Is your soil going for a swim?
By Kammy Kern-Korot, WMSWCD Senior Conservationist
Looking out at an unusual snowy, wintery day, one’s brain does not automatically go to thoughts of mud and erosion. But on a more typical, rainy winter day in northwestern Oregon, and as the snow begins to melt, it can be hard to avoid. One common area of erosion is along the banks of streams and canals, but we also need to look upslope.
During and after a large storm event, you may see chocolate brown water full of suspended sediment rushing down a stream. This sediment is made up of fine particles of soil and it comes from eroded streambanks or stream flow that has overtopped it banks and picked up sediment from the floodplain. It can also come from rainwater or melting snow flowing through bare dirt on your land on its way to the stream. This type of overland flow is increased by the removal of trees and other plants and the existence of impervious surfaces like paving and rooves that don’t allow water to infiltrate the soil. Excessive upland and streambank erosion can jeopardize water quality and lead to loss of valuable soil resources and property.
Streambank erosion is a natural process, but it can be exacerbated by a lack of vegetation (and, in the case of canals, banks that were engineered to be vertical). As with most erosion, a large part of the solution is to put in plants along the stream banks, which will trap sediment and reduce the erosive energy of a stream. Another way to slow the velocity of a stream is to create meanders – a winding curve or bend in direction.
Sometimes, there is vegetation along a stream or canal bank, but it is dominated by invasive blackberry or reed canary grass and doesn’t provide the complexity of root structure that a diverse plant community does. Oregon ash trees, red osier dogwood shrubs and native willows, such as Pacific and Scouler’s willow, make thickets with strong roots that help hold the soil. Red alder trees and cottonwoods are also common in riparian areas and are easy to establish and fast growing. You can also add native conifers, such as Western red cedar. All of these plants also provide excellent wildlife habitat, both above and in the stream’s banks, and help keep the water clean and cool in summer.
If your streamside areas are lacking native vegetation, start by controlling your worst weeds like Armenian blackberry, formerly known as Himalayan blackberry, and English / Irish ivy, and then replace them with deeper-rooted native trees and shrubs. You can also sow bare areas with a native grass seed mix in fall-to-winter or in the spring (depending on the mix and species) to avoid surface erosion and new weeds. You generally can’t go wrong with a fall-to-winter seeding assuming the soil is still bare and not covered in snow or leaf litter; the seed will germinate in spring. Be sure to cover bare areas with weed-free straw after seeding or as a temporary protection through the winter.
Winter is a great time to plant young native shrubs and trees. They are both economical and easy to successfully transplant if purchased in bulk as bareroot, dormant seedlings from wholesale native nurseries. You can also collect willow and dogwood cuttings from existing plants on-site and plant them immediately.
Besides streambanks, the soil health principle of “Keep it Covered” also applies to pastures, garden beds, farms fields, lawns and construction sites. Farm fields and vegetable beds can be protected and enriched with cover crops, and soil in garden beds can be protected with mulch or leaves. Farm fields on slopes (less than 10 percent) can also benefit from grass filter strips that run across the slope. Bare spots in pastures and other grassy areas caused by overgrazing, rodents or other disturbance, should be re-seeded as soon as possible before weeds become established, either with pasture or lawn seed mix. Native grass seed is best in habitat areas, as non-native grasses are generally aggressive and can out-compete native ground cover.
Vegetative buffers and plant cover of all types, whether woody or herbaceous, slow water speed, filter pollutants, and trap sediment. They protect streams, lakes, ponds, and ditches and keep your soil on your property, and they work. Studies show that a dense tree stand at the top of a stream bank can reduce meander erosion by half. Pastures with 70 percent or more plant cover have little erosion and produce more forage. Set aside a “sacrifice area,” covered with geotextile fabric, gravel and sand, where livestock are held when pastures are wet or recovering from grazing.
For construction sites, use seeding and straw on bare soil, and down-slope silt fencing as an immediate mitigation measure as plants establish. For any grass plantings, plan on 2 bales of straw per 1,000 square and keep off of the fragile new grass as it establishes, as much as possible. Shrub and tree plantings can be mulched with leaves, bark dust, or compost.
Soil takes hundreds of years to restore, but with proactive action and attention, you can preserve this valuable resource. After all, it is the foundation for all of our food and life as we know it!
For tips for streamside landowners, see the Healthy Streams Program page of the West Multnomah Soil and Water Conservation District. For technical assistance on how to restore your rural riparian areas, contact Kammy Kern-Korot, Senior Conservationist, at [email protected]. For general soil erosion questions, you can also email [email protected].
Ridge Runner, Jan. '17
Looking out at an unusual snowy, wintery day, one’s brain does not automatically go to thoughts of mud and erosion. But on a more typical, rainy winter day in northwestern Oregon, and as the snow begins to melt, it can be hard to avoid. One common area of erosion is along the banks of streams and canals, but we also need to look upslope.
During and after a large storm event, you may see chocolate brown water full of suspended sediment rushing down a stream. This sediment is made up of fine particles of soil and it comes from eroded streambanks or stream flow that has overtopped it banks and picked up sediment from the floodplain. It can also come from rainwater or melting snow flowing through bare dirt on your land on its way to the stream. This type of overland flow is increased by the removal of trees and other plants and the existence of impervious surfaces like paving and rooves that don’t allow water to infiltrate the soil. Excessive upland and streambank erosion can jeopardize water quality and lead to loss of valuable soil resources and property.
Streambank erosion is a natural process, but it can be exacerbated by a lack of vegetation (and, in the case of canals, banks that were engineered to be vertical). As with most erosion, a large part of the solution is to put in plants along the stream banks, which will trap sediment and reduce the erosive energy of a stream. Another way to slow the velocity of a stream is to create meanders – a winding curve or bend in direction.
Sometimes, there is vegetation along a stream or canal bank, but it is dominated by invasive blackberry or reed canary grass and doesn’t provide the complexity of root structure that a diverse plant community does. Oregon ash trees, red osier dogwood shrubs and native willows, such as Pacific and Scouler’s willow, make thickets with strong roots that help hold the soil. Red alder trees and cottonwoods are also common in riparian areas and are easy to establish and fast growing. You can also add native conifers, such as Western red cedar. All of these plants also provide excellent wildlife habitat, both above and in the stream’s banks, and help keep the water clean and cool in summer.
If your streamside areas are lacking native vegetation, start by controlling your worst weeds like Armenian blackberry, formerly known as Himalayan blackberry, and English / Irish ivy, and then replace them with deeper-rooted native trees and shrubs. You can also sow bare areas with a native grass seed mix in fall-to-winter or in the spring (depending on the mix and species) to avoid surface erosion and new weeds. You generally can’t go wrong with a fall-to-winter seeding assuming the soil is still bare and not covered in snow or leaf litter; the seed will germinate in spring. Be sure to cover bare areas with weed-free straw after seeding or as a temporary protection through the winter.
Winter is a great time to plant young native shrubs and trees. They are both economical and easy to successfully transplant if purchased in bulk as bareroot, dormant seedlings from wholesale native nurseries. You can also collect willow and dogwood cuttings from existing plants on-site and plant them immediately.
Besides streambanks, the soil health principle of “Keep it Covered” also applies to pastures, garden beds, farms fields, lawns and construction sites. Farm fields and vegetable beds can be protected and enriched with cover crops, and soil in garden beds can be protected with mulch or leaves. Farm fields on slopes (less than 10 percent) can also benefit from grass filter strips that run across the slope. Bare spots in pastures and other grassy areas caused by overgrazing, rodents or other disturbance, should be re-seeded as soon as possible before weeds become established, either with pasture or lawn seed mix. Native grass seed is best in habitat areas, as non-native grasses are generally aggressive and can out-compete native ground cover.
Vegetative buffers and plant cover of all types, whether woody or herbaceous, slow water speed, filter pollutants, and trap sediment. They protect streams, lakes, ponds, and ditches and keep your soil on your property, and they work. Studies show that a dense tree stand at the top of a stream bank can reduce meander erosion by half. Pastures with 70 percent or more plant cover have little erosion and produce more forage. Set aside a “sacrifice area,” covered with geotextile fabric, gravel and sand, where livestock are held when pastures are wet or recovering from grazing.
For construction sites, use seeding and straw on bare soil, and down-slope silt fencing as an immediate mitigation measure as plants establish. For any grass plantings, plan on 2 bales of straw per 1,000 square and keep off of the fragile new grass as it establishes, as much as possible. Shrub and tree plantings can be mulched with leaves, bark dust, or compost.
Soil takes hundreds of years to restore, but with proactive action and attention, you can preserve this valuable resource. After all, it is the foundation for all of our food and life as we know it!
For tips for streamside landowners, see the Healthy Streams Program page of the West Multnomah Soil and Water Conservation District. For technical assistance on how to restore your rural riparian areas, contact Kammy Kern-Korot, Senior Conservationist, at [email protected]. For general soil erosion questions, you can also email [email protected].
Ridge Runner, Jan. '17