What is the term for a river hazard that allows water to flow but not objects?

A strainer is a specific type of river hazard characterized by its ability to allow water to flow through while obstructing larger objects, including people or debris. This occurs because a strainer typically consists of partially submerged branches, trees, or other debris that create a barrier. While water can pass through the gaps, the structure catches and holds back anything larger that may be caught in the current, which can pose significant risks for individuals in the water.

Understanding strainers is crucial for water rescue technicians, as they often need to navigate or rescue individuals in environments where such hazards exist. Recognizing a strainer can help in devising safe strategies to approach or mitigate the risk associated with it during rescue operations. The other options, such as a dam, weir, and siphon, represent different hydraulic structures or phenomena that do not exhibit the same properties as a strainer regarding the flow of water and objects.