SCMD-03-CH01-Introduction Stormwater Conveyance Modeling Design

STORMWATER CONVEYANCE MODELING AND DESIGN

Authors

Haestad Methods

S. Rocky Durrans

Managing Editor

Kristen Dietrich

Contributing Authors

Muneef Ahmad, Thomas E. Barnard,

Peder Hjorth, and Robert Pitt

Peer Review Board

Roger T. Kilgore (Kilgore Consulting)

G. V. Loganathan (Virginia Tech)

Michael Meadows (University of South Carolina)

Shane Parson (Anderson & Associates)

David Wall (University of New Haven)

Editors

David Klotz, Adam Strafaci, and Colleen Totz

HAESTAD PRESS

Waterbury, CT USA

Click here to visit the Bentley Institute Press Web page for more information

C H A P T E R

1Introduction to Stormwater Conveyance Modeling and Design

Stormwater is water from rain, snowmelt, or melting ice that flows across the land surface. Conveyance systems for dealing with stormwater are everywherein backyards, streets, parking lots, and parks. They frequently affect people but typically go unnoticed unless they fail. The consequences of failure range from nuisance flooding of yards, basements, and roadway travel lanes, to temporary road or bridge closure and minor property damage, to widespread destruction and even loss of life.

Another consideration when dealing with stormwater that has received increased attention in recent years is stormwater quality. In urban areas, stormwater often comes into contact with pollutants such as oil from roadways and parking lots, which it then carries into surface waters such as lakes and streams. Sediment loads from construc-tion sites can also be problematic, as can runoff from agricultural lands exposed to fertilizers, pesticides, and animal waste.

This book presents information necessary to appropriately analyze and design storm-water conveyance systems, including the following topics:

Basic components of stormwater systems and conveyance modeling

Creation of project design storms

Determination of the runoff rates to the system that will result from these storms

Conveyance structure design alternatives

Hydraulic analyses to determine which alternatives meet design criteria

Practices for improving stormwater quality

Other factors to be considered, such as cost and available budget and the upstream and downstream impacts of a project, are also discussed.

2 Introduction to Stormwater Conveyance Modeling and Design Chapter 1

This chapter begins the book by citing statistics and providing background on the fac-tors driving the need for stormwater conveyance systems. Section 1.2 gives a brief history of stormwater management, and Section 1.3 provides an overview of issues that must be addressed in system design.

1.1 NEED FOR STORMWATER CONVEYANCE SYSTEMSThe need to manage stormwater runoff to protect vulnerable areas against destructive flooding is an age-old problem. Flooding poses a threat to developed areas, agricul-tural crops and livestock, human life, and highways and other transportation systems. Flooding happens across all spatial scalesfrom individual properties and neighbor-hoods along small creeks, to entire regions bordering major rivers.

Of course, the largest part of the losses is due to major flooding along large streams and rivers. Therefore, proper designs of storm sewers and culverts, which are the focus of this book, will only partly cure the growing cost of flooding in terms of mon-etary damage and loss of life. (Chapter 2 provides an overview of the types of storm-water facilities presented in this text.) Nevertheless, careful stormwater conveyance designs that consider not only the service of an immediate local area, but also how this area merges into and interacts with regional-scale stormwater and flood protec-tion plans and facilities (sometimes called a major system of drainage conveyance facilities), can alleviate many of the damages associated with frequent storm events.

The magnitude of the flooding problem can be appreciated by citing a few statistics. Figure 1.1 illustrates the trend in annual flood losses in the United States over the period from 1903 to 1999, where all losses are expressed in 1997 dollars. The general upward trend is significant in view of the fact that the vertical axis is logarithmic. Over the period from 1992 to 1996, it has been estimated that losses due to natural hazards averaged $54 billion per year, or over $1 billion per week (National Science and Technology Council, 1997). Flooding alone accounted for about 26 percent of that total, or roughly $270 million per week.

It is staggering to realize that these huge losses have occurred despite the fact that for most of the twentieth century, the United States has been largely spared the expense of a catastrophic natural disaster in a highly populated and developed area. For exam-ple, a great earthquake of magnitude 8 or more on the Richter scale has not struck a major metropolitan area since the one in San Francisco, California, in 1906. A Class 4 or 5 hurricane has not struck a major urban area directly since 1926 in Miami, Florida (van der Vink et al., 1998). However, even though hurricanes have largely spared major population centers in recent years, they do pose threats every year and have caused substantial property damage, mainly to the Gulf and Atlantic coasts.

Sobering also is the cost of natural disasters in terms of loss of life. Figure 1.2 shows estimates published by the U.S. National Climatic Data Center and cited by the National Research Council (1991). The estimates indicate that during the period from 1941 to 1980, U.S. population-adjusted death rates due to flooding have generally increased, but those due to lightning and tornadoes have dropped dramatically. Popu-

Section 1.1 Need for Stormwater Conveyance Systems 3

Figure 1.1Annual flood losses in the United States from 19031999 (as reported by the U.S. National Weather Service, 2000)

lation-adjusted death rates due to tropical cyclones (hurricanes) have remained fairly constant over that time period. As of 1980, the population-adjusted death rate due to flooding alone was about as great as that due to lightning, tornadoes, and tropical cyclones combined. Although the greater share of the loss of life from floods indi-cated in Figure 1.2 is due to major flooding, a substantial portion is due to flooding of drainageways in urbanized areas. Since such drainageways are often engineered as part of an urban stormwater management and conveyance system, they fall within the scope of this text.

Many factors contribute to the upward trends in flood damages. However, the escala-tion is due largely to the increased occupancy and use of floodprone lands and coastal areas. Despite good intentions, public financing and implementation of so-called flood control projects are partly to blame for this state of affairs. The public, including politicians and decision-makers, are accustomed to hearing the term flood control without fully understanding the limitations of such projects. Often, one con-sequence of these projects is a false sense of security, so that when the inevitable large flood does occur, damages are greater than they would have been otherwise.

History has shown that floods cannot be controlled completely. Technical experts have never intended the term flood control to be interpreted in an absolute sense, but the phrase is often misleading to the public. To avoid public misconceptions about the level of protection provided by flood control projects, terminology such as excess water management, which is less suggestive of absolute control, should be considered.


Figure 1.2Population-adjusted death rates in the U.S. due to natural disasters from 1941 to 1980

The monetary damage and the loss of life illustrated in Figures 1.1 and 1.2, respec-tively, are aggregates representing totals for the entire United States. Similar informa-tion may be obtained for other parts of the world. The Natural Hazards Center at the University of Colorado, Boulder is a clearinghouse for data and other information on natural hazards worldwide, and provides Internet links to many useful sources. The Web site for the Hazard Reduction and Recovery Center at Texas A&M University also provides useful research tools.

Damage and loss of life will continue to be among the most important factors driving stormwater management. These factors are also the most tangible indicators of the success (or failure) of the stormwater management process. Other considerations that drive the need for stormwater management are environmental and water quality con-cerns, aesthetics, and legal and regulatory considerations. The complexity of the driv-ing factors and the consequent need for evaluation of the trade-offs among competing alternatives make stormwater management an exciting and challenging process.

Section 1.2 History of Stormwater Management Systems 5

1.2 HISTORY OF STORMWATER MANAGEMENT SYSTEMS

As noted in Section 1.1, the need for dealing with stormwater runoff is an age-old problem. A number of accounts of historical developments in wet-weather flow man-agement have been published over the years; the summary by Burian et al. (1999) is one of the most recent and serves as a model for the briefer presentation here. Addi-tional historic information relevant to regulatory requirements is presented in Chapter 14.

Ancient PracticesSeveral ancient civilizations constructed successful surface-water drainage systems. Some civilizations incorporated the removal of sanitary wastes into the surface runoff system to form a combined system of sewage. For example, around 3000 B.C., dwell-ers of the Indus civilization in the city of Mohenjo-Daro (now in Pakistan) con-structed combined sewers consisting of a simple sanitary sewer system with drains to remove stormwater from streets. The masonry work and clever design of this system demonstrate that, in some instances, more care was taken with the sewage system than with construction of some of the buildings. Other ancient sewer systems were con-structed by the Mesopotamian Empire in Assyria and Babylonia (circa 2500 B.C.), and by the Minoans on the island of Crete (30001000 B.C.). Yet others were constructed in parts of the city of Jerusalem (circa 1000 B.C.); and in central Italy by the Etruscans around 600 B.C. Ruins of some major cities in China indicate that partially under-ground systems were constructed around 200 A.D. Other examples of ancient sewage-system builders include the Greeks in Athens, the Macedonians and Greeks under the rule of Alexander the Great, and the Persians.


Of all the societies of western Asia and Europe, from antiquity until the nineteenth century, only the Romans built a carefully planned road system with properly drained surfaces. Specific drainage facilities used by the Romans included occasional curbs and gutters to direct surface runoff into open channels alongside roadways. They also graded roadway surfaces to enhance drainage to the channels. This channel-based sewer system collected not only stormwater runoff from roadway surfaces but also sanitary and household wastes. During periods of dry weather when flows were insuf-ficient to flush the channels, the wastes accumulated and caused unsanitary conditions to develop. Therefore, the channels were covered, evolving into combined sewer sys-tems. These covered drains ultimately developed into the Roman cloacae, or under-ground sewers (see Figure 1.3). These sewers were a source of civic pride and symbolized the advanced stature of the Roman civilization.

Figure 1.3Outlet of the Cloaca Maxima on the Tiber River, Rome (Blake, 1947)

Post-Roman Era to the 1700sFrom the time of the Roman Empire through the 1700s, European sewage manage-ment strategies experienced little advancement and even regressed in terms of sanita-tion. Along with the decreasing populations of cities after the fall of the Roman Empire came the abandonment of municipal services such as street lighting, running water, and sewer systems.

During the Dark Ages, Western society was indifferent to such issues. Most citizens ignored matters of hygiene and cleanliness, for example. As the Middle Ages pro-gressed, drainage and sanitary services were developed in response to aggravating conditions and disease outbreaks. Unfortunately, these systems were disjointed and


poorly planned. Paris and London exemplify European cities with piecemeal systems at that time.

Resurgence in the development of planned sewage systems from the haphazard sys-tems of the Middle Ages occurred between the fourteenth and nineteenth centuries. The sewers constructed in Europe during this time, such as those in London and Paris, were simply open ditches. Besides being conveyances for stormwater, these channels became receptacles for trash and other household and sanitary wastes, the accumula-tion of which caused overflows. As a remedy, the channels were covered to create combined sewers, essentially replicating the practice of the Romans some 1500 years earlier.

In Paris, the first planned covered sewer dates to 1370, when Hugues Aubriot con-structed the Fosse de St. Opportune. This beltway sewer discharged into the Seine River and acted as a collector for the sewers on one side of the Seine. However, for the most part, sewer systems before the 1700s lacked proper design and were conducted in a piecemeal fashion. Maintenance and proper operation were virtually neglected. The systems were poorly functioning and subject to repeated blockages, resulting in nuisance flooding.

The Nineteenth CenturyAt the end of the 1700s, the outlook was improving for wet-weather flow manage-ment in Europe. Society held a belief in progress that became increasingly linked to technology throughout the 1800s. Until the 1820s, European sewers were constructed of cut stone or brick with rectangular or roughly rounded bases that contributed to deposition problems. Substitution of millstone and cement mortar stone made con-struction of curved and smooth sewer floors easier, thus improving both the self-cleansing properties and hydraulic efficiency. A variety of new pipe shapes were developed, including egg-shaped, oval, and v-notch cross sections. Additional improvements in the early 1800s consisted of increased attention to sewer mainte-nance and the adoption of minimum slope and velocity criteria to provide adequate flushing during dry-weather periods.

Comprehensive planning was the next major step in sewage system design. In 1843, William Lindley, an Englishman living in Hamburg, Germany, was commissioned to plan and design a system following a major fire (see Figure 1.4). London followed Hamburgs successful example by commissioning Joseph Bazalgette to plan and design its system. Construction of the Main Drainage of London was completed in 1865. In 1858, E. S. Chesbrough designed the first comprehensive wet-weather flow management system in the United States for the City of Chicago, Illinois. About the same time, J. W. Adams designed a comprehensive sewer system for Brooklyn, New York. The designs implemented in the United States often made use of empirical data obtained from European practice. Because rainfall intensities and storm durations are highly location dependent, as are factors such as time of concentration and soil type, the topographic and climatological differences between the United States and Europe ultimately contributed to design deficiencies.


Figure 1.4Map of Hamburg,

Germany sewer

system from 1857

(Chesbrough, 1858)

In the middle to late 1800s, rapid urbanization in the United States led to increases in water consumption and consequent overwhelming of privy-vault and cesspool sys-tems for wastewater disposal. After much debate, city councils, engineers, and health groups generally agreed that centralized sewage systems were more cost-effective and provided greater benefits than did other options.

The question arose, however, as to which type of sewage system should be con-structedseparate or combined. Initially, the combined sewer scheme was widely implemented for several reasons, including the fact that there was no European prece-dent for successful separate systems. Further, a belief existed that combined systems were cheaper to construct.

There were opponents to this practice, however. For example, Colonel George E. Waring designed relatively successful separate sewer systems in Lenox, Massachu-setts, and Memphis, Tennessee. Around the same time (about 1880), at the request of the U.S. National Board of Health, Rudolph Hering visited Europe to investigate practices there. Herings report recommended combined systems when serving exten-sive and densely developed areas, and separate systems for areas in which rainwater did not require removal underground. By the end of the 1800s, engineers had embraced Herings ideas, and combined sewers were recommended for most urban-ized areas. This philosophy did not change until the 1930s and 1940s when more wastewater treatment was required, because the contribution of stormwater volume translated into higher treatment costs. Consequently, separate sewers then became the more commonly recommended option.

Regardless of the type of sewage (separate or combined), control and treatment of wastewater discharges were limited. It was commonly assumed that cities could safely dispose of their wastes into adjacent waterways, with dilution being the solution to pollution. By the middle to late 1800s, epidemiological research by John


Snow and William Budd, which showed waters ability to transmit infectious disease, and germ and bacterial research by Louis Pasteur and Robert Koch, were beginning to challenge the effectiveness of dilution strategies. Despite the fact that this fundamen-tal scientific research demonstrated a connection between polluted waters and dis-ease, wastewater treatment was not widely practiced at this time. Debate centered on whether it was better to treat wastewater before discharging it to a stream or for down-stream users of the water to treat it before distribution as potable water. Most engi-neers subscribed to the latter approach, effectively ignoring the effects on the habitats and recreational uses afforded by receiving waters.

In the mid-1800s, estimation of surface stormwater runoff, which was needed to design appropriately sized conveyance structures, was based mainly on empirical results. Among the tools used was Roes table, a simple look-up table indicating the pipe size required to convey runoff for a given drainage area and slope based on Roes observations of London sewers (Metcalf and Eddy, 1928). Other methods were based on empirical and, frequently, ill-founded formulas developed by Adams, McMath, Talbot, and others. The empirical nature of these methods and their development for site-specific conditions often resulted in very poor estimates and designs when they were applied under conditions different from those for which they had been devel-oped. For example, Talbots formula predicts the required cross-sectional area of a drainage pipe as follows (Merritt, 1976):

(1.1)

where A = required cross-sectional area of drainage pipe (ft2)C = coefficient ranging from 0.2 for flat country not affected by accumu-

lated snow or severe floods to 1.0 for steep, rocky ground with abrupt slopes

M = the drainage basin area (ac)

Talbots formula was based on a rainfall intensity of 4 in/hr, but could be adjusted for other intensities by proportion. The formula does not consider pipe slope or rough-ness, factors that are now known to greatly influence required conveyance pipe diameters.

In the second half of the nineteenth century, hydrologic and hydraulic methods were enhanced considerably through the research of such notable figures as Antoine Chzy and Robert Manning, who developed uniform flow formulas, and T. J. Mulvaney and Emil Kuichling, who developed what is known today as the rational method for stormwater runoff rate estimation. In 1899, Arthur Talbot performed some of the ini-tial work on rainfall estimation, producing curves that eventually evolved into present-day intensity-duration-frequency curves.

The Twentieth CenturyBy the 1920s, the growing accumulation of rainfall records enabled the use of design storms in which the time variation of rainfall intensity during a storm event was explicitly acknowledged and accounted for. Additional advancements during the

4 3/ 2A C M


twentieth century consisted of the development of unit hydrograph theory by L. K. Sherman in 1932, and studies of rainfall abstractions and infiltration by W. H. Green and G. A. Ampt in 1911 and by Robert Horton in 1933. By the middle to latter part of the century, the U.S. Soil Conservation Service (now the Natural Resource Conserva-tion Service) had developed simple but effective methods for runoff estimation for both rural and urban areas. Methods for statistical and probabilistic analysis of floods, droughts, and other hydrologic, hydraulic, and water quality variables also advanced rapidly during the twentieth century.

With the development of the digital computer came rapid advancements in technical tools and methods for wet-weather flow management. Included among these advances were developments of specialized hydrologic and hydraulic computer pro-grams (see Figure 1.5), as well as more general computational and data processing technologies such as spreadsheets, databases, pre- and postprocessors, and geographic information systems. The computational power of computers enabled engineers to efficiently optimize their designs through the use of advanced mathematical optimiza-tion and statistical techniques. Whereas just a few decades ago it was uncommon to find even a single computer in most design engineering offices, a computer is now an indispensable tool on every engineers desk.

Figure 1.5Computer programs for designing storm sewers became available in the latter part of the twentieth century

Perhaps some of the most significant developments that have occurred in the past few decades have been related to the recognition of the impacts of stormwater runoff on receiving waters. By the early 1970s, the U.S. Congress had passed the Water Pollu-tion Control Act, and increasingly strict water quality regulations have since been developed. To mitigate wet-weather flow impacts on receiving waters and habitats, methods of control and treatment of urban stormwater runoff are required. Among these methods are physical, chemical, and biological treatment processes and storage and treatment combinations. It should be noted, however, that water quality is not the only wet-weather factor contributing to habitat degradation downstream of urban areas. Other factors, including channelization, debris and cover removal, and channel straightening, must be addressed more adequately in the future.

Section 1.3 Overview of Stormwater Conveyance System Design 11

Summary and OutlookMost of the tools and methods currently used for prediction of runoff discharges and volumes and for appropriately sizing required conveyance facilities have been devel-oped within the last 200 years. That ancient civilizations were able to effectively deal with stormwater runoff indicates that advanced knowledge and sophisticated tools are not necessary for relatively simple conveyance systems. This is not the case in mod-ern society, however, where competing infrastructure needs vie for resources and mul-tiple goals require evaluation of several designs. Computers and automated control technologies enable modern designers and system operators to optimize and maintain complex systems and make the design and operation much more efficient than they would be otherwise.

What the future will bring is always uncertain. A report by the U.S. EPAs Urban Watershed Management Branch (Field et al., 1996) describes five areas in which research is needed. They are

Characterization and problem assessment

Watershed management

Impacts and control of toxic substances

Control technologies

Infrastructure improvement

The third of these areas, which deals with pollutants, has received the least attention in the past. However, it is beginning to receive considerable attention in the research community and can be expected to become more of an issue in practice in the coming years. A growing research area that is absent from this list is sustainable development, which is concerned with preserving water quality for human use and the environmen-tal preservation into the future.

1.3 OVERVIEW OF STORMWATER CONVEYANCE SYSTEM DESIGN

Design of a stormwater conveyance system is a trial-and-error process. The art of design involves defining the objectives and determining, from among a number of feasible options, the one that best meets those objectives. The design engineer opti-mizes the use of resources (materials, construction labor, operation and maintenance costs, and so on) to meet the objectives while satisfying certain constraints (such as project budgets, right-of-way limitations, and design storm criteria).

Design is different from analysis. Design is more complex than analysis. In a design, the engineer is not limited to the evaluation of any single combination of inputs in seeking to meet the desired objectives. An analysis, on the other hand, is simply a technical evaluation of a possible choice to determine whether it meets the objectives while satisfying the constraints. The design process may be viewed as consisting of many analyses, each of which determines whether the design is feasible (that is,


whether it satisfies the design constraints) and whether it meets the project objectives. Finally, from among all the feasible designs, the best one is selected.

With this view of the design process in mind, several questions need to be addressed:

What is (are) the objective(s) of the design?

What resources need to be allocated?

What are the constraints that need to be satisfied?

How does one define the best feasible design? What makes one choice bet-ter than another?

Only when these questions are explicitly acknowledged and addressed can the design be considered acceptable. The following subsections are intended to clarify these questions. However, the issues surrounding these questions are specific to each design.

Design ObjectivesThe design objectives are the project goals that the engineer attempts to meet as much as possible without violating the design constraints. There may be more than one objective associated with the design of a stormwater conveyance system. The most obvious objective is probably adequate conveyance of stormwater runoff. However, in the face of specific regulations regarding return periods for which design flows must be computed, stormwater conveyance capacity is more likely to be viewed as a con-straint than as an objective.

It is usually not possible to develop a design that is optimal for all objectives. In other words, if a particular design alternative is optimal for one objective, then it will usu-ally be less than optimal for the other objectives. Therefore, some weighting or trade-

Section 1.3 Overview of Stormwater Conveyance System Design 13

off analysis to quantify the relative importance of the objectives is necessary. For fur-ther reading on multiobjective planning, the reader is referred to Loucks, Stedinger, and Haith (1981); Goodman (1984); and Grigg (1996).

Many possible objectives may be adopted for a particular project. Historically, mini-mization of the total life-cycle cost of the project has been an attractive one, probably due in part to the relative ease with which it can be quantified. For cases in which the engineer is faced with developing a design for which the capital cost may not exceed an available budget, cost may not be a design objective, but instead a design con-straint.

Other possible objectives are

Minimizing flood damages or traffic hazards during a storm event of a mag-nitude greater than that for which the primary, or minor, storm sewer system is designed

Minimizing aesthetic, physical, chemical, and biological impacts to existing receiving waters

Maximizing potential recreational and aesthetic benefits provided by wet detention facilities

The engineer should seek to define the design objectives with input from the entity funding the project, other relevant regulating and/or operation and maintenance agen-cies, the general public, and special-interest groups.

ResourcesIn conveyance system design, resources allocated to a project (or project costs) con-sist of raw materials and labor for construction. Operation and maintenance resources (equipment, manpower, and so forth) required over the project lifetime should also be included. For instances in which natural channels, wetlands, or other areas where eco-systems are disturbed, the loss of habitat and the associated biotic communities should also be considered as resources allocated to a project.

Other types of resources that should be considered are those related to acquisitions of rights-of-way and/or temporary or permanent easements. In some cases, it is neces-sary to purchase or condemn residential or other properties so that they can be demol-ished to make way for the planned project improvements. In these instances, resources allocated to the project should include purchase and relocation costs, but these costs may be offset in part by less frequent flooding in the project locale.

ConstraintsAs already noted, a limited budget within which a project must be implemented is one type of constraint. Additional constraints may be geometric in nature, such as limited pipe burial depths, existing underground utilities that cannot be relocated, and limited rights-of-way. Other constraints consist of federal, state, and local regulations within which a project must be developed, as well as laws regarding water rights and flood protection.


As a general rule, constraints can be of two types. One type of constraint specifies a requirement that cannot be violated at any cost. The second type of constraint can be violated, but the cost associated with its violation may be high. For example, if a design constraint were to say that an existing underground gas transmission line can-not be moved, the reality is that the line could be moved, but the cost could be prohib-itive.

What Is Best?After the engineer identifies a number of feasible designs, the task turns to the issue of selection of the best design. But how should one define what is best? What makes one design better than another? The answer depends on many factors, but the degree to which each design meets the stated project objective(s) is certainly one basis for com-parison. For example, if cost minimization were the only objective, then the lowest-cost alternative would be chosen. The design engineer does not necessarily make the final selection of the design. Often, the engineers client or a regulatory body is the decision-maker. In such instances, the role of the designer is to provide the decision-maker with options and quantifications of costs, benefits, and impacts. The designer essentially acts as an advisor on complex technical issues.

Factors that might be considered in judging the suitability of the various choices are issues such as safety and aesthetics. Other measures might relate to equity in the dis-tribution of project benefits. For example, if a citywide stormwater drainage improve-ment project were to make improvements only in new or politically powerful districts, while overlooking needs in poor and disadvantaged areas, matters of fairness and equitability would not be satisfied.

The design process as outlined by this section may seemingly imply that the storm sewer and culvert design process can be viewed as a mathematical optimization prob-lem (Loucks, Stedinger, and Haith, 1981). That approach, however, is usually not for-mally applied in design practice because the degree of quantification necessary to do so is usually not possible. The practitioner must instead rely heavily on experience and knowledge of the problem at hand to identify suitable alternatives for detailed evaluation. Nevertheless, the general idea of optimizing the use of resources to achieve adopted objectives within certain constraints does succinctly characterize the overall design process. After the preferred design is identified through this heuristic process, one can prepare detailed construction plans and specifications.

1.4 CHAPTER SUMMARYThe need to protect against flooding is driven primarily by the loss of life and prop-erty that flooding causes. Most of the losses can be associated with major flooding of streams and rivers, and the stormwater conveyance systems described in this text have a limited effect on events of this magnitude. However, these primary systems signifi-cantly reduce the damages caused by smaller but more frequent events.

In modern society, storm drainage design is complicated by competing infrastructure needs and goals that require careful balancing of resources and evaluation of multiple

References 15

possible designs. Computers have greatly simplified this process. Considerations such as water quality and the need to deal with pollutants are receiving more attention in recent years.

The design of stormwater conveyance systems is an iterative process that involves defining project objectives and determining the design alternative that best meets them, but does not exceed available resources or violate design constraints. The design process can be viewed as a series of analyses, or technical evaluations of indi-vidual design alternatives. The best design is then selected from among these alter-natives.

REFERENCES

Blake, M. E. 1947. Ancient Roman Construction in Italy from the Prehistoric Period to Augustus. Washing-ton, D.C.: Carnegie Institution of Washington.

Burian, S. J., S. J. Nix, S. R. Durrans, R. E. Pitt, C-Y. Fan, and R. Field. 1999. Historical Development of Wet-Weather Flow Management, Journal of Water Resources Planning and Management 125, no. 1: 313.

Chesbrough, C. S. 1858. Chicago sewerage report of the results of examinations made in relation to sewerage in several European cities in the winter of 185657. Chicago, Illinois.

Field, R., M. Borst, M. Stinson, C-Y. Fan, J. Perdek, D. Sullivan, and T. OConnor. 1996. Risk Management Research Plan for Wet Weather Flows. Edison, N. J.: U.S. Environmental Protection Agency.

Goodman, A. S. 1984. Principles of Water Resources Planning. Englewood Cliffs, N. J.: Prentice Hall.

Grigg, N. S. 1996. Water Resources Management: Principles, Regulations, and Cases. New York: McGraw-Hill.

Loucks, D. P., J. R. Stedinger, and D. A. Haith. 1981. Water Resource Systems Planning and Analysis,Englewood Cliffs, N. J.: Prentice Hall.

Merritt, F. S., ed. 1976. Standard Handbook for Civil Engineers, 2d ed. New York: McGraw-Hill.

Metcalf, L., and H. P. Eddy. 1928. Design of Sewers. Vol. 1 of American Sewerage Practice. New York: McGraw-Hill.

National Science and Technology Council. 1997. Committee on Environment and Natural Resources: Fact Sheet, Natural Disaster Reduction Research Initiative.

National Research Council. 1991. Opportunities in the Hydrologic Sciences. Washington, D.C.: Committee on Opportunities in the Hydrologic Sciences, Water Science and Technology Board, National Academy Press.

National Weather Service. 2000. Flood Losses: Compilation of Flood Loss Statistics. National Weather Service, Office of Hydrologic Development. www.nws.noaa.gov/oh/hic/flood_stats/Flood_loss_time_series.htm.

van der Vink, G., R. M. Allen, J. Chapin, M. Crooks, W. Fraley, J. Krantz, A. M. Lavigne, A. LeCuyer, E. K. MacColl, W. J. Morgan, B. Ries, E. Robinson, K. Rodriquez, M. Smith, and K. Sponberg. 1998. Why the United States is Becoming More Vulnerable to Natural Disasters, EOS, Transactions of the American Geophysical Union 79, no. 44: 533537.

Workers construct a large, triple-

barrel box culvert (top). Low flows are temporarily

diverted around the disturbed area

through bypass piping (bottom).

SCMD-03-CH01-Introduction Stormwater Conveyance Modeling Design

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