Time to "convergence"?

[Page Weil]

I am building a temperature sensitivity model and want to understand how QUAL2K convergence works.

From what I read in the QUAL2K user manual, the model runs in a "dynamic steady state" and reports min/max results. Also, there is a parameter called "Final Time" that appears to be the number of days that the model runs through before reporting results.

A few questions that were not answered in the documentation:

 - Am I interpreting the "Final Time" parameter correctly?

 - What are the model initial conditions? Does it assume a set flow volume throughout the system and water temperature in timestep 0 and then perturb it based on the relevant physical equations? Does the system start "empty" and then water flows from the input points?

[Dr. Kyle Flynn]

Page - 

 - Final Time. Yes you are interpreting final time correctly. Technically, the model should be run for as long as the residence time of your system, but you should find that the number of days in your simulation will not influence water temperature results as these converge on a single day (note: there are some other variables in the model like benthic algae that take many days to reach steady state) 

 -Model Initial Conditions. These are user specified and are required to support the backward/upstream difference solution scheme (this is the numerical technique for solving for the water temperature for a given element based on the upstream conditions and associated sources/sinks in the element next downstream element). For hydraulics, the volume of each element is computed first under assumed steady state uniform flow hydraulics (using the flow in the headwater boundary condition tab and reach worksheet), and then the governing equation for heat (e.g., Equation 26 in the model documentation) is applied. Due to the steady hydraulics, the volume is  constant throughout the simulation for each element and water temperature is Initialized in all elements as headwater boundary condition and computed based on heat source/sinks in each element. 

Necessary boundary conditions therefore include: the diurnal variation of incoming temperature at the upstream end of the simulated reach (in the Headwater tab), and conditions at the air/water boundary (e.g., air temperature, dewpoint temperature, wind speed, cloud cover, and shade - along with some atmospheric and evaporation information in the Light and Heat tab), and sediment boundary conditions.   

Hope that helps,

Kyle

[Page Weil]

This is very helpful, thank you.