Age ( maximum) and Travel Time

Hello RSP,

I assume you will agree that travel time is a constant value for fixed velocity and a given length of pipe. So, if a pipe has velocity of 3 ft/s and length of 30 ft, the travel time for the mass is10 sec. Now, this number remains constant as long as the pipe length and the velocity remains constant. If we look at the water age it could vary. Water age for that section of pipe could be 4 second, just an example (if we look at results after 4 second of simulation) or it could be lot higher if the water has already aged (received water with a higher water age)

So, the travel time and age are related but not the same.

If you could send us your model and let us know where the elements/scenario you are looking at then we can look into the model. To upload the model, please click on upload in my signature.

Hi Akshaya thanks for the response. I am facing problems in the procedure for uploading my model. If you provide your email id i can forward the model for the further review.

Thanks,

RSP.

RSP,

I got your model and looked at it. All the water is being supplied from a reservoir which has fresh water i.e. age = 0. (I noticed all your tanks are inactive)  Since, a fresh water is being pumped to the system the water age in the network is relatively short around 7 hrs in an average.

Best way to see water quality results is by creating some color-coding on Age (Calculated), and opening up Time Result Browse ( from Analysis menu) and changing the time to update the element colors. For specific element, it's good to look at the graph.

Here's one of the graph:

If water goes into the tanks, stays there for some and that water from tank is distributed to the network then you will see some higher age. With the current model set up all water ages are less than 10 hrs except 3 nodes and I am not surprised with that.

Dear Akshaya,

Thanks for the response. My basic doubt is again in AGE calculation. ie my client was asked us to do age calculation as per the model. Now, which AGE valve i need to show to client as actual water AGE, AGE in node or AGE in pipe. Since, these two ages are having different values.

For Example, in pipe P-685 AGE maximum is 23.8 hrs, but in junction j-51 - age is 2.44 hrs and at J-34 is 2.3 hrs. why?

Thanks for the support,

RSP

That's a very good question and most of the time you will find a very good explanation in Water Quality books. So, I encourage you to go through some of the books to fully understand the nature. Here's what I generally do for reporting Water Quality results.

1) Don't report the Water Age from a dead-end location (with no demand) because it will not truly represent your network water age. Here's a proof from your model. Based on the graph below the water age is 120 hours and that's certainly is not the case. So, avoid dead end water age.

2) We don't want to report water age right at the treatment plant (a water source) either. Here's why. The graph below shows water age immediately downstream of a reservoir. In this case the water age is 0 (zero) which definitely doesn't represent the system water age.

3) Also avoid odd-ball area like the one that you mentioned, pipe P-685. Can you guess why? Let's look at some the image below where I have graphed couple of elements with flow and water age.

Notice the Flow in P-54 and the flow in P-685. Compared to P-54, there is very very small flow going through P-685. When the flow is smaller, the water will stay longer (stagnant water) in the pipe (or a network). When water stays longer in the system, you will see high water age. Hence, you are seeing a higher water age. The water age you are seeing in junctions are same as the water age around that node so no surprise here. 

4) Not applicable to this specific model but you ALWAYS want to look at the water age in tanks.

5) Before reporting water age, you want to run the hydraulic model for quite some duration, like 30 days or so.  Basically once the model ran for longer duration it reaches water age equilibrium. (N/A for this model as it doesn't have any tank and it's the tank that takes long time to reach equilibrium because of higher water volume). Literature will explain this better

6) When reporting Water Age, it's a common practice to look at the last 24 hours worth of result. So, if the model ran for 360 hrs then report result from 336th hour to 360th hour. [Analysis > Post Calculation Processor can help to get the last xx hours of data. Use this link for help]