Bathymetry

Users often require to assign constant or spatially varying values across the entire model domain or within subsets for a variety of water column, sediment, and other spatially variable parameters and concentrations. The form used to assign the initial bathymetry conditions is shown in Figure 1.

There are two approaches for setting the Initial Bottom Elevation. Using the approach familiar to earlier users of EEMS, model bathymetry can be assigned from measured data using the Assign button. A new option available with EE10 is to download data from an online open-source site. These options are described further below. 

Regarding the Adjustment (Legacy) option, EE allows users to make changes to older (legacy) models whose functions have been superseded by changes in the EEMS modeling system. It is not recommended users edit these fields unless they need to maintain consistency with some legacy model.

Figure 1. Initial Conditions: Bathymetry. 

Apply Cell Properties: Bottom Elevation

After click on the Assign button (Figure 1), the Apply Cell Properties: Bottom Elevation form will be displayed as shown in Figure 2.

Grid Options frame:

In this frame, the user defines the number of grid cells of the model domain that will be assigned bottom elevation values by choosing options All grid cells or Only grid cells inside polygons. In case the Only grid cells inside polygons option is selected then the Add File button of the Polygon Files frame below will enable allow the user to browse to the existing polygon file. The file can be in *p2d or *.dat formats that contain one or more polygons.

Values to Set frame:

In this frame, with the Constant option, the user needs to enter a value in the text box. It means all defined cells of the model will be assigned a constant value. Another option is Scatter(XYZ) data which requires the user to upload a measured or an otherwise determined data file (in *.dat format) to assign to the model cells.

Interpolation Options frame:

Regarding interpolation approaches, there are four methods as shown Figure 2, these include centroid interpolation, average value, maximum value, minimum value.

Centroid Interp: Use this option if the topographic data is relatively sparse as compared to the grid. This approach uses the inverse distance interpolation scheme to compute the elevation at the X and Y of the cell centroids.

Avg. Value: Use this option if the topographic data is very dense, relative to the grid.

Max. Value: This option scans the data and applies the maximum value for any data points located inside the model cell.

Min. Value: This option scans the data and applies the minimum value for any data points located inside the model cell.

Finally, the user needs to click the Apply Defined Conditions button to proceed with the bottom elevation assignment.

 Figure 3 is an example for assigning the bottom elevation of cells inside the polygon with the data file. The format of the polygon data file is described in details in Appendix Data Format B-1 Overlay P2D Polyline / Polygon File.

Figure 2. Apply Cell Properties.

Figure 3. Bottom elevation assignment by using polygon and data file.

Download Online Data

EE10 supports the download of online bathymetric data from open-source data sets by clicking on the Download button (Figure 1), the Download Online Data form will be displayed as shown in Figure 4. Users are able to select data set from using the drop-down Data Set. The currently available open-source sites are:

• GEBCO 08: a continuous terrain model for ocean and land with a spatial resolution of 30 arc-seconds released by the General Bathymetric Chart of the Oceans (GEBCO) in 2009. Bathymetric data is available to download and the user manual can be found on the website GEBCO 08.

• GEBCO 2014: the updated version of GEBCO 08. The data information can be found on GEBCO's website GEBCO 2014.
• ETOPO 1: a 1 arc-minute global relief model of Earth's surface that integrates land topography and ocean bathymetry. It is developed by National Oceanic Atmospheric Administration (NOAA) and the data information is provided on its website ETOPO1. 

Depending on the data set selected, different data information is provided in the Spatial Information section. The Data Extraction Limits is auto-set to the whole model domain, but the user can manually select the specific area by checking to Using Polygon File and browser to the closed polygon that contains the area inside.

Click on Download button and EE will download and apply the latest bathymetry data of the selected Data Set to the whole model or specific defined area. The user can also save the extracted data to a file if needed by checking on Save Log File checkbox before downloading. 

Figure 4. Extract Online Data.