EM 1110-2-1100 (Change 1)
31 Jul 03
MATTRESS
A blanket of brushwood or bamboo, poles, geotextile and reed lashed together to protect a shoreline, embankment
or river/sea bed against erosion. Sometimes placed on the sea bed during JETTY construction to prevent stone from settling
into soft bottom.
MEAN DEPTH
The average DEPTH of the water area between the still water level and the SHOREFACE profile from the waterline
to any chosen distance seaward.
MEAN DIAMETER, GEOMETRIC
See GEOMETRIC MEAN DIAMETER.
MEAN HIGH WATER SPRINGS (MHWS)
The average height of the high water occurring at the time of spring tides.
MEAN HIGH WATER (MHW)
The average height of the high waters over a 19-year period. For shorter periods of observations, corrections are
applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. All high water heights
are included in the average where the type of tide is either semidiurnal or mixed. Only the higher high water heights are
included in the average where the type of tide is diurnal. So determined, mean high water in the latter case is the same as
mean higher high water.
MEAN HIGHER HIGH WATER (MHHW)
The average height of the higher high waters over a 19-year period. For shorter periods of observation, corrections
are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value.
MEAN LOW WATER (MLW)
The average height of the low waters over a 19-year period. For shorter periods of observations, corrections are
applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. All low water heights
are included in the average where the type of tide is either semidiurnal or mixed. Only lower low water heights are included
in the average where the type of tide is diurnal. So determined, mean low water in the latter case is the same as mean lower
low water.
MEAN LOW WATER SPRINGS
The average height of low waters occurring at the time of the spring tides. It is usually derived by taking a plane
depressed below the half-tide level by an amount equal to one-half the spring range of tide, necessary corrections being
applied to reduce the result to a mean value. This plane is used to a considerable extent for hydrographic work outside of the
United States and is the plane of reference for the Pacific approaches to the Panama Canal. Frequently abbreviated to LOW
WATER SPRINGS.
MEAN LOWER LOW WATER (MLLW)
The average height of the lower low waters over a 19-year period. For shorter periods of observations, corrections
are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. Frequently
abbreviated to LOWER LOW WATER.
MEAN RANGE OF TIDE
The difference in height between MEAN HIGH WATER and MEAN LOW WATER.
MEAN RISE OF THE TIDE
The height of MEAN HIGH WATER above the plane of reference or DATUM of chart.
MEAN SEA LEVEL
The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from
hourly height readings. Not necessarily equal to MEAN TIDE LEVEL. It is also the average water level that would exist in
the absence of tides.
A-48
Appendix A Glossary of Coastal Terminology
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