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It's wetter. What that means and what to do.

Post Date:12/12/2019 10:21 AM

The Thanksgiving holiday snowstorms broke the record. Officially, 2019 is the wettest year on record dating back to 1884. We received 40.81 inches of precipitation in 2019 at the MSP Airport, slipping past the previous record of 40.32 inches from 2016. Precipitation patterns are changing. Minnesota is getting wetter. Even locally, in Carver County, we are seeing changes in precipitation patterns and effects on local lakes and rivers.

 

How rainfall is changing in Carver County

Staff at Carver County Water Management Organization compared rainfall amounts, storm intensities, and storm frequency from two recent periods of time; 1997 to 2006 and 2007 to 2018.  They found the intensity of storms has changed. We are having fewer storms each year, but they are stronger and bring more rain each time.  The data also showed a decrease in the number of smaller, gentle storms that produce 0.5” of rain or less. On average, we are having 16 fewer events of these small storms a year. The month of June showed the greatest increase in rainfall, followed by October and December. Rain in December is becoming more common while January and November are becoming dryer.

We are experiencing more mega rains statewide. A mega rain storm is when at least 6” of rain falls over at least 100 square miles with the center of the storm dropping 8 inches of rain. The Minnesota Department of Natural Resources State Climatology Office has tracked rainfall since the early 1990s. Their website says Minnesota has had 14 mega rains since the 1973 when the ability to reliability detect them increased. The 20 years from 2000 to 2019 saw 2.5 times as many mega-rains as the 27 years before from 1973 to 1999.

 

More rainfall means more runoff

Soil can only hold so much water. When it rains the soil soaks up the water, allowing it to move through to groundwater below. If the soil becomes saturated and can’t soak in water as fast as the rain is falling, then that extra rain runs off.  The gentle rains where it drizzled all day, provided time for rain to soak into the ground with little runoff. The more intense storms we experience now leave less time for the soil to catch up. This results in less water soaking in and replenishing groundwater supplies, and more runoff causing flooding and water quality problems in lakes and rivers.

 

Lakes and streams respond

Changes in rainfall are affecting how lakes and rivers function and the quality of water and habitat in them.Streams are struggling. More rain falling quickly means the streams are at flood capacity often with fast flowing water. Staff have noticed streams in Carver County becoming wider to handle the larger yet more infrequent flows.  Flooded streams erode soil from their streambanks, create unstable banks, wash away property and degrade the water quality.  Loss of baseflow in some streams is affecting fish and other wildlife. Small soaking storms provided slow and constant feed of water into the streams, creating baseflow. Fewer of these types of storms means less baseflow.

With lakes, staff have witnessed both good and bad.  For many lakes, more rain means more polluted runoff washing in and harming the lake’s health. More runoff also means high-water levels which erode shorelines causing loss of property and reducing water clarity. For a few lakes, the extra rainfall can force water to move through the lake quicker, essentially flushing pollutants out, leaving clearer water.

 

What to do   

The rain is coming. It’s coming fast and in high volumes. We must adapt and create landscapes that can handle extra water.  Residents can make changes on lawns and in gardens creating space for extra water. Changes are often in the plants, grass and soil. Examples below.

  • Keep your grass at least 3” high. Taller grass equals longer roots. Longer roots use extra water during wet times and create paths for water to flow deeper into the soil.
  • Plant native sedges and flowers, especially in soggy areas. Native Minnesota plants have deep roots which again use water and move it deeper into the soil.
  • Increase your soil’s ability to absorb and move water by reducing compaction and increasing organic matter.Aerate your soil at least once a year in the fall. This will loosen the soil and provide pore space for water to go. Sprinkle with compost to increase organic matter which absorbs water.

Carver County Water Management Organization provides funding to residents who want to do larger projects such as native plantings, raingardens or cisterns for water reuse. Our program will fund 75% of a project up to $5000.

 

Restoration is key

There are two types of projects the organization is focusing on that protect lakes and rivers by providing more space for extra water and preventing erosion; wetland restorations and streambank restorations. Restoring healthy streambanks by stabilizing them prevents erosion during high water times, reduces sediment in the water, provides habitat, and prevents streambank collapses. Wetlands act like sponges absorbing extra water, holding on to it, and releasing it slowly. Unfortunately, many of the original wetlands in Carver County are gone, having been filled in or drained.  The organization is working to restore wetlands throughout the county. Studies within the county show streams with wetlands nearby are more stable.

Carver County Water Management Organization will continue working on these and other projects to protect lakes and rivers. Our Water Management Plan identifies projects and priorities for the next 20 years and can be found on our webpage at www.co.carver.mn.us/water.

 

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