most popular for the restoration of wetlands and estuaries,” observes Dennis Barkmeyer, a project consultant for the company. “By containing sediment, we can reestablish lost habitat, and [the Concertainer] acts as a buffer for reducing wave fetch. Rocks tend to sink fast when placed in those soft sediments you often find in marshes and estuaries. The Concertainers are linked together by HESCO’s helical coiling system and that provides a large footprint for weight distribution.” After Katrina struck New Orleans, the US Army Corps of Engineers used Concertainers to give the damaged levees a backbone of strength. They were filled with limestone and soil to create an impermeable structure that would hold back the floodwaters. It worked. A similar system was used to reestablish some of the barrier islands, too. For channel protection projects like riverbank and canal towpath reconstruction, the Concertainer lets concrete dry quickly when it is inserted as the infill, and the drainage is quick when gravels or river silt are involved.
Armortec (now a Contech company) offers several solutions for erosion control problems. One often used for channel and shoreline protection is A-Jacks. (The units look like large jacks, those little shapes you tried to scoop up quickly from the playground as the little rubber ball bounced.) They are made of high-stability concrete and have a range of size and weight that can be appropriate to many sites. The length of the A-Jacks goes from 24 to 120 inches, with volumes from 0.56 to 70.69 cubic feet and weights from 78 to 9,699 pounds. One of their most successful uses has been for protection against bridge scour, where they resist high-velocity flows and will protect piers from local scour. Their shape and configuration reduce the rate of sediment transport, by offering a flexible, non-erodible barrier between the subgrade of the channel and the (potentially harmful) flow of the water.
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Photo: HESCO Bastion |
| The Concertainer works like a concertina but holds infill instead of music. |
Streams Are Not Always Rural
In a presentation at last year’s IECA conference, “Stream Design in Urban Area,” authors Donald W. Baker, P.E., CPESC, and Pablo González-Quesada, Ph.D., both engineers for Black & Veatch, reminded us that all water channels are not in the countryside. “Urban areas require stable fluvial systems to assure the integrity of the infrastructure,” they write. “At the same time, conditions for urban streams are constantly changing as the urban environment evolves. Changes in flow regimes and in composition of transported sediments alter the geomorphological behavior of streams. Physical constraints such as rights of way and existing or proposed infrastructure, in addition to the constraints placed on the design by economic, cultural and political issues, provide further challenges to stream stabilization and design efforts in urban areas.” The challenges of water channel protection may, then, be the most demanding in our cities because the more impervious surfaces we build, the more the water is confused. All situations require considerable knowledge of existing conditions before remedies can be suggested and approved, and that means work by experts in water resources. As you know, tipping some loads of rubble from the latest construction project onto the banks of a stream or river will neither help nor solve the problem of erosion.
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Photo: John Francis |
| "How nice! Somebody has done something to improve my neighborhood." |
In the city of Lenexa, KS, Black & Veatch worked on the Manchester Park Improvements Project, also described in the presentation. The intent of the project was to create a neighborhood park, including a stream and wetland system, within the limits of the subdivision common area. This would provide recreation opportunities while incorporating the stabilization of the existing low swale/channel and giving some level of ecological restoration to the area. Residents who lived adjacent to the subdivision common area had complained about wet, boggy areas and erosion along the drainage swale within that common area. Does that sound familiar? Black & Veatch designed a stable stream for the Manchester Park area.
A topographic survey for the project revealed that there were two distinct valley slopes. Using what is best known as the Rosgen classification procedure, the consultants determined the stable stream form for the upper two-thirds of the proposed channel would be a B4 channel. That means it is somewhat entrenched and has a slope in the 2% to 4% range and a sinuosity of 1.2 or more. “Bed material for channels consists mainly of gravels with some boulders, cobbles and sand,” explain Baker and González-Quesada. “The lower portion of the valley was much flatter, a Type E4 channel. E4 channels are very sinuous and have slopes below 2%. Bed material for such channels comprises gravels and sands, with a few cobbles present.” Channels of appropriate widths were calculated with the radius of curvature and sinuosity. The armoring material was chosen according to the results of the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model of the designed stream. The result of the research and classification was a stream design supported by a solid scientific basis that public works agencies can review and have confidence that the design is appropriate. What prompted the excellent approach to this project? “There are many varied approaches to stream design,” observes Baker. “The results of these approaches are also just as varied. This wide range of approaches and results often leaves public works agencies with more questions than answers, and results in low confidence in the design. In order to establish a higher confidence, a design procedure was developed that utilizes the techniques and approaches that have been published by some of today’s leading authorities in stream mechanics.” Hence we have the successful project at Manchester Park.
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Photo: Mainstream Restoration |
| You can tell much about a stream even when it's almost dry. |
Changing Habits
The most common reason for continuing to use a system or materials when there are better alternatives often seems to be “We’ve done that for 20 years and we’ll it do for the next 20.” This applies to some of those contractors who insist that wood is the best material for pilings, even when the wood they use is promptly attacked (and eaten) by underwater bugs like marine borers. For your protection system, wood may be the best material, but it must be the right wood, treated correctly, according to your channel’s specific needs. In freshwater channels, treated wood may be prohibited. A common perception encountered by manufacturers like Crane Materials International (CMI) is that vinyl couldn’t possibly be as effective as wood. “It could,” explains Eric Stein of CMI. “After hurricanes last year, when old walls were ripped out, they were replaced by vinyl. An important consideration is that wood solutions must be built, whereas vinyl can simply be driven in.” CMI vinyl has been used successfully in different locations, with many projects in the Caribbean and the UK as well as in the US. “Vinyl’s qualities have been proven in canals in New Jersey, runoff channels in Missouri, and in Jefferson Parish in Louisiana,” adds Stein.
“Advances in new construction material involving a vinyl structural sheet pile offer a new application for stream bed grade control structures,” comments Bruce M. Phillips, in a presentation on streambank restoration (Phillips 1997). “The vinyl sheet pile system offers unique properties for a hydraulic structure, including minimizing normal construction impacts and the heavy equipment usually required. Grade control structures offer the advantage of minimizing the impact to natural stream features through adjustment of the dominant hydraulic forces rather than providing measures to resist those forces.” He cites an example of the successful use of this method in California for Martin Creek. More than 4,000 feet of the meandering stream was experiencing lateral erosion. Control structures of GeoGuard vinyl sheet piles from CMI were embedded 5 feet beyond the top of the channel banks and extended the width of the channel. “A unique feature which is part of the reason for the selection of the vinyl sheet piles is the flexibility in the installation, eliminating the requirement for pile driving equipment,” notes Phillips. Excavated rather than pile-driven installation was possible, with a slurry mix used to backfill the piles after installation.
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Photo: HESCO Bastion |
| Protecting the shoreline in Kivalina, which is located on an 8-mile-long barrier reef |
Study and Planning
If I seem to stress the importance of study and planning before attempting any channel protection project, it is because that’s the message I’ve heard from most of the professionals with whom I spoke. Of one of my correspondents, it was written, “He is adept at conveying complex technical concepts to lay audiences.” That gentleman is Dale Miller, CPESC, a hydrologist–fluvial geomorphologist with his own company called Mainstream Restoration. I asked him the reasons people choose one or another remedy for their channel problems. “Cost is always a factor,” says Miller. “Then there are the environmental regulations, which vary in stringency from state to state. People who are seeking solutions have learned well in recent years. They understand the need and they are beginning to understand the terminology. There is currently plenty of dialog about training in fluvial geomorphology and that is probably good for this sector.” Using information and deductions that have been unchallenged for decades may not be the best approach for today; scientific evidence can always mature.
“Physics doesn’t change,” comments Miller. “At channel protection sites there are always similarities and many components are the same. But hydrology varies. The frequency of storms changes. Shapes of channels differ. Every project is relatively new.” (In his 25 years of experience, Miller has managed hundreds of channel restoration and similar projects.) He points out that an excellent start to a project is recognizing the dynamic nature of a stream. “There’s a huge amount of information available, even from a dry stream, and the damage you see may be natural or caused by human action.”
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Photo: Presto |
| Workers install Geoweb products to protect a creek. |
The key to success, then, in channel protection seems to be twofold. First, let’s not try any solutions until we (and knowledgeable experts) have studied our particular, local problem and determined how our water channels should behave. Second, be assured that the products and equipment necessary for solving our community’s problems are available and many of them affordable. It’s that first step that’s proved difficult for many of us. There is much to study, much to learn and understand, and there are apparently conflicting opinions about this or that approach. The best news is that others like us have been successful and we are winning the battle through our diligence and patience.
Reference
Phillips, Bruce M. 1997. “Streambank Restoration Design with Vinyl Sheet Pile Grade Control Structures.” In Aesthetics in the Constructed Environment. Proceedings of the 24th Annual Water Resources Planning and Management Conference held in Houston, TX, April 6–9. American Society of Civil Engineers.
Paul Hull writes on construction topics for several international magazines.
EC - January/February 2007 |
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