How to include a closed water reservoir (For eg. clear water sump from treatment plant, Ground level service reservoir, Mass balancing reservoirs - partially below GL) in the model. Can it be a reservoir element or only tank element in the model?

Question

We have to revalidate the design of the network system consisting of Transmission main(s), feeder main(s) and distribution network system of a city using Watergems. The system consists of Transmission main(s), feeder main(s) with Intake sump, WTP clear water sumps, Booster station, mass balancing reservoirs, Ground level service reservoirs and over head tanks supplied by both gravity and pumping. Whether these closed Intake sump, WTP clear water sumps, Booster station, mass balancing reservoirs and Ground level service reservoirs be a reservoir element in the model or only tank element?. I feel that unless the supply is from a dam these elements should be designed with a tank element only.

MPachlhofer · Answer

Tamil,

Based on your description it seems like you want to model a submersible pump or pump ground water well. We have a wiki that explains how to do that which you can find here:

communities.bentley.com/.../16108.modeling-a-submersible-pump

There is also a help topic that comes with the software titled "modeling a pumped ground water well " that explains what you need to do in a little bit more detail how to model this.

As you stated in your question, you could use a reservoir, which has a fixed hydraulic grade line, even through an EPS simulation, and is an infinite source of water. If your source is not infinite you should use tank. It also has a fixed hydraulic grade line if you're only running a steady state analysis, but will draw down or fill over the course of an EPS simulation.

Regards,
Mark

Mark

Tom Walski · Answer

Just to expand on what Mark says, if you are doing only steady runs, it doesn't matter whether you use a tank or reservoir element. 
 
Most users, set the WTP clearwell (clear water sump) as a reservoir in the EPS runs. If you set it as a tank, then it will drain unless you specify an inflow to the clearwell that matches the outflow. Since you don't know the plant outflow a priori, trying to match inflow and outflow at the clearwell can get tricky. What you usually do know is that the level doesn't change by much over a day, so a reservoir makes sense.