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{Model Implementation}

To implement the geometric model in ArcView, the NOAA Coastal Services Center worked with the Oregon Department of Land Conservation and Development (DLCD) to parameterize many of the variables in the formula. Below is a detailed explanation of the calculations performed by the Dune Hazard Assessment Tool.

The parameters involved in the calculation are:
h T MSL Greek beta HJ HC Greek alpha R Y
Significant Wave Height (feet) Wave Period (seconds) Mean Sea Level (feet) Beach Slope (degrees) Dune Toe Elevation (feet) Dune Crest Elevation (feet) Angle of Repose (degrees) Recession Rate (feet/year) Planning Period (years)

Significant wave height, Wave period, and Mean Water Level are embedded in the Storm Event Magnitude drop-down list in the Dune Hazard Assessment Modeler application. All other parameters are derived from choices or entries made by the user.

The formulas used are:
S1 = (h*(5.1*(T*T)))*tan(Greek beta)
RunUp = 0.27 * sqrt(S1)
TotalWaterLevel = RunUp + MSL
Sdune = (TotalWaterLevel - HJ)/tan( Greek beta)
D = (HC - HJ)/tan( Greek alpha)
DHZ =Sdune + D + (R*Y)

where:
Sdune = the total horizontal extent of wave undercutting projected to occur during a designated storm event or cluster of storm events (feet);
D = the dune topographic stability factor (feet);
LR= the average annual rate that the shoreline is projected to migrate landward due to sediment budget considerations (feet/year);
DHZ = the distance the dune is calculated to erode given the above parameters (feet).

Note:
0.27 is an empirically derived dimensionless constant.
5.1 is a constant with units of 1/seconds².
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