HOW DO SURFACE WATER AND GROUND WATER INTERACT?
Streams in Hawaii gain water along some reaches and lose water along other reaches depending on local geohydrologic conditions. Where the streambed is above the water table, the stream can lose water. Some streams do not flow continuously to the coast because water infiltrates into the streambed and recharges the ground-water body. Where the stream intersects the ground-water table, the stream can either gain or lose water, depending on whether the water level in the adjacent ground-water body is respectively greater than or less than the water level in the stream. The hydraulic properties of the rocks near the stream affect the rate of flow between the stream and ground-water body. Where stream channels are lined with concrete, interaction between ground water and surface water is unlikely. The upper reaches of many Hawaiian streams are within or near the area where volcanic dikes (thin, near-vertical sheets of massive, low-permeability rock that intrude existing rocks) impound ground
