collected along each of the ADCP transect lines. The areas in which these transect lines 

 were located include the north and south bays, the Intracoastal Waterway (ICWW), the 

 inlet, and on the ebb shoal. Additional bathymetric data were collected between each of 

 the inlet transect lines, many of the north and south bay transect lines, along depth 

 contours in the inlet and ebb shoal, and along the center lines of the bay and inlet channels. 

 These data were collected to aid in the interpretation of the ADCP results, as well as 

 provide information for updating the 1996 SHOALS survey in designated critical areas. 

 The constant presence of swells, particularly in the area of the ebb shoal, made for poor 

 surveying conditions. As a result, the depth soundings recorded the up and down 

 movement of the boat and gave the appearance of sand waves forming on the shoal. The 

 bathymetric data were collected concurrent with the ADCP data collection using a 

 200-kHz Echotrac fathometer. 



These data were corrected to National Geodetic Vertical Datum using information from 

 CHL's Prototype Measurement and Analysis Branch (PMAB) water-level gauges. Time- 

 history plots of the tide data from one of the PMAB water-level gauges during the two 

 ADCP and bathymetric survey periods (August and September) are shown in Plates Al 

 and A2. The PMAB water-level gauge located near the Coast Guard Station in the south 

 bay area was used due to its relative proximity to the inlet. Data are plotted in Eastern 

 Standard Time (EST) for correlation with the ADCP data. The maximum neap tide range 

 during the week of 25 August was 1 .05 m. The maximum spring tide range during the 

 week of 15 September was 1.35 m. 



ADCP Surveys 



ADCP surveys were performed to measure the current distributions (variations across 

 the channel and through the vertical) and discharges in the inlet system. These roving 

 measurements provide a means for obtaining comprehensive information on the spatial 

 variability throughout the inlet system, unlike the more limited in situ gauges (tide and 

 PUV), which provide data on the temporal variability at only a few locations. The two 

 1-week ADCP surveys were conducted during 25-29 August and 15-19 September. These 

 dates coincided with periods of neap and spring tide conditions, respectively. 



An RD instruments Broadband ADCP was used to obtain the velocity magnitude and 

 direction profiles for each transect. This instrument uses a 1, 200-kHz operating 

 frequency. The equipment is mounted over the side of the boat with the acoustic 

 transducers submerged and data are collected while the vessel is under way. 



The ADCP transmits sound bursts into the water column which are scattered back to 

 the instrument by particulate matter suspended in the flowing water. The ADCP listens 

 for the returning signal and assigns velocity to the received signal based on the change in 

 the frequency caused by the moving particles. This change in frequency is referred to as a 

 Doppler shift. The ADCP is also capable of measuring vessel direction, current direction, 

 and bottom depth. Communications with the instrument for setup and data recording are 

 performed with a portable computer using manufacturer-supplied software, hardware, and 



A2 Appendix A Velocity and Discharge Measurements at Ponce de Leon, FL 



