What is the primary characteristic of a retention basin?

The primary characteristic of a retention basin is that it is designed to hold water indefinitely, allowing for long-term water storage without any planned release. This means that a retention basin collects stormwater, which may include runoff from rain or snowmelt, and retains it in the basin to slowly infiltrate into the ground or evaporate. This function is essential for reducing peak flow during storms, improving water quality, and promoting groundwater recharge.

In contrast, other options describe different types of basins or systems. For instance, periodically releasing water pertains to detention basins, which are designed to temporarily hold stormwater and then release it at a controlled rate, helping to manage flooding and erosion. Filtering pollutants is more indicative of designed systems like constructed wetlands or biofiltration systems, where the focus is on removing contaminants from water before it reaches the drainage system or waterways. Therefore, while the other choices represent functions related to stormwater management, they do not capture the defining feature of a retention basin.