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How can I troubleshoot my model when my water age results don't appear correct?
1) Open your pipes flextable and edit it to add the following fields: a) Is Active? b) Has user defined length? c) Length (user defined) d) Travel Time (This is the length of the pipe divided by the velocity) e) Length f) Velocity
*If you're not familiar with how to edit a flextable please refer the help documentation that comes with the software and look for the document titled "Editing Flextables"
2) After determining if your pipes has a user defined length or scaled length, right click on the appropriate column header and choose Sort > Ascending. This will bring the shortest pipes to the top of the table.
Look at those to see if there are any short pipes, which could be considered any pipe under 10 ft. (3.05 m) for this first round of troubleshooting. An easy way to do this is to use a custom query filter on length column. This can be done by right clicking the appropriate column header and choosing Filter > Custom.
The query you should use will have the following syntax: (This example assumes that your model uses scaled lengths)
IdahoPipeResults_PipeUnifiedLength <= 10
If you aren't familiar with how to a create custom query you can have a look at this wiki, which explains a few ways to filer a flextable based on a custom query:
3) Once filtered locate your "Travel Time" column and if necessary change the units to minutes in order to make it easier to understand. The following wiki will show you a few ways to do that if you are unfamiliar with it:
Just as in step 2 sort this column in ascending order and look for pipes with very short travel times (< 30 seconds). The reason we are looking for pipes with short travel times is because these pipes can potentially impact the water age calculation. Too short a travel time can make a graph of the water age in pipes or tanks look like it is increasing exponentially.
4) Choose a few of the pipes that show an short travel time and browse to them in the drawing pane by right clicking on the flextable row header and using the "Zoom to" option. Then right click on a few of those pipes and graph them for the Water Age(Calculated) property to see if it's less than 30 second for the entire simulation. You don't have to do this for all of them, but doing it for a few should give you an idea of the travel times for the other shorter pipes in that general area.
5) If you own WaterGEMS or WaterCAD with a Skelebrator license then use Skelebrator to do your best in skeletonizing your model to remove the short pipes with short travel times.
6) After you finish skeletonizing your model compute it again and use steps 3-4 to check for any pipes that still might have short travel times. If you find any graph them and determine if there is a way to skeletonize the model more to remove them.
7) Compute your model again and this time use step 3 to determine the shortest travel time in your model and note this.
8) Open the calculation options properties (Analysis > Calculation options) and set the "Set Water Quality Time Step?" property to 'True'. You will set the "Water Quality Time Step" field that is revealed to be less than whatever your shortest travel time was in your model. If your shortest travel time was 1 minute then you might enter 30 seconds for the Water Quality Time Step. Doing this will help to assure that the age analysis is able to capture the changes in water age for all your pipes.
9) Compute your model again and observe the results to see if they look better. If they still don't look correct open the calculation options again and try making your "Hydraulic Time Step" and "Reporting Time Step" smaller and then computing again. You can also always try a slightly smaller "Water Quality Time Step" too. Finally, if the results still do not look correct look at the travel times in your pipes and make sure they are also not too large. If you have travel times that look overly large for the length of the pipe look until you can find where the issue starts. Once you find the starting point try to determine what is causing the issue or contact technical support for additional help.
Discrepancy in the water age results for model with short pipes and short travel times