Book SectionsTable of Contents
The Problem Puddle Power Frog-Friendly Backyard Why are we concerned about amphibians?
Wetlands - function/type Wetland issues
How to help amphibians
Community Green Plans
Ecological planning beyond the birdbath Before you start Urban Wetlands Marshes
Drainage ditches Stormwater retention ponds Ephemeral ponds River valleys
Swamps Wet meadows Beaver pond Management
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.
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.
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