Swells and waves are not taken into account. These readings are measuring a relatively flat surface, or tidal curve. What's more, tide readings are not taken from the location being surveyed and any interpolation is just that there isn't an actual tide for each sounding.
Further, it is quite difficult to attach and maintain a gauge or staff on the structures that do exist, due to the surf and height of such structures. For one, there are very few hard structures, if any, in the ocean suitable for attaching a gauge or staff. (Middlefield, Conn.).īut there are several problems with measuring tide this way. McKim & Creed uses HYPACK MAX by Coastal Oceanographics Inc.
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These tide readings are entered into a post-processing software program that interpolates between readings and applies the corrected tide to each individual sounding.
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The tide (water level) at the gauge is monitored and recorded at a pre-determined interval, either automatically or by manual readings. Typically, tides have been measured by a tide gauge or a staff attached to a fixed structure or anchored to the bottom, somewhere in the general vicinity of the project. The accurate measurement of tides is extremely important in coastal hydrographic surveys because the origin of all measurements is a point attached to the surface of the water. Tide values vary greatly with geographical location and are affected by up to 37 different forces, including the gravitational forces of the sun and the moon, winds, currents, and the topography and bathymetry of the area. "Tide" refers to the elevation of the surface of the water, disregarding waves and swells. This, in turn, can reduce the cost of the coastal monitoring surveys and provide the accuracy needed for better planning and design documents that can lower construction costs, and ultimately save taxpayers money. McKim & Creed went one step further and proved that, with their systems, the RTK GPS data could be used in real time for heave corrections, eliminating many of the post-processing requirements. The scope of work stated that Differential GPS (DGPS) data be augmented by heave/pitch/roll information to smooth the vertical position in the post processing of the data. In the spring of 2003, in a monitoring survey for barrier island beaches in Brunswick County that included Ocean Isle Beach, Holden Beach and the Shallotte Inlet area, the Corps required that Real-Time Kinematic Global Positioning System (RTK GPS) be used for monitoring water levels. To help them make these determinations, the Corps uses coastal monitoring surveys.Īs part of an indefinite quantity contract with the Corps' Wilmington District, McKim & Creed, a multi-disciplined firm with locations throughout the Southeastern United States, provides coastal monitoring surveys along many beaches of the North Carolina coast. Army Corps of Engineers, the agency studies and monitors many of the nation's beaches to determine coastal nourishment and re-nourishment responses, especially in response to such devastating storms. This area has been hard hit by numerous hurricanes in recent years, including Hurricane Bertha in 1996, Hurricane Fran only two months later, Hurricane Bonnie in 1998, Hurricanes Dennis and Floyd in 1999 and, most recently, Hurricane Isabel in 2003.