p = tidal prism corresponding to the diurnal or spring tide prism 



n = exponent of P 



Jarrett (1976) found that for the same tidal prism A values for Atlantic coast 

 inlets are greater than those on the Pacific coast, citing a difference in wave 

 climate among the contributing causes with the higher waves occurring along the 

 Pacific coast. He hypothesized that the amount of littoral material entering 

 an inlet would be greater there, and consequently the average flow velocity re- 

 quired to maintain Pacific coast inlets would probably be greater. In addition, 

 Jarrett cited differences in the characteristics of the astronomical tides, and 

 errors introduced by computational procedures in determining the tidal prism, 

 as possible causes of the difference in Atlantic and Pacific coast A/P ratios. 

 In all cases, the tidal prism/ inlet channel area relationships were found for 

 inlets where the predominant sediment was sand which was primarily moved as bed- 

 load. Tides were the major factor in controlling flow in the inlets, but long- 

 shore transport resulting from wave and wind action moved much of the sand to 

 the inlet region. 



The regime method, in wnicn a channel in regime is defined as having no net 

 erosion or deposition over a hydrological cycle, has been widely used since 

 Lacey (1929) first proposed the method as a basis for the design of irrigation 

 canals. Regime equations relating to channel cross-sectional geometry are 

 essentially of the form 



L = rqs (2) 



in which L is some length characteristic of the cross section, q is some 

 characteristic unidirectional discharge, and r and s are constants. A num- 

 ber of investigators have applied regime concepts to tidal flow conditions, and 

 Chantler (1974) summarized and reanalyzed some of the data. The characteristic 

 discharge used by the different investigators varied, but was usually some form 

 of "dominant" or maximum discharge. 



2. Approach . 



Past studies indicate that development of a relationship between channel 

 geometry and some measure of the flow through the channel will be a useful ap- 

 proach. However, two problems arise — the first in choosing a characteristic 

 cross section, the other in choosing a flow parameter. In areas of high tidal 

 range, the cross-sectional geometry will likely vary as the slope of the tidal 

 flat and channel varies. The procedure used should, therefore, be adaptable to 

 any cross section. Two flow characterizations have been used in the past. An 

 instantaneous flow is considered in the regime theory. In calculating the tidal 

 prism the total volume of water which passes through the cross section during 

 a specified time period (usually one-half the tidal period) is used. For pre- 

 dictive purposes before harbor construction, the tidal prism approach is better 

 because the prism can be calculated using data obtained from tide and river dis- 

 charge records and topographic information such as may be available on natural 

 channel dimensions. Data on maximum channel discharge rates, especially for 

 tidal channels, are usually unavailable. 



