Harrington and Hoyle Ltd., Landscape Architects  

Natural Channel Design - Building Healthy Rivers

  
In their natural state, rivers meander within their valleys, ever-changing, naturally eroding and repairing their banks in a process that is dynamic yet stable.

In contrast, urban streams have historically been "managed" to control flooding, improve drainage, and conform to human use of the lands that surround them.

Image: air photo of naturally meandering stream
   Image: air photo of piped and hardened urban stream.


Such streams were often straightened, had their banks hardened by concrete or stone, and were sometimes even forced into pipes. While these management practices have long been accepted as necessary for insuring human safety, they have had a devastating effect on the stability and health of the streams, and that affects the quality of the water we use for drinking and recreation.

More and more it is accepted that a naturally meandering channel within a naturally vegetated floodplain is the most effective, efficient, and stable method of controlling flows, maintaining healthy streams, and ultimately protecting life and property in a watershed.
Image: sketch of pool/riffle sequence in a natural river


How Healthy Streams Work

Healthy streams are complex systems made up of many living and non-living parts, each with an important role to play in the health and sustainabliity of the system as a whole.

Plants contribute to the health of the system in many ways. They are a primary food source for aquatic animals and insects; they shade and cool the stream; their root systems help to hold soil in place, preventing erosion; and they act as natural filters, trapping sediment and pollutants that would otherwise enter the stream.

The physical movement of water and sediment down a valley gradually sculpts the landform and shapes the stable bed of a meandering stream. Pools (deep sections) form at the outside bends of the meanders. By slowing the water flow, pools also help reduce the impact of heavier flows during rainstorms. Riffles are steeper, rocky sections between the pools where water is cooled and oxygenated.


Fish and insects have evolved to take advantage of these natural conditions. The clean, stony streambed in riffle areas is home to many aquatic insects that find shelter between the stones. Pools provide deeper areas and undercut banks where fish find shelter. The complex interactions in this dynamic system help to create the natural balance of earth, water, plants and animals that make up a healthy valley.
Image: riffle - a shallow, rocky section

Click here for pictures of a successful stream restoration project in southern Ontario.

Click here to see our award-winning project on the Little Rouge River.

 

 

Image: pool - deep water area

Read articles on Urban Stream Restoration and Stream Restoration in Urban Parks.

 

Download our fact sheet: Creating Healthy Streams

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