When you have questions regarding condition categories, condition groups, performance, and preventative maintenance schedules, one resource is the Environmental Protection Agency's (EPA's) 2004 Stormwater Best Management Design Guide: Volume 3, Basin Best Management Practices.
Although there is useful information throughout the document, section six, Maintenance and Operation, is particularly strong in advocating for regular inspections and maintenance of stormwater management systems and best practices for conducting them.
Per the EPA, there are two primary types maintenance: functional and aesthetic; it discusses their overlapping requirements. It advises best practices for managing aesthetics including graffiti, grass, weeds, debris, and litter. It further advocates for functional maintenance including preventive and corrective maintenance such as managing grass, trash, and debris, as well as mechanical components such as valves, gates, pumps, and access control.
It points out that corrective maintenance is not planned, and provides equations to estimate the depth of sediment accumulation to assist in removal and control of pond sediment.
Other areas of concern discussed include structural repairs; dam, embankment, and slope repairs; mosquitoes; erosion; trees, woody vegetation, and animals; snow and ice; and general maintenance.
Because poor planning yields bad results, the EPA also addresses planning a stormwater management system, including access control, vegetation, avoiding clogs, placement of the riser, pond drains, and safety considerations.