Water Distribution System.

Table of Contents

The aim of this manual is to provide guidance on conducting a household survey as part of a Water Safety Plan for organized piped water supply systems in resource-limited settings. Specific examples intended to guide the planner in designing the survey are provided in the appendices. Household water supply (piped) 32 What is the frequency of water supply? 1- 24 hour supply (skip to q. 36) 2- More than once a day 3- Once a day 4- Once in two days 5- Once in three days 6- Other 33 Is this frequency sufficient for your needs? 1- Yes (skip to q. 36) 2- No 34 How often would you like to get water? WATER SUPPLY HANDBOOK A Handbook on Water Supply Planning and Resource Management Institute for Water Resources Water Resources Support Center U.S. Army Corps of Engineers 7701 Telegraph Road Alexandria, Virginia Prepared by Theodore M. Hillyer with Germaine A. Hofbauer Policy and Special Studies Division December 1998 Revised IWR.

• Water Distribution System.
  • Distribution Reservoirs.
  • Construction and Maintenance of Water Distribution System.

Extensive water distribution system is needed to deliver water to the individual consumer in the required quantity and under a satisfactory pressure.

This water distribution system is often the major investment of a municipal waterworks.

Types of Water Distribution System.

If topographic conditions are ideal, gravity distribution is used.

This requires a reservoir at a sufficient elevation above the city so that water can reach to any part of the distribution system with adequate pressure without pumping.

If pumping is necessary, water may be pumped directly into closed distribution lines, or it may be pumped into distribution reservoirs which serve to equalize pumping rates throughout the day and provide for peak use.

A tree-like water distribution system with many dead ends is unsatisfactory because water may become stagnant at the extremities of the system.

Moreover, if repairs are necessary, a large district must be cut off from the water.

Finally, with locally heavy demand, or during a fire, the head loss may be excessive unless the pipes are quite large.

A single-main system is one in which a single main serves both sides of a street.

In a double-main system, there is a main on each side of the street. One pipe supplies fire hydrants and domestic service on its side of the street.

While the other (and smaller) pipe serves only domestic needs on the other side.

The chief advantage of the two-main system is that repairs can be made without interfering with traffic and without damage to the pavement.

Pressure Requirements in Water Distribution Systems.

In designing water distribution systems, pressure requirements for ordinary use and fire fighting must be considered.

In residential districts, tire pressures of 60 psi at the hydrant are recommended.

In commercial districts, a minimum pressure of 75 psi is tolerable, but higher pressures must be provided in districts with tall buildings.

The American Water Works Association recommends a normal static pressure of 60 to 75 psi throughout a system.

Watch the Video Below for Better Understanding.

Many cities use fire-department motor pumpers to develop the necessary tire pressure so that normal operating pressure can be less than that quoted above.

The maintenance of high pressure in mains means increased pumping costs and usually also increased leakage.

Some large cities have installed dual systems in business districts, a low-pressure system for ordinary use and a high-pressure system (150 to 300 psi) for fire fighting only.

Other cities use standby pumps to raise the pressure in the entire system whenever a fire occurs.

Faucet pressures of 5 psi are satisfactory for most domestic needs.

Assuming a maximum pressure loss of 5 psi in the meter, about 20 psi in the house service pipe and plumbing, and with the main about 5 ft below ground level, a total pressure of about 35 psi in the main is adequate for residential districts with one and two-story houses.

Allowing about 5 psi for additional stories, a pressure of 75 psi should be satisfactory for buildings up to 10 stories in height.

Many cities require owners of tall buildings to install booster pumps in order to avoid the need for very high pressures in the mains.

Unnecessarily high pressures should be avoided since leakage loss in the mains and from leaky plumbing fixtures will be increased.

Distribution Reservoirs.

Distribution reservoirs are used to provide storage to meet fluctuations in use, to provide fire storage, and to stabilize pressures in the water distribution system.

The reservoir should be located as close to the center of use as possible.

The water level in the reservoir must be high enough to permit gravity flow at satisfactory pressures to the system which it serves.

In large cities, several distribution reservoirs may be located at strategic points throughout the city.

Water is usually pumped into a distribution reservoir when the demand is low and withdrawn by gravity flow during periods of high demand.

Elevated storage may be advantageously employed for pressure stabilization.

Various types of distribution reservoirs are built to meet the topographic and structural conditions encountered.

If hills of adequate elevation exist in or near the town, a surface reservoir, either below ground level or of the cut-and-fill type, is usually the best selection.

Small reservoirs may be simple excavations lined with gunite, asphalt, an asphalt membrane, or butyl rubber.

Larger reservoirs require a concrete lining, with side walls designed as retaining walls to resist external soil loads with reservoir empty.

Most surface reservoirs are covered to prevent contamination by animals, birds, and human beings, and, by shutting out sunlight, the growth of algae.

Reservoir roofs may be of wood, concrete, or steel. Pre-cast slabs of light weight concrete are widely used.

In at least one instance a reservoir roof has formed part of a city street. An open distribution reservoir should have a high fence around it to keep out trespassers.

If the topography does not permit sufficient head from a surface reservoir, a standpipe or elevated tank may be used to gain the necessary height.

Steel, reinforced concrete, and timber are used for the construction of standpipes.

Stand Pipes.

A steel standpipe is made of steel plates which are joined together by welding or riveting.

Pre-stressed construction is extensively used for concrete standpipes to minimize cracking. Pre-stressing is usually accomplished by wrapping the tank with a continuous wire, which is then covered with mortar.

Since large variations in pressure are undesirable in a distribution system, fluctuation of the water level in a stand pipe is usually limited to 30 ft or less.

Generally, standpipes over 50 ft high are not economical since the lower portion of the standpipe serves only to support the upper useful portion.

The economic limit of height for standpipes is reached when the supporting structure for an elevated tank becomes less costly than the lower ineffective portion of the standpipe.

There are many different types of elevated tanks.

The selection of type, number, and location of distribution reservoirs is an economic problem in which annual cost of reservoirs, pipe, and pumping should be minimized.

Surface reservoirs can be larger, and hence fewer might provide adequate storage.

However, if suitable surface sites are not favorably located in the distribution area, longer supply mains may be necessary.

In addition, larger mains may be required to keep pressures at proper levels.

Read More: Earth Dam: Types of Earthen Dam and its Construction.

Construction and Maintenance of Water Distribution System.

The basic requirements of pipes for water distribution system are adequate strength and maximum corrosion resistance.

Cast iron, cement-lined steel, plastic, and asbestos-cement compete in the small Sizes, while steel and reinforced concrete are competitive in the larger sizes.

In cold climates, pipes should be far enough below ground to prevent freezing in winter.

For even the coldest parts of the United States, a depth of 5 ft is generally more than adequate.

In warm climates, the pipes need to be buried only sufficiently to avoid damage from traffic loads.

Service connections to cast iron or asbestos cement pipe are made by tapping the distribution main with a special tapping machine which provides a threaded hole 1/2 to 2 inches in diameter.

A corporation cock is then installed with a flexible gooseneck pipe leading to the service pipe.

The gooseneck prevents damage if there is an unequal settlement between the main and the service pipe.

Service pipes leading from the main to the consumer are usually copper tubing or galvanized steel.

For single-family dwellings, 3/4 to 1-1/4-inches pipe is common for service pipes, but larger sizes may be needed for apartment houses or business establishments.

When a new pipe is first filled, all hydrants and valves are opened so that air can escape freely.

The filling is done slowly and may require several days for large systems. Excessive pressures can develop if the air is not properly driven out of the system.

When a steady, uninterrupted stream issues from a hydrant, it is closed. The procedure is continued until all valves, and hydrants are closed and the system is full of water.

Leakage in Water Distribution System.

Leakage from distribution systems will vary with the care exercised in construction and the age and condition of the system.

Construction contracts usually specify an allowable leakage in the range from 50 to 250 gpd (gallon per day) per inch of pipe diameter per mile of pipe.

The test is made by closing off a length of pipe between valves, and all service connections to the pipe.

Water is introduced through a special inlet, and normal working pressure is maintained for at least 12 hours while leakage is measured.

In an operating system, the total loss is estimated from the difference between the measured input to the system and metered deliveries to the customers.

There are several possible methods of locating a specific leak. Patented leak detectors use audio phones to pick up the sound of escaping water or the disturbance in an electrical held caused by saturated ground near the leak.

Network Survey Managerdesign Water Supply Systems

Watch the Video Below for Better Understanding.

Similar devices may be used to locate the pipe itself if the exact location is unknown.

If pressure gauges are installed along a given length of pipe from which there are no take-offs, a change in slope of the hydraulic gradient will indicate a leak.

In some instances, the escaping water itself or unusually lush vegetation may show the location of a leak.

If the leak is due to a faulty joint, it may be necessary only to repack and re-caulk the joint.

If the pipe itself is cracked, the entire length of pipe may have to be replaced.

The location of all pipes, valves, and appurtenances should be entered on maps. This information is essential in case repairs are required at a future date.

Disinfection of Distribution System.

While the pipe is being handled and placed, there are many opportunities for pollution. Hence, it is necessary to disinfect a new system or an existing system after repairs or additions.

Disinfection is usually accomplished by introducing chlorine, calcium hypochlorite, or chlorinated lime in amounts sufficient to give an immediate chlorine residue of 50 mg/l.

Watch the Video Below for Better Understanding.

The chemical is introduced slowly and permitted to remain in the system for at least 12 and preferably 24 hours before it is flushed out.

The flushing may be accomplished by opening several fire hydrants.

The hydraulic efficiency of pipes will diminish with time because of tuberculation, incrustation, and sediment deposits.

Flushing will dislodge some of the foreign matter, but to clean a pipe effectively, a scraper must be run through it.

The scraper may be forced through by water pressure or pulled through with a cable. Cleaning, even though costly, may pay off with increased hydraulic efficiency and increased pressures throughout the system.

The effects of cleaning may last only a short time, and in many cases, the pipes are lined with cement mortar after cleaning to obtain more permanent results.

Read More: What is Gravity Dam and its Construction?

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What do a city engineer, a backhoe operator, and a pizza delivery person have in common? They all need “location” information.

by Paul Ginther

What do a city engineer, a backhoe operator, and a pizza delivery person have in common? They all need “location” information.

Keeping tabular information in a database, a spreadsheet, or hardcopy records has long been standard practice. Knowing the street address for facilities, customers, or work orders provides a general “where” factor.

However, tabular data tied to an address is generally not sufficient in the utility business. Geographic Information System (GIS) technology has added an entirely new level of functionality - and opened the world up to a wealth of information.

GIS is in use in almost every industry. People use it every day whether they realize it or not. Obtaining driving directions from the airport to a hotel uses a form of GIS that relates addresses to street networks and traffic patterns. Obtaining an Internet list of nearby restaurants of a specific type uses a GIS search function to query business data associated with geographic locations within a user-defined radius.

There are many advantages to using GIS in the utility business. Eighty to 90 percent of a utility’s data is somehow tied to a geographic location. Utilities must know where their pipes, valves, pumps, meters and other facilities are located. They also need to know the location and water usage patterns of their customers. And they need to know where their crews are working and what facilities need maintenance. GIS allows users to query and analyze information based on its location and its spatial relationship to other features-often where no other relationship is available.

Utilities typically maintain numerous databases that have been developed independently over many years. By relating shared locations, these otherwise unrelated data sets can be associated. As an example, GIS applications can help identify trends in water main breaks to prioritize pipe replacement and rehabilitation projects. Such projects are typically analyzed using a variety of weighted criteria such as pipe material, diameter, age, surrounding soil conditions, proximity to critical locations (such as hospitals and schools), main-break history, water quality, and coordination with other public works projects. These criteria can be represented spatially in a GIS and associated with the pipe inventory. Utilities can then decide not only what improvements to make but also when to best make those improvements.

The most obvious use for GIS is to record and analyze current conditions. The digital representation of a water or wastewater utility’s network typically includes pipes, meters, valves, manholes, and other critical facilities referenced to some sort of land base background of streets, parcels, contours, and political boundaries. This as-built picture provides the what, where, and when of the utility’s history. However, the same data are extremely useful in looking forward - especially when integrating the GIS with other data sets and applications.

Once established, a GIS can be enhanced to serve as a critical link for meeting ongoing data maintenance requirements, supporting numerous data analysis/reporting activities, and interfacing with other applications. A few examples are described below.

Integration with Hydraulic/Hydrologic Modeling

Hydraulic and hydrologic (H/H) modeling is commonly used to analyze water and sewer utility networks - especially for developing master plans and capital improvement plans. This modeling activity can help utilities evaluate system performance and identify improvements necessary for such parameters as meeting water pressure requirements or reducing water-in-basement problems.

Although much of the data needed for modeling can be maintained within a GIS, modeling and GIS have historically developed along separate but parallel paths. The primary goal for a GIS analyst typically has been to create a geographically accurate and up-to-date depiction of the actual utility system - the more detail, the better. The main objective for a modeler has been to create a hydraulically correct representation of the network, under various operating conditions, that would support flow/pressure modeling analysis - the simpler, the better. Historically, creating new H/H models has required tedious and costly data collection and model construction efforts, often duplicating work already performed in the creation of the GIS or previous models.

Recent advancements in software and database functionality have dramatically narrowed the gap between these two powerful applications. When properly designed, a GIS can now be used to efficiently develop the majority of an H/H model. Data cleanup and integrity tools streamline the effort to establish required network connectivity and verify correct network construction - such as preventing a 4-inch pipe from being inserted into the middle of a 24-inch pipe.

Additional benefits can be achieved by maintaining connectivity between the model and GIS. This integration significantly improves the ability to update or enhance future modeling efforts. Use of the advanced spatial analysis capabilities of GIS can further enhance modeling results. Examples include:

• Fire Flow Analysis. Most hydraulic modeling software can calculate available flow values at nodes throughout the system network. Different land-use categories have different fire flow requirements. Associating model results with land-use requirements in GIS enables users to evaluate the ability of a distribution system to meet fire flow requirements for various land uses. This information is useful for planning distribution system improvements to provide adequate fire protection.

This analysis can be taken to a higher level by using risk analysis tools to assign risk factor ratings to specific land uses (e.g., hospitals, schools, tall buildings). Specific fire risks can be determined by using GIS to overlay these ratings with the fire flow data. This analysis can help determine or support a city’s ISO (Insurance Services Office) rating.

• Drinking Water Source Analysis. Utilities that obtain water from multiple sources need a good understanding of how the water mixes throughout the network. This is especially important where source quality varies. Customers may want to know which source provides their water. However, over time a customer may be served from a number of sources, and the proportional mix of the various sources may be constantly changing. A long-term proportional (or percentage) mix of source water is a good indication of overall customer water quality.

For a specific operating scenario, the hydraulic model can be used to calculate the percentage of total demand supplied by each water source at any location in the distribution system. Using the GIS, percentage contours can be generated for each source. Overlaying this data onto a digital street or parcel map can help users correlate street addresses with source percentage polygons to determine the approximate percentage of water each customer gets from each source.

• Water Usage Demand Allocation. To accurately model a water distribution network, engineers must understand where water is being consumed under a variety of water usage conditions. Demand allocation is a process in which current or predicted future water consumption data is assigned to locations in the network. Ideally, existing water demand is allocated using water meter data tied to specific points in the water network system. This method works well for established neighborhoods. However, good meter data tied to physical addresses or to a location on the network may not be available. Through use of GIS tools, water usage demands can be indirectly derived based on population data or land-use maps. This method is also helpful in predicting water usage in future growth areas.

• Establishing Facility Elevations: GPS survey data (if available) or Digital Elevation Models (DEM) can be used to automatically determine node elevations required for H/H modeling. These GIS-based methods are far superior to the painstaking process of manually estimating elevations from contour maps.

Integration with Customer Information System

Establishing common database links between the GIS and customer records lets utilities associate real-time demand usage with the GIS network model. This is useful in supporting H/H modeling and other analysis/reporting capabilities. Network tracing functions within the GIS can also provide useful reports such as a list of customers impacted by valve closures, identification of “critical” customers served by a section of the system, or a mailing/notification list of specific customers.

Relating customer records to geographic locations can provide additional customer service benefits. When a customer calls with a complaint, the customer service agent can immediately see the location of the current complaint as well as any recent complaints nearby. A work order tied to that location can then be generated.

Customer address records often present a limitation to this integration. Address data is often tied to billing addresses, which are not necessarily the same as meter addresses. Therefore, there may not be a dependable relationship between a customer record and a meter location. Likewise, many utilities lack dependable relationships between meter records and locations along the mains. A variety of GIS tools can be used to establish these relationships.

Integration with Asset Management

Aging infrastructure, demands imposed by rapid growth, and concerns about system optimization and GASB 34 continue to fuel interest in improving asset management. Most utilities have moved, or are moving, from hardcopy record-keeping systems to computerized systems for asset tracking and maintenance. Computerized systems not only provide for superior record management but also provide a tool for planning and scheduling work activities-such as valve and hydrant maintenance programs or pipe cleaning and inspection programs.

Computerized systems specifically developed to improve asset management include Computerized Maintenance Management System (CMMS) and Work Order Management (WOM). These database applications are often the primary source of attribute information for pipes, fittings, valves, and other components of distribution systems. They are often used to track material inventories and work-order purchases.

Linking (or migrating) this asset data to the GIS relates it directly to the network system without the need to reenter it or maintain a duplicate data set. It also allows for reporting the values of infrastructure assets by geographic area (e.g., tax/city boundaries, pressure zones) or for use in pipe replacement prioritization and rehabilitation projects.

Field Data Collection

Many utilities are now taking GIS data out into the field where it can be directly used to support maintenance activities, facility inventories, construction, location of buried facilities, etc. Such use eliminates many labor-intensive activities such as manual entry of field collected data forms, data consolidation at the office, additional QC verifications, and field re-visits. Handheld, ruggedized computers with combined GIS/GPS capabilities provide:

• Immediate ties to location and other features (even photos)
• Review of existing data used to support field activities
• Immediate validation of previous and collected data
• Reduced need for field sketches to show facility layouts
• Elimination of data re-entry

Pipeline Alignment Sheet Generation
Up-to-date, construction-quality alignment sheets for transmission pipeline projects have previously been only a dream. Advancements in GIS-based alignment sheet generation software have made this a reality. Pipeline alignment sheets essentially become reports that can be generated from data stored in a GIS database. As environmental, right-of-way, site condition, and engineering data are collected or revised, new sheets can be generated from the GIS to provide all users with the most current information available. A variety of sheet formats, contents, and scales can be used from pre-construction planning through as-builts and ongoing operations. This same data can be used for other purposes and analyses throughout the project life cycle.

Conclusion

Although GIS and its related technologies have made major impacts on the way utilities manage both infrastructure and operations, there are still many opportunities to improve both the way in which GIS is used and the management of infrastructure and operations. The greatest limitation still haunting the industry is the quality of available data. Even in this information age, much of the data available is outdated, incomplete, inaccurate, or in the wrong format. The good news is that as low quality data is validated, verified, and/or migrated using GIS technology, it will continue to improve.

So the next time you call for pizza delivery, you can thank GIS technology not only for its role in finding your address and mapping the directions-but also for supporting the infrastructure to field phone calls, provide clean water, and carry wastewater to treatment facilities.

About the Author:

Paul Ginther is the Manager of the recently established GIS Department for the water business of Black & Veatch, a global engineering, consulting and construction company. The company recently expanded its GIS offering to meet the increasing demand for geospatial technologies among U.S. water and wastewater utilities. One of the department’s goals is to promote a better understanding of the uses for GIS-related solutions. Ginther has more than 25 years of experience in project management, consulting, and implementation experience on GIS projects. He has a master’s degree from Washington State University and a bachelor’s degree from the State University of New York at Albany.

In general, GIS technology is used to answer questions such as:

Network Survey Managerdesign Water Supply System

• Where is ... ?
• How big is ...?
• When did it ...?
• When will it ...?
• How many ... are near ...?
• What would it look like if ...?
• What is the shortest path?
• How do these two relate?
• Can we combine this with data from ...?
• What has changed since ...?