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Selection of sewer system modeling software products

Robert W. Carr, P.E.
Project Manager
Earth Tech
Milwaukee, WI

The use of hydrologic and hydraulic software programs to model sewerage systems has become commonplace in the engineering community. A recent review of available software programs found over 20 such programs available. The price of the software ranged from free to over $30,000 per license. With such a large variety of software and range of costs, how does a community select the right software package? Selecting the right software is critical to the success of a modeling program. A reasonable but logical approach to evaluate available software is necessary prior to the selection of software. This paper will outline a methodology that could be followed to select the right modeling software for your community and sewer system.

What will I use the software for?
The answer to this question is the first step in determining what software package is best suited for your community. Nine basic questions should be answered before you even look at available software packages. These questions will allow you to develop a set of specifications to be used to evaluate the software packages. The questions and why they are important to the selection process are described below.

1. What type of sewer system are you modeling? The type(s) of sewers present in your community is very important to the model selection. Do both storm and sanitary sewers serve your community or do combined sewers serve your community? If you have storm and/or combined sewers, are you planning to model them? If so, the software package you select should include a hydrologic component or you must estimate the storm flows outside of the model. Beyond that, different models have varying hydrologic methods built into them. Knowing the methodologies you wish to apply and if they are available in the software package is important.

2. How complex is the sewer system? Does your sewer system include complex hydraulic structures, such as pumps, weirs, regulators, overflows and/or syphons? If your sewer system generally includes only sewers and standard pumps, a steady state model would likely be sufficient to model the sewer system. However, if your system includes the above mentioned complex hydraulic structures, a dynamic model using the Saint Venant equations may be better suited for your community than a steady state model.

3. How big is the sewer system? Most models are sold based on the number of nodes or manholes to be modeled. Therefore the size of the sewer system to be modeled is important to determine the cost of the model.

4. What will I use the model for? Will I be using the model to: (a) evaluate existing problem areas in my community; (b) determine the size of new sewers needed to serve growth areas in my community; and/or (c) determine the impacts of increasing flows from either inflow and infiltration (I&I) or new development on existing sewers? Your answer to this question will help you write the model specifications you need to select the right software.

5. Are graphics important? The use of graphics to convey information to the public is often very important in order for the public and decision-makers to understand complex technical issues. Most of today's software packages include graphics in one form or another. However, some models have limited graphic capabilities. The need to interface with a specific graphic package such as AutoCAD and/or ARCView can also guide your selection. Also, some of the higher cost packages may provide more graphics than necessary for your community.

6. Do I have the staff available to learn and use software? This factor is very important for communities, which either plan to develop the software model or use the model after a consultant develops it. Many software packages are reasonably complex to use. For the modeler to remember the specific nuances of the software, frequent use of the software is often necessary. If your staff is too small or no one on your staff is interested in sewer system modeling, you may want to use a consultant to model your sewer system. If that is your choice, ask the consultant to use an over-the-counter software rather than a proprietary software, so that you or another consultant can use the model in the future if needed.

7. Will I need to run multi-year simulations? The need to run long-term simulations can also dictate the best model. The amount of time necessary to run a multi-year simulation varies significantly between the various models. Therefore, if the need to run long-term simulations is important to your community, compare the amount of time necessary to run a shorter (i.e. three-month) simulation. This will give you a general idea of the length of time each software package will take to run a longer (i.e. multi-year) simulation. Be careful to check on the computer power and speed to ensure that you are comparing apples to apples in run time.

8. Is inflow and infiltration (I&I) a significant factor that I am evaluating? The impact of I&I on sewer systems is well documented. The complexity of I&I flows makes the modeling of I&I very difficult. Most software packages have a methodology for estimating I&I flows and that methodology should be reviewed carefully to ensure that the software can adequately model the I&I flows present in your community.

9. How much am I willing to spend on the software? As mentioned above, the cost of the various software packages varies greatly. Some software packages are available for free while others can cost over $30,000 per license.

After you have answered these questions, you will be better able to determine the sewer system software needs for your community. Use these needs to write a set of model specifications. These model specifications must be carefully written to allow you to evaluate the numerous software packages that exist.

Evaluate available software
Now that you have prepared the model specifications, it is time to review available software packages. Below is a partial list of available software. As you can see by the amount of available software, if you were to ask all of the companies for detailed information, it would likely take weeks to sort through all of the data. Therefore, using their web pages and your specifications, you can briefly evaluate the software and eliminate those that will not meet your specifications or those software packages that may be too expensive. Hopefully, you can narrow the list down to six to eight software packages.

The next step is to use the model specifications to write a questionnaire. This questionnaire should be detailed enough that you can distinguish and compare the various software packages. After the questionnaire has been developed, send it to the companies whose software you want to evaluate further. While the software companies are preparing a response to your questionnaire, prepare your plan to evaluate them. Do you want to do a subjective evaluation or do you want to develop a numerical evaluation based on the answers provided by the software companies? After you receive the responses from the companies, use the plan you prepared to evaluate the software. It is very possible that you may be able to choose the appropriate software at this point.

Additional evaluation options
Sometimes it may be necessary to do further evaluations beyond the questionnaire. If this is the case for your community, the next step would be to shortlist the best two to four packages and request that a demonstration of their software be done. It is a good idea to provide the companies a small area (data set) of your system and ask them to prepare a model of this area. The purpose of this effort is to allow the software company to show you how well their model can do the type of analyses required for your sewer system. The availability of flow monitoring data to compare the estimated flows from the model is very helpful for the evaluation process.

Unless you are planning to buy numerous licenses, a small fee to help offset the company's costs to develop and demonstrate the model may be appropriate. While the companies are preparing the model, it is important that again you prepare your evaluation criteria. After the presentations by the software companies, you should be able to choose the right software for your community.

Summary
It is typically possible to model your community's sewer system with many of the available software programs. The distinction between the programs (other than cost) is often the differences in the requirements for developing the sewer model(s) and the subsequent long-term application of the software programs. The identification of these application requirements and their relative importance is subjective and can be affected by the reviewer's past modeling experiences. By involving several persons during the review process, the subjective nature of the process can be minimized. Another factor in the long-term use of any software package is that any shortcomings associated with a software package are often minimized, if not eliminated, as the modeler's experience with the software increases and the "tricks" necessary to fully use the software are learned. However, a careful evaluation of the software packages available will help minimize the number of "tricks" that the modeler must learn.

Robert W. Carr, a member of the APWA Water Resources Management Committee, can be reached at 414-225-5135 or bob_carr@earthtech.com.

Partial List of Sewer Modeling Software and Company

Civil Tools Renaissance Endeavours
Civil Tools Harper Houf Righellis, Inc.
Eagle Point Eagle Point
EPA-SWMM USEPA
Flow Pro ZD Net
FlowMaster Haestad Methods
Fluid Flow Flite software
Hydraflow Water Resources Consulting Services
Hydragraphics Pizer
HYDROFLO Tahoe Design Software
HydroWorks Wallingford Software
InfoWorks Wallingford Software
Mike-SWMM DHI
MOUSE DHI
PC-SWMM Chi
SewerCADD Haestad Methods
SEWERCAT Reid Crowther
Storm and Sanitary SelectCAD Intergraph
Storm Cadd Haestad Methods
SWHYMO J. F. Sabourin & Associates
Terramodel Geocomp Systems
Visual Hydro CaiCE
XP-SWMM XP Software