When it must regulate service to existing customers or plan for future community growth, a municipality's ability to document and analyze its water distribution network properly is the key to optimizing the system's performance. To eliminate deficiencies, it is necessary to determine how a system responds to different seasonal and emergency situations, as well as how it can be altered to meet new demands or design requirements.
Historically, municipal engineers and system operators have performed field operations, tests, and intricate mathematical computations in order to develop and study a model of their municipality's system. However, this method has often proven to be inaccurate, time consuming and costly. Through the application of current information systems technology to network analysis, a computer modeling alternative has been developed which eliminates many of these concerns.Creating a Computer Model
Computer modeling software functions on two levels. First, a program stores information on network components such as distribution pipes, distribution nodes, minor loss locations, pumps, and boundary nodes, all of which is obtained from municipal records and thorough investigation. This permanent database then is used to determine pressure, flow and other characteristics of the system. Once calibrated, the model reduces significantly the field exploration effort required, instead limiting its use to isolated instances when supplemental data is needed.Planning for Rehabilitation and Expansion
Through computer modeling, municipal staffs have the capability to accurately plan changes or additions to a system by determining which sections of a network need rehabilitation or upgrade, and how future growth can be accommodated. For example, when a new subdivision is proposed, a model can be used to determine the ranges of pressure and flow values available to the development without relying on conventional field testing, which would only produce the same scope of information after numerous tests were performed during periods of various demand levels. The system-wide effect of the proposed project can also be assessed to determine what improvements need to be made to accommodate the increased usage. Municipalities can then charge the developer, the beneficiary of these improvements, for a portion of the associated costs as part of the application fee.
Long term planning is also facilitated through the scheduling, staging, sizing and routing capabilities of the model. A System Improvement Plan which specifies, for example, which pipes should be cleaned and cement mortar-lined, and where new mains should be constructed, can be generated from the computerized evaluation of system performance as well. After assessing the need for future improvements and devising an appropriate schedule, the municipality then can incorporate the associated costs into a Long Range Capital Improvement Plan.Avoiding Costly Design Errors
A computer model also is a valuable design tool for providing engineers with an accurate depiction of a distribution system, and the ability to manipulate its components. In this way, costly mistakes can be avoided, such as the millions of dollars spent on the design of a water distribution tank for a municipality in upstate New York. When the tank was put into service, the pressure in the system was insufficient for many residents living at higher elevations within the district. To correct this inadequacy, a booster pump station had to be designed at an additional cost.
Likewise, when another municipality put into service a filter plant designed without the use of a model, the distribution mains and internal house plumbing fixtures exploded from excessive pressure. In each of these instances, a model could have been used to simulate the designs and correct mistakes before construction began. A computer model eliminates much of the guesswork involved in sizing piping and equipment by keeping track of countless variables in the system, thereby reducing instances of under- and over- design.
Guidelines such as the Ten State Standards for Distribution Systems, which regulate the design of municipal water systems in the Northeast, set criteria for the sizing and diameter of water mains, fire protection, dead ends, valves, hydrants, pressure, mains protection, and distribution storage. Municipalities can determine whether or not they are in compliance with such regulations by evaluating separate sections or the system as a whole through the computer model, pinpointing instances of non-compliance and testing various solutions. In addition, fire flow capabilities can be examined to determine how the entire system performs when faced with an emergency situation, and what design changes need to be made to optimize the system's performance under these conditions.Improving Daily Operations
Daily operations of municipal water systems are improved by computer modeling as well. A model can be incorporated into the procedures controlling the treatment and chemical feed processes to monitor and apply specific dosage rates to the system, which can translate into significant savings in chemical use. Operations strategies also can be tested on the model before they are implemented.
Emergencies or any specific combination of circumstances which might strain a system's performance can be simulated on the computer model so that problems can be addressed and eliminated before a true emergency occurs. A model therefore can be incorporated into a municipal water department's Emergency Action Plan. Operator training is made easier because all the information about the water system is contained in the computer model and therefore accessible to all employees. This method eliminates the confusion which can arise when municipalities are forced to rely on a few selected employees who have a detailed knowledge of the system when problems occur.Obtaining Available Funding
The cost of developing a computer model varies depending on which software is used, and also obviously the individual needs of each municipality. Funding may be obtained to help offset the expense through several sources. Grants and loans are available to municipalities from programs such as the Energy Conservation Program, the Farmers Home Administration Loans and Grants, and state agencies similar to the New York State Energy Research and Development Authority.
Once the federal government approves the proposed low interest loans for the drinking water industry, funding may also be available through the State Revolving Loan Program. In order to be eligible, the grant or loan application will have to specifically address the energy and capital cost savings associated with the use of these models.A Computer Modeling Case Study: Mt. Pleasant, New York
From simply storing data about localized network components to performing complex system-wide analyses, computer modeling has transformed the way the Town of Mt. Pleasant, New York, manages its 70-year-old water distribution system. The network comprises 8 districts and serves over 25,000 residents. In an effort to regulate this ever-expanding system, the Town's consultants, Charles A. Manganaro Consulting Engineers, P.C., first developed district-wide computer models and later created a consolidated town-wide model. Using the software's capabilities, both minor changes and major additions to the distribution network can now be quickly and accurately identified, scheduled, budgeted and designed to optimize the performance of the water supply system.
Several years of system expansion in the municipality's Valhalla Water District resulted eventually in the existence of both inadequate and excessive pressure conditions, along with other distribution network problems. To identify existing deficiencies as well as analyze future expansion capabilities, information about the district's system was fed into the town's first computerized water distribution system model. The model pointed to improvements as simple as interconnecting mains, replacing sections with greater diameter pipes, and resetting pressure valves to address the problems. Similar models were created separately later for six other districts.
When a new 10 mgd water filtration plant to serve the needs of all of the water districts from a single source was required, Mt. Pleasant's officials and staff recognized the value of consolidating these into a unified system. Using information from the individual district models, a consolidated model was prepared and the improvements required to physically interconnect the districts were studied. The time and costs associated with these projects then were scheduled as part of the town's Long Range Capital Improvement Plan. Using the new town-wide model, it was possible to determine existing and future system-wide demands and incorporate them into the design of the new water filtration plant.
An example of the value of the model was evident when the engineers recommended the installation of variable frequency drive pumps at the proposed transfer pumping station. This proposal was based on the model's calculations, rather than the more conventional constant speed pumps which would have required pump replacement to satisfy the variable flow demands. As a result the community has been assured that the new equipment will accommodate current and future drinking water demands. Preparation of the final design and construction documents for the new facilities is currently underway.
While the development of the computer models for Mt. Pleasant is now complete, they continue to play an active role in the management of the town's water system. The models have been installed on the municipality's computers and are constantly being revised to reflect changes in the system. Water department personnel use them on a day-to-day basis to monitor water distribution operations and facilities, as well as to anticipate and plan future improvement projects.
About the Authors: Arshad Jalil, P.E., a project manager at Charles A. Manganaro Consulting Engineers, P.C., developed the model for Mt. Pleasant, NY. James A. Caggiano, P.E. is director of marketing for the Charles A. Manganaro firm and manager of its New York State office. The authors wish to acknowledge the contributions of Robert Guena, P.E., superintendent of water and sewers at Mt. Pleasant. Charles A. Manganaro Consulting Engineers, P.C., is headquartered in Hackensack, NJ.; Tel. (201)342-4200.