Page 294 - Nutrient Management Planning Guide

284

Constructed Erosion Control Measures to Reduce Nutrient Losses in Runoff

Figure 8.3.3 Constructing Grassed Waterways.

Run-on Diversion Channels or Basins

In certain situations it may be possible to divert or control water coming onto cropped land and stop water erosion from causing nutrient loss from the soil. This water may be from natural runoff from upslope land parcels or natural areas or controlled releases from intensive livestock operations.

Diversion Channels or Berms

Earthen channels are constructed below the existing surface to contain water within its banks whereas berms are built above grade and pond or divert water back onto cropped land upslope.

Constructing a run-on diversion channel (or interception ditch) may be most suitable when an alternative waterway, natural or manmade, has adequate safe capacity a short distance away with minimal elevation rise between them. Because a change to natural flow patterns is caused, careful planning and approval is required ahead of construction.

Terracing is a coupling of a channel and a berm and provides a similar result as run-on diversion channels but it is integrated on to the cropped land. Terracing breaks up the length of a slope. Multiple diversion channels or berms are formed at intervals perpendicular to the dominant field slope (following contours) and divert water to a safer, less erodible outlet. Terracing is common in some parts of the world especially where they can be constructed by hand on smaller farms. These have been tried in Alberta with mixed results but are not commonly constructed or seen.

Basins

Basins can store water as it runs off or is generated from upstream land or facilities. While this water is being held or ponded, solids and some contaminants can be settled out of the water column. Water with less sediment in it is less erosive. Examples of basins on agricultural landscapes include feedlot catch basins, exercise yard runoff basins, sediment control basins, and irrigation return flow catchments. Basins are most effective when they are regularly emptied so as to have the maximum volume available for runoff retention with less earthwork construction. Water held temporarily in basins can be emptied in a number of ways including:

Release it to downstream channel at a lower flow •

rate or at a better time when less erosion is likely to occur. Spray irrigate it over a larger land area at rates not to •

cause runoff or erosion

Vegetative Field Borders

Vegetative field borders (VFB) are areas of natural or managed vegetation situated between a non-point source of pollution, such as a field that has received manure or fertilizer, and an environmentally sensitive area, most often a water body.

tip

VFBs are an “edge-of-field” beneficial management practice. Use them in combination with crop and field management practices that minimize soil and nutrient losses in runoff. The VFB on their own have limited ability to reduce the amount of nutrient lost from a field, particularly from large, sloping sites. They are much more effective if used with direct seeding, reduced tillage and conservation fallow.

more info

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

Ontario Ministry of •

Agriculture, Food and Rural Affairs. 1990. Use of Earthen Berms for Erosion Control. Agdex 751. www. omafra.gov.on.ca/ english/ engineer/facts/99-047.htm