Ecological planning beyond the birdbath    Before you start     Urban Wetlands    Marshes
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Wetland restoration

Drainage ditches

Drainage ditches serve a similar function as hedgerows in providing corridors for wild life. Many ditches dry out when sediment loads fill in the original basin or when the only source of water is from occasional periods of surface runoff. Their vegetation is tolerant of short term flooding and species diversity is low. For example, a cattail swale or drainage ditch may drain and hold water in the spring and local toads may breed in this warm shallow water. However, due to the lack of groundwater and the slope of the drainage ditch, the water dries up before the tadpoles can transform into toadlets (this usually takes six to eight weeks).

There are two options which will not interfere with the swale's ability to drain away melt water and ground water after heavy rains. The bottom of the ditch can be lined with a few bags of bentonite clay which acts as a barrier to percolation. Water cannot drain into the soil and remains long enough for amphibians to breed. If the ditch is shallow or if it does not have a catchment large enough to supply it with water, evaporation alone may be responsible for the loss of water and toad breeding habitat.

In this case the drainage ditch can be maintained with the same slope so that water still drains away as originally intended.

St. Anne school, with the help of the Richmond Hill Parks Department, dredged pools in their drainage ditch to increase the breeding habitat of toads.

As a second option, a backhoe can dig out sections of cattails and the resulting pools of permanent water will increase diversity. As cattails grow in, they will have to be removed every five years or so. However, unless we address the issue of sedimentation our wetland will always require inputs of energy to maintain the desired state. Basins with gently sloping sides are better for wildlife. Most channels are steep sided and square in keeping with the shape of a backhoe or drag line. Excavators are very skilled at providing the shape you require if given proper direction.

Try to excavate around shoreline shrubs and stands of poorly represented plants. Leave shoreline stands of cattails to cover the interior excavations and to provide shoreline buffers. Rather than a straight channel which directs water quickly through the system, consider including several meanders to slow water at some points. Broad berms of vegetation, perpendicular to the direction of water flow, slow water flow and provide islands of vegetation in the deepened channel. The berms will keep water at different elevations after peak flows have passed through the system. Be sure to establish your final elevations in advance so you do not interfere with the engineering function of the ditch in removing water from surrounding grass swales or berms. Each berm should be a little lower in elevation than the preceding one so that water continues to flow down the sloping grade. Your objective is to retain a water resource in pools or slowly release water after a storm.

Before you begin contact your local park, planning or roads department. They will approve your project if wild life habitat is created and they are assured that drainage will not be affected. In many cases you can also convince the local employ ees to bring a backhoe to do the digging under your supervision. Contact local residents as they may have concerns about safety or mosquitoes. Ditches may accumulate pollutants if they receive much urban or agricultural runoff. If we are encouraging wildlife to colonize drainage ditches, it is advisable to rehabili tate ditches in rural areas or away from crops until the issue of pollutants can be addressed. Remember your remedial action should both improve habitat and help to change attitudes about wetlands.

Restored stream or drainage ditch - remove cattails and sediments but leave a series of pools in the channel and cattails as cover along the edges of the stream.

Newly formed ponds have little vegetation and a high proportion of open water.	After a year or two the edge of the pond is colonized and there is a good diversity of emergent and submergent vegetation. Open water represents 50-75% of the wetland.
As bottom sediments create large areas of shallow water, emergent plants dominate the wetland. There is an equal ratio of vegetated and open water areas.	Sedimentation reduces water volume and area. The wetland has a high ratio of vegetated areas and very little open water.
Water is lowered and organic matter in sediments is exposed to air.	Bottom sediments dry and oxidize. The soil seed bank maintains a diversity of wetland species.
As water slowly returns to the wetland, seeds germinate.	A diverse vegetational community is once again established. Although seeds of all species may germinate together, it is the variation in water level that determines which species survive.

Cattails do not grow in water over a metre in depth. The "islands" of cattails provide cover for wild life.
Sediments removed to increase depth to over a metre will limit cattail growth to margins of the pond or stream. Dredging is repeated as the channel becomes filled with sediment.	Cattails that choke small streams or ponds can be removed to increase the volume of water. Leave several underwater raised berms about 30 cm high to create pools to hold water as the drainage channel dries.