The Surface Heat Exchange
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tab contains the Main Heat Exchange Options and is where the user sets the Surface Heat Exchange Sub-model as showninFigure 1. This drop down list now contains six options, one more than previous versions of the EFDC_Explorer Modeling System. The user will note that the Settings button is no longer provided. These settings have been moved to more appropriate places, adjacent to the option that requires these setting to simplify the modeling process. Only settings which are relevant are now provided in the Surface Heat Transfer Coefficient Frame and in the Light Extinction Coefficients frame, depending on which option is selected. For example, if sediments are not being simulated the Light Extinction for TSS is hidden as not applicable.
The options for the Surface Heat Exchange Sub-model are now:
- No Atmospheric Linkage
- Full Heat Balance (Legacy)
- External Equilibrium Temperature
- Constant Equilibrium Temperature Coefficient
- Equilibrium Temperature (CE-QUAL-W2
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- Method)
- Full Heat Balance with Variable Extinction Coefficient
These options are described further below.
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Note that to activate the heat sub-model in EFDC, the temperature constituent must be activated (Active Modules | Sub-Model Computational Options | Details). The ASER.INP file must be used for all of the thermal sub-models to compute the surface and bottom heat exchange processes. Depending Also, depending on whether the current model is EFDC_GVC or EFDC_DSI+, the EFDC_Explorer form will have different options shown in the Main Heat /Temperature frame. The following provide an overview of the approaches.
The EFDC_GVC model uses a new thermal bed model to determine the bed/water column heat exchange (Tetra Tech, 2007c). A sediment thermal thickness is assigned for the entire model. This thickness is not related to either the sediment transport model's bed or the water quality sediment bed. This thermal layer is then divided into KBH layers (must be >2). A constant initial bed temperature can be used or alternatively the TEMPB.INP file can be used to assign a spatially variable initial temperature, by layer. Check the Use TEMPB.INP checkbox in the Bed Thermal Options frame for this option.
The EFDC_DSI version of the model has two different approaches for the bed heat sub-models. If the standard EFDC full heat balance (ISTOPT(2)=1) sub-model is used, the water/sediment bed heat exchange model of the pre-GVC version is used. If the user has selected the equilibrium temperature sub-model (ISTOPT(2)=4) then the bottom heat exchange is computed using the heat exchange coefficient and the user can assign spatially varying sediment thicknesses and initial temperatures using the TEMB.INP file.
Various atmospheric parameters can be adjusted using the Settings button in the Heat/Temperature form. An example of the Atmospheric Parameters values box is shown in Figure 1. The parameters shown in Figure 1 change slightly depending on which heat sub-model is being used.
Exchange Options frame.
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Figure 1 Atmospheric Parameters.
The Full Heat Balance with Variable Extinction Coefficient option was added in EE8.2 and provides the user with the option of allowing light extinction to be dependent on the total suspended solids in the water column, thereby making light extinction temporally and spatially varying. The extinction factors are determined on a cell by cell basis for each time step based on TSS, and if the water quality model is active, based on POM, DOM and Chlorophyll-a as well.
With this option the user may also set the evaporative and convective heat transfers to be impacted by the wind speed. The user should select the appropriate check box for the Vary with Wind Speed option, and then ensure a correct setting for the heat transfer coefficient for each option.