Good Science - Part III
How Does Livestock Grazing Affect the Watershed?
Case Study: McComas Meadows Restoration
How Does Timber Harvest Affect the Watershed
Case Study: The Warm Springs Huckleberry Ecology Project
How Do Roads Affect the Watershed?
Passive Restoration (Continued)
How Does Livestock Grazing Affect the Watershed?
Livestock grazing is a major land use in the Columbia Basin. It peaked in the 1880s, when there were millions of cattle and sheep in or moving through the Intermountain West.
(Simpson, 1987; Meinig, 1968) Because of this early and widespread alteration of the landscape, it is hard to determine what the natural range communities would look like without the effects of livestock grazing. It is also hard to realize that streams that look "normal," in the sense that they have looked that way during several generations of human impact, may not be biologically or hydrologically healthy.
Effects of Livestock in Riparian Areas
Riparian areas are critical to the survival of native fish, wildlife, and plants in the Columbia Basin, and to the landscape as we know it. They provide habitat for some four-fifths of the total number of species in the basin. Like so many birds and mammals, cattle naturally prefer the lush, shady areas near streams to the hot, dry uplands. Unfortunately, cattle can love the stream to death. While sheep may have less effect per animal, in the aggregate they also exert a major toll. Some areas significantly damaged by sheep grazing from roughly 1890 to 1930 have not yet recovered.
(Rhodes et al., 1994) Since that time, cattle have become the predominant livestock in the region.
Cattle are water-lovers. An adult cow drinks 15 gallons of water a day in the summer.
39 When cattle hang out along the stream, they create major changes in riparian plants, topsoil, and stream channel. Trampling breaks down the banks and compacts the soil. Young shoots of willow, alder, aspen, or cottonwood are cropped down and do not survive. With the removal of plant cover, widespread surface soil erosion increases, gullies and rills develop, and topsoil goes into the stream.(Rhodes et al., 1994)
These effects are synergistic; with the loss of topsoil, it is harder to reestablish vegetation. With little or no vegetation, the trampled streambanks are much more likely to erode, weaken, and slump into the stream.
Uncompacted soil absorbs precipitation and lets it slowly recharge the groundwater, while trampled, compacted soil lets water run off quickly, contributing to erosion and flooding. As the surface soil loses its ability to hold moisture, native plants fail to survive the summer and are replaced by less desirable, drought-resistant species, or introduced, weedy species that do well in disturbed soil.
Livestock are a major dispersal agent for exotic species and other weeds. They create disturbed soil conditions more favorable to weeds and exotics and distribute the seeds in their manure. They reduce the competition from native species, both by browsing selectively on them and by causing the generalized effects of more erosion and drier summer soil.
Effects on the stream channel vary with the nature of the soil and rock substrate, vegetation, gradient, sinuosity, and other site characteristics. In some areas the combined effects of grazing on soils, vegetation, erosion, and hydrology cause downcutting and headward channel erosion, while in other areas (often a different part of the same stream) the channel widens.
The wide, shallow stream is more susceptible to summer heating and winter icing. The downcut, deeper channel lowers the water table. Vegetation dies away to be replaced by sagebrush and drought-tolerant weeds on the banks high above the water. The result is less forage for both livestock and wildlife.
These changes add up to loss of fish habitat. Stable, well-vegetated, overhanging banks provide areas of refuge for both juvenile and adult salmon. Riparian vegetation shades the stream, providing cooling and also moderating daily temperature changes. Vegetation also provides habitat for insects that drop into the stream and are eaten by fish.
With erosion, more sediment goes into the stream, where it clogs the gravels. If salmon spawn in those gravels, the young may not emerge. Fine sediment hinders the flow of water and oxygen to the embryos and, ultimately, suffocates them.
(Bjornn and Reiser, 1991) Summer water temperature rises because of the lack of shade and lack of groundwater infiltration. Some streams that have lost significant amounts of riparian vegetation can reach summer temperatures as high as 90° F, causing direct mortality to salmon. Lack of deep pools, combined with overall excessive temperatures, deprives fish of summer rearing habitat and areas of thermal refuge.
Many ranchers are finding that managing grazing for watershed health is actually more profitable than pushing the land to its limits.
(Holcheck, 1992; Holcheck, 1994; Klipple and Costello, 1960; Houston and Woodward, 1966; Johnson, 1953; Martin, 1975) When riparian areas are in better condition, they produce more forage.(Elmore, 1998) When the adjacent uplands are in better condition, they produce more forage, too. When streams are unhealthy, fish and wildlife suffer, property values are lower, and the landowner may have to deal with violations of water quality standards and Endangered Species Act provisions against "take" of listed species. Good management prevents damage downstream and improves relations between neighbors.(Chaney et al., 1993)
Depending on the current condition of the watershed, improved management may involve excluding cattle from the riparian area or changing grazing regimes, providing off-stream water sources, and changing uplands management to improve soil and water retention.
|
|
|
|
Meacham Creek (a small tributary of the Umatilla River) in 1988 before livestock exclusion. 35 |
Meacham Creek in 1992, three and a half years after livestock exclusion. Vegetation rebounded from 20 percent cover to 80 percent cover in some reaches. 35 |
Excluding Cattle from Riparian Areas
Keeping the cattle out of the stream and away from the riparian area is one of the most beneficial actions that can be taken to restore fish habitat. Research shows that removing cattle from riparian areas results in rapid improvement in riparian vegetation, as well as gradual improvement in stream channel morphology.
(Platts, 1981b) Channel morphology improvements include natural rebuilding of streambanks,(Platts et al., 1983) decreased bank angles, more undercut banks that provide cover for fish, and narrower and deeper channels.(Keller, 1979) Because channels are narrower and deeper, water velocity increases.
Another benefit of establishing riparian reserves is that shade to the stream from vegetation increases markedly. One study demonstrated 75 percent more alder and willow shade 10 years after grazing was redirected out of riparian areas.
48 More overhanging brush, more vegetative biomass, and taller vegetation have been attributed to removal of cattle from streamside areas.
Some studies show, further, that artificial structures placed in streams to improve fish habitat are much more likely to stay in place in areas that are not grazed than in areas that are grazed.
(Duff, 1980)
The speed and quality of recovery after exclosure vary with the characteristics of soil, vegetation, and stream channel. Native vegetation will not come back quickly if it has been entirely eliminated from an area overgrazed for decades. A combination of fencing, replanting of native vegetation, and some form of active restoration may be necessary to bring a heavily damaged reach back to healthy function within the owner's lifetime.
The tribal salmon recovery plan recommends setting aside riparian corridors and suspending grazing until standards for recovery of soil, stream channel, vegetation, and fish habitat are met.
(CRITFC, 1995; Rhodes et al., 1994) The plan recommends protecting the entire floodplain and, ideally, extending the buffer zone 300 feet from the outer edge of the floodplain or to the ridgetop, whichever is less.Monitoring is an important part of the strategy. When riparian vegetation, stream channel, bank stability, and fish habitat have been restored to acceptable standards,
(Rhodes et. al., 1994) limited grazing, with continued monitoring, can be resumed. (See Monitoring and Evaluation section for further discussion.)
Case Study: McComas Meadows Restoration
|
|
|
McComas Meadows, 1998. 36 |
McComas Meadows, a 400-acre meadow in the Nez Perce National Forest of Idaho, adjacent to sacred lands of the Nez Perce Tribe, is a passive restoration project that is showing good results after six years of cattle exclosure. Part of the Nez Perce ceded lands, McComas Meadows was homesteaded in around 1860. The land was drained to raise hay. In more recent decades it was leased for season-long grazing.
The meadow's recovery is of major cultural significance to the Nez Perce Tribe. "People would come there to rest on their way to the holy mountain or to other places," explains Felix McGowan, a Nez Perce fisheries biologist. "It has a lot of special significance to my family and many others. My father and grandfather told me the family went up there every year to go hunting and fishing. It wasn't very far to go from there over into the Salmon River or the Bitteroots, then come back and rest and return to the lowlands before the snow."
"The whole area was medicine," Silas Whitman, Nez Perce fisheries manager, says. "It was a place of a lot of happiness. My elders would tell about the wildflowers that used to grow in the meadow, how good it would smell, how quiet it was. The water was cold and clear, and there was always game. It was said that all the animals were represented there. In late summer the meadow would be full of camps, with racks to cure hides."
When the Nez Perce National Forest acquired it in 1991, the meadow was in "terrible condition," according to Wayne Paradis, USDA Forest Service fisheries biologist. Streambanks were unstable and completely devegetated, and the deep-cut channel was mostly sandy. In 1986, BPA had funded the modification of a natural migration barrier at the mouth of Meadow Creek. Chinook salmon had been planted in the area in 1988, but virtually no returning fish had been observed.
The Forest Service excluded cattle from the meadow in 1992. The Nez Perce tribal fisheries department obtained BPA "early action watershed" funds in 1996 to remove the former fence and expand the enclosed area to the surrounding ridgetops. Salmon Corps crews removed the old fence, which crisscrossed the meadow and surrounded the old homestead, and Nez Perce Fisheries and McFarland Enterprises of Lapwai installed five miles of new fencing.
The Forest Service established monitoring systems and collected baseline data; the monitoring is now being continued cooperatively by the tribe and Forest Service staff. The tribe plans to plant willow and alder along 2.5 miles of Meadow Creek in the summer of 1999.
After six years of exclosure, the meadow has now "recovered tremendously," Paradis says. Bank stability has increased by 40 to 50 percent; the sandy bottom is now predominantly cobble; and a storm in 1995 deposited enough sediment to help reduce the width/depth ratio. The storm also caused some channel migration, which restored some of the natural meanders. The meadow is now well covered with grasses, forbs, and some shrubs. The grasses are a mix of the species introduced by previous owners and a few hardy native species.
The tribe hopes to reintroduce important food species such as camas and couse-couse, which were formerly gathered there in summer, as well as naturally spawning fall chinook. "We are trying to revitalize it with a mixture of cultural knowledge and science," Whitman says.
Changing Grazing Regimes
Some grazing regimes, particularly short rotations in winter and/or early spring, have been shown to allow significant improvements in riparian vegetation and channel under some conditions of soil and topography.(Sippel, 1995) |
|
|
|
Nez Perce crew who fenced the perimeter of McComas Meadows, holding fence post pounder affectionately dubbed "Brutus." 37 |
A joint publication of the US Bureau of Land Management (BLM) and USEPA, "Managing Change: Livestock Grazing on Western Riparian Areas,"
All streams do not respond the same way to the same grazing regime. To plan a grazing regime, you need to know your stream's characteristics. The Rosgen system is widely used to classify streams. The Coarse Screening Process provides specific standards for assessing fish habitat.
(Rosgen, 1996; Rhodes et al., 1994) The highest priority should be placed on streams that are the most sensitive to grazing disturbances and have the highest potential for recovery.There are limitations, however, to what the best-planned and shortest grazing rotation can do in a damaged riparian area; it is difficult to re-establish woody vegetation without a period of complete rest from grazing. If livestock are present when the soil is moist, trampling will still cause soil compaction and damage to the streambank. For areas that have been heavily grazed, an initial period of rest is probably necessary for recovery.
To protect fish habitat, at the least, livestock should be kept out of the stream along any spawning reaches, before and during spawning and during the incubation period (two to eight months).
Managing Uplands for Watershed Health
It's essential to include the uplands in any plan to restore riparian areas or streams. Partnerships with public agencies and tribes can help defray the initial costs of change.
For example, Dan Carver, a central Oregon rancher, found technical assistance and funding sources so that he could significantly increase water infiltration in the uplands and provide offstream water sources for his cattle.
Carver, a third-generation logger on the Oregon coast, moved inland to central Oregon in 1988 to raise cattle. He went to the Soil Conservation Service (now the Natural Resources Conservation Service) for technical advice on improving his land. A steelhead-bearing stream, Buck Hollow Creek, a tributary of the Deschutes River, runs through his property.
"They assigned a guy to take an inventory, find out what my goals were, and help design a plan," Carver says. A cornerstone of the plan they jointly developed was to disperse the cattle over more of the land. He set his priorities to do two things: get more forage in the uplands, and develop more offstream water sources. The two are related, and both help to disperse the cattle.
"If you have a plan, you don't always need to spend money to make changes," he says. "For example, the usual way to salt the cattle was to roll a block of salt off a cliff into the creek. Since my plan said to disperse the cattle, I don't salt in the creek any more."
|
Offstream water sources, such as this "nose pump" operated at will by the thirsty cow, help to disperse cattle. 38 |
"When I took over, the cattle weren't using much of the range," Carver says. "They were hanging out on the creeks. When they mess up the creek they're licking mud, getting worms, and costing me money. My goal is to get the cattle where the grass is." He developed eight springs and drilled two wells for livestock watering away from the creek.
"We want our cows to get a drink and get back to work," he says. "Cattle using offstream water sources gain more weight. In some pastures we haul water, and that's not fun, but hauling water is cheaper than hauling hay, and you're using the feed that's out there." |
Another part of Carver's plan was to "catch the rain" with terraces, grassed waterways, and sediment basins. Carver obtained funding from various sources, including the NRCS Small Watershed Program, the BPA's fish and wildlife mitigation program, and the Governor's Watershed Enhancement Board, for some of these projects.
"We've built about 50 sediment basins in the high drainages. They capture water in a storm and the water trickles out over months," Carver says. "It creates lots of greenery, feeds the streams lower down, and provides watering ponds for wildlife as well as cattle. In 1990, a 50-year storm would all run off. Now we figure we stop about a third of the water."
After 10 years of conservation management, Carver finds that his cows are fat, his land is green, and steelhead are returning to Buck Hollow Creek in the largest numbers since the 1960s. The credit for this last success must go, not only to one person's efforts, but to the community of landowners and public agencies in the Buck Hollow Creek watershed.
In 1990 the Sherman and Wasco County Soil and Water Conservation Districts started up a watershed restoration program for Buck Hollow Creek, with technical assistance provided by the Oregon Department of Fish and Wildlife (ODFW) and NRCS, and with additional support from the Confederated Tribes of the Warm Springs Indian Reservation, the Oregon Department of Agriculture, and the BLM. Since 1990, nearly all of Buck Hollow Creek has been fenced. While some of the riparian corridor is still grazed, the grazing is of short duration and takes place in the winter. A fish passage barrier has been removed, and Oregon Water Trust has leased one irrigation water right for instream flow. High school students received training to help with long-term monitoring.
ODFW monitors Buck Hollow Creek yearly. In 1994, fisheries technicians found only 10 or 12 redds. In 1998, they counted 180 redds, more than in any year since 1968. Assuming three adult fish per redd, there would be more than 500 spawners. Very few of these were wild steelhead; most were naturally spawning hatchery fish. ODFW personnel reported an increase in the number and quality of pools in the stream, improved channel definition, increased amounts of woody debris, abundant new alders 4 to 14 inches tall emerging from gravel bars along the stream, beaver activity, 70 to 80 ducks, and six bald eagles.
|
|
|
Sediment basin in uplands of Buck Hollow Creek watershed. 39 |
How Does Timber Harvest Affect the Watershed?
Because harvesting timber typically involves roadbuilding, road use, heavy equipment, soil compaction, and removal of trees and other vegetation, it has multiple effects on the watershed. These are not necessarily direct or intended effects; rather they are the result of long-term relationships between human actions and runoff, erosion, sedimentation, and other physical processes.
A survey of cumulative, long-term effects of forestry on fish habitat in the Pacific Northwest found one clear overall trend: "simplification of stream channels and loss of habitat complexity,"(Bisson et al., 1992) including fewer and smaller pools, a long-term reduction in large woody debris, and the loss of "edge" habitat-the backwaters and small side channels that are important feeding and refuge areas for juvenile fish.
Loss of fish habitat is the end-product of many interrelated changes on the land. Timber harvest creates a relatively short-term soil disturbance but removes trees that may take generations to regrow. A road may create erosion and runoff that continue for as long as the road is there, whether it is used or not.
Trees hold the soil on steep slopes and stabilize streambanks. Well-vegetated hillsides catch the rain and release it slowly. Removing vegetation makes slopes unstable and causes more rapid runoff, which increases soil erosion and carries more sediment to the streams. Logging also alters the snowpack size and melting regime. Gaps in the forest are more likely to accumulate snow, releasing larger quantities of water at once when the snow melts.
When rain falls or snow melts on compacted soils and devegetated slopes, more water from a wider area runs off quickly into the stream, making storm flows higher. An increase in storm flows is likely to cause channel erosion and more sedimentation in the stream.
Removing trees from the riparian area deprives the stream of its future source of large woody debris. This has a major influence on small streams. Water flowing around logs and root wads forms pools, which are important areas of refuge for fish. Large woody debris also makes waterfalls and creates storage sites for sediment and organic material such as leaves and twigs. This organic material is an important source of nutrients at the bottom of the food chain. The net effect of large woody debris is to increase habitat diversity in the stream. Its loss accordingly diminishes survival opportunities for fish.
Logging road construction and the roads themselves may cause even more erosion and delivery of sediment to streams than the removal of vegetation.(King, 1993) Logging roads are often built along watercourses or on steep slopes subject to landslides. Stream crossings contribute large amounts of sediment to the streams. Roads can function as drainage channels, carrying heavy sediment loads. Heavy equipment used off-road compacts the soil and leaves skid tracks, which also become water channels when it rains. |
|
|
|
This road has become a drainage channel. 41 |
A USDA Forest Service study found erosion to be two to three times the natural rate in logged areas in the Snake River Basin, declining gradually with regrowth of vegetation.
Sediment has many consequences downstream. Increased sediment from logged and roaded areas may be stored in tributaries and small streams until a big storm washes it out into the mainstem rivers, where it increases turbidity, clogs potential spawning gravels, and has other deleterious effects on water quality and fish habitat. Further, when the flows subside, the sediment settles out, building up the channel. The stream then uses its excess energy laterally to further erode streambanks. Erosion of streambanks can lead to landsliding, which deposits more sediment in the stream.
(Mount, 1995)
Full protection is the best alternative for the following:
Prevention is more effective than restoration. Although improved forest management can reduce some of the deleterious effects of logging on the watershed, it cannot entirely eliminate them. In some areas where salmon runs are threatened or endangered, it may be necessary to stop logging in the watershed to allow the streams to recover.
Some companies or agencies voluntarily adopt "best management practices" (BMPs) to protect soil and water; some BMPs are required in state and federal regulations. One computer simulation study of forest practices in the watershed of the South Fork of the Salmon River in Idaho found that helicopter logging and maximum erosion mitigation could theoretically have reduced sediment yields significantly from those generated by past operations. The same study concluded, however, that "some increases in sedimentation are unavoidable even using the most cautious logging and roading methods."
The following are some of the options for improving forest practices. When in doubt, use this test: are the effects of this action reversible? Once too many trees are removed, it takes generations to replace them. On the other hand, it's easy to reduce a buffer zone if monitoring shows it's wider than necessary to protect a stream.
Leave Riparian Buffers
Leaving wide buffer strips along the streams can reduce logging impacts. How wide? The goal should be to protect all the riparian functions, including sediment filtration, groundwater recharge, recruitment of large woody debris, water temperature moderation, bank and channel maintenance in "dynamic equilibrium," and diversity of habitat. For this purpose, all streams, including their floodplains, should be protected, not just fish-bearing streams. The network of smaller streams has a large influence on downstream water quality. CRITFC scientists recommend riparian buffers extending 300 feet from each side of the floodplain or to the ridgetop, whichever is less.
Minimize Road Erosion
In watersheds that are already significantly degraded, BMPs are not adequate to protect streams from the continuing and cumulative impacts of roads. Consider which unused or unnecessary roads might best be obliterated and revegetated. (See further discussion on page 37.)
Reduce Soil Compaction
There are various ways to reduce soil compaction and erosion during harvest operations.
The "harvester-forwarder" logging system uses tractor-trailers with low-pressure, big rubber tires that cause somewhat less soil compaction. The National Marine Fisheries Service has accepted the use of this method in some watersheds where there are listed salmon runs.
When a skid trail must cross a watercourse, it should cross it at right angles over a temporary culvert covered with rocks. Water bars at intervals along the tracks can be used to redirect the water into vegetation so that it does not build up erosive force.
Manage for Forest Diversity
American agriculture and forest management have favored "monocropping"-replacing the natural variety of vegetation with single, desired species. Single-species systems have biological disadvantages; they are more unstable and more vulnerable to environmental change. Worldwide, traditional agricultural systems maintain more variety within a single field or forest. Some modern managers are experimenting with more biologically diverse production systems.
Case Study: The Warm Springs Huckleberry Ecology Project
The Confederated Tribes of the Warm Springs Reservation of Oregon hope to manage their forests to enhance growth of huckleberries and other wild plant resources, as well as maintain sustainable timber harvest. In 1992, the tribes started operating on an "Integrated Ecosystem Management Plan" for the reservation.
Huckleberries are a culturally important food to the Columbia Basin tribes. Traditionally, they were picked in late summer at high-elevation camps and preserved for later use in the winter. They are rich in vitamin C and have medicinal properties. But huckleberries have become both less prevalent and less productive in recent decades.
|
Huckleberries were more abundant in the past-why? The tentative answer is that they benefited from traditional management with periodic fires. USDA Forest Service research indicates that huckleberry productivity increases slowly but dramatically after fire clears out the smaller trees. The berries also respond well in areas where trees are thinned. But they don't do well in clearcuts-and that may explain the current decline. |
|
|
|
Warm Springs Tribes Culture and Heritage Committee with Forestry Department Manager Bodie Shaw (back to camera) among the huckleberries. 43 |
"With the exclusion of fire and the introduction of grazing, huckleberries were outcompeted by other vegetation," Warm Springs Forestry Department Manager Bodie Shaw says. "Huckleberries need sunlight. We don't know exactly how much. With a full canopy cover, there are few plants. In a clearcut there are lots of plants but few berries."
Shaw, with a master's degree in forestry, is also on the faculty of the Oregon State University School of Forestry. In partnership with Oregon State University and the Forest Service, the Warm Springs tribes are conducting a three-year study funded by the Ford Foundation that will integrate ecological, historical, economic, sociological, and cultural research about huckleberries and how to manage the forest for their benefit.
Tribal members of the Culture and Heritage Committee will conduct oral history interviews with elders. They want to document historical camps and trails and map the places huckleberries were found, including the traditional place names. The committee also wants information on traditional methods of land management.
Both the Forest Service and the tribes have built management for huckleberries into recent timber sales. The tribes have placed conditions on the harvest to protect huckleberries from excessive soil compaction. The Forest Service has required thinning of trees and protecting certain open areas. The results will be carefully monitored.
"We want to identify issues and concerns of the tribes," John Davis, a forester with the Mt Hood National Forest said, "and find opportunities to do something different."
How Do Roads Affect the Watershed?
Roads are a major source of sediment delivery to streams (see also discussion on page 34). Roads also compete with rivers and streams for use of the floodplains.
Once a road is built in a floodplain, people expect the river to stay in its bed. The river's normal flooding cycle creates maintenance problems. Flood waters may flow over the road or undercut it. The road usually wins this battle, and the river gains hard embankments but loses a good deal of its fish habitat. The landowners win a very costly road.
|
|
|
A road under water. 44 |
The many small gravel or paved roads used for logging can cause more erosion and sedimentation in streams than removing trees and other vegetation. Unused roads continue to distribute sediment into streams if they are not properly maintained, or if they are abandoned but not decommissioned.
(Harr and Nichols, 1993) Even after decommissioning, stream recovery is slow.
The point where a road crosses a stream is often a source of sedimentation. If high streamflows exceed the culvert's capacity, the stream will back up. Trees, branches, and sediment carried down in storms can also plug culverts and start this chain of events. If the culvert is not at the lowest point of the road, water can travel down the road or along the road in a drainage ditch, eroding the ditch. Or the water may cross the road, eroding it, and dumping sediment directly into the stream.
Excessive sediment in the stream is extremely harmful to salmon. It can fill in the spaces around spawning gravels, depleting the oxygen and smothering the eggs. It can impair the ability of juvenile or adult fish to navigate and feed by reducing visibility.
(Bjornn and Reiser, 1991)
Because roads are often cut into hillsides, they can sever subsurface flow pathways and cause flow that would normally travel underground to surface. Roads can serve as drainage networks during high flows, increasing runoff significantly. A combination of these factors alters the flow regime, making higher high flows and lower low flows.
(Furniss et al., 1996)
Impacts on streams from erosion and sediment delivery are rapid, significant and long-lasting, while the benefits of restoration, such as road obliteration, are relatively slow. That's why it makes more sense to prevent road impacts by not building new roads and by restoring and decommissioning wherever possible. (See the Resources section for more information on preventing road erosion and sediment delivery to streams.)
|
|
|
Logging road washout, Second Creek, Mt. Hood National Forest. A debris torrent plugged the culvert, overflowed the road, and continued downstream. 45 |
Restoration of existing roads can proceed in several ways, as follows.
Control Erosion During Construction
If a new road is to be constructed, locating it well away from the floodplain saves maintenance costs and protects the stream. During construction, there are many methods to prevent soil erosion, some required in federal contracts. One example is the use of "slash filter windrows." As a road is built, the slash is piled at the toe of the new construction so that it catches and filters sediment. Other forms of erosion control include dry seeding of cut-and-fill slopes, straw mulch on cuts and fills, filter windrows on fill slopes at drainage crossings, and using good quality gravel on the road surface.
|
Replace Inadequate Culverts The Forest Service is currently developing risk assessment guidelines to help determine which culverts are most in need of replacement.
|
|
|
|
This culvert was too small to carry flood waters and has been replaced. Improperly designed or sized culverts can block miles of upstream spawning and rearing habitat. 46 |
Control Stream Crossing Failures
The road should slope up on either side of the culvert to prevent an overflowing culvert from sending water down the length of the road. A road that slopes down on one side of the culvert can be corrected by building a mound of earth, called a dip, downslope of the culvert. The dip will funnel the water from an overflowing culvert across the width of the road and back into its natural stream channel on the other side of the road. Dips can often be built inexpensively.(Furniss et al., 1996)
Outslope the Road
Outsloping means building a convex slope on the downhill side so that the water runs off onto the adjacent hillside. In the past, roads have generally been insloped. Insloped roads have a ditch on the uphill side. The ditch can serve as a stream channel during high flows, eroding for long distances and eventually depositing the sediment into the stream.
Decommission Roads That Are No Longer Needed
Decommissioning involves removing culverts and surrounding road fill, pulling sidecast material upslope onto the stable portion of the road surface, regrading banks, and reestablishing natural drainage patterns. The former road surface and cleared area is then revegetated.
