PHYSICAL
PROCESS VARIABLES
The relative
sea-level change variable is derived from
the increase or decrease in annual mean water elevation over time
as measured at tide gauge stations along the coast. The rate of sea-level
rise is 2.65 +/- 0.10 mm/yr and 2.59 +/- 0.12 mm/yr in Boston Harbor
and Woods Hole, based on 79 and 68 years of data, respectively (Zervas,
2001). This variable inherently includes both eustatic (global) sea-level
rise as well as regional sea-level rise due to isostatic and tectonic
adjustments. Relative sea-level change data are a historical record,
and thus only portray the recent sea level trend (<150 years).
Relative sea-level rise for CACO (2.59 - 2.65 mm/yr) fall within moderate
vulnerability.
Mean Significant
Wave height is used here as a proxy for wave energy which
drives the coastal sediment budget. Wave energy is directly related
to the square of wave height;
E = 1/8 ρgH2
where E is energy density, H is wave height, ρ is water density and
g is acceleration due to gravity. Thus, the ability to mobilize and
transport beach material is a function of wave height. In this report,
we use hindcast nearshore mean significant wave height data for the
period 1976-95 obtained from the U.S. Army Corps of Engineers Wave
Information Study (WIS) (see references in Hubertz et al., 1996).
The model wave heights were compared to historical measured wave height
data obtained from the NOAA National Data Buoy Center to ensure that
model values were representative of the study area. For CACO, mean
significant wave heights range from very high to moderate risk.
Tide
range is linked to both permanent and episodic inundation
hazards. Tide range data were obtained from NOAA/NOS for three ocean
tide stations along Cape Cod; the values were contoured along the
park shoreline and mapped to the 1-minute grid cells. Most of CACO
has a tidal range between 2 and 4 meters (moderate vulnerability),
but a small portion of the outer Cape is between 1 and 2 meters (high
vulnerability).
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