Department of Natural Resources MARYLAND GEOLOGICAL SURVEY Emery T. Cleaves, Director COASTAL AND ESTUARINE GEOLOGY FILE REPORT NO. 01-2 Bathymetric Survey of Assawoman Bay, St. Martin River, Sinepuxent Bay and Newport Bay by Darlene V. Wells and Richard A. Ortt, Jr. Submitted to Fisheries Services Department of Natural Resources in fulfillment of Contract #AR-00-020 Draft June 2001 Bathymetric Survey of Assawoman Bay, St. Martin River, Sinepuxent Bay and Newport Bay Executive Summary The Maryland Geological Survey, under contract with Fisheries Service, Maryland Department of Natural Resource, conducted hydrographic surveys in Assawoman Bay, St. Martin River, Sinepuxent Bay and Newport Bay. The purpose of the study was to provide a consistent bathymetry data set that may be used in other scientific studies. The hydrographic surveys were collected in May and June 2000, using differential global positioning service (DGPS) techniques and digital dual-frequency echo sounding equipment. Hydrographic survey lines were spaced 200 meters apart and extended from shore to shore. Five hundred kilometers of hydrographic records were surveyed and over 500,000 discrete soundings were recorded. In addition to the hydrographic surveys, water level data were collected at 10 different sites within the study area. The water level data were used to correct the echo sounding data for tide and wind offsets. Sounding depths were adjusted to North America Vertical Datum of 1988 (NAVD88) and are listed in ASCII XYZ (northing, easting, depth) format. Location coordinates are in UTM, NAD83. The adjusted sounding data were used to generate 10-meter, regularly spaced grids for the four sub-basin areas and bathymetry (depth contour) map were created from the gridded data. The XYZ data, metadata, and maps are presented on CD-ROM. ii Table of Contents Introduction......................................................................................................................................1 Previous bathymetric surveys ..........................................................................................................2 Study area.........................................................................................................................................3 Methods............................................................................................................................................5 Study approach.....................................................................................................................5 Hydrographic surveys ..........................................................................................................6 Depth determinations ...............................................................................................6 Horizontal positioning .............................................................................................9 Data recording..........................................................................................................9 Water level measurements .................................................................................................10 Elevation determinations of water level recorders.................................................14 Water level data reduction and tide analyses.........................................................15 Hydrographic survey data processing................................................................................15 Depth data filtering ................................................................................................15 Sounding depth adjustments ..................................................................................15 Gridding techniques for bathymetry model...........................................................17 Data accuracy.........................................................................................................17 Discussion......................................................................................................................................17 Bathymetric grid ................................................................................................................17 Overview of the bathymetry of the northern Coastal Bays................................................17 Tides...................................................................................................................................18 Applications of bathymetry and tide data ..........................................................................21 Recommendations for future work ....................................................................................21 Acknowledgments..........................................................................................................................21 References cited .............................................................................................................................23 Appendices A. QA/QC ........................................................................................................................A1 1. Echosounder depth calibration..........................................................................A1 2. Elevation determinations of water level sensors-Vertical control....................A3 3. Post-Processing Data- GPS Surveys ...............................................................A17 B. Knudsen operating parameter settings ........................................................................B1 C. MathCAD splining process for interpolating water level adjustment .........................C1 D. Final XYZ sounding data on CD ................................................................................D1 iii List of Figures Page Figure 1. Study area.................................................................................................................4 Figure 2. Track lines for hydrographic surveys collected north of Ocean City Inlet..............7 Figure 3. Track lines for hydrographic surveys collected south of Ocean City Inlet..............8 Figure 4. Example of echogram produced by Knudsen software .........................................10 Figure 5. Locations of water level recorders and tide gauges used in this study. .................12 Figure 6. The graph showing the change in tide range and tidal phase progression (time lag) with distance from Ocean City Inlet (Marsh Harbor). ..........................16 Figure 7. Plots of water levels from recorders in Sinepuxent Bay........................................19 List of Tables Table 1. NOAA hydrographic data summary........................................................................2 Table 2. IHO Classification of Surveys (IHO,1998) .............................................................5 Table 3. Information on water level recorders and tide stations used in this study.............13 Table 4. Comparison of tide station mean water levels (MWL) elevations in NAVD88 determined by GPS and traditional differential leveling.......................14 Table 5. Comparison of preliminary tide datums for water level recorders operated in Assawoman and Isle of Wight Bays ..................................................................20 Table 6. Comparison of preliminary tide datums for water level recorders operated in Sinepuxent Bay..................................................................................................20 Table 7. Regression analysis of calibration data for Knudsen echosounder.......................A1 Table 8. Elevation leveling data for the water level recorder installed on a private bulkhead in Keenwick Community, in Delaware .................................................A3 Table 9. Elevation leveling data for the water level recorder installed on the Ocean City Recreation Pier (125th Street, Ocean City) ....................................................A4 Table 10. Elevation leveling data for the water level recorder installed on steel bulkhead, southeast point of Isle of Wight ...........................................................A5 Table 11. Elevation leveling data for the water level recorder installed on piling at the Hudson Boat Marina (Holiday Harbor) in St. Martin River ...........................A6 Table 12. Elevation leveling data for the water level recorder installed private bulkhead in Bayshore Estates in Ocean City (~27th Street)..................................A7 Table 13. Elevation leveling data for the water level recorder installed on the community pier in Marsh Harbor Marina.............................................................A8 Table 14. Elevation leveling data for water level recorder installed on a private bulkhead in Snug Harbor ......................................................................................A9 Table 15. Elevation leveling data for the water level recorder installed on the Rum Point community dock in Sinepuxent Bay..........................................................A10 Table 16. Elevation leveling data for the water level recorder installed on the bulkhead at the South Point boat ramp ...............................................................A11 Table 17. Elevation leveling data for the water level recorder installed on a private dock Newport Bay..............................................................................................A12 iv Page Table 18. National Geodetic Survey vertical control bench marks used as check points during GPS surveys ..................................................................................A13