Demand per Unit Length of Pipe Allocation in WaterGEMS/WaterCAD- Discussion

It is a general practice in Rural Water Supply projects in some parts of the world to allocate demands per unit length of the pipeline where spatial distribution of the population is not available or is very difficult to determine. The per capita demand is fixed initially (say 135 LPCD) and then is multiplied with the population of the entire area/region. This results in total demand of that area/region. This total demand is then distributed along the pipelines as flow per meter length. The total demand for entire length of a pipe is then transferred equally of the start and stop junctions of the pipe.

In this article, how to use this method in WaterGEMS/WaterCAD is discussed. I shall soon write more on the merits and demerits of this process/method and also work on an example showing how GIS information of population is more effective and efficient approach as compared to this method.

How to allocate Demand per Unit Length in WaterGEMS/WaterCAD-

We will follow the workflow below for the allocation of demands per unit length:

1. Fixing the Demand per Capita
2. Calculating Total Population, Total Demand, Total Length of pipes in MS Excel
3. Calculating the Demand per unit Length of pipes in MS Excel
4. Creating User Data Extensions for Pipes for Demand for entire Length of pipe viewing the above parameters in Flextables
5. Dividing the demands and transferring the Demands from pipes to the Junctions in MS Excel
6. Using Model Builder to import the Demand per unit Length, Demand for entire Length and Junction Demands
7. Viewing the imported results and Computing the model

Let us now see every step in detail,

1.     Fixing the Demand per Capita

In most of the countries, there are standard organizations that specify the standard demand per capita. For example, in India the Central Public Health and Environmental Engineering Organization (aka CPHEEO) has specified the standard design demand of water per capita per day as 135 LPCD.

2.     Calculating Total Population, Total Demand, Total Length of pipes in MS Excel

The Population data of the region can be collected from the municipal council or from Census Data. The total population is then multiplied with the per capita demand to get the Total Demand of the System.

This total demand is then divided by the total of Length of all pipes to get the Demand per Meter (L/D/m). This is very simple operation in Excel.

3.     Calculating the Demand per unit Length of pipes in MS Excel

The Demand per Meter length of pipe is then individually multiplied with the length of pipes to get individual demand throughout the length for each pipe. This should also be done in MS Excel for simplicity. Here is a snapshot:

4.     Creating User Data Extensions for Pipes for Demand for entire Length of pipe & viewing the parameters in Flex Tables

WaterGEMS/WaterCAD by default doesn’t have the Demand per Meter and Demand for entire Length as the Element property. But the user can create her/his own project specific Element properties using the User Data Extensions. Here for Demand for entire length of pipe. Follow this to know more on User Data Extensions. The user can create more such extensions such as shown in the figure below:

5.     Dividing the demands and transferring the Demands from pipes to the Junctions in MS Excel

The demand per pipe is then equally transferred to the Start and Stop Junction of that particular pipe. This is done in MS Excel (refer the snapshots below):

6.     Using Model Builder to import the Demand per unit Length, Demand for entire Length and Junction Demands

Now that we have the demands per junction, we can use Model Builder to import the demands from MS Excel. See this to find more information on how to update models using model builder.

7.     Viewing the imported results and Computing the model

After the completion of Model Update using Model builder, user can go to Flex Tables to view the imported properties (from MS Excel) of user data extensions that we have created. The user can also view the imported demands from MS Excel using the tool Demand Control Centre.

Validate and Run the model: The user can then successfully run the model to view results.

I would love to read your comments, queries on this. Happy Modelling!