What action must be taken when the trapped material increases head loss in a rapid sand filter?

When the trapped material in a rapid sand filter increases head loss, backwashing is the appropriate action to take. Backwashing is a process where water is reversed through the filter media to dislodge and remove the accumulated particles. This action helps restore the filter's efficiency by reducing the head loss, which can affect the flow rates and the overall performance of the filtration system. Regular maintenance and monitoring are essential, but in the case of increased head loss specifically, backwashing is necessary to ensure that the filter operates effectively without significant interruptions in service or potential contamination issues.

Other options, such as regular monitoring, are important for ongoing maintenance but do not directly address the head loss that has already occurred. Media replacement, while a solution in some scenarios, involves significant downtime and expense, and is typically not required unless the filter media is degraded. Reducing the flow rate can be a temporary measure to avoid excessive pressure, but it does not resolve the underlying issue of trapped materials in the filter that causes increased head loss.