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Water Level Observations
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What are Water Level Observations?A water level observation is the measured, in-situ (at a given location), surface height of a water body as compared to a given vertical reference level. Vertical reference levels (known as vertical datums) can be established from average local water levels or tied into a nationally defined elevation network. Water level at any given place and time is influenced by a combination of tides and other meteorological effects such as changes in atmospheric pressure and wind. Why is Measuring Water Level Important?Measuring water level benefits society and the environment in many ways. It provides information needed for a variety of management issues including more accurate predictions of coastal flooding by storm surge, aiding emergency managers in planning flood evacuation, tsunami warning, safety and efficiency of marine navigation, particularly minimizing ship groundings, surveying and mapping, dredging and coastal construction, marine boundary determination, tide predictions, oceanographic research, climate research, and absolute sea level monitoring. Who Uses Water Level Observations?Water level observations are used by many sectors of the community including coastal zone managers, coastal engineers, ports and navigation personnel (maritime operations), recreational boaters and fishermen, and researchers (oceanographic modelers and climatologists). SEACOOS near real-time water level observations serve the needs of these diverse groups by providing data in formats traditionally used by each. Mariners navigating coastal waters are expected to consider local water level observations and tidal current predictions, sea-state, and predictions of marine weather. Scheduling of a vessel may be adjusted so that the estimated time of arrival coincides with the most favorable conditions. Mariners make use of local nautical charts for decision making in navigating in a coastal region. The predicted heights of tides from tide tables are referenced to a chart datum on the local nautical charts - Mean Lower Low Water (MLLW) for US Coastal waters. Planning for and responding to natural disasters such as coastal flooding due to storm surge and flash floods due to local storms is the responsibility of Emergency Management Agencies (FEMA or state). The vertical datums (known reference levels for elevation) of interest may be North American Vertical Datum of 1988 (NAVD88), National Geodetic Vertical Datum of 1929 (NGVD29), or local Mean Sea Level (MSL). Physical, biological, and chemical modelers who use hydrodynamical models (tools that predict how water moves) to predict tides, water levels, storm surges, and tsunamis, evaluate and calibrate the accuracy of their sea surface height fields with observed water level data. The vertical datum of interest may be Mean Sea Level (MSL). What is unique about this tool?SEACOOS collects water level observations from different sources, developing the spatial resolution needed for a comprehensive view of nearshore and offshore water levels. Water level observations are reported in near real-time along with their vertical offsets to 3 common vertical datums: MSL, MLLW, and NAVD88. These datums cover most applications relevant to the three user groups previously mentioned. Regardless of the datum shown, what is truly unique about this tool is the aggregation of many disparate observations, acquired in different ways, from different agencies and institutions. The ability to view real-time observations, from across the region, relative to both chart and model reference levels is an extremely powerful tool for those who need accurate and extensive water level measurements. More Water Level Info • Interactive Map Tutorial
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