Detention and retention may be used interchangeably in other fields, but not when it comes to implemented stormwater solutions. Each has its own distinction, and a faux pas it would be if a person were to mistakenly call one by the other’s name.
Speaking in terms of stormwater BMPs (best management practices), the reason detention and retention are often interchanged is because both are methods of flood damage reduction. However, that’s where their similarities end. By definition, a detention stormwater BMP is an area where stormwater is temporarily stored, or detained, and is eventually allowed to drain slowly when water levels recede in the receiving channel.
The United States is increasingly becoming an urban society. Despite its many benefits, there are certain downsides to urbanization that severely affect the environment. For instance, vegetation and soil need to be removed, drainage networks need to be built, and land surface needs to be reshaped—all of which contribute to peak discharge, frequency, and volume of floods in nearby streams. Put simply, some of the biggest aspects of urbanization contribute to flooding in many different ways.
Due to the increased risk of flooding, city planners make it a point to include flood protection in their priorities. A variety of technologies are available toward this end, including bioinfiltration, enhanced tree pits, pocket wetlands, green roofs, and subsurface detention, retention, and infiltration practices. Four types of subsurface stormwater systems are briefly described below.
According to a study by the National Oceanographic and Atmospheric Association (NOAA), the Midwest and Great Lakes region has seen a 31 percent increase in heavy rainfall and snow events over the last 50 years. In Ohio, when these events occur, floodwater and stormwater runoff typically flow over urban grounds. This can overwhelm an area’s sewer infrastructure and pour into local waterways, thereby seriously disturbing local ecosystems and water quality.
One Akron, Ohio resident in particular saw Yellow Creek waters tear through her backyard and take half of her home in a recent flood. The resident, Brenda McShaffery, attests to what the NOAA scientists are alluding to: it’s raining more often in Ohio. This should compel residents to consider implementing effective solutions, one of which is subsurface drainage.
Soil erosion is one of the world’s biggest environmental concerns. The problem is not limited to any locale—in fact, it’s a widespread problem that affects both urban and rural settings. The good thing with the latter is that they have nature to protect them. Coastal wetlands, such as mangroves, help in mitigating soil erosion during disaster, and play a key role in stabilizing coastlines. Urban settings don’t typically have that level of protection working for them.
How mangroves work
Mangroves help protect shores and coastlines in three ways: Firstly, each kilometer of mangrove can reduce storm surge levels by up to 0.5 meters. Secondly, the first 100 meters of mangroves can reduce the height of high wind and swell waves by 13 to 66 percent.