Data Used Sea Level Change and Its Impact To The Coastal Area of Semarang City, Central Java

3.4.1. Measuring Daily Sea Level Change

One of the important factor affecting sea level change is tidal. Tidal level can be estimate using tides harmonic analyst where on of tools that can deriving realistic tide model is FVCOM Finite Volume Coastal Ocean Model. FVCOM has incorporated the Foreman tidal forecasting program Chens, 2006 to compute realistic tidal elevation data for the initial conditions and on the open boundary. It needs coastline and bathymetry as the data to build boundary of study area. Unstructured triangular mesh has to generate as the basic data to obtain tidal harmonic data as the input for the model. Up to six tidal harmonic constituents can be included in the model. The six included tidal constituents are: 1 S 2 tide period = 12 hours; 2 M 2 tide period = 12.42 hours; 3 N 2 tide period=12.66hours; 4 K 1 tide period = 23.94 hours; 5 P 1 tide period = 24.06 hours, and O 1 tide period = 25.82 hours. The tidal forcing at the open boundary can be specified by either amplitudephase of each tidal constituent. The harmonic analysis is carried out by using a least square fitting. In the second case, true clock time must be specified and the results can be analyzed directly using Foreman’s harmonic analysis program. All of data input must be in the same directory and format so that model can be run. UNIX programing was used to obtain the result of the model while some license software was used to displaying the result. The general step of realistic tidal modeling using FVCOM can be seen in figure 3.2 Figure 3.2. Flowchart for daily sea level change modeling using FVCOM Global and regional sea level rise as the other factor that causing sea level change is taken from research institution. In this research, data of global sea level rise was acquired from CSIRO, regional sea level change was acquired from University of Colorado, and local sea level change was acquired from Coastline Bathymetry Editing Coordinate Transformation Geoprocessing Merge Extraction Extraction Input data UNIX Programing Coordinate Transformation Coordinate Transformation Format Conversion Grid Generation - Create boundary - Define Resolution - Build Mesh - Mesh Quality Control - Interpolate bathymetri based on mesh pattern UNIX Programing Realistic tides model