Which of the following is not typically associated with stormwater management?

The angle of repose is the correct choice as it is a concept primarily related to the stability and integrity of soils, particularly regarding the maximum slope at which loose material can rest without sliding. This principle is more concerned with soil mechanics and geotechnical engineering rather than stormwater management.

In contrast, area drains, bioretention systems, and backfill are all integral components of stormwater management practices. Area drains are used to collect and convey stormwater away from surfaces to prevent flooding. Bioretention refers to the practice of using vegetation, soil, and microbes to naturally filter and absorb stormwater runoff, making it an eco-friendly approach to managing stormwater. Backfill is often utilized in construction and drainage systems to support structures and manage soil stability around drainage facilities. Thus, while area drains, bioretention, and backfill directly contribute to effective stormwater management, the angle of repose does not have a direct role in this context.