Hydraulic Capacity Assessment of a Tidally-Affected Reach of the Loxahatchee River by Direct Hydroacoustic Flow Measurements

The Loxahatchee River is a small stream that discharges into the Loxahatchee Estuary on the eastern side of South Florida. The river runs through an environmentally sensitive area where the combination of low flows and tidal influence has been subjecting the coastal ecosystem to harmful salinity concentrations. This paper summarizes the bankfull channel capacity analysis of a river reach subject to tidal influence, conducted in support to the development of the Loxahatchee River Restoration Plan (LRRDP). The analysis is based on direct measurements of discharge and stage at four stations between river mile 11.2 and river mile 14.5. The discharge measurements were made with a four-transducer, 2400-kHz Acoustic Doppler Current Profiler (ADCP) with Janus configuration during low flow and high tide amplitude conditions for about half a tidal cycle. Hydraulic analysis of the stage-discharge relations developed from the data collected at each station during this period allowed us to establish that for low flows during high-range tides, the tidal effect propagates upstream up to river mile 12. As a result, the bankfull channel capacity at all stations downstream from this river station is affected by both the tidal range and the base flow from inland. The field data collected at river mile 11.2 shows that, at high tide, the bankfull channel capacity at this station is about 15 percent less than that during low tide.