AWWA Water Treatment Operator Certification Practice Test 2025 - Free Practice Questions and Study Guide

The phenomenon where denser water sinks from the surface toward the bottom of a reservoir is most accurately described by the term "reservoir turnover." This process involves the movement and mixing of water layers within a body of water, primarily driven by temperature and density differences.

During reservoir turnover, warmer, less dense water forms a layer at the surface, while cooler, denser water occupies the bottom. As changes in temperature occur, such as during seasonal shifts, this denser water can sink, creating a circulation pattern that helps distribute nutrients and oxygen throughout the water column. This mixing is crucial for maintaining the health and balance of aquatic ecosystems.

In contrast, the other options refer to different processes. Thermal stratification specifically discusses the layering of water based on temperature, but does not necessarily imply the sinking of denser water. Water renewal refers to the process of replacing water in a reservoir but does not focus on the movement of water layers. The layering effect could describe thermal stratification but lacks the precise focus on sinking denser water that reservoir turnover implies.