Water age calculation formula

Hello, I have several questions about the “water age” module of EFDC:
1.what is the specific formula for “water age” calculation in version EE7.0 ?
2.When calculating the “water age”, the longer the model running time, the larger the “water age”. How to set the model running time and correctly evaluate the “water age”?

For your first question, EFDC uses a dye proxy to calculate age of water. You can find the formula used in EFDC for age of water in section 4.2 here:

Regarding your second question, it is not clear. Can you explain further?

When I simulate the water age of a area, if the model running time is set to one year, the water age is about 360 days; If the running time is changed to 2 years, the water age will be about 680 days. If the running time of the model continues to increase, the water age will continue to increase. When will the water age calculation reach equilibrium? How to determine the final value of water age during analysis? Or is the water age generally limited by how long the simulation time is

This indicates your system does not have appreciable boundary conditions for inflow or outflow so the model does not reach a steady state, then the water age will continue to increase with your run time. Where inflow and outflow are higher you will expect to see the water age reach equilibrium."