Water Level Determination for Transportation Projects: Mean High Water Manual

摘要

To ensure proficient network management and safe usage of navigable waterways especially in waters that are subject to tides, it is essential that the height of the water at various tidal phases be known. This knowledge is also essential for property ownership determination and for construction projects in areas that are subjected to tidal waters. Construction applications that require the knowledge of various tidal water levels include determination and implementation of bridge clearances, design of caissons, cofferdams, fenders, and weep holes. Bridge clearances are calculated from tide observations, tide predictions and an assessment of the size of vessels expected to travel beneath them. Additional considerations that are to be addressed during bridge construction are minimum underclearances necessary to operate construction equipment, the season of construction and its effect on the water level, regulatory requirements of agencies such as the US Coast Guard, etc. Water levels and clearances are expressed in terms of elevations in a particular height system. To avoid implementation errors, it is essential that proper research, analysis, methods and procedures be exercised prior to construction to ensure that a consistent height system is being used. Insufficient determination of the current water levels and misunderstanding of height systems could become a public safety problem and/or result in property damage or damage to the integrity of the transportation network. The objective of this manual is to establish a uniform NJDOT procedure for determining water level as applied to safety, construction projects, and bridge clearances determination in tidal areas. It includes an introduction to the phenomena of tides, discussions on tidal and vertical datum, legal issues of tides, and methods for establishing the mean high water (MHW) at a construction site. The manual includes a detailed outline of a MHW study that consists of planning, observation sessions, data reductions, computations, quality assessment of the established MHW and documentation of the established MHW. NJDOT consultants and in house staff should use the manual as a general reference for work in areas subject to tidal waters.