Computational techniques for tidal datums handbook.

Abstract

This handbook is intended to provide education and training for both internal and external audiences to NOAA. It presents the National Ocean Service (NOS) methodology for the computation of tidal datums and explains how to use the Center for Operational Oceanographic Products and Services (CO-OPS) water level data and bench mark information available on the internet for tidal datum computations. Fundamental background for tide measurement and data processing is also reviewed. Detailed descriptions of tidal datum procedures, the background mathematical formulas, and example spreadsheets are interwoven in the various sections. The handbook is designed to be both a technical reference and a guidance document for the practical determination of tidal datums using tide gauge measurements. It does not present methods for surveying, or address the problems associated with instrument installation, calibration, data collection, or quality assurance of water level data. Nor does it present specific algorithms for computation, or recommend what software packag es should be used. However, a knowledgeable coastal engineer or scientist should be able to follow the key steps and arrive at the same results posted on the CO-OPS website (http://www.tidesandcurrents.noaa.gov). 1.2 Statement of Philosophy The philosophy of this handbook is that fairly simple, straight-forward examples should be presented. CO-OPS is confident that coastal engi neers will be able to compute datums similar to these “straight-forward” examples using this ma nual. The emphasis is on education and training, illustrated by clear real-world examples of tidal datum calculations. By reading this material, coastal engineers and surveyors will gain an understanding of how to reduce the data that they may have collected themselves, and gain necessary skills to handle more difficult cases. The datum computational methods described in this handbook produce valid datums where the tidal conditions and tide station locations for datum determinati on are straightforward. Difficult cases should be referred to CO-OPS for consultation. These cases might include project areas of rapidly changing tidal characteristics either temporally or geogr aphically, measurements collected during extreme events, cases of poor data, data records with too many gaps, or poor station coverage. Additional special cases that may render the methods not applicable include situations where the astronomic tide is frequently masked by non-tidal effects (such as areas where wind-driven water level variations dominate and areas affected by river runoff); and where man-made structures (such as locks or water gates) affect the water level variations. 1.3 Prerequisite Knowledge The reader will need to possess a mathematical understanding of means, standard deviations, differences, and errors. The reader should posse ss knowledge of suitable computer software such as spreadsheet programs, and have an internet browser and should have some basic scientific knowledge of tides and water levels, and some know ledge of the legal and practical significance of tidal datums (e.g, NOS, 2000).