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Constructed Erosion Control Measures to Reduce Nutrient Losses in Runoff

VFBs on Steep Slopes

Runoff from slopes greater than 10 % would overwhelm the capacity of the VFB to remove sediment and contaminants from runoff. Since most major runoff events in Alberta occur during a relatively short period during spring thaw, consider alternative control strategies for sites with steep slopes.

Among vegetation types, grasses are more effective than broadleaf plants in reducing erosion and filtering nutrients since they form a dense sod, have a fibrous root system and provide more extensive ground cover. Sod forming grass species are preferred to bunchgrasses since they form a more consistent ground cover reducing the likelihood of channelling through the VFB, thereby reducing its effectiveness. Legumes such as alfalfa or clovers may be seeded in a mixture with grasses in order to improve fertility of the stand. However, legumes can reduce the capacity to filter sediment, and as such should not be used as the dominant species in a VFB.

Trees and shrubs require additional maintenance but are superior for stabilizing streambanks, reducing flood risk and maintaining groundwater quality. Select tree and shrub species suitable for site conditions, to minimize problems with establishing and maintaining the VFB.

Maintain Natural Wetlands and Sloughs

Water bodies such as wetlands and sloughs provide a place for runoff waters to pond temporarily or completely depending on their size and the area draining to them. Unlike previous measures discussed in this chapter, they may require no additional investment other than their maintenance and protection.

Advantages of Natural Wetlands and Sloughs

Slow the movement of water though a landscape •

or watershed reducing the erosion or destruction that can result.

Provide an interface between surface water, •

groundwater and the air where shallow groundwater supplies can be recharged or evaporation can generate new rainfall.

Improved water quality downstream due to the •

filtering and biological processes that are part of this aquatic environment.

Provide a habitat for local wildlife. •

While land area unavailable for cropping or lost crop production to wildlife may be viewed as disadvantages, the advantages are growing. Those listed above plus potential social and stewardship incentives to maintaining natural wetlands and sloughs are becoming more apparent.

Keeping in place natural waterways leading in or out of wetlands and sloughs may be all that is required to maintain this productive aquatic environment. Conservation farming practices such as zero till can reduce sediment deposit in these water bodies. Sediment deposits can shorten the effective lifespan of these water bodies, reduce their volume holding capacity and cause them to spread further onto productive crop land during major runoff events. Remote livestock watering devices, fencing, or use of alternative pastures for livestock production can reduce damage to key flow components in sloughs or wetlands. Vigilance in reporting unauthorized upstream water diversions or pumping may also keep this water body intact.

more info

For more information on the design, installation and maintenance of VFSs can be found in the following online resources:

AF. 2003. Buffer Zones for a •

Healthy Watershed: www1. agric.gov.ab.ca/$department/ deptdocs.nsf/all/irr6419

Ohio State University •

Extension. The Economics of Vegetative Filter Strips http://ohioline.osu.edu/ ae-fact/0006.html