freshwater influx, wind forcing wave setup, and storm surge. Several sources 

 (e.g., Wright and Sonu 1975 and Mobile District 1986) have reported a diurnal 

 astronomical tide in East Pass with a mean range of 0.6 ft and a maximum spring 

 tidal range of 0.9 ft. 



In addition to these sources, the USACE has documented the results of 

 several tide-monitoring efforts including measurements from 1938, 1983-1984, 

 and 1987. These measurements show that the bay's geometry plays a role in the 

 tidal amplitude and phase within the bay as compared with tidal records in the 

 Gulf. The Mobile District report Monitoring Program, East Pass Channel 

 (1986) documents that measured tidal ranges in Choctawhatchee Bay 

 corresponding to 0.5 and 1.5 ft have associated tidal ranges in the Gulf of Mexico 

 of 1.2 and 2.5 ft. These values respectively translate to a 40- to 60-percent 

 reduction in amplitude between the bay and the Gulf. In addition, an estimated 

 5.7-hr phase difference occurs between the tidal elevation in the bay and in the 

 Gulf. These differences are mostly attributable to the bay's large surface area 

 (-122 square miles) and particular channelization. The 1939 U.S. Engineer 

 Office report Study of East Pass Channel, Choctawhatchee Bay, Florida offers 

 the most comprehensive analysis of this phenomenon. The report attributes the 

 reduced amplitude to the large hydraulic resistance through East Pass (mainly a 

 function of the flood-tidal shoal). The report also attributes the phase lag to that 

 part of the bay's tidal inflow that travels along the much longer route to 

 Pensacola Bay via Santa Rosa Sound. 



The two known sources of tidal current measurements are the 1939 U.S. 

 Engineer Office report and the 1992 USACE study (Morang 1992). The 1939 

 report presents the results of float studies performed at various times during the 

 tidal cycle. In the main body of the text, the authors report measured maximum 

 flood velocities of 1.97 and 4.37 ft/sec (two different field measurements) and a 

 maximum ebb velocity of 3.39 ft/sec. In a table found in the report, however, the 

 reported maximum flood and ebb velocities through East Pass — 1.5 and 

 1.7 ft/sec — are presumably based on measurements of the maximum discharges 

 through the inlet and a representative cross-sectional area. Morang (1992) 

 reports the results from field investigations in 1983, 1984, and 1987. Maximum 

 currents measured during flood tide across the inlet were between 4.5 to 

 5.0 ft/sec at the surface and 2.5 to 3.0 ft/sec at the bottom (measured at a distance 

 of 0.2 times the water depth from the bottom). Maximum currents during ebb 

 were between 4.5 to 5.0 ft/sec at the surface and 3.0 to 3.5 ft/sec at the bottom. 



As the literature identifies, only two sources have developed estimates of the 

 tidal prism through East Pass: the 1939 U.S. Engineers Office report and the 

 1992 USACE study (Morang 1992). The 1939 report estimates 1.23 x 10 9 cu ft 

 of water moves through the inlet on flood and 1 .59 x 10 9 cu ft on ebb. These 

 estimates correspond to maximum discharges of 50,000 cfs on flood and 

 53,000 cfs on ebb. The discrepancy between the two is attributed to artesian 

 wells located in Choctawhatchee Bay and freshwater runoff into the bay. 

 Adjacent tidal inlets may also play a minor role. The 1992 study does not present 

 computed estimates of the total tidal prisms. However, it does present graphs of 

 the measured discharge through the pass. Numerical integration of the discharge 

 curves for 16 May 1984 and 16 April 1987 gives flood tidal prisms of 2.49 x 

 10 9 cu ft and 1.25 x 10 9 cu ft, respectively (with maxima of 88,000 cfs and 

 63,000 cfs), and ebb prisms of 4. 16 x 10 9 cu ft and 3.40 x 10 9 cu ft (with maxima 

 of 99,000 cfs and 76,000 cfs). 



Chapter 1 Background and Problem Statement 



