GIS & Hydraulic Modeling

Our first few blog posts focused on the Water Resource Templates, specifically how to configure them and get the templates to work with your data.  Aside from sharing technical information we also created this blog to share observations and stories of how Esri customers benefit from GIS and to explore how GIS relates to industry trends in water, wastewater and stormwater.   After all, GIS isn’t just about feature functionality, it’s also about solving business problems.
So let’s start with a common question from our W/WW user community – what is the relationship between GIS and hydraulic modeling?
From our perspective, GIS and hydraulic modeling are related through data and workflows.  Most of the GIS data models that water and wastewater utilities use contain many of the same data items that a hydraulic model requires.  This includes features, geometries and attributes.  For example many water utilities use GIS as their system of record to store features of their water distribution system (pipes, valves, pumps, treatment plant, reservoirs, storage tanks, etc) as well as customers locations and past usage, elevations, etc.  Using the example of geometry data for pipes a typical W/WW GIS has location and elevation, so you know where the pipe is, how long it is, it’s elevation and where it connects to other pipes – necessary for a hydraulic model.  Also the pipe has attributes such as installation date, diameter, and material – all of these items are used for a hydraulic model.  
Beyond using your geodatabase as input data to build a model, GIS and modeling are also related through workflows.  A change to your GIS, such as adding the water assets of a proposed sub-division to your utility’s proposed water distribution feature classes could kick off a hydraulic modeling activity to determine the impact of the new sub-division on the hydraulic performance of your distribution system.  Another example of the workflow relationship is when hydraulic modelers create a model and uncover an error in the underlying GIS data, for example the wrong diameter on a pipe which caused strange modeling results.  The corresponding workflow should be that the hydraulic modeler makes an edit to the GIS data or passes a redline of the error back to GIS data editors.
Some Esri business partner’s hydraulic modeling packages can directly read a geodatabase to start the process of building a hydraulic model.  By selecting a hydraulic modeling solution from an ESRI business partner you will increase your return on investment in ArcGIS software and GIS data.  Some of these partner solutions work directly in ArcMap, which gives you a seamless workflow between GIS and modeling. To find our partners with hydraulic modeling solutions go to and search for Solutions with the keyword “hydraulic”.
Once the model is completed, many utilities bring data from the model back into GIS for visualization and further analysis. For example, in ArcMap you could create a map that shows hydraulic problems in your distribution system overlaid on your water assets along with a layer of proposed capital projects from your CIP. Doing this allows you to understand where you need to address hydraulic deficiencies that are not part of a proposed capital project.  Better yet, you could do some GIS analysis in conjunction with your model results – such as generating a report of customers that have complained about their water service of over the past year and have hydraulic issues upstream of them.
Beyond this general discussion there are additional nuances when integrating GIS with hydraulic modeling. For example – how often do you update your model, how do you keep track of changes to the GIS that would cause a change in the model, the benefits of an all pipe model versus skeletonizing, where do you store data such as pump curves & C factors? ESRI, our water/wastewater user community and a number of our business partners are currently collaborating on a white paper to explore these topics. 
Have any thoughts on GIS and hydraulic modeling? Please comment on this post or send us an email at:  
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  1. Patrick.Moore.IDM says:

    GIS definitely appears to be where most hydraulic models are being built from. Our company is focused primarily on building, calibrating , and analyzing models and I would say in the last three years probably 90% or more of our models were built using a GIS geodatabase as the basis of the models. Most of the major modeling software packages our clients use have the ability to run directly within ArcGIS.

    As noted in this article many utilities are now moving form simply constructing their models from GIS data to linking the model and GIS together in a 1:1 relationship. In other words the same element in the GIS is identical to the element used in the model. The GIS then serves as the primary database that is maintained by the utility and the model is periodically updated from the master GIS database.

    This article raises several great issues of how to use both the model and GIS applications that are quite relevant. Model tools can be used to help identify areas in the GIS that have missing or incorrectly attributed elements (such as pipe diameters in series going 20 inch – 2 inch – 20 inch) that have a significant impact on model results. In addition the hydraulic models require very specific topological connections between elements because the way elements are connected represents how the model allows water to flow through the system. Most major modeling software packages have tools built in to help identify potential locations where topological issues are found. These issues are then resolved in the GIS and the model is updated to reflect the change from the GIS database.

    We have presented the ten primary challenges that integrating a model and GIS together at the AWWA 2008 DSS conference. These issues represent many of the hurdles that must be addressed to effectively combine a model and GIS database into a long term 1:1 relationship to effectively maintain a model directly from a GIS database. A summary copy of our presentation can be found at this link and may be of assistance in helping GIS staff understand the issues from the perspective of the hydraulic modeler.::

    Addressing specific questions raised:

    1) How often do you update your model

    a. Most water systems do not undergo enough changes that would impact the system hydraulics enough to justify the expense of updating a model within a years time. Thus most systems may not benefit from a model update occurring more than once per year.

    b. Fast growing systems or systems undergoing major updates may justify more frequent periodic updates, but most systems would not appear to benefit from updating the model more than once per year.

    c. The primary challenge we see is that every update introduces the possibility of topological or data errors into the model. Models that have been updated would require calibration or at least validation after updates to document and verify the model is still producing reasonable results.

    2) How do you keep track of changes to the GIS that would cause a change in the model

    a. Different utilities have viewed this differently. Some use fields to indicate the date element data was modified. Other utilities use programs such as FME to compare the old and new geodatabases and can identify elements that have been deleted, modified, or represent new elements.

    b. Documenting changes is a key element to minimizing model efforts during a model update. If 80% of elements do not change during updating the modeler can focus efforts on the 20% or less of elements that do change to make sure the updated elements are correct for modeling purposes.

    3) The benefits of an all pipe model versus skeletonizing

    a. With the advances in GIS and computing power in the last five years, we have not encountered any systems that use skeletonized models. It is easier and more reliable to simply use all GIS elements in the model in most cases.

    b. Models can easily skeletonize a GIS if necessary, but this tool is rarely used anymore.

    4) Where do you store data such as pump curves & C factors?

    a. These are great questions. The best location utilities have used is to either create tabular data in the GIS that is only viewed by the model and is not associated with the GIS elements or it can be stored within the model itself. This issue is also discussed in our article along with identifying where to store additional model specific data (Is the element included in the model (Y or N), Is the element allowed to be assigned demand (Y or N), are there additional model specific naming for this element that may differ from the ID used in the GIS, and other items that if tracked in the GIS can save significant effort during model updating.

  2. Ming_zhang says:

    Very interesting articles by both ESRI water team and Patrick! We have done both GIS and hydraulic modeling for a number of rural water utilities. In addition to every said in both articles, I’d like to add a few comments below:
    1. Benefits of GIS based hydraulic modeling: In addition to the efficiency and cost-savings mentioned in both articles, GIS-based modeling also increases the model accuracy and currency. Not only GIS data enables the creation and maintenance of a full-scale and all-pipes modeling, it also enables the use of real-time and historical consumption data from customer billing database for accurate demand calculation. This is very helpful for the model calibration and building scenario, such as peak model, winter model.
    2. Regarding the frequency of model updates, our clients update their model far more often than once or twice a year. I think this is because the needs and costs. For rural water utilities in a suburban or growth areas, often its service area sprawling across large region and sometime on a complex terrain. These characteristic made the model more sensitive to physical changes. At the same time, we added a lot of custom functions that made model updates very easy, such as automatic extract/updating modeling network from GIS, Modeling-network topology check and fix, calculate and assign demand based on billing data, etc. Updating a model with minor changes would only take a few minutes.
    3. Ultimately, benefits and cost of the frequency for model updates depend on the purpose of the modeling. Historically, hydraulic model primarily has used for major capital improvement plan, large expansions, and long-term growth planning. With the convenience and low-cost of model updating, our clients have used model far more frequent for evaluating small line extensions, subdivision connections, and impact of large new costumers. In short, the modeling is not only used for planning, but also used for day-to-day operations.
    The key is integration. We have developed automated procedures that utilize GIS, modeling, and billing system all together. Of course, this is much easier to achieve for small rural water utilities.
    Ming Zhang
    GIS Coordinator
    Bennett & Williams Environmental Consultants, Inc.