III. SURVEY PLANNING 



1. Amount of Data . 



The amount of data to be collected depends on several variables: dimen- 

 sions of the geographic area to be surveyed, zones within the survey area 

 where more detailed subbottom information is desired, and most important, the 

 survey budget. It is good policy to investigate the possibility of existing 

 data in the area of interest which might compliment or even reduce the amount 

 of data needed for the survey. This can be done by contacting other agencies 

 (e.g.. National Oceanic and Atmospheric Administration (Sea Grant) and U.S. 

 Geological Survey) and universities involved in coastal research and also by 

 conducting a literature search. 



Predetermined seismic survey tracklines are laid out, usually in two basic 

 trackline patterns, on a hydro graphic chart to sufficiently cover the survey 

 area. The grid-line pattern is used to cover areas where more subbottom detail 

 is required; e.g., areas suspected of containing desirable quantities of sand. 

 In areas where the subbottom geology and bottom topography are suspect of a 

 high degree of variability, the grid should be more closely spaced, i.e., 0.5- 

 mile (0.8 kilometer) spacing. The grid lines may be spaced at greater inter- 

 vals, i.e., 1-mile (1.6 kilometers) spacing if the subbottom geology and bottom 

 topography illustrate a low degree of variability. One or more shore-parallel 

 or a zigzag reconnaissance line usually provides sufficient coverage between 

 the grided survey areas. This pattern, in many cases, will illustrate buried 

 stream channels or other subbottom structures which might require further in- 

 vestigation (see Fig. 2). Tracklines should be plotted on navigation charts 

 which show hazards to navigation so that these hazards can be avoided by the 

 survey vessel . 



Depending on the degree of variability of the subbottom geology and the 

 bottom topography, the ratio of cores to seismic trackline mile should range 

 from 1:6 (1 core per 6 trackline miles) to 1:10; i.e., the higher the degree 

 of variability the higher the core to trackline mile ratio (Williams and 

 Duane, 1972). Preliminary core locations may be selected while plotting the 

 tentative seismic tracklines; however, final site selection should be based 

 on the results of seismic records. Core sites should be selected as close 

 as possible to the seismic lines so that the cored sediment can be correlated 

 with the seismic reflectors. For this reason, the positioning system used 

 requires a high degree of accuracy. Core site selection also depends on the 

 results of visual observations during collection of the cores. Where possible 

 it is advantageous to select core locations in a grided area at the intersec- 

 tion of seismic profile tracklines or where the seismic reflectors are near 

 the surface of the sea floor. This enables correlation of the seismic infor- 

 mation and cores which can then be extrapolated laterally. 



2. Field Data Collection . 



A well-developed data collection plan will yield the maximum amount of 

 data for the least expenditure of time, effort, and money. The cost of field 

 data collection in most cases will absorb the greatest percentage of the total 

 project costs which includes data reduction and analysis and report writing. 

 One item which must be considered in the development of the data collection 



