Herald Journal - Enterprise Dispatch - Delano Herald Journal
HL property owners encouraged to install rain gardens
April 18, 2011

By Jennifer Kotila
Staff Writer

Howard Lake has historically been one of the cleanest lakes in the area, but it has been gradually degrading over the 30 years that Kerry Saxton has been with Wright County Soil and Water Conservation District (WSWCD), Saxton said.

The lake is what Saxton called a “tipping lake,” and is “on the cusp of going bad.”

“Some lakes out there are so bad, it would cost almost $1 million to fix,” Saxton said. But Howard Lake may be helped by some fairly inexpensive, relatively easy corrections.

This is why an informational meeting took place April 4 for residents whose properties would benefit the lake by having rain gardens installed.

Rain gardens are meant to catch the first wash, or first one-half-inch, of rain that falls. The first one-half-inch of rain will carry the most pollutants into the lake or stormwater system, according to Brian Sanoski from WSWCD.

Rain gardens not only help stormwater from being infiltrated into the stormwater system and the lake, protecting the water quality, but they help to beautify an area, as well, Sanoski said.

Other benefits of rain gardens are protection from flooding and drainage problems, increases in the amount of water being filtered into the ground while recharging the groundwater, and providing valuable wildlife habitat for birds and butterflies.

Pollutions of concern

The most concerning pollutions for Howard Lake are phosphorous and nitrogen, which are nutrients plants need to grow, Sanoski said.

Farmers and property owners use phosphorous and nitrogen to help grow their crops, gardens, and lawns.

Unfortunately, once these pollutants reach a lake, they also help the algae to grow, creating a green lake.

“One pound of phosphorous in a lake can grow up to 500 pounds of algae,” Sanoski said.

Also of concern is the suspended solids, or sediment, being carried to the lake in the rain water, and the volume of rain water that reaches the lake.

Redirecting the “first flush” of water running down the street during a rain event into a rain garden will capture the most polluted water before it reaches the stormwater system or the lake.

How were properties selected?

Thirty-one sub-watersheds, or areas that collect stormwater runoff, were studied throughout Howard Lake by WSWCD to analyze the existing annual pollutant loading (how much pollution it carries to the lake and into the stormwater system) and the sub-watershed’s stormwater retrofit potential, according to Sanoski.

A stormwater retrofit is a correction made in the existing infrastructure of an urban area to reduce the amount of stormwater runoff flowing into the stormwater system and area lakes.

There are many different stormwater retrofit options to reduce pollutant loading in the lake.

They range from fairly inexpensive solutions, such as pond retrofits ($4 per square-foot), to more expensive solutions, such as an intensive green roof ($505 per square-foot).

The rain gardens being proposed for Howard Lake are fairly inexpensive at an estimated cost of $14 to $18 per square-foot.

For each sub-watershed, stormwater retrofit options were compared using specific site constraints and characteristics.

After analysis and comparison, there were nine sub-watersheds identified that showed the greatest need, or that would be most appropriate to receive additional retrofits.

Locations were chosen either because of the capacity to greatly reduce the amount of stormwater and pollutants going into the stormwater system and the lake, or because the location was in an area that would be reconstructed with the street improvements.

“For Howard Lake, the most cost-effective way to reduce pollutants running into the lakes was rain gardens,” Sanoski said.

Installing rain gardens

When planning the location of a rain garden in the yard, the site should be at least 10 feet away from the house, and away from any septic systems or ponds.

A good site for a rain garden is on a flat or gently sloping surface, in full to partial sun, and along a street with a curb and gutter.

The typical size for the rain gardens being proposed throughout Howard Lake is 150 square-feet, Sanoski said.

Because the soil in Howard Lake is “severely polluted with clay,” soil at the site of the rain garden may have to be removed and replaced with about a foot of sand and soil mix with a drainage tile at the base, Saxton said.

Rain gardens are planted in a shallow depression, the depth of which is determined by the slope of the lawn.

During a rain event, the rain garden will fill with stormwater runoff. When it is full, the stormwater will flow past the rain garden and into the city’s stormwater system. The surface of the rain garden should be dry within 48 hours.

Native plants, such as blue lobelia, sneezeweed, turtle head, and bottlebrush sedge are the preferred choice for rain gardens, as they will establish a deep, thick root system, that will naturally inhibit weed growth and help to filter the water.

“You can tailor your rain garden the way you want, though,” Saxton said.

Mulch can also be added to the rain garden to inhibit the growth of weeds and help retain moisture.

The most labor intensive maintenance of a rain garden occurs in the first three years after planting when noxious, invasive weeds will need to be removed, Sanoski said.

There will also have to be minimal watering during the first three years to make sure the plants become well-established. After that, because native plants root systems are so deep, they typically do not need watering, Saxton said.

Any damaged vegetation in the rain garden will also have to be replaced.

Ongoing maintenance of the rain garden includes cleaning out any trash that has collected in them after heavy precipitation and the spring runoff, inspecting the sediment traps and emptying them when needed, and checking the garden for sediment accumulation.

A sediment trap is a pretreatment chamber (or forebay) that is used to concentrate and collect the stormwater runoff before it enters the garden.

This allows the majority of debris and larger sediments (sand and silt) to settle out prior to the stormwater entering the rain garden.

Sediment traps need to be cleaned after every rain event to ensure the longevity of the rain garden and maintain the designed storage by reducing the amount of sediment collected in the rain garden itself.

Assistance to property owners interested in rain gardens

Owners whose properties have been identified as those most compatible for installing a rain garden will receive help from both the city of Howard Lake and the WSWCD.

Property owners can use as little or as much assistance as they desire.

Representatives from the WSWCD will design the rain garden and provide the property owner with estimates and quantities of materials and cost.

They will also direct property owners to vendors for plants, and help them chose what species of plant would best be suited for colors and texture desired in the rain garden.

Construction oversight of the rain gardens will also be provided by the city and WSWCD, as well as maintenance training for the property owners.

Property owners will also be assisted with the cost of installing a rain garden.

A $50,000 grant from the clean water, land, and legacy fund was received by WSWCD to help with the construction and installation of rain gardens in Howard Lake.

Property owners wishing to take advantage of the financial assistance and expertise of the WSWCD would only be required to contribute 10 percent of the costs associated with installing a rain garden on their property.

The contribution can be given in a number of ways, such as cash, or in-kind labor and time, providing materials, or assisting in the installation and construction, Sanoski said.

The city and the WSWCD will also be looking for donations and volunteers from various businesses and groups, such as lake associations, FFA and 4-H clubs, to help with costs and installation.

Property owners who wish to install rain gardens will be required to sign a contract, which basically is to record who the property owner is and where it is located, as well as agreeing to properly maintain the rain garden over the course of 10 years, Sanoski said.

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