Velocity Exponent Research Articles

Laminar flow in the Honolulu aquifer

It has commonly been found that the flow of ground water through natural aquifers is laminar, with discharge in linear proportion to hydraulic slope. High permeability of the Honolulu aquifer and the large amounts of water derived from it in single wells have led engineers and others to consider whether some of the flow might not be turbulent. In earlier studies, distinction was not made between head loss very close to the well and that at greater distances, with the result that turbulent flow in, the aquifer was thought to exist, and values of the velocity exponent, N, were calculated as distinctive of particular parts of the aquifer. The present study shows that turbulent flow is found within the first few feet of large wells at large rates of discharge, but that such flow is quite restricted, and that it is incorrect to deduce a value of N differing from unity as characteristic of the aquifer rock itself. The study shows that flow under all known natural conditions is laminar, thus with N equal to unity, and that all calculations of seaward or lateral leakage or transfer under natural head differences should be made on that assumption. Any deviations in the direction of turbulent flow are characteristics of the operating station or well at high discharges, and invade the rock only for very short distances.