Historical Summary
1.4 The Modeling Process
Modeling can be used to quickly perform a large array of “what-if” analyses to inves-tigate optimal facility sizing, I/I control, and operational changes before such changes are made in the actual system. Modeling is not a single linear process, but a series of steps, some of which can be performed in parallel (see Figure 1.7). The importance of some steps depends on the nature of the project. Moreover, each of the steps can be repeated. For example, even after a model has been used to design a project, the mod-eler may go back to the loading step and determine the effects of other loads.
The complexity of a system model depends on the application, software, availability and extent of data, budget, and skill level of the modeler. The modeling process illus-trated schematically in Figure 1.7 begins with a clear definition of purpose and scope for the project. It is important to have all wastewater collection utility personnel
Define Scope of Project
Collect Calibration Data
Obtain Loading Data
Prepare System Description
Select Modeling Software
Verify Data
Enter Loading Data
Enter System Data
Learn Software
Develop Alternatives
Refine Alternatives
Initial Model
Calibrate and Verify Model
Apply Model
Develop Solutions
Archive Model Document
Results Update with New
Flow Data and Construction
Changes
Figure 1.7 Flow chart of the steps in modeling a wastewater collection system.
including upper management, engineering, operations, and maintenance commit to the modeling effort in terms of human resources, time, and funding. Modeling cannot be viewed as an isolated endeavor by a single modeler, but rather as a utility-wide effort with the modeler as the integrator. Once the vision of modeling is accepted by the utility, key decisions on issues such as flow rate generation, data accuracy, and cal-ibration precision may be addressed.
As shown in Figure 1.7, the initial development of the model is accomplished in four parallel tracks. These steps may be conducted by different personnel, but they must be coordinated. The actual calibration of the model is the responsibility of the lead modeler. Often the calibration step reveals deficiencies in the system or in the loading (flow rate) data and requires that additional data be obtained.
When the model has been calibrated and verified, simulations may be performed for other configurations, loadings, and pipe sizes. Results from these simulations may lead to the development of additional options. The end product of modeling is a rec-ommended master plan, design, operating plan, or rehabilitation plan. When the task has been completed, it is important that the model and results be documented and the model stored so that it can be readily updated when the sewer configuration or the loadings change.
The modeling process is described in great detail in the remaining chapters of this book. A network model is just another tool (albeit a very powerful, multipurpose tool) for an experienced engineer or operator. It is still the responsibility of the user to understand the real system, understand the model, and make decisions based on sound engineering judgment.
References
American Society of Civil Engineers (ASCE). 1930. Design and Construction of Sanitary and Storm Sewers. ASCE Manual 37 and WPCF MOP 9. New York: American Society of Civil Engineers.
American Society of Civil Engineers (ASCE). 1982. Gravity Sanitary Sewer Design and Construction. ASCE MOP 50 (WEF MOP FD-5). Reston, VA: American Society of Civil Engineers.
American Society of Civil Engineers (ASCE). 1992. Design and Construction of Urban Stormwater Management Systems. ASCE MOP No. 77 (WEF MOP-FD-20). Reston, VA: American Society of Civil Engineers.
Babbitt, H. E., and E. R. Baumann. 1922. Sewerage and Sewage Treatment. New York:
John Wiley & Sons.
Bechman, G. 1905. Hydrologique agricole et urbaine (Agricultural and Urban Hydraulics).
Paris: Belanger.
Camp, T. R. 1946. Design of sewers to facilitate flow. Sewerage Works Journal 18, no. 3.
Chow, V. T. 1964. Handbook of Applied Hydrology. New York: McGraw-Hill.
Delluer, J. W. 2003. The evolution of urban hydrology: Past, present and future. Journal of Hydraulic Engineering 129, no. 8: 563–573.
Ecenbarger, W. 1993. Flushed with success. Chicago Tribune, 4 April.
Federal Water Pollution Control Act [commonly referred to as Clean Water Act], Public Law 92-500, October 18, 1972, 86 Stat. 816; 33 US Code 1251 et seq. Amended by PL 100-4, February 4, 1987.
Field, R., D. Sullivan, and A. N. Tafuri. 2004. Management of Combined Sewer Overflows, Boca Raton, Florida: Lewis Publishers.
Foil, J., J. Cerwick, and J. White. 1999 Where we’ve been—wastewater collection.
Missouri Water Environment Association Newsletter (Fall).
Frühling, A. 1910. Die entwasserung der stadte (Drainage of Cities). In Handbuch der Ingenieurwissenschauften (Handbook of Engineering Studies). Leipzig: Englemann.
Gayman, M. 1996. A glimpse into London’s early sewers. Cleaner, March.
Geyer, J. C., and J. L. Lentz. 1964. An Evaluation of the Problems of Sanitary Sewer System Design. Baltimore, MD: The Johns Hopkins University Press.
Haestad Methods and R. Durrans. 2002. Stormwater Conveyance Modeling and Design.
Waterbury, CT: Haestad Press.
Hager, W. H. 1994 (English edition 1999). Wastewater Hydraulics. Berlin: Springer.
Heaney, J. P., W. C. Huber, and S. J. Nix. 1976. Stormwater Management Model, Level I, Preliminary Screening Procedures. EPA 600/2-76-275. Cincinnati, OH: US Environmental Protection Agency.
Hunter, R. B. 1940. Methods of Evaluating Loads on Plumbing Systems. Report BM865.
Washington, DC: National Bureau of Standards.
Imhoff, K. 1907. Tashenbuch der Stadtentwasserung (Pocket Guide for City Drainage).
Berlin: Oldenburg.
Kuichling, E. 1889. The relation between rainfall and the discharge in sewers in populous districts. Transactions of the American Society of Civil Engineering 20, no. 1.
Mays, L. W. 2001. Stormwater Collection Systems Design Handbook. New York: McGraw-Hill.
Metcalf, L., and H. Eddy. 1914. American Sewerage Practice.
Metcalf & Eddy, Inc. 1972. Wastewater Engineering. New York: McGraw-Hill.
Moody, L. F. 1944. Friction factors for pipe flow.” Transactions of the American Society of Mechanical Engineers 66.
Mulvaney, T. J. 1851. On the use of self-registering rain and flood gauges in making observations of the relation of rainfall and of flood discharges in a given catchment. Transactions of the Institute for Civil Engineers, Ireland 4, Part 2: 18.
Pomeroy, R. D. 1974. Process Design Manual for Sulfide Control in Sanitary Sewerage Systems. EPA 625/1-7-005, US Environmental Protection Agency.
Random House. 1970. American College Dictionary, edited by C. P. Barnhart. New York: Random House.
Reid, D. 1991. Paris Sewers and Sewermen: Realities and Representations. Cambridge, MA:
Harvard University Press
Reyburn, W. 1971. Flushed with Pride: The Story of Thomas Crapper. Englewood Cliffs, NJ: Prentice-Hall.
Rouse, H., and S. Ince. 1957. History of Hydraulics. Iowa Institute of Hydraulic Research.
Shields, A. 1936. Anwndung der aehnlichkeitsmechanik und der turbulenz forschung auf die geschiebebeweung (Application of Similarity Mechanics and Turbulence
Research upon Bedload Movement). Mitteilungen der Preussischen Versunchsanstalt fur Wasserbau und Schiffbau (Prussian Research Institute for Hydraulic Engineering and Shipbuilding) 26.
Sirapyan, N. 2001. A history of personal computing. PC Magazine 20, No. 15.
Steel, E. W. 1938 & 1947. Water Supply and Sewerage. New York: McGraw-Hill.
Tarr, J. A. 1996. The Search for the Ultimate Sink: Urban Pollution in Historical Perspective.
Akron, OH: University of Akron Press.
US Environmental Protection Agency (US EPA). 1991. Alternative Wastewater Collection Systems. EPA 625/1-91/024. US Environmental Protection Agency.
US Environmental Protection Agency (US EPA). 1999. Combined Sewer Overflows, Guidance for Monitoring and Modeling. EPA 832-B-99-002. US Environmental Protection Agency.
US Environmental Protection Agency (US EPA). 2000. Compliance and Enforcement Strategy Addressing Combined Sewer Overflows and Sanitary Sewer Overflows. US Environmental Protection Agency.
Zurad, J. T., J. P. Sobonski, and J. R. Rakoczy. 2002. The metropolitan water reclamation district of greater Chicago: Our century of meeting challenges and achieving success. In J. R. Rogers and A. J. Fredich, eds. Environmental and Water Resources History. Reston, VA: American Society of Civil Engineers.
Problems
1.1 Match the name with the works in the following table. Place the letter in the blank.
1 ___ Wrote History of Hydraulics a Manning
2 ___ Early calculating machine b Navier-Stokes
3 ___ Boundary Layer Theory c Newton
4 ___ Flow measuring flume d Pitot
5 ___ Open channel head loss equation e Reynolds
6 ___ Laminar vs. Turbulent Flow f Venturoli
7 ___ Head loss in laminar flow g Archimedes
8 ___ 1-D open channel flow equations h Parshall
9 ___ Velocity measurement i Pomeroy
10 ___ Punch cards j Rouse and Ince
11 ___ Patent for flush toilet k Huber, Heaney, Nix
12 ___ Hydrogen sulfide corrosion in sewers l Hunter
13 ___ Fixture unit method m Venturi
14 ___ Equations for fluid motion n Prandtl
15 ___ Law of Viscosity o Pascal
16 ___ Backwater curves p Hollerith
17 ___ Buoyancy principle q Woltman
18 ___ SWMM model r Crapper
19 ___ Closed pipe flow meter s Hagen-Poiseuille
20 ___ Current meter t St. Venant
1.2 What law passed in 1972 requires discharge permits for any discharges in the United States?
1.3 What is I/I and what are its adverse environmental impacts?
1.4 Name five types of flow conditions in sewer systems.
1.5 How can SewerCAD and the Manning equation both be considered “models”?
1.6 Why are graphical user interfaces important?
1.7 Where are relief sewers used?
1.8 Moody diagrams are based on what diagrams developed by an earlier researcher?
1.9 How did the invention of the flush toilet change the nature of sewage?
The flow of liquid in a conduit may be classified as full pipe (or closed conduit) or open channel, depending on whether the free liquid surface is subject to atmospheric pres-sure. In open-channel flow, gravity alone provides the force to move the fluid. It is the most common flow condition in sewers, and engineers attempt to effectively use the work done by gravity to move sewage through the network.
Open-channel flow may be further categorized as steady or unsteady, and uniform or nonuniform. With steady flow, there is no significant variation in flow rate with time.
Under uniform flow conditions, flow properties remain constant along the channel length. Uniform flow occurs in long inclined channels of constant cross section (i.e., prismatic channels) when the energy loss due to fluid friction is exactly supplied by the reduction in potential energy due to the downward slope of the channel. The depth of uniform flow is called the normal depth.
Because uniform flow can only occur if the flow is also steady, the term “uniform flow”
is often used as shorthand to denote what is actually steady, uniform flow. This condi-tion is often assumed in the hydraulic design of sewer systems. The analysis of steady, uniform flow requires the application of continuity and energy conservation principles.
Steady, nonuniform flow is constant over time, but a variation does occur along the channel length. This type of flow can occur in a channel with a transition in cross-sec-tional shape or slope. Gradually varied flow is the term for gradual changes in flow properties along a channel.