Stormwater Management
Submitted by admin_green on Tue, 08/25/2009 - 14:28
What goes up must come down. What comes down must go…where?
It's not nice to fool Mother Nature, but sometimes you have to. Wisconsin gets a fair amount of rain…enough to cause statewide flooding last year…and in recent years we've added near-record levels of snow, as well. That water is naturally going to head wherever gravity takes it. And it's going to carry whatever is lying around at ground level with it. Water is the ultimate equalizer.
This natural process can have very unhappy consequences. There are an awful lot of things lying around at ground level that we don't want flowing freely, and equally, around us (let's just say we have three dogs and leave it at that.) Flooding can cause catastrophic damage to lower-lying areas. Silt can dam up free-flowing streams. Contaminants from the parking lot can make their way into Lake Geneva.
We've created a gallery of images showing some of the stormwater management systems we will incorporate into the Inn. Click the image to see them.
Good stormwater management requires you to think like a sheriff's posse: you have to head that storm water off at the pass. Give it place to settle and percolate, work its way gradually into the ground (this is known as "infiltration"), and leave the silt and contaminants behind in a place where they won't do much damage.
Our stormwater assessment was done by Chris Jackson of CJ Engineering. He came out to the grounds on October 27, 2008 for the assessment, and gave us a complete set of recommendations, including comparisons of drainage for the current and proposed sites for 2, 10, and 100 years.
Our goal is to meet or beat all local ordinances, as well as Wisconsin NR 151, which sets standards for the state. That means less runoff from our property than now, and 80% of sediment and contaminants removed.
You can read their report, in a Word doc, here.
There's alsoa nice overview of the technologies we will use here. This is a PDF document.
If you build it, it will stay
Water, that is. The basic concept behind sustainable stormwater management is to landscape your site strategically, so that the flow of water moves automatically…and, ideally, unobtrusively…into places where it can be naturally filtered, then seep slowly into the ground soil. Contaminants are removed by plants, by organisms in the soil, and by the soil itself as the water moves passively through it. Given our current soil (learn more about it here), that's going to require some serious landscaping!
A bioswale, bordered by berms, allows runoff water to be directed and to gradually return to the soil, watering the native vegetation as it goes.
In our case, because of the quality of our soil, we will be doing a fair amount of soil treatment as well as landscaping. We'll be adding sand and other highly porous soils to the natural mix to make it easier for water to head down into the groundwater, rather than sitting at the surface.
We are going to use several techniques to make this happen on the Green Leaf Inn site. Click here to see an enlargement of the site map highlighting the stormwater management areas:
Rainwater capture
Just like the least expensive energy is the energy you don't use, the easiest stormwater to manage is the stormwater that never hits the ground. We will be capturing and reusing stormwater from all of the structures, and will feature a "green roof" area on the Welcome Center.
Permeable surfaces - driveway and footpaths
Everybody loves the feel of a a freshly paved road, and in many ways our modern society would not have been possible without them; unfortunately, from an environmental standpoint, paving is a disaster. The very thing that makes for easy travel…the fact that paving is waterproof…prevents water from naturally seeping into the groundwater table.
We will be using a porous paving product called GravelPave2 (visit their Web site here) for all paved surfaces at the Green Leaf Inn, including the driveway and all walkways. This material keeps a firm, level surface while allowing water to seep through naturally. Pretty cool stuff.
Rain gardens
Rain gardens are planted in slight depressions in the ground, and feature low-maintenance native plants. You can read a good description here, or visit our friends at Midwest Permaculture, to learn more. Storm water naturally gathers in the depression, where much of it is absorbed by the plants (if you pick the right plants, you may never need to water them), and the rest gradually settles into the soil. Contaminants are naturally filtered at the root level…this is why you pick hardier native plants…and the water that passes into the ground is clean.
Bioswales and spillways
These are raingardens for high water flow areas where a standard rain garden might become oversaturated and flood. Rather than a depression, a bioswale is a long, gradually sloping trench. Water flows down it slowly, percolating as it goes. Natural plants on the surface perform the first level of purifying; a sublayer of highly permeable soil or even pebbles does the rest. You can think of a bioswale as an environmentally responsible sewer. We will resist the urge to call it a rain garden on steroids. There a very good brochure on bioswales which you can download by clicking this link.
Berms
A fancy term for "wall." You build berms around your bioswales, and sometimes around your rain gardens, to help direct water into these places. Berms are non-porous as much as possible; you want water to drain off them and into the landscaping you've built to handle the water.
The key challenge to our landscaping will be to provide the desired level of stormwater management without turning the grounds into something that looks like a pitch and putt golf course! More on this to come.
Retention pond
At a certain point, your soil has absorbed as much water as it can. If that's not enough to handle all of your stormwater, you've got to give the water a place to sit for a while and filter down more gradually. Our plan includes a retention pond in the southwest corner of the grounds, which is the lowest lying area on the grounds. Our main bioswale will drain into this pond, where it will both permeate and evaporate over time. If possible, we may be able to turn this into a mini-wetlands; this will largely depend on how these plants take to the local environment.
