Hydraulic Model Studies for Whiting Field Naval Air Station

The Naval Auxiliary Air Station, Whiting Field, is to have a stormwater disposal system in which the existing pipes and terraces under and in the vicinity of the runways and building area will discharge into paved trapezoidal open channels. Many of the channels join other channels as they pass down the sides of the plateau on which the airfield is located. The grades of the main channels and of many of the lateral channels are such that water flows at supercritical velocities or at velocities greater than that of a gravity wave. The difficulties anticipated in joining two streams of water, one or more of which is flowing at supercritical velocities, led to the request for model studies of several of the channel junctions. The primary objectives in the present study include (1) the development of junction designs for specified operating conditions which would result in reasonably smooth flow downstream of the junction and (2) the determination of the necessary wall heights in the vicinity of the junction. Economic and structural considerations involved in the junction designs were considered in the final selection. Dependent upon the junction design, the discharges, velocities, and related phenomena of the flow in the vicinity of the junction, a hydraulic jump may form in one or both of the inlet channels. This may necessitate a large increase in the height of the sidewalls in the vicinity of the junction. On the other hand, if the flow passes through the junction at velocities greater than the critical, standing waves may form which have a height greatly in excess of a normal freeboard and which continue to oscillate back and forth across the channel for a considerable distance downstream from the junction before being damped by frictional forces. These standing waves necessitate higher sidewalls not only in the vicinity of the junction but for a considerable distance downstream. As available information on junctions of this type is almost nonexistent, it was necessary to resort to model studies in order to determine the flow conditions and the minimum sidewall heights. Two general types of junctions were studied. One type consists of the junction of two large channels in which the lateral and inlet main have comparable discharges. The other type, called terrace outlets, consists of a junction between a main channel and a terrace channel having a relatively small discharge. The maximum discharge ranges from 380 to 960 cfs in the main channels and from 25 to 70 cfs in the terrace channels. The maximum velocity of flow encountered is approximately 30 fps.