oceanic data set and that, despite the efforts that had gone into North Atlantic 

 hydrography over the last 100 years, the true general circulation was still 

 unknown. Applying inverse theory to model instrument deployment in 

 shallow water and to estimate, before the actual deployment, what types and 

 magnitudes of errors can be expected, promises to be a fruitful line of 

 research. The results may show that fewer instruments will suffice, providing 

 a significant cost savings. On the other hand, the results may reveal that flow 

 in inlets continues to be an under-determined problem and that past instrument 

 practices have been inadequate to define the flow field. 



Analysis of error from various types of current sensors has been the 

 subject of extensive study in the last 30 years. Numerous types of error can 

 occur, both during field deployment of the instrument and during data 

 processing. These can result from instrument calibration, clock time errors, 

 and data recording and playback. In addition, the user is cautioned that each 

 of the many types and brands of current meters is capable of recording 

 accurately only a segment of the spectrum of water motions because of the 

 influence of the mooring assembly, type of velocity sensor used, and record- 

 ing scheme of the instrument (Halpern 1980). Halpern's (1980) paper lists 

 many references that discuss tests of moored current meters. 



Manufacturers of current meters publish accuracy standards in their 

 literature. These standards may be optimistic, especially under the adverse 

 conditions encountered in many coastal settings. In addition, the type of 

 mooring used for the instrument affects the quality of the measured data 

 (Halpern 1978). For these reasons, the user of existing data is urged to obtain 

 as much information as possible regarding the specifics of the deployment and 

 the type of mooring in order to try to assess the accuracy of the results. 

 Ultimately, successful use of current gages is critically dependent upon the 

 planning of the experiment and upon the care and skill of the technicians who 

 maintain and deploy the instruments. 



River discharge 



River outflow has a major effect on some coastlines, particularly where 

 massive deltas have formed (e.g. Mississippi, Nile, Niger, Ganges, Mekong, 

 Indus, Irriwadi Deltas). Even if a study area is not located on a delta, coastal 

 researchers must be aware of the potential impact of rivers on coastal 

 processes, especially if the study region is affected by freshwater runoff at 

 certain seasons or if longshore currents carry river-derived sediment along the 

 shore. 



The physics of unidirectional flow in rivers has been extensively studied 

 for more than a century. It is beyond the scope of this report to discuss the 

 mechanics and procedures of current measurement in rivers, and the reader is 

 referred to texts on hydraulic engineering for methods and additional details. 

 An introduction to riverine hydraulics is provided in Linsley and Kohler 

 (1982). Calculation of river discharge is reviewed in HQUSACE (1959, 



Chapter 5 Analysis and Interpretation of Coastal Data 



103 



