How We Are Restoring Burns Bog?

The Bog is being restored with hydrology as the principle focus.  Peripheral and internal drainage ditches are being progressively blocked to increase the retention of winter precipitation into the dry summer months.  The restoration goals are to return a high water table throughout the Bog, but particularly in the pine forests at the edge of the Bog, to re-establish Sphagnum cover and to re-start the peat-forming process in degraded sectors.  No other restoration has been undertaken to this point, with the assumption that a higher water table would bring about system-wide changes favouring bog species and the bog ecosystem.

Ditches have been blocked with peat dams, wood dams, steel weirs, as well as naturally occurring beaver dams.  During the summers of 2007 and 2008, a concerted effort was begun to block the interior ditches of the Bog, in order to retain as much precipitation as possible within the water mound. Ditch blocking will continue in this vein over the next 5-10 years until results of hydrological monitoring indicate that the water level in the main mass of the water mound fluctuates within the 0-50 cm range judged to be appropriate for sustaining Sphagnum growth and peat formation.

Access to interior ditch-blocking sites by vehicles and machinery is rarely possible, and where possible is undesirable due to the impact of vehicles on the vegetation and risk of fire.  Consequently, interior ditches are being blocked by hand.  Construction methods vary according to the size and depth of each ditch, and on locally available materials.  In most cases, construction materials are limited to fallen trees, borrow pits of nearby peat, and materials that are carried to the site on foot such as plywood and wooden stakes.

For shallow, narrow ditches, a sheet of plywood is inserted across the ditch and held in place by wooden stakes.  If necessary, plywood extensions are added to the sides to minimize re-routing of water around the blockage. Plywood dams are then covered in peat, dug from a nearby borrow-pit.

For deep, wide ditches, particularly those with a significant rate of flow, it is necessary to engineer a structure that could withstand considerable water pressure.  To this end, a double row of plywood dams are constructed across the ditch, about 30 cm apart.  The interior space created by the plywood is filled with logs and packed with peat.  The downstream end of the dam is braced with stakes for additional reinforcement.  The dam structure is then covered with peat.

Working with the Beavers

Beavers have been instrumental in blocking many of the ditches throughout Burns Bog.  Most of the time, we are very happy with their work.  However, sometimes the dams are built in ditches near roads and adjacent lands, which can cause flooding and damage to access routes and property.  In these cases, our crews will maintain the dams at a level that retains water in the bog areas, while allowing excess water to flow through the dam and prevent flooding.

Beavers can often be seen as a nuisance, but they are actually an ally when it comes to bog restoration. To take advantage of the incredible engineering abilities of the beavers, Delta is trying a pilot project where we install a special pipe through the beaver dams.  The pipe is called a “beaver pond leveler”, and the idea is that the beavers are left to continue building up their dam as high as they wish, while we quietly control the water level behind the dam with the pipe.  This way, the beavers stick around and continue their great work, and we have control over the water levels and significantly reduce the risk of flooding.

Beaver lodge (right) and construction materials in a Burns Bog ditch (Photo: Sarah Howie)

Beaverdam blocking a ditch at the north edge of Burns Bog (Photo: Sarah Howie)

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