[EFDC+] This is one of the areas where EFDC+ has diverged furthest from the legacy code. Where standard EFDC offers a single surface heat exchange approach with constant coefficients, EFDC+ offers three methods with spatially and temporally varying coefficients plus ice, bed heat exchange, three light attenuation models, and eleven evaporation options, none of which the legacy code simulates.

EFDC+ offers three methods, all supporting spatially and temporally varying heat exchange coefficients and light extinction factors. By comparison, standard EFDC allows only constant coefficients, apart from wind effects.

• Full heat balance: long wave back radiation, latent heat, and sensible heat computed term by term.
• COARE 3.6 bulk algorithm: [EFDC+] added in EFDC+ 12.1. Uses Monin-Obukhov similarity theory to derive turbulent heat fluxes and surface stress from standard meteorological data.
• Equilibrium temperature: the CE-QUAL-W2 approach, condensing seven heat exchange processes into a surface exchange coefficient and an equilibrium temperature.

[EFDC+] How solar radiation penetrates the water column sets where heat is deposited, and EFDC+ gives you three ways to represent it: a one-band Beer’s Law model; a two-band model separating rapid attenuation of red wavelengths near the surface from slower attenuation of blue-green light at depth, with published parameters for Jerlov water types; and a water-quality-linked model in which the extinction coefficient varies in space and time with simulated algae, organic matter, and suspended solids.

Incoming radiation can also be reduced by terrain and canopy shading, by emergent plant shoots, and by ice cover.

[EFDC+] Heat exchange between the sediment bed and the water is small compared with exchange at the air-water interface, so it is frequently neglected but including it measurably improves temperature simulation in deep lakes and reservoirs. EFDC+ provides both convective and conductive coefficients, and bed temperature can be held constant or allowed to evolve.

[EFDC+] EFDC+ implements a robust ice sub-model where ice formation and melt is simulated using the coupled heat model. It resolves growth and melt at both the air/ice and ice/water interfaces and solar transmission through the ice, and is linked to both the full heat balance and equilibrium temperature methods. This feature is not available in other versions of EFDC.

Forced evaporation is the additional evaporation in receiving waters caused by the discharge of heated cooling water. Federal and state agencies now consider it a consumptive use for thermal electric power plants, and EFDC+ has the toolbox to evaluate it in space and time.

[EFDC+] Evaporative water loss is treated separately from evaporative heat flux, with eleven options: none, measured or externally estimated evaporation, the original EFDC latent heat approach, and eight published wind speed functions. Three of those target cooling facilities directly — Ward (1980) and Harbeck (1964) for cooling lakes, Brady et al. (1969) for cooling ponds — alongside Anderson et al. (1954) for large lakes, Webster and Sherman (1995) for lakes, Fulford and Sturm (1984) for rivers, Gulliver and Stefan (1984) for streams, and Edinger et al. (1974) for lakes and rivers.