Tidal current analysis procedures and associated computer programs.

Abstract

The National Ocean Service (NOS) has been charged with producing tidal current tables for the coastal areas of the United States. Tidal currents are almost always the strongest current experienced by vessels operating offshore and for cons iderable distances inside of bays and river estuaries. Tidal currents are usually fastest where water level fluctuations on wide continental shelfs are amplified as they approach the coast and water is forced through a narrow constricted channel into a large bay or estuary. Knowledge of the timing and strength of tidal currents is extremely important for safe navigation in coastal waters. Mariners are primarily interested in the timing and strength of four phases of the tidal current cycle which are printed in the NOS Tidal Current Tables. These phases are slack before flood (SBF), maximum flood current (MFC), slack before ebb (SBE), and maximum ebb current (MEC). Two other phases are also included in the NOS Tidal Current Tables. These are minimum currents between two successive maximum currents in the same direction and are known as slack flood current (SFC) and slack ebb current (SEC). Although a standardized procedure has developed for analyzing water level data to obtain the parameters required to produce the NOS Tide Tables, there has not been such a procedure developed for tidal currents. This publication se ts forth a suggested step-by-step procedure to follow for obtaining the parameters needed to produce the NOS Tidal Current Tables. This is followed by detailed explanations of each of the computer programs used. These sections are designed to be stand-alone user’s guides for each of the programs, giving a complete explanation of how the calculations are carried out, options to be set by the user, and sample input and output files. Table A indicates the inputs and outputs for the major programs used in the analysis of tidal currents. All the programs are written in FORTRAN.