Stormwater basins are designed to manage stormwater runoff from developed areas to reduce flooding and erosion. They temporarily hold water after rain events before releasing it at a controlled rate. The design of stormwater basins is influenced by the site's hydrology and needs to be large enough to retain a reasonable amount of additional runoff from new impervious surfaces like roads and buildings. Stormwater basins can provide benefits like reducing water pollution and creating wildlife habitat if designed as wetlands. Proper landscaping and plant selection around basins also enhances their appearance and environmental benefits.