AUSABLE WATER WISE: What is a healthy Adirondack stream?

The Stream Functions Pyramid from the May 2012 publication, “Function-Based Framework for Stream Assessment and Restoration Projects” by Harman and others

If you love rivers and streams, you probably have your own idea of what a “healthy stream” looks like. Maybe you think of clear, cool water cascading over rocks under a thick canopy of shade provided by mature trees on an Ausable stream. Or maybe it’s a river that supports a self-sustaining population of native fish.

To scientists like us at Ausable River Association, a healthy stream is more than a collection of subjective ideas that mean many different things to many different people. Ten years ago this month, a group of scientists that specialize in the study and restoration of rivers and streams established a framework to better understand and quantify the health of these critical natural systems.

The Stream Functions Pyramid Framework is a tool for assessing and addressing the deficiencies in the rivers on which many communities depend for a range of services, from efficient drainage of stormwater to recreational opportunities like kayaking and fishing. The pyramid is composed of five categories of stream functions. The base of the pyramid rests upon the foundation of geology and climate, which are the primary factors that determine the development of streams within a given region. As you move up the pyramid, each function is supported by the functional category beneath it.

For example, populations of healthy native fish and other aquatic organisms (biology) cannot thrive outside of the physical and chemical (physicochemical) parameters of water quality that make their survival and reproduction possible. Water quality issues cannot be addressed until we have stable forms and processes that transport wood and sediment (geomorphology) which depends on the efficient movement of water (hydraulics) downstream through the channel and its floodplain. And none of these efforts are worth addressing until we fully understand the processes and factors (e.g., runoff, baseflow, impervious surfaces, etc.) that affect the delivery of water to the channel (hydrology).

Once we recognize that higher level functions like biology and water quality in rivers and streams depend on stable geomorphology and hydraulics, our approach to restoration can more effectively address the root causes of dysfunction.

The framework is used to establish effective project goals that are tied to the appropriate level of function. If our goal is to restore habitat for native brook trout, then we must be aware of the lower-level functions that ultimately allow for that restored habitat to remain functional. The framework is also an important part of the assessment process before restoration takes place. We can incorporate data from our assessments of biology, water quality, and geomorphology to determine the functional improvements that can be realized by implementing a restoration project. By looking at a variety of potential sites, we can prioritize our projects to make sure that we are targeting the areas that could benefit the most from restoration work.

On the occasion of the 10th birthday of the Stream Functions Pyramid Framework, we at the Ausable River Association continue to develop and refine our approach to restoring and supporting healthy streams in the region. We continue to work closely with our partners at the U.S. Fish and Wildlife Service to restore functions within degraded segments of rivers and streams in our watershed.

Recent grant awards from the Lake Champlain Basin Program will fund our ongoing efforts to conduct research on the geomorphology of the watershed and to establish a monitoring program for our restoration sites.

Our watershed is a complex landscape that reflects the balance between communities, infrastructure, recreation, and nature. We need effective tools to help maintain that balance in ways that are long-lasting and self-sustaining, and the Stream Function Pyramid is a critical part of our process for protecting and restoring the health of streams in our watershed.

(Gary Henry is the stream restoration manager for the Ausable River Association.)

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