Water Level

The user can choose to define the time series for the water level in three ways. 

1. Paste/ import data from ASCII data files as introduced in External Forcing Data.
2. Select the Generate from Harmonics to generate a time series computed as astronomical tidal forcing, as highlighted in Figure 1
3. Download the data from online open sources by using Download Online Data feature 

Option 2 - Generate from Harmonics

Figure 1. Boundary Data Series form for Water Level.

The basic formula for the oscillation of water level due to astronomical tides is based on the combination of the tidal constituents as follows:

In which

η = tide level (m)

z₀ = mean sea level above the datum (m)

f_i = nodal coefficient to adjust amplitude for the i^th component

H_i = amplitude of the i^th component (m)

ω_i = speed or angular velocity of water for the  i^th component (radians per second)

t = time (s)

(V₀ + u)_i = astronomical arguments of the i^th component

g_i = phase lag of the i^th component from Greenwich longitude

It should be noted that the units used in EE can be changed to be convenient for the users.

The Astronomical Tides provides the ability to generate pressure time series from astronomical tidal forcing. The user must first define a New station. Afterward, the user can add constituents (identical to the process in Harmonic Tides ) and then input the constituent parameters (name, amplitude, phase) or import them from a data file if available. 

The user can change units for amplitude and phase, apply a datum shift (z_o) in meters or time shift in hours to the series. 

Figure 2. Astronomical Tides form.

Download Online Tidal Harmonics for a Specific Location

Instead of manually adding (or importing) a constituent and entering the constituent parameters, online data can also be applied using the Download button. Figure 3 shows the Download Harmonics form.

To download constituent data, the station must first be defined in the Selected Location frame. The station name should be entered by the user along with the longitude and latitude of the station. This must be precise enough for accurate constituent data to be downloaded. Next select Add to add the station to the List of Locations. More than one station can be added. A highlighted station in List of Locations frame can be removed from the list with the Remove button or replaced with the Update button. The user can also load/save this data set for further use with the Load and Save buttons. The phase lag of the harmonic constants is referenced to zero UTC, so the user may need to change the time shift to adjust for the local time of the model. Once everything is ready, the user can click the Get Data button to download the online data for all the stations in List of Locations. The generated water level data series will be populated to the Water Level group in External Forcing Data and can be used for model boundary conditions.

Figure 3. Download Harmonics form.

Option 3 - Download Online Data 

On the main form, open Tools | Download Online Data | Model Open Boundary Conditions as shown in Figure 4.

Figure 4. Open Download Online Data feature for Open Boundary Conditions.

In Download Online Data for Open Boundaries form choose the Boundary and corresponding Data Type to be downloaded. Next, click the Get Times button to get the time range available for this data set. The model timing is then automatically updated here. However, it is recommended to extend Time Begin and Time End to cover the model time and remain within the data set time range. Set the Time Zone and click on Get Data to download (Figure 5).  This operation can take some time, depending on the time range that the user is downloading. Once the operation is finished, click OK. EE will automatically create and assign time series to the corresponding boundary condition. 

Figure 5. Download Online Data for Open Boundaries form.