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Network with many reservoirs

Hello,

 I am simulating on Watercad a water network with 6 reservoirs and I am running the scenario at stady state.

The reservoir which has the highest elevation gives water to three other reservoirs (the one has outflow, the other 3 have inflow).

The problem I am comfronting is that  the rest two reservoirs should only have outflow (they are in the opposite side of the network), but instead they have inflow. This happens because the pressure in the last junction before each reservoir results to be higher than the elevation difference between the last junction and the reservoir.

Of course the high pressure is due to the high elevation of the other reservoirs, and especially of the one which has the outflow.

Has anyone an idea of how to simulate that the last 2 reservoirs have only outflow, without resulting in the wrong pressures of the junctions? Or at least correct the pressures in some way.

Thank you.

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  • Blossom,

     I would need to know a lot more about your system in order to give you a definitive answer.

    I assume that you are cedrtain that the 2 intermediate tanks are indeed having their levels drop.

    My initial guess is that you don't have enough demand between the high tank and those tanks such that the high tank water has nowhere to go but into those tanks.

     The second hypothesis is that there is insufficient head loss between the high tank and the other two.

    As with any calibration problem, you need to keep eliminating reasons for this mismatch between the model and your real system until you hit on the reason for this discrepancy and correct it.

     What are the HGL levels in each reservoir and how many miles (km) apart are they?

    Tom

  • Thank you both for your answers. The 2 reservoirs I am referring to, are 1,5 km apart from the highest reservoir, which is 100 m higher.

    I can understand that the real network (I am simulating an existing network), can in fact have reservoirs that are "accepting" water, due to the hydraulic grade.

     But the reason that these reservoirs exist in the first place, is that the water from the first reservoirs(tanks) that were built, is insufficient.

     If I know the amount of water they can accumulate, or if know the demand that each reservoir must cover (depending on the section of the city that they serve), how can I simulate it on the program? Must I "cut" the sections that each reservoir serves and create different networks (although the network is in fact inseperated)? I hope I am comprehensible.

  • Hi Blossom:

    Since you say you know the demands that each reservoir must cover, you should enter that data into the software.  Demands are entered on Junctions, either in their Property Grid, in the Junction Flex Table, or in the Demand Control Center.  As a very simple case, you could take the total demand you know a tank supplies and enter it as a Demand on a single nearby junction.  This will get the flows out of the tanks correct; however, this will not yield very realistic flows and hydraulc grade values in other parts of the system.  A much better way to simulate this would be to spread the loads out around the tanks, within the areas that they serve.  You could do this fairly easily using Demand Control Center. There are also some clever ways to do this with Load Builder (see the help for more information on this) but it will require you to create shapefiles to use as input.  If you have Bentley Map or some other GIS, you can do this in that software.

    HTH,

    Kim

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  • Hi Blossom:

    Since you say you know the demands that each reservoir must cover, you should enter that data into the software.  Demands are entered on Junctions, either in their Property Grid, in the Junction Flex Table, or in the Demand Control Center.  As a very simple case, you could take the total demand you know a tank supplies and enter it as a Demand on a single nearby junction.  This will get the flows out of the tanks correct; however, this will not yield very realistic flows and hydraulc grade values in other parts of the system.  A much better way to simulate this would be to spread the loads out around the tanks, within the areas that they serve.  You could do this fairly easily using Demand Control Center. There are also some clever ways to do this with Load Builder (see the help for more information on this) but it will require you to create shapefiles to use as input.  If you have Bentley Map or some other GIS, you can do this in that software.

    HTH,

    Kim

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