Water Supply System Modelling using WaterGEMS (Tutorial 6)

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Water Supply System Modelling using WaterGEMS (Tutorial 6)


Water Supply System Modelling (Tutorial 6)

Mastering water supply system modelling using computer software is essential for engineers these days. TheFluidMechanic would help you with the modelling process through a set of water supply systems tutorials. For this tutorial, Bentley WaterGEMS SELECTseries 5 will be used. You can follow this step by step tutorial (including screenshots) to understand how water supply systems are modeled from scratch. Finally, you can download the WaterGEMS hydraulic model for this tutorial at the end of the post to double check your work and make sure that everything is working all right. Let’s start with our tutorial.

Problem Statement

A distribution system is needed to supply water to a resort development for normal usage and emergency purposes (such as fighting a fire). The proposed system layout is shown in the following figure. The source of water for the system is a pumped well. The water is treated and placed in a ground-level tank (shown in the figure as a reservoir because of its plentiful supply), which is maintained at a water surface elevation of 64 m. The water is then pumped from this tank into the rest of the system.

Water Supply System Modelling Network Schematic

The well system alone cannot efficiently provide the amount of water needed for fire protection, so an elevated storage tank is also needed. The bottom of the tank is at 114.6 m (high enough to produce 243 kPa at the highest node), and the top is approximately 6.1 m higher. To avoid the cost of an elevated tank, this 24.4-m-diameter tank is located on a hillside, 610 m away from the main system. Assume that the tank starts with a water surface elevation of 115.8 m. The pump was originally sized to deliver 1,135 L/min with enough head to pump against the tank when it is full. Three defining points on the pump curve are as follows: 0 L/min at 610 m of head; 1,135 L/min at 54.9 m of head; and 2271 L/min at 45.7 m of head. The pump elevation is assumed to be the same as the elevation at J-1, although the precise pump elevation is not crucial to the analysis.

The system is to be analyzed under several demand conditions with minimum and maximum pressure constraints. During normal operations, the junction pressures should be between 243 and 555 kPa. Under fire flow conditions, however, the minimum pressure is allowed to drop to 139 kPa. Fire protection is being considered both with and without a sprinkler system.

Pipe Network : The pipe network consists of the pipes listed in the following table. The diameters shown are based on the preliminary design and may not be adequate for the final design. For all pipes, use ductile iron as the material and a Hazen–Williams C factor of 130. The junction information for this problem is given in the following table.

Pipe Data :

Pipe Data

Junctions Data :

Junctions Data & Demands

Part 1 : Summarize the results after each run in a table to get a feel for some of the key indicators during various scenarios.

Part 2 : For the average day run, what is the pump discharge ?

Part 3 : If the pump has a best efficiency point at 1,135.5 L/min, what can you say about its performance on an average day ?

Part 4 : For the peak hour run, the velocities are fairly low. Does this mean you have oversized the pipes ? Explain.

Part 5 : For the minimum hour run, what was the highest pressure in the system ? Why would you expect the highest pressure to occur during the minimum hour demand ?

Part 6 : Was the system (as currently designed) acceptable for the fire flow case with the sprinkled building ? On what did you base this decision ?

Part 7 : Was the system (as currently designed) acceptable for the fire flow case with all the flow provided by hose streams (no sprinklers) ? If not, how would you modify the system so that it will work ?

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