projects > high resolution bathymetric mapping > scope of work
Project Scope of Work
Project Scope of Work 2001
High Resolution Bathymetric Mapping
I. INTRODUCTIONHigh resolution, acoustic bathymetric surveying is a proven method to map sea and lake floor elevations. Of primary interest to the South Florida Water Management District (SFWMD) is the quantification of the present day lakebed in Lake Okeechobee. This information can be used by water management decision-makers to better assess the water capacity of the lake at various levels.
The water levels in Lake Okeechobee are at record low levels this summer (2001) making hydrographic surveying ideal in that less area must be covered by boat to fully map the lake floor. This condition also allows the upper elevations of the lake, which are now exposed, to be mapped by traditional survey techniques or airborne topographic LIDAR technology. Conversely, due to the very flat slope of the lake floor, much of the lakebed is now less than 0.6m (2') deep making surveying by any method very difficult at best.
The U. S. Geological Survey (USGS) has developed a hydrographic survey system specifically designed to map in very shallow water. The system can acquire data in water depths of ~25cm (10"), but in practice boat/motor draft limitations prevent surveying in water depths less than 45cm (18"). Precise differential GPS receivers are used to measure boat position and dynamic elevation, a survey quality 200 kHz depth sounder acquires water depth measurements, and a motion sensor measures heave, pitch, and roll of the boat. A measurement is collected each second or about every 3m (10') along a survey line. The vertical accuracy of the system is +/- 8cm (3") and +/- 4cm (1.6") inches horizontally. To achieve this accuracy, the boat cannot operate more than 20 Km from any one GPS base station. It is anticipated that two GPS base stations will be used for the Lake Okeechobee survey, located probably upon the lake levee. Several new survey benchmarks will be established around the lake perimeter for GPS base station occupation.
Previous reports indicate that a portion of Lake Okeechobee's lakebed consists of fluid mud. This situation is not uncommon in low energy water bodies but does require some criteria on where to define the bottom. It is suggested that some testing be done with the USGS depth sounder compared to penetrometer or other depth measurement devices in order to derive this criteria. The advantage of using a digital depth sounder is that the measured depths will be consistently derived based upon a specific water/mud density.
II. SCOPE OF SERVICESHigh resolution bathymetric mapping will be conducted in Lake Okeechobee by the USGS in cooperation with SFWMD. Survey trackline spacing will be 1000m apart orientated in a north-south direction as depicted in "Exhibit A". A perimeter survey line and several east-west lines will be collected. In addition, random crossing lines will be collected daily. Crossing lines serve to crosscheck and verify the survey. Soundings will be collected along each track line at 3m (10') spacing. A minimum of 1550 kilometers of survey line will be collected. In shallow areas, data will be collected in a minimum of 2 feet water depth except where there is potential damage to the bottom environment or the boat/motors. All sites will be assessed by both parties for safety, access, and other factors, before proceeding with any work.
III. RESPONSIBILITIES OF THE SFWMD
IV. RESPONSIBILITIES OF THE USGS-CCRMS
VI. TIME FRAMEA schedule of fieldwork will be mutually agreed upon, although it is anticipated that fieldwork will begin on or near September 5, 2001. All fieldwork shall finish within 60 days of execution of this agreement. All required deliverables will be provided to the District within 60 days of completion of the fieldwork. All work will be completed within 12 months of execution of this agreement.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:08 PM(KP)