System curve

Hello Mary,

The system head curve is essentially the head for a series of discharge rates. There is a fair bit of information in the Help documentation, Bentley Communities (some links can be found below), and in the Advanced Water Distribution Modeling and Management (or AWDM) book (http://www.bentley.com/en-US/Training/Products/Resources/Books/AWDM.htm).

The system head curve is dependent on the system itself, but independent of the pump. A hand calculation of a system head curve would basically remove the pump from the system and replace it with a suction node (with a demand) and a discharge node (with an inflow, or negative demand). A user would apply a series of flows, starting with a flow of zero, and calculate the the hydraulic grade at both the suction node and the discharge node. The head used in the system head curve is the difference between the discharge node and the suction node. The AWDM book has a brief sample of these hand calculations.

WaterGEMS and WaterCAD do something similar. You enter in a maximum flow (such as the potential max flow of a pump) and the number of intervals. WaterGEMS/WaterCAD when a applies a series of flow values, staring with zero and ending with the max flow value) and solves for head. The program is able to solve for far more complicated systems; hand calculations can become cumbersome with large, looping systems.

The links below will hopefully be of some use, as well as resources in the Help documentation and the AWDM book, but if you have any other questions please let us know.

How to manually generate a system head curve

System head curve changing depending on the status of other pumps

System head curve with no downstream storage

The following forum post has a good discussion of system head curves, as well as links to other discussions: http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/60048