For a losing stream, how does the hydraulic head in the stream compare to the hydraulic head in the adjacent shallow groundwater system?

For a losing stream, the hydraulic head in the stream is higher than the hydraulic head in the adjacent shallow groundwater system. A losing stream, also known as an influent stream, is characterized by water flowing from the stream channel into the surrounding groundwater system. This water movement is driven by differences in hydraulic head, which represents the total energy of water at a particular point. Hydraulic head is expressed as an elevation, typically above a fixed datum like sea level, and it reflects the sum of the water's elevation (elevation head) and the pressure exerted by the water (pressure head). Water always flows from a region of higher hydraulic head to a region of lower hydraulic head. Therefore, for a stream to lose water to the ground, the hydraulic head of the water within the stream must be greater than the hydraulic head of the water in the immediately adjacent shallow groundwater system. The adjacent shallow groundwater system refers to the saturated zone of water found beneath the land surface, directly next to the stream channel, including the water table. This higher hydraulic head in the stream creates a hydraulic gradient that forces water to infiltrate through the streambed and downward into the subsurface, recharging the groundwater. For example, if the water level in the stream corresponds to a hydraulic head of 50 meters, and the hydraulic head in the adjacent shallow groundwater is 48 meters, water will move from the stream to the groundwater.