Flooding in a Southwestern MN Ag. Field

Minnesota is one of the states most impacted by climate change. Official precipitation and temperature data has been collected in Minnesota from 1895 through today, showing some striking statistics about our changing climate:

• 13% increase in the size of the heaviest annual rainfall.
• Since 2000, rains of more than 6" are four times more frequent than the previous 30 years prior.
• 65% increase in the number of 3" rains.
• Average temperatures in Minnesota have warmed by 3˚F since 1895.
• Overall, Minnesota's climate is warmer and wetter.

These changes are impacting Minnesota's wildlife, forests, water quality, infrastructure, and outdoor recreation (especially winter sports). Below are some links to MN DNR infographic GIFs that shows the change to our 30-year average winter temperature and 30-year average yearly precipitation:

Sinkhole in Duluth Following a 7"+ Rainfall

We witnessed the impact of elevated precipitation in 2012 when the most damaging flood in Duluth's recorded history began when heavy rains fell over already saturated ground on June 19^th and 20th. At the Duluth National Weather Service (NWS) the rainfall total for those two days was 7.24 inches. A NWS volunteer observer in Two Harbors recorded the storm's largest value of 10.45 inches in 24 hours.

The aftermath included millions of dollars of insurance losses to repair roads, bridges, homes and businesses. Many homes foundations were damaged extensively and the houses were razed. One state highway (MN 23) was closed for 3 years while it was repaired. The City of Duluth has had to adapt their stormwater infrastructure to withstand events that 30 years ago were considered 500-year events, but now happen regularly. In June 2018, just southeast of Duluth, the area received up to 10" of rain and once again damaged Highway 23.

Here in Anoka County, we've witnessed a similar story in 2019, with all of the monitored lakes, rivers, and streams in the County reaching historic water level averages for the year. This increase in precipitation only solidifies the need for comprehensive watershed management to make sure that our infrastructure and waterways can handle the increased erosion and flow produced by this additional rain. 

What can we do about it?

Here are some helpful tips you can use to make your driveways and sidewalks safer and better for the environment this winter:

Shovel!

Salt is never a substitute for shoveling. Shovel your snow and ice first so that salt is only used for melting ice stuck to the ground.

Salt!

Traditional salt (sodium chloride) does not melt ice when the temperature is below 15 degrees Fahrenheit. Use a low-temperature alternative such as magnesium chloride or calcium chloride to melt ice at lower temperatures or use sand to add traction. There is no such thing as an "environmentally friendly" salt, so it's best to stick to salt that will work in the given range of temperatures.

Scatter!

Did you know you only need a 12-oz. mug of salt to effectively de-ice a 20-foot driveway or 10 sidewalk squares? When applying salt, aim to leave 2" between grains.

Sweep!

Sweeping up leftover salt and reusing it later is a great way to save money and limit the amount of salt getting into nearby waterways.

Failed rain garden that doesn't drain between rain events

Design

• For a standard rain garden, the water table should be at least five feet below the bottom of the garden. This will require an eight-foot-deep soil boring during the design process because the bottom of the garden is often two to three feet below the original ground elevation. Rain gardens with shallower water tables are feasible, but require an underdrain to function properly.
• Soils should have high infiltration rates, generally one to three inches per hour. Rain gardens can be built in soils with lower infiltration rates, but may require an underdrain or a ponding depth shallower than 12".
• If an underdrain is needed, install a control mechanism that allows variable draw down rates and levels. This provides a mechanism to capitalize on natural infiltration that may increase as the deep root structure of the native plant community matures and creates pathways for infiltration.
• Water must be able to get into the garden consistently, predictably, and without causing erosion. The curb-cut should be sized to safely pass sufficient water volumes.
• Utilizing a retaining wall along the back of the garden can improve the aesthetic appeal and allow the garden to store more water. Rain garden side slopes should be no steeper than 3:1. Therefore, for every foot of wall height, three feet of rain garden bottom is gained. In many cases this simple addition more than doubles the size of the garden.
• Consider using a pretreatment chamber. A pretreatment chamber functions like a filter, capturing floatables like leaves, trash, seeds, and sediment to ensure rain gardens are able to properly receive water and dry between storms

Rain garden mid-construction, with a retaining wall and intact curb

• Rain gardens should be sited where they will capture runoff from a sizeable contributing drainage area that would otherwise make it into a priority water resource.
• They should treat stormwater that isn't already routed to a stormwater pond or other installation for stormwater management.
• They should be strategically located on properties where they will quickly fill during storms and quickly drain between storms.
• They need to be located where they won't interfere with utility lines. Utility companies have minimum cover requirements over lines that may not be met following rain garden excavation. While some utilities like cable lines can be moved or lowered for a relatively low expense, others like gas and electrical lines can be cost-prohibitive to relocate when they conflict with the proposed rain garden location.
• If a rain garden is installed in an area where the road routinely floods over the curbs, water will flow into the rain garden over the sides and cause erosion. It will also result in deeper water than intended, which will take longer to drain out.
• If a rain garden receives water from a large neighborhood with non-natural runoff sources like irrigation systems or sump pump discharge, the rain garden may never have the chance to drain completely.

Rain garden pretreatment chamber

Installation

• Curb-cut rain gardens are one of the few conservation practices where landowners volunteer to use their property to treat runoff from other properties. The landowner volunteering contributes relatively little to the problem and benefits relatively little from the solution. They also commonly assume maintenance responsibility for 10 years. For these reasons, local government should consider covering 100% of the construction costs.
• Avoid equipment traffic within the garden.
• Check soil infiltration rates. If they are under the design specification, loosen soil throughout the
• garden with a four-foot auger.
• Plant gardens in the spring and early summer, not in the fall.
• Lay no more than three inches of mulch.
• If possible, consider leaving the curb intact until the plants are established and then complete the curb-cut. Minimally, when installing a curb-cut rain garden as a retrofit, leave the curb intact until the basin is completed. This ensures the basin is stable and ready to receive runoff as soon as the curb-cut and apron are installed.
• Install informative temporary signage during construction and permanent signage upon project completion that explains the value and function of the rain garden.

Ideal rain garden

Maintenance

This is a list of suggestions that can be provided to a homeowner after installation:

• Get your neighborhood involved! If your neighborhood has several rain gardens, try to schedule a periodic neighborhood cleanup day.
• Mulch will break down and should be refreshed every couple years.
• Stay on top of weeding. Err on the side of pulling too much.
• Homeowners should not be afraid to experiment with the plants in their rain garden. Try using native plants to encourage pollinator presence!
• Pretreatment chambers should be cleaned out after each rain event. This should take no more than a few minutes.
• Remove excess leaves in the fall. Having a few leaves is great for catching sediment and creating critter habitat, but too many leaves will create mats and slow down water infiltration.
• Regularly remove sediment that makes it past the pretreatment chamber.

Community rain garden cleanup in Anoka county

Follow-Up

• The sponsoring local government should connect annually with homeowners to remind them of maintenance needs, expectations, and flexibility.
• Make sure homeowners know who to call if they experience problems.
• Consider providing a maintenance program to help with plant replenishment or other incentive to keep gardens well maintained.
• After the 10-year life of the garden, consider a refresh. Hire professionals to remove all plants, mulch, and accumulated sediment and debris, and power wash the retaining wall and pretreatment chamber. Then, add new mulch and replant, salvaging mature plants whenever possible. This relatively inexpensive investment can buy another 10 years of function.