Contrasting discharge computation methods in riverine and tidal-affected flows in Mississippi

Recent advancements in acoustic science have improved the measurement of real-time flow conditions in complex open-channel flow systems with dynamic channel geometry, velocity distribution and direction, and other gradually varying hydraulic characteristics. In the lower Pascagoula River Basin, a drainage area of about 9,500 square miles in Mississippi, riverine and tidal-affected river reaches exist that exhibit fairly steady flows during and after rainfall runoff events, and unsteady flows during low flow, tidal-affected events. Fairly steady flows can be computed usually within 5 percent by using methods developed by the USGS. Accurate measurement and computation of varied, non-uniform open-channel hydraulic streamflow conditions have historically been difficult or impossible. Acoustic and conventional methodologies to measure velocity in an open-channel riverine and tidal-affected reach have been combined to compute continuous discharge during varied, nonuniform flows by using the relations of stage and area in concert with average velocity and index velocity. Due to the unique flow characteristics on the lower Pascagoula River in Mississippi, an independent means of computing high flows based on conventional methods of a log regression of stage and discharge for a range of stages was also used. The two methods were contrasted and had good correlation. Copyright ASCE 2004.