Streamflow measurements indicate that Pololu Stream, which is on the northeastern side of Kohala Volcano, is intermittent, although the stream has previously been interpreted as perennial. The main channel of the stream does not gain water from ground-water sources except at a wetland and shallow pond at the terminus of the stream channel. Ground water in the area is found as high-level dike-impounded ground water in the higher altitudes, as basal ground water in the form of a freshwater lens at lower altitudes, and as perched ground water lying above dike-impounded ground water or the freshwater lens. The water tables of the dike-impounded ground water and the basal ground water are below the altitude of the streambed of Pololu Stream and its tributaries except near the ocean at the wetland and pond area. Two of the three tributaries to the stream are perennial, fed by springs that are possibly perched. These tributaries lose water in their lower reaches and go dry before joining Pololu Stream. The third tributary has flow from a leaking flume in Kohala Ditch; the flow reaches Pololu Stream, flows for about 4,000 feet, then is lost in the lower reaches of the stream.
Streamflow is affected by geology. Where the streambed is composed of a single thick volcanic lava flow, streamflow is maintained, whereas farther downstream streamflow disappears where the streambed is composed of alluvium.
The pond and wetland at the terminus of the stream channel are where the land surface intersects the basal ground-water body. Although the pond is perennial, conditions at the pond can be highly variable. During dry periods, seepage and wave overwash from the ocean, small amounts of rainfall, and springs add water to the pond. During high rainfall, the lower reach of Pololu Stream flows, the lower valley floods, the beach berm erodes, and the pond is transformed into a stream outlet to the ocean.