After tax time, I spent some hours shredding old documents. Now, some may snicker that I'm shredding water bills from 1991, but it was the inspiration for this newsletter. My water bill has tripled since 1991, and in part this increase is due to the Stormwater Fee. In common language, this fee is what we all pay to correct the centuries old, metro-wide problem of raw sewage overflowing from the sewers into the waterways after a rain. Before 1985, the storm and septic drains were combined. Then, the Met Council began a ten year, multi- million dollar program to separate and update the region's municipal systems.
Along with this, the Cities and the Met Council have created numerous programs over the years to control runoff; because stormwater caused not only sewer overflows, but also high phosphorus levels. But government programs weren't enough, the overflows and high phosphorous levels persisted, every property owner in the metro area needed to be proactive. So, in 2005, Minneapolis revised its Stormwater Fee to include a Stormwater fee credit to encourage run-off reduction.
Here's the Math.
One inch of rainfall produces around 600 gallons of runoff from a 1,000 square foot roof. Multiply this by the several rooftops, driveways and other impermeable surfaces on your block. Now, visualize the millions of gallons draining into our lakes and rivers via storm drains, carrying along with it the refuse and chemicals found on every parking lot, road, street.
The Rain Garden
At its most basic a rain garden is a shallow, sponge-like depression, its purpose is to collect run-off and filter from it the nutrients, sediment and pollutants before these reach surface and groundwaters. Plantings of ornamental shrubs, plants and grasses will absorb the nutrients, the sediment settles to the bottom, and the whole effect beautifies the landscape, attracting butterflies and birds.
Rain Garden Placement
First, call the Digger’s Hotline 811, or (800) 242-8511, to locate electrical, gas or telephone lines. Your garden's location should be as far as possible from all these utilities. Experts recommend positioning a rain garden 10’ or more away from buildings to prevent water damage to basements and foundations; 35 feet or more from septic system drain fields, and 50 feet or more from drinking water wells.
Test Your Soil
The rain garden soil needs to drain standing water within 48 hours, as most plants can survive a soaking for this amount of time, and it prevents the garden from becoming a mosquito nursery. You can do a simple soil percolation test by digging a hole 10” deep and filling it with water. If the water is gone in 48 hours, then it's likely that site is suitable. Generally speaking, Minnesota soil has a high sand content, but if your particular location has low permeability, you can add a mixture of organic fill and sand to make it more sponge- like.
There are several native species that are suitable for rain gardens, and from among these you should choose plants that are tolerant of 48 hours in standing water. Plants the MN DNR recommends are: Meadow blazing star, bottled gentian, fringed brome, prairie cordgrass, Culver's root, and turtlehead. Be aware that the MN DNR regulates vegetation on and near lakes, rivers and creeks. If you locate your garden close by a body of water, then you'll need to check your plant selections against DNR regulations. Plus, some municipalities also have site specific, local Soil and Water Conservation District, or other regulatory agency statutes on shoreland vegetation. This is not a mere trifle, certain plant species, particularly those categorized as invasive, can trigger fines and their forced removal!
Install the Rain Garden
Now that the design phase is complete, the construction can begin. Layout a general shape and location guide using rope or garden hose. Note the slope of the terrain. The soil that's removed for the depression can be used to build up a berm on the downhill side of the rain garden. Otherwise, remove the extra soil from the site entirely. The depth of the depression can vary from 4” to 8”, and the bottom of the rain garden should be flat and level. Arrange and plant the vegetation; connect the runoff source to the rain garden via a downspout, a rock lined spillway, a rainbarrel hose, or use under/above ground plastic pipe.
Rain barrels are useful tools in the stormwater run-off control effort. However, observe safety precautions in their installation and use. 1) Provide a tight fitting lid or screen on the barrel. There are three reasons for this: One, there’s a risk of children climbing into an open rain barrel. Second, a lid reduces things falling in the water, clogging the outlet, or animals drowning and contaminating the water. Third, a lid prevents the barrel from becoming an insect party palace. 2) A barrel should be installed on a secure, elevated platform. Well secured so it will not tip over, possibly injuring someone; and elevated to improve the water flow. Finally, the rain barrel must have an overflow outlet.