Stormwater: Detention vs. Retention EarthCache
Stormwater: Detention vs. Retention
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This is an EarthCache. There is no physical container to be found. Read below to find out the requirements to claim your "Found It".
Stormwater is rainwater and melted snow that runs off streets, lawns, and other places. When storm water is absorbed into the ground, it is filtered and either replenishes aquifers or flows into streams and rivers.
In developed areas, however, impervious surfaces such as roads, sidewalks and roofs prevent precipitation from naturally soaking into the ground. Instead, the water runs rapidly into storm drains, sewer systems, and drainage ditches which can cause downstream flooding, stream bank erosion, habitat destruction and contamination of streams, rivers, and coastal water.
Both Detention Ponds and Retention Ponds are practices used to manage stormwater, but they do so in different ways.
A Detention pond, or “dry pond,” is a low-lying area that temporarily holds water until the water drains to another location. It is not filled with water all the time. A detention pond is generally used for flood control when large amounts of rain and storm water runoff could cause flash flooding if not dealt with properly.
A Retention pond holds a specific amount of water indefinitely. The pond is designed to have drainage leading to another location to keep the pond from overflowing during heavy rains, but otherwise the pond is intended to always be full. You’ll frequently see these types of ponds in commercial properties or subdivisions, often with decorative fountains in the center.
These particular ponds (or basins) on the Milwaukee County Grounds, were recently constructed as part of a stormwater management project by the Milwaukee Metropolitan Sewerage District. You can view them from your car or you can get out and walk around them following the bike/hike trail. If you do, please note that there is no parking on Swan Blvd. Use Underwood Parkway instead.
Please send answers for the following questions to the Cache Owner using the link at the top of the page. Do not post the answers in your “Found It” log.
(1) If a Detention pond is usually empty, where do you think the drain would be located? Near the top or near the bottom of the basin?
(2) If a Retention pond is usually full, where do you think the overflow would be located? Near the top or near the bottom of the basin?
(3) If a Retention pond holds on to water without releasing it until it overflows, what added benefit does it provide in terms of solid contaminants / sediments?
(4) Based on the amount of water in these ponds, which type are they?
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