We have a growing problem in stormwater, and by that I mean a problem regarding things that grow. Our stormwater ponds, places where water is impounded either permanently, as in the case of a water quality pond, or temporarily, in the case of a detention pond, are a natural breeding ground for plants and trees. Those plants remove vital stormwater volume from the facility, leaving less volume for the function of the pond.
Now, in truth, an entire thesis could be written discussing whether the plants that grow are actually better for water quality than the stormwater volume they displace, but that is definitely beyond the scope of this article. At this point, the research completed and direction given is that the stormwater volume is king, and we need to remove the volunteer plants and trees and make way for the stormwater. So be it - back to our growing problem.
Remove the Culprit
When a lot of water is impounded in a facility, a lot of things grow. Those things are typically plants that like water - Cattails, Alder trees, Cedar trees, Cottonwood trees, Blackberries, etc. It is exactly those growing things that need to be removed if the pond is going to do its job. This is a great example of "easier said than done." These trees grow fast, which means ponds can get out of control fast.
Red Alders, a species seen in a lot of storm ponds in Washington State, have a growth rate that can exceed 6 ft/year for the first 5 years, and "slowing" to several feet/year after that. In 20 years, those trees can attain heights of 60 to 80 ft. That is a lot of tree to remove if you have neglected your storm pond for two decades. Cue the logging truck, the excavators, and the chippers. And, oh yeah, time to don the cork boots and suspenders.
What is the answer? The answer is vegetation management. Get into your pond area and remove the saplings before they become trees. But beware - there are at least two snares awaiting you as you do this:
1. Removing vegetation that was designed to be part of the pond
2. The fact that you might be tromping around in a critical or sensitive area
There are many horror stories of owners who have experienced one or both of these snares. Don't be a statistic. If you are caught negatively effecting a critical area, it won't be a cheap lesson. If you remove things that should have been there, the best case is that you put it back. The worst case is that you re-construct the pond.
So still we are left with the question - what is the answer? The answer is professional vegetation management. Bring in the people with the degrees and the letters after their name, so they can determine what stays, what goes, and how much tromping can be done. If it is really bad, they can design a new system and get it permitted like it should be. Also, if your project is just getting constructed, ask for and keep the Operations & Maintenance Manual that should be produced by your civil engineer. It will contain information on what you can and can't do in all your stormwater facilities.
In general, more maintenance is always better than less maintenance. Most of that maintenance can be done by the owner, but some should be left to the experts. If in doubt, ask somebody who knows about stormwater. but just make sure you are staying ahead of the growth - you will definitely be happy you did.
Jeff McInnis, P.E.
Founder, CatchAll Environmental
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