What indicates that a stream is experiencing base flow?

A stream is considered to be experiencing base flow when it maintains a consistent volume of water, which typically supports various forms of life, including aquatic organisms. The presence of these organisms suggests a stable and continued water supply, which is crucial for their survival. Aquatic organisms, such as fish and invertebrates, thrive in environments where water is available all year round, indicating that the stream is not only full at times but also has a baseline flow that sustains its ecosystem during drier periods.

In contrast, the presence of terrestrial plants alone may not be a reliable indicator since they can grow in a variety of conditions and might not specifically require constant aquatic conditions. The absence of water suggests that a stream is not experiencing base flow but rather is dry, which would not support aquatic life. Highly variable water levels would indicate fluctuating conditions that are inconsistent with a stable base flow, as a true base flow would contribute to a steady streambed level conducive to habitation by aquatic organisms. Thus, the identifying characteristic of base flow is the continued presence of aquatic organisms.