Man versus machine in District’s ditches

The best way to eliminateinvasive plants from drainage channels is to shade them out

As a member of the new Kent-Harrison drainage committee, I read with interest your recent story on the organizational changes made by the mayor and council of the District of Kent. (Ditch drainage uprising in Kent, Friday Feb 17, 2012). However, the role of hand-clearing local waterways requires some clarification.

Typical hand-clearing – two or three people with brush saws – is only used in shallow watercourses with solid bottoms of sand and gravel. That way, the workers can easily and safely remove reed canary grass, blackberry brambles and other obstacles that impede water flow. There are several important advantages to this approach.

First, hand-clearing leaves the banks of the watercourse undisturbed, so there are no bare soils left exposed to erosion. Second, there is no need for a time-consuming ‘salvage’ of fish and amphibians from the project site, as is required for machine-clearing. Third, there is no requirement to do ‘compensation’ work (habitat restoration) elsewhere on the system, as is the case with machine-clearing. For these reasons, hand-clearing is both effective and cost-efficient, and is used extensively in other districts, such as Chilliwack and Abbotsford.

The problem in the District of Kent is that the Department of Fisheries and Oceans (DFO) has sometimes requested hand-clearing in watercourses that are too deep and muddy to be safely and effectively hand-cleared. That is why last year District staff, landowners and local biologists successfully united to convince DFO to allow machine-clearing in sections of McCallum Ditch (a channelized stream).

Left unsaid in the debate between hand-clearing and machine-clearing is that the best way to eliminate reed canary grass, blackberries and other sun-loving invasive plants from drainage channels is to shade them out. That is achieved by planting a vegetated buffer along at least the south and west sides of a watercourse, which has been done on several sites in the District of Kent.

Vegetated buffers also provide other benefits. Most importantly, the plant root systems bind the banks, reducing the loss of precious topsoil – a big issue in the Fraser Valley – and preventing the buildup of silt in drainage channels. Vegetated buffers also help keep agricultural chemicals out of watercourses, and filter out phosphorous and nitrogen from animal manure, which otherwise provide abundant nutrients to channel-clogging grasses and plants. Last but not least, vegetated  buffers provide food and habitat for fish, frogs, birds and other wildlife, as well as green corridors along which species can safely move around the landscape.

 

Detmar Schwichtenberg