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Disable Ice Model
External Ice Time Series (ISER & ICEMAP)
Specified ON/OFF Ice Cover
Heat Coupled Ice Model
Heat Coupled Ice Model with Frazil Transport
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Figure 1. Ice module.
The application and operation of each of these options are explained in the following sections.
Use External Ice Time Series (ISER & ICERMAP)
This option does not compute ice formation/melt, and it is not linked to the heat balance. This option simply requires the user to provide a fraction of ice coverage and thickness of ice for every cell using formats provided in Appendix B - Data Formats. The primary impact of the ISICE =1 option is on processes that occur at the air/water interface and has no direct impact on ice melt. For those cells where ice is present, the ice sub-model will:
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For the option ISICE=1, EFDC uses the ISER.INP to read time and ice thickness for externally specified ice cover. However, the ice thickness is not actually used by EFDC. The time series of a flag (0 – off, 1 – on) in the ISER is interpolated between the earlier and later times to the current time. If the flag is > 0.5 then ice is on, and if the flag is < 0.5, then ice is off. The ICEMAP.INP is used for the weighting coefficients of ice thickness in case more than one time series is given in the ISER.INP. ICEMAP with the NISER weightings (the number of ice series) when NISER>1 can be both read and written.
Figure 2. Ice Parameters: External Ice Time Series.
Use Specified ON/OFF Ice Cover
This option is effectively a global toggle so that ice may be turned on or off over the whole domain. The time series file that populates this option lists a date and toggle on and toggle off with the input file ISTAT.INP.
Figure 3. Ice Parameters: Specified ON/OFF Ice Cover.
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Appendix B shows the format for this file. EFDC reads the file and applies it in the same way as ICECOVER.INP. All the other computations are the same as those for ISICE=1, except the initialization is the whole model on or off rather than based on the ICEMAP.INP file. EFDC can also handle multiple ice series and weights based on different series like NISER.
Use Heat Coupled Ice Model
The Heat Coupled Ice Model applies mass conservation during ice growth/melt. Ice is always calculated in the heat coupled ice model, similar to CEQUAL-W2 model upon which the EFDC_DSI ice sub-model is based. This option is most recommended for model simulations of lakes and reservoirs with relatively thick layers. For rivers, this option and the frazil ice option are not fully representative. This is due to the small layer thickness in most river models. Generally, the layers used in rivers are too thin to produce ice. Even though ice crystals form, they are not thick enough to form an ice cover.
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Figure 4 shows the default values of the ice parameters that are required to simulate ice in EFDC+ model. A checkbox is provided for the Use Ryan Harleman Wind Function option if desired.
Figure 4. Ice Parameters: Heat Coupled Ice Model.
ICE.INP is the initial conditions file that is only needed for ISICE = 3 & 4. The format for this file is provided in Appendix B. Note that EFDC assumes the top of the ice is equal to the water surface elevation thereby allowing for higher flows in restricted depth.
Use Heat Coupled Ice Model with Frazil Ice Transport
When calculating ice formation in a river, if the air temperature is less than freezing temperature (a value that may be lower than zero in saltwater), generation of ice crystals takes place in the water. These crystals are called frazil flakes. As the frazil flakes are lighter than water, they float and cause "ice pans" which may then become "ice floes". As the frazil ice rises, it is necessary to input a rising velocity into EE to account for this.
In addition to the modification to the EFDC subroutines outlined for ISICE =3, a new routine, CALTRANICE, is created to simulate frazil ice as a concentration.
Figure 5. Ice Parameters: Use Heat Coupled Ice Model with Frazil Ice Transport.
Visualization
Output from the ice sub-model can be displayed in a number of ways in EE. A 2D plan view of the ice thickness or temperature may be viewed by selecting 2DH View and then add layer Thermal/Ice | Ice Thickness. Figure 6 shows an example of frazil ice formation in a river in Alberta, Canada. Note that initially, ice forms on the river banks where depths are shallower and flow is lower.
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