How Water Models Are Created

In part two of our blog series discussing hydraulic water models, we will deal with the building of the components that create a model. As you can probably guess, the availability of detailed water system mapping has an impact on the level of detail and accuracy included within the model. The most detailed, and presumably most accurate, water models are created using already established computer mapping. On the other hand, “skeletonized” water models can be built without any computer mapping available and with as little information as the memory of distribution system Owners and Operators.

Materials From Which to Model

Many water system Owners have already created computer-based water maps, namely in AutoCAD and even GIS formats. These file types can be configured in a way that allows the raw data (location, size, age, material, etc.) to be directly incorporated into the hydraulic computer modeling software. In this way, very little is required to build the base existing model.

Maybe computer mapping isn’t available. Instead, an Owner may only have hard copy maps of the water system. These hard copy maps can be used by the modeler to build the computer hydraulic model. A simple method for a modeler would be to scan hard copies and import these images into the model as a background layer. As long as these maps were to a scale, they can be used to trace the various components and input the required data into the hydraulic model. If hard copy maps aren’t to scale, a modeler must rely on landmarks (typically roads and rights-of-way) included on the maps to approximate the location of components.

Skeletonized Modeling

In the increasingly rare event that electronic and/or hard copy maps aren’t available, “skeletonized” hydraulic models can still be created using the knowledge of the Owners and Operators. These “skeletonized” models will use the most basic information to approximate results and provide a basic level of hydraulic understanding. Of course, as better field information becomes available, the basic “skeletonized” model can be updated as needed to increase the level of confidence in the results.

Modeling Components

Various components make up a hydraulic water model. Pipes, junction nodes, pumps, tanks, and valves are the basic components. However, each of these components has numerous modeling options. For instance, valve components can be broken into options such as isolation valves, pressure reducing valves, pressure dependent valves, pressure sustaining valves, and on and on and on. It isn’t important to discuss these options here, but it becomes important for a modeler to understand which option should be selected when processing data.

Pipes and junction nodes are the most basic components making up a hydraulic model. Of course, pipe size is critical for accurate data, but information such as material and pipe age can also be utilized to increase the level of detail and accuracy of the modeled results. Junction nodes are utilized to connect the various pipes throughout the distribution system. Anytime pipes change size or at all tee or cross connections within the distribution system, junction nodes are required.

In addition to connecting pipes, junction nodes are also utilized to apply water usage demands to the hydraulic model. The application of water demands is one of the critical aspects of creating a hydraulic model, so we won’t discuss it today, but look for the upcoming third part (Benefits of Water Modeling for Your System, May 4) of our blog series discussing the hydraulic water model.

The driving mechanism behind water distribution systems is storage tanks and pumps. Without a storage tank to establish the beginning water level (hydraulic grade) of the system, a hydraulic model is incomplete. Even manual hydraulic calculations must have a starting hydraulic grade. Additionally, for pumps to be utilized within a hydraulic model, they must ultimately be pulling water from a tank somewhere in the distribution system. Again, utilizing pumps correctly within a hydraulic model could be a topic on its own, so it won’t be discussed here.

Hydraulic Grades and System Pressures

Once the basic components of the hydraulic model are created, the next step is to assign elevations to these components to accurately predict hydraulic grades and system pressures throughout the system. Today, many communities and counties have rather accurate topographic data available in the form of GIS maps and shapefiles. Most hydraulic computer models have tools that can use the data from these files to directly assign an elevation to all components within the system. In some cases, though, it may be necessary to manually input elevation data to components using a combination of USGS topographic quad map data and record drawings.

Now that the basic components are created, the last major task is assigning water system demands to various nodes throughout the hydraulic model. As alluded to already, this is a critical component in creating an accurate hydraulic model. Without those water demands pulling water through the correct pipe paths, predicted pressures can vary a great deal. We will deal with the many different methods of assigning demands in the next part of our hydraulic water modeling blog series!

Part 1 - Hydraulic Water Modeling

Part 3 - Benefits of Water Modeling Your System

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