What factor determines whether a stream is classified as gaining or losing?

A stream is classified as gaining or losing primarily based on the elevation of the water table in relation to the stream surface. When the water table is higher than the streambed, groundwater flows into the stream, making it a gaining stream. Conversely, if the water table is lower than the stream surface, water from the stream can infiltrate into the ground, resulting in a losing stream. This hydraulic interaction between the groundwater and surface water is critical for understanding the dynamics of stream flow and the overall hydrological cycle.

The other factors may influence the stream's environment but do not dictate its classification as gaining or losing. The volume of water in the streambed pertains more to the stream's flow and capacity rather than its relationship with groundwater. The temperature of the water can affect various ecological and biological processes but does not determine the groundwater-surface water interaction; this interaction is fundamentally linked to the elevation of the water table. Vegetation along the stream bank can impact erosion, habitat, and water quality, but it does not have a direct effect on whether the stream gains from or loses to groundwater.