"Watersheds are not all created equal," states Will Marsh at the second in the 2011 Comox Valley Seminar Series
Note to Reader:
In April, Seminar #1 in the 2011 Comox Valley Series painted a picture of the ‘legacy liability’ of existing hard infrastructure (i.e. roads, water, sewers). On May 19, Seminar #2 dealt with green infrastructure and how it enables ‘sustainable urban drainage’ at a lower life-cycle cost.
The Seminar #2 spotlight was on urban watershed protection and restoration issues, with emphasis on a ‘design with nature’ approach to green infrastructure that integrates rainwater management and drought management. Connecting the dots between watershed health and infrastructure type is emerging as an important piece in ‘sustainable drainage infrastructure’, both fiscally and ecologically.
In the morning, Jim Dumont presented a short course on rainwater management in a watershed context. This set the staqe for Northeast Comox as a real-world example in the afternoon. This “course within a seminar” stimulated a lively town-hall sharing and learning discussion. The article below is a transcript of the commentary by the legendary Will Marsh, author of the classic textbook titled Landscape Planning: Environmental Applications.
Understand How a Watershed Functions
“Watersheds are not all created equal. And when we begin to examine them, we find that they function in all kinds of different ways. And what I often see missing in most engineering methodologies is an understanding of how a particular watershed actually functions,” stated Will Marsh.
Watersheds as “Partial Area Systems”
“J.D. Hewlett at the University of Georgia studied forested watersheds in the southern Appalachian Mountains for 20 years. Even during intensive rainstorms, he found that forested watersheds never produce overland flow. Streams received all their discharge from interflow.” (J.D. Hewlett is the author of Principles of Forest Hydrology, published in 1982)
“Research by Tom Dunne at the University of California showed that most of the watersheds that we are dealing with in North America function as ‘partial area systems’. This means that only a fraction of the watershed – as little as 20%,10% or 5% – actually makes a direct discharge contribution to streamflow, even during the biggest and wettest events.”
“In British Columbia, depression storage in a forested watershed is the single biggest reservoir of water during wet weather periods. Yes, depression storage! When you walk through second growth watersheds in BC, it is hard walking across them because they are so ‘bumpy’. And, if you go out there during a heavy rainstorm, guess where most of the water is going? It is going into depressions.”
Five Questions that Serve as a Mind-Map
“Most of the watersheds that we have in BC, in particular the smaller ones, function at best as ‘partial-area’ systems. Also, most of them function as interflow systems. This means they have never seen overland flow. So, when we come into a problem area, before we start thinking about best management practices and computer models, we have to ask some basic questions:
- What kind of watershed system are we in?
- Where are we in that system?
- How does the system function at that particular location/sitte?
- What is the site’s role in the larger system?
- How do we then begin to coordinate the site’s hydrologic function with whatever we put there such that our occupancy turns out to be invisible to the system?”
“During the planning and design stages of a project, we really have to begin to pay attention to how things function. Before advancing the engineering, it would help to bring a little natural science into this – for example, some elementary physiography. We too often jump too quickly to the engineering computations about this method or that method….when what we really need is a basic understanding of the land and its functions followed by application of appropriate landscape planning and design measures. In other words, think like a watershed.”
Application of Water Balance Methodology
“Will, we are in agreement,” responded Jim Dumont, Engineering Applications Authority for the Water Balance Model Partnership. “Our starting point in applying the Water Balance Model is to identify how the watershed is functioning currently. In some cases, however, we will not have the streamflow gauging stations at the locations where we need them.”
Understand Conditions Before and After
“So, we have to take a broader view of different watersheds that actually look similar. And we try to understand how those watersheds are functioning. And we build that understanding into the model. Then we are ready to model changes or alterations to the surface of the watershed landscape. We ask this question: What is the change?”
Re-Establish the Connection to the Stream
“The modified systems that are simulated in the Water Balance Model really do strive to mimic the interflow system by providing storage, and by providing the baseflow discharges. The goal of the water balance methodology is to re-establish the connection to the stream, recognizing that we will not able to provide a direct connection to the soil…..because that is what has been lost, unfortunately.”
“The first construction with urban development will destroy the interflow system. The reality is that it’s gone when we build a road or install services. We are trying to build something to mimic that natural operation,” summarized Jim Dumont.
Mimic Nature
“Jim, that is exactly what I am talking about,” concluded Will Marsh. “We need to understand the sub-systems that are in play between the time that rainfall is received at the top of the tree canopy and the time that it actually gets to the stream as streamflow or other kinds of releases. THAT’S THE KEY TO THE WHOLE SYSTEMS APPROACH. If we unlock that key, if we can just begin to get a handle on that, then we can then begin to put in place the appropriate kinds of measures (to protect watershed health).”
“We have to build this approach into the planning, design and architecture at the start. This is where we have got to be. We have gotten into this game of saying let it go, let development take its conventional course; then we go in with all kinds of best management practices and mitigation measures in an effort to correct the situation.”
“And every time we do that, we implement measures that do not mimic what was originally there. We get involved in arguments about stream erosion, peak discharges, magnitude and frequency, and channel behaviour. We are always trying to reconstruct an original reality; WHEREAS if we just pay attention to a little bit of what the original reality was, we can mimic it to begin with.”
“When you settle the money and liability question, you solve the ecological equation,” concluded Will Marsh in reflecting on what he had heard from Jim Dumont and others at Seminar #2 about the implications of the infrastructure liability for local government decision-making.
To Learn More:
Click 
on Rainwater Management in a Watershed Context: Do More With Less & Achieve Stream Health Benefits (1.6MB PDF) by Jim Dumont — Natural landscape-based assets reduce runoff volumes, have lower life-cycle costs, decrease stresses applied to creeks, and enhance urban liveability.
For additional context regarding protection of stream health and reduction of infrastructure liability, the reader is referred to Green Infrastructure: Achieve More With Less, published in Construction Business Magazine in February 2011.
To learn more about Thinking Like a Watershed, click on Conservation Hydrology and follow the link to read the story behind the graphic below. Conservation Hydrology emphasizes the need in many areas for human development designs to move from drainage to retainage.
About Will Marsh
Willam Marsh came to the Comox Valley from the University of Michigan where he enjoyed a diverse career as a landscape planner, teacher, author, and consultant. He is aformerChairman of the Department of Earth and Resource Sciences and a former Director of the Laboratory for Land and Water Management, both at the University of Michigan-Flint.
He has authored numerous papers on landscape planning and environmental management and is the author of several books including the classic 2005 text, Landscape Planning: Environmental Applications (4th ed) from John Wiley publishers.
UBC Connection
William Marsh is currently an Adjunct Professor in the Landscape Architecture Department at the University of British Columbia.
Professor Marsh teaches courses and workshops in landscape analysis for site planning and design, with emphasis on small towns, coastal environments, and watersheds. He also participates in thesis committee work and advises watershed organizations, developers, and communities on problems of land use change, system-based design, and landscape management.