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Abstract
Introduction
Map
Methods
Results
Discussion
PDF File
Abstract:
Rain gardens are a very important part of the overall health of the Lake
Wingra watershed. Without rain gardens, stormwater carries much of the
pollutants generated in the watershed directly into Lake Wingra, and this water
has less opportunity to recharge the groundwater aquifer. Soil type is an
important dimension of rain garden design, because different soils allow
different amounts of water to infiltrate and recharge the groundwater. The
purpose of this experiment was to determine the infiltration rates of different
soil types in Edgewood’s rain gardens. The rain gardens we tested on the
Edgewood campus were the Mazzuchelli rain garden, the rain garden north of the
Regina parking lot, and three locations within the large rain garden behind the
Edgedome. Our hypothesis was that the infiltration rates would be higher in the
rain garden outside of Mazzuchelli, because of its sandier, less compact soil.
We measured the infiltration rates of soil from these different locations under
different conditions, two in field tests and one in the lab. We also measured
the soil compactness and the soil texture. The results from these series of
tests support our hypothesis that the rain garden outside of Mazzuchelli has
higher infiltration rates as a result of both its soil type and its level of
compaction. The effects of soil compaction and soil types have many implications
on rain gardens and the design of rain gardens.
Introduction:
Rain gardens are an important part of the overall health of the watershed
because they capture runoff from surfaces like rooftops and parking lots. Rain
gardens replace areas of lawn and are planted with diverse wildflowers and other
native vegetation. The rain gardens fill with a few inches of water and allow
the water to slowly filter into ground rather than running off into the storm
drains (University of Wisconsin Extension, 2004). Because pavement and
buildings can’t soak up the water that falls onto these surfaces, the water is
carried away down sidewalks and streets and eventually into the storm drains
where it is then carried into larger bodies of water, such as lakes, rivers and
streams. Not only is the water carried down this path, but it also carries the
pollution with it. A watershed is a land area that drains into a lake or river.
Runoff on the Edgewood campus originates from Monroe Street or falls onto the
roofs of the buildings and then flows onto the parking lot where it eventually
flows into Lake Wingra. From Lake Wingra, it then flows to larger bodies of
water like Lake Monona and in time it will flow into the Mississippi. Rain
gardens are effective in preventing some of this stormwater pollution from being
carried into the streams, because they can fill with a few inches of water and
then slowly infiltrate into the soil. Rain gardens allow 30% more water to be
infiltrated into the soil than a normal piece of land (University of
Wisconsin-Extension, 2002).
Although the rain gardens are a very effective tool for absorbing stormwater the types of soil that are found in rain gardens determine how much water can be absorbed into the soil. There are three main particles, which make up different soil types; clay, sand, and silt. The ratio of sand, silt, and clay determines the soils’ ability to hold moisture and nutrients. Our watershed project is designed to find how the different soil types in the rain gardens around campus affect the infiltration rate of water in the soil. Our hypothesis for this experiment is that the rain garden outside of Mazzuchelli will have higher infiltration rates as a result of both its soil type and its level of compaction. To test this hypothesis we came up with a series of tests to measure different aspects of the soil under certain conditions.
Discussion:
Our watershed project was designed to test how the different soil types in the
rain gardens around campus affect the infiltration rate of water in the soil.
Our hypothesis for this experiment was that the rain garden outside of
Mazzuchelli would have higher infiltration rates as a result of both its soil
type and its level of compaction. The results from our tests support our
hypothesis, as the infiltration rates were faster in the rain garden outside of
Mazzuchelli.
These tests show that the soils with the higher sand ratios had faster infiltration rates and the soils with higher clay ratios infiltrated much more slowly. The Mazzuchelli Rain Garden has a high concentration of sand in its soil, so it makes sense that it had the fastest infiltration rates in the tests.
The Large Rain Garden Middle is a Silty Clay Loam and the Large Rain Garden Sonderegger is Clay. Knowing this we are able to see that although the compaction levels are the same in each of these rain gardens, it is the type of soil that likely plays a major role in how the water infiltrates into the soil, because the clay soil did not allow any water to pass through it.
