Imagine Two Raindrops…

Imagine Two Raindrops…

One falls into a watershed full of old-growth Douglas-fir. It works its way through the lush, moss-covered branches to the ground where it is absorbed by spongy humus on the forest floor. The other raindrop falls into a watershed that has been clear-cut. It takes a direct path to dry ground where there is little capacity to absorb or retain water. The first drop will gradually make its measured way to a clear stream and join its fellow drops in their path to the sea. The second drop will quickly join others to form a muddy rill that will scour the dirt and drag bits of mud and debris along the way. A healthy, functioning watershed is resilient to excessive flooding and drought. So obviously, the watershed that received the second drop is not as resilient and not as healthy, hydrologically speaking, as the watershed that received the first drop.

Now, this may sound like one of those dreaded story problems from high school math, but it is important. You might say the first watershed is 0% unhealthy (an odd way to think about it but bear with me) and the clear-cut water- shed is not healthy at all, or 100% unhealthy. This is the concept behind Equivalent Clearcut Area (ECA), a methodology used by forest scientists to assess watershed health. If a watershed covered in old-growth has half of its trees harvested, leaving it in a half old-growth and half clear-cut state, it could logically be described as 50% unhealthy, which would be an ECA of 50%. Of course, watersheds are never a perfect mix of old-growth and clear-cuts. Indeed, there is truly little old growth left. So, forest scientists have developed ways to estimate the ECA for mixed forests using average tree heights and other metrics. This allows them to study a particular watershed and determine that it behaves, for example, like a watershed with 25% clear-cut area, even though it has no actual clear-cut areas.

BWS Vice President, Dave Weaver is a retired Professional Forester. He has created a Hydrological Health Report Card, which includes ECA calculations, for four of our watersheds – Mud Bay, Waterloo, Cowie, and Wilfred. The full report, which includes other important watershed metrics (area harvested, density of logging roads, number of stream crossings, etc.) as well as subjective assessments of riparian protection, can be found on our website ( Here are a few of the ECAs to whet your appetite. Remember, a lower ECA is healthier. And keep in mind that an ECA over 30% is considered problematic.

Mud Bay’s watershed has an ECA of 21%. Waterloo, with its unique stand of mature Grand Fir, has an ECA of 28%. Wilfred, which stretches all the way into the snowpack, has an ECA of 30%. Cowie has the worst ECA of the bunch with a total of 31%. When you consider the importance of these watersheds to our drinking water, these numbers are not great. Ideally, they would all be 0% unhealthy, or in other words, perfectly healthy! The only way for these numbers to decline would be if logging companies reduced their rate of harvest. While this is not something likely to happen on its own, there is a growing sentiment that rates of harvest should be reduced and more closely regulated.

This Watershed Report Card, like much of the work BWS is doing, provides a baseline against which we can measure change. When those two raindrops fall ten years from now, we hope the change is such that they fall in watersheds with much lower ECA scores than today.