Watershed Management

What is a watershed?   Everyone lives in a watershed – an area of land whose waters drain to a single point such as a river, lake, or ocean. A watershed can be as compact as a single catchment draining a small area of waterfront to as expansive as the Amazon Basin, the largest watershed on Earth, consisting of tens of thousands of streams converging as they flow to the Pacific Ocean.

What is Watershed Management?   Watershed management is an inventory of the characteristics, conditions, and issues in a watershed, and the development and implementation of policies and programs to manage the water, natural heritage, and anthropogenic impacts within the watershed and upon its receiving waters. The OHI believes that improved watershed management is fundamental to the continued ecological, social, and economic well-being of Ontario.

Scale:  One way to describe the relative scale of a watershed is through stream order: assigning values to streams as they converge. In the Strahler stream order method, as per the drawing below, a first-order stream is one with no tributaries, while a second-order stream starts where two first-order streams converge, and so on. In general, first to third order streams are considered headwater streams; fourth to sixth are medium streams; and those above sixth are considered large streams.

A first-order stream is one with no tributaries, as above, while a second-order stream starts where two first-order streams converge.
First and second-order streams can be ephemeral (where flow is based on precipitation) or intermittent (where flow occurs when the water table rises).

It is worth noting that drainage area essentially doubles as stream order rises. For example, think of the area and network of streams needed to provide a second fourth-order stream to converge in the diagram above to form a fifth-order stream. Another way to think about scale is to guess what order of stream is assigned to the final section of the Amazon. Is it a 23, 34, 56?? 

In fact, the Amazon is just a twelfth order stream. Again, think about the scale involved. To make a ninth order stream, two eighth order streams –  the size of the Columbia or Ohio Rivers – have to come together. Then two tenth order streams, and then two eleventh order streams. An interesting aspect of this is that, while the Amazon’s end-stream order is created from two eleventh order streams, the only other watercourse in the world that is an eleventh order stream is the Nile. And there are only three tenth end-order streams world-wide. One is completely in Canada, the Mackenzie, while Canada also hosts a fraction of the headwaters of a second: the Mississippi.

While various forms of human activity remain nestled around major bodies of water or clustered along the larger branches of our main watercourses, the majority of drainage area, stream length, base flow, and biodiversity resides in our headwater areas. As a result, the Ontario Headwaters Institute is uniquely positioned to seek the right balance between headwater protection and other aspects of watershed management in Ontario.  

Note of June 29, 2019:  Given initiatives announced this spring by the Ontario government, we have been forced to focus near term on pending policy changes rather than expand this educational page, and will voice our concerns on the need to restore watershed management to the role of conservation authorities and retain meaningful definitions for watercourses and wetlands in proposed new regulations under Bill 108. We will also be making comments on any other reductions to core watershed and biodiversity protections in various planning initiatives, including under the Planning Act and the PPS. 

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