Part II. CONDUCT OF SAND INVENTORY SURVEYS 



1. General 



Procedure for the conduct of sand inventory projects has re- 

 mained fairly consistent since their beginning. The few significant 

 changes which have been made resulted from experience gained in earlier 

 surveys. In general, the conduct of a particular survey is divided into 

 three phases; planning, exploration, and data analysis. 



2. Planning 



Perhaps the most essential aspect of planning a regional sub- 

 bottom survey is flexibility. Although it is a practice to gather avail- 

 able background data about the survey area to assist the planner, detailed 

 information concerning the continental margins is generally deficient. 

 Once the survey gets underway, new data is generated and a clearer picture 

 of the area emerges. The nevsr data often suggest desirable alterations in 

 the basic plan. To prevent excessive downtime in offshore surveying, the 

 plan should provide means for rapidly making changes. 



Survey planning involves laying out tentative survey tracklines, 

 determining the total survey mileage and the number of cores needed, and 

 scheduling the time needed to complete all field work. It is equally 

 important to schedule the field work at the most favorable season, since 

 offshore operations are especially affected by weather and sea conditions. 

 Existing dredge capabilities and economic hauling distances are significant 

 factors in planning a reasonable offshore limit for the survey. Presently, 

 surveys are terriinated at either of 100-foot depths (MLW) or 10 miles off- 

 shore. The inshore termination depth is controlled by the safe operating 

 depth needed, generally about 15 feet. These limiting conditions are 

 guides only, and are often exceeded where local circumstances permit 

 extension of survey boundaries. 



In laying out survey tracklines, the pattern and density of lines are 

 partly based on the need for sand in the area. If a large supply of sand 

 fill is needed and onshore sources are- limited, a detailed survey will be 

 projected for the area even if information indicates only a marginal prob- 

 ability of finding a good offshore supply. In laying out lines near areas 

 where the current need for sand fill is light, the most detailed coverage 

 is given those regions where information indicates a promise of sand. 



Basic trackline patterns used in the sand inventory surveys are 

 illustrated in Figure A-3. A navigation overlay of a completed survey 



is shouTi in Figure A-2. 



Grid patterns provide the most detailed coverage of an area and give 

 maximum data control. Normal grid spacing is 1 statute mile, however, 

 highly detailed seismic coverage of some sand deposits require much closer 



A-6 



