Water distribution systems — the pipes and pumps that deliver clean water to our taps. In Madera there are more than miles of underground water pipes. Wastewater collection systems — the pipes and pumps that take away used water from our toilets, drains, bathtubs, and laundry. These are also called sewers. In Madera, there are over miles of municipal wastewater collection pipes underground. Wastewater treatment — the processes to remove contaminants from our used water so that it can be safely returned to the environment.
This is also called sewage treatment. Stormwater systems — the pipes, ditches and natural systems that channel our rain water and snow melt away from our homes and businesses and back to the natural environment. In Madera there are over 45 miles of stormwater pipes underground. It enables better land use planning and the management of its impacts on fresh water supplies, treatment, and distribution; wastewater collection, treatment, reuse and disposal; stormwater collection, use and disposal; and solid waste collection, recycling, and disposal systems.
It makes urban development part of integrated basin management oriented toward a more economically, socially, and environmentally sustainable mixed urban—rural landscape. While recognizing the need for and the benefits derived from a systems approach to urban planning and development, including its water related components, this chapter will serve as an introduction to each of these components separately, and not all together as a system.
This understanding of each component is needed if indeed they eventually will be modeled, designed, and managed as part of the overall urban infrastructure system. Schematic showing urban surface water source, water treatment prior to urban use, and some sources of nonpoint urban drainage and runoff and its impacts. Generic data-driven simulation models of components of urban water systems have been developed and are commonly applied to study specific component design and operation issues.
Increasingly optimization models are being used to estimate cost-effective designs and operating policies. Cost savings can be substantial, especially when applied to large complex urban systems Dandy and Engelhardt ; Savic and Walters Most urban water users desire, and many require, high quality potable water.
In such situations water treatment prior to its use is required. Once treated, water can be stored and distributed within the urban area, usually through a network of storage tanks and pipes.
Pipe flows in urban distribution systems should be under pressure to prevent contamination from groundwater leakage and to meet fire protection and other user requirements. Wastewater treatment plants remove some of the impurities in the wastewater before discharging it into receiving water bodies or on land surfaces.
Water bodies receiving effluents from point sources such as wastewater treatment plants may also receive runoff from the surrounding watershed area during storm events. The discharge of point and nonpoint pollutants into receiving water bodies can impact the quality of the water in those receiving water bodies. The fate and transport of these pollutants in water bodies can be predicted using water quality models similar to those discussed in Chap.
This chapter briefly describes these urban water system components and reviews some of the general assumptions incorporated into optimization and simulation models used to plan and manage urban water infrastructure systems. The focus of urban water systems modeling is mainly on the prediction and management of quantity and quality of flows and pressure heads in water distribution networks, wastewater flows in gravity sewer networks, and on the design efficiencies of water and wastewater treatment plants.
Other models can be used for the real-time operation of various components of urban systems. This ongoing case of urban water management in Flint, Michigan US illustrates what can happen even in so-called developed regions if decisions are made without adequate analyses of possible health impacts and the consequences of poor follow-up decisions at various governmental levels.
This has created a serious public health danger. As a result, thousands of residents have severely high levels of lead in their blood and are experiencing a variety of serious health problems. Local, state, and federal authorities, and political leaders, did not seem sufficiently concerned until inhabitants of Flint, with the help of others who performed water quality analyses and obtained public health statistics from local hospitals, made it a national issue.
In November, , some of the residents filed a federal class action lawsuit against the Governor and 13 other city and state officials. Additional lawsuits have been filed after that and resignations have occurred. In January , the Governor declared the city to be in a state of emergency. Less than 2 weeks later the President of the US declared the drinking water crisis in Flint as a federal emergency authorizing additional help from the federal government. Before water is to be used for human consumption its harmful impurities need to be removed.
Communities that do not have adequate water treatment facilities, common in developing regions, often have high incidences of disease and mortality due to contaminated water supplies. A range of syndromes, including acute dehydrating diarrhea cholera , prolonged febrile illness with abdominal symptoms typhoid fever , acute bloody diarrhea dysentery , and chronic diarrhea Brainerd diarrhea result in over 3 billion episodes of diarrhea and an estimated 2 million deaths, mostly among children, each year.
Contaminants in natural water supplies can include microorganisms such as Cryptosporidium and Giardia lamblia, inorganic and organic cancer-causing chemicals such as compounds containing arsenic, chromium, copper, lead, and mercury , and radioactive materials such as radium and uranium. As Box As shown in Fig. Next, a chemical such as alum is added to the raw water to facilitate coagulation of remaining impurities.
As the wastewater is stirred the alum causes the formation of sticky globs of small particles made up of bacteria, silt, and other impurities. Once these globs of matter are formed, the water is routed to a series of settling tanks where the globs, or floc, sink to the bottom. This settling process is called flocculation.
After flocculation the water is pumped slowly across another large settling basin. In this sedimentation or clarification process much of the remaining floc and solid material accumulates at the bottom of the basin.
The clarified water is then passed through layers of sand, coal, and other granular material to remove microorganisms—including viruses, bacteria, and protozoa such as Cryptosporidium—and any remaining floc and silt.
This stage of purification mimics the natural filtration of water as it moves through the ground. The filtered water is then treated with chemical disinfectants to kill any organisms that remain after the filtration process. An effective disinfectant is chlorine but its use may cause potentially dangerous substances such as trihalomethanes.
Alternatives to chlorine include ozone oxidation Fig. Unlike chlorine, ozone does not stay in the water after it leaves the treatment plant, so it offers no protection from bacteria that might be in the storage tanks and water pipes of the water distribution system. Water can also be treated with ultraviolet light to kill microorganisms, but it has the same limitation as oxidation. It is ineffective outside the treatment plant. Water distribution systems include pumping stations, distribution storage, and distribution piping.
The hydraulic performance of each component in the distribution network depends upon the performance of other components. Of interest to designers are both the flows and their pressures throughout the network. A more precise representation includes a kinetic energy correction factor, but that factor is small and can be ignored. For open-channel flows, the elevation head is the distance from some datum to the top of the water surface.
For pressure pipe flow, the elevation head is the distance from some datum to the center of the pipe. The parameter p is the pressure, e. The energy grade is the sum of the hydraulic grade and the velocity head. This is the height to which a column of water would rise in a Pitot tube, but also accounting for fluid velocity.
When plotted in profile, as in Fig. For open-channel flow, the depth of flow, y , is the elevation head minus the channel bottom elevation. For a given discharge, the specific energy is solely a function of channel depth. There may be more than one depth having the same specific energy. In one case the flow is subcritical relatively higher depths, lower velocities and in the other case the flow is critical relatively lower depths and higher velocities.
Whether or not the flow is above or below the critical depth the depth that minimizes the specific energy will depend in part on the channel slope. The friction loss per unit distance along the channel is the average of the friction slopes at the two ends divided by the channel length. This defines the energy grade line, EGL. Given these equations it is possible to compute the distribution of flows and heads throughout a network of open channels or pressure pipes.
The two conditions are the continuity of flows at each node, and the continuity of head losses in loops for each time period t. An example of a pipe network, showing the values of K for predicting head losses from Eq. A typical wastewater treatment plant showing the sequence of processes for removing impurities. Flows and heads of the network shown in Fig.
This solution shown in Table Losses are usually expressed as a linear function of the velocity head, due to hydraulic structures such as valves, restrictions, or meters at each node. This solution suggests that the pipe section between nodes A and C may not be economical, at least for these flow conditions. Other flow conditions may prove otherwise. But even if they do not, this pipe section increases the reliability of the system, and reliability is an important consideration in water supply distribution networks.
Many of the water quality models discussed in Chap. The assumption of complete mixing such as at junctions or in short segments of pipe, is made. Reactions among constituents can occur as water travels through the system at predicted velocities. Water-resident times the ages of waters in various parts of the network are important variables for water quality prediction as constituent decay, transformation, and growth processes take place over time.
Computer models typically use numerical methods to find the hydraulic flow and head relationships as well as the resulting water quality concentrations. Most numerical models assume combinations of plug flow advection along pipe sections and complete mixing within segments of the each pipe section at the end of each simulation time step.
Some models also use Lagrangian approaches for tracking particles of constituents within a network. See Chap.
Computer models that simulate the hydraulic and water quality processes in water distribution networks must be run long enough for the system to reach equilibrium conditions, i. Equilibrium conditions within pipes are reached relatively quickly compared to those in storage tanks. Flows in urban sewers and their pollutant concentrations vary throughout a typical day, a typical week, and over the seasons of a year. Flow conditions can range from free surface to surcharged flow, from steady to unsteady flow, and from uniform to gradually or rapidly varying non-uniform flow.
Urban drainage ditches normally have uniform cross sections along their lengths and uniform gradients. Because the dimensions of the cross sections are typically one or two orders of magnitude less than the lengths of the conduit, unsteady free surface flow can be modeled using one-dimensional flow equations. When modeling the hydraulics of flow it is important to distinguish between the speed of propagation of the kinematic wave disturbance and the speed of the bulk of the water. In general the wave travels faster than the water particles.
Thus if water is injected with a tracer the tracer lags behind the wave. The speed of the wave disturbance depends on the depth, width, and velocity of the flow.
Flood attenuation or subsidence is the decrease in the peak of the wave as it propagates downstream. Gravity tends to flatten, or spread out, the wave along the channel. The magnitude of the attenuation of a flood wave depends on the peak discharge, the curvature of the wave profile at the peak, and the width of flow. Flows can be distorted changed in shape by the particular channel characteristics. Additional features of concern to hydraulic modelers are the entrance and exit losses to the conduit.
Typically at each end of the conduit is a manhole. Manholes are storage chambers that provide access for men and women to the conduits upstream and downstream. Manholes induce some additional head loss. An important parameter of a given open-channel conduit is its capacity, that is, the maximum flow that can occur without surcharging or flooding. Assuming the hydraulic gradient is parallel to the bed of the conduit, each conduit has an upper limit to the flow that it can accept.
Pressurized flow is much more complex than free surface flow. In marked contrast to the propagation speed of disturbances under free surface flow conditions, the propagation of disturbances under pressurized flow in a 1 m circular conduit m long can be less than a second. Some conduits can have the stable situation of free surface flow upstream and pressurized flow downstream.
The wastewater generated by residences, businesses, and industries in a community is largely water. One measure of the biodegradable constituents in the wastewater is its biochemical oxygen demand, or BOD 5. BOD 5 is the amount of dissolved oxygen aquatic microorganisms consumed in 5 days as they metabolize eat the organic material in the wastewater.
The Activated Sludge system is designed to treat 48 million gallons of wastewater per day mgd with a peak hydraulic capacity of mgd. As illustrated in Fig. The goal is to reduce or remove organic matter, solids, nutrients, disease-causing organisms, and other pollutants from wastewater before it is released into a body of water, or on to the land, or is reused. The first stage of treatment is called preliminary treatment.
Preliminary treatment removes solid materials sticks, rags, large particles, sand, gravel, toys, money, or anything people flush down toilets. Equipment such as bar screens, and grit chambers are used to filter the wastewater as it enters a treatment plant. The wastewater then passes on to what is called primary treatment. Clarifiers and septic tanks are usually used to provide primary treatment. Primary treatment separates suspended solids and greases from wastewater.
Wastewater is held in a tank for several hours allowing the particles to settle to the bottom and the greases to float to the top. The solids drawn off the bottom and skimmed off the top receive further treatment as sludge. The clarified wastewater flows on to the next secondary stage of wastewater treatment.
Secondary treatment is typically a biological treatment process designed to remove dissolved organic matter from wastewater. Sewage microorganisms cultivated and added to the wastewater absorb organic matter from sewage as their food supply.
Three approaches are commonly used to accomplish secondary treatment; fixed film, suspended film, and lagoon systems. Fixed film systems grow microorganisms on substrates such as rocks, sand, or plastic. The wastewater is spread over the substrate. As organic matter and nutrients are absorbed from the wastewater, the film of microorganisms grows and thickens. Trickling filters, rotating biological contactors, and sand filters are examples of fixed film systems.
Suspended film systems stir and suspend microorganisms in wastewater. Activated sludge, extended aeration, oxidation ditch, and sequential batch reactor systems are all examples of suspended film systems. As the microorganisms absorb organic matter and nutrients from the wastewater they grow in size and number. After the microorganisms have been suspended in the wastewater for several hours, they are settled out as sludge.
The remainder is sent on to a sludge treatment process. Lagoons, where used, are shallow basins that hold the wastewater for several months to allow for the natural degradation of sewage. These systems take advantage of natural aeration and microorganisms in the wastewater to renovate sewage. Advanced treatment is necessary in some treatment systems to remove nutrients from wastewater. Chemicals are sometimes added during the treatment process to help remove phosphorus or nitrogen. Some examples of nutrient removal systems include coagulant addition for phosphorus removal and air stripping for ammonia removal.
Final treatment focuses on removal of disease-causing organisms from wastewater. Treated wastewater can be disinfected by adding chlorine or by exposing it to sufficient ultraviolet light.
High levels of chlorine may be harmful to aquatic life in receiving streams. Treatment systems often add a chlorine-neutralizing chemical to the treated wastewater before stream discharge.
Sludges are generated throughout the sewage treatment process. This sludge needs to be treated to reduce odors, remove some of the water and reduce volume, decompose some of the organic matter and reduce volume, and kill disease-causing organisms.
Following sludge treatment, liquid and cake sludge free of toxic compounds can be spread on fields, returning organic matter and nutrients to the soil. These components or processes are briefly discussed in the following subsections. Surface runoff of precipitation and the need to collect urban wastewater are the primary reasons for designing and maintaining urban drainage systems. Storms are a major source of flow into the system. Even sanitary sewer systems that are designed to be completely separate from storm drainage sewers are often influenced by rainfall through illicit connections or even infiltration.
Rainfall varies over time and space. These differences are normally small when considering short time periods and small distances but they increase as time and distance increase. The ability to account for spatial differences in rainfall depends on the size of the catchment area and on the number of functioning rainfall recording points in the catchment.
The use of radar permits more precision in estimating precipitation patterns over space and time, as if more rain gauges were used and as if they were monitored more frequently. In practice spatial effects are not measured at high resolution and therefore events where significant spatial variations occur, such as in summer thunderstorms, are usually not very accurately represented. There are two categories of rainfall records: recorded real events and synthetic not-real events. Synthetic rainfall comes in two forms: as stochastically generated rainfall data and as design storms.
These events are derived from analyses of actual rainfall data and are used to augment or replace those historical real data. Design events are a synthesized set of rainfall profiles that have been processed to produce storms with specific return periods, i. Design events are derived to reduce the number of runs needed to analyze system performance under design flow conditions.
Professionals can argue over whether infrastructure design capacities should be based on real rainfall records or synthetic storm events. The argument in favor of using synthetic storms is that they are easy to use and require only a few events to assess the system design performance. The argument in favor of a time series of real rainfall is that these data typically include a wider range of conditions, and therefore are likely to contain the conditions that are critical on each catchment.
The two methods are not contradictory. The use of real rainfall involves some synthesis in choosing which storms to use in a time series, and in adjusting them for use on a catchment other than the one where they were measured. Time series of rainfalls are generally used to look at aspects such as overflow spill frequencies and volumes. On the other hand, synthetic design storms can be generated for a wide range of conditions including the same conditions as represented by real rainfall.
This is generally considered appropriate for looking at pipe network performance. Rainfall varies in space as well as in time, and the two effects are related. Short duration storms typically come from small rain cells that have a short life, or that move rapidly over the catchment. As these cells are small of the order of a kilometer in diameter there is significant spatial variation in rainfall intensity.
Longer duration storms tend to come from large rainfall cells associated with large weather systems. These have less spatial intensity variation. Rainfall is generally measured at specific sites using rain gauges. The recorded rainfall amount and intensity will not be the same at each site. Thus the use of recorded rainfall data requires some way to account for this spatial and temporal variations. The average rainfall over the catchment in any period of time can be more or less than the measured values at one or more gauge sites.
The runoff from a portion of a catchment exposed to a high intensity rainfall will more than the runoff from the same amount of rainfall spread evenly over the entire catchment.
A convenient way of using rainfall data is to analyze long rainfall records to define the statistical characteristics of the rainfall, and then to use these statistics to produce synthetic rainstorms of various return periods and durations.
The frequency with which it is likely to occur, or the probability of it occurring in any particular year. In most of the work on urban drainage and river modeling, the risks of occurrence are expressed not by probabilities but by the inverse of probability, the return period.
An event that has a probability of 0. An event having a probability of 0. Rainfall data show an intensity—duration—frequency relationship. The intensity and duration are inversely related. As the rainfall duration increases the intensity reduces. The frequency and intensity are inversely related so that as the event becomes less frequent the intensity increases. An important part of this duration—intensity relationship is the period of time over which the intensity is averaged.
It is not necessarily the length of time for which it rained from start to finish. In fact any period of rainfall can be analyzed for a large range of durations, and each duration could be assigned a different return period.
The depth of rainfall is the intensity times its duration integrated over the total storm duration. Design rainfall events hyetographs for use in simulation models are derived from intensity—duration—frequency data. A design storm is a synthetic storm that has an appropriate peak intensity and storm profile. Most models assume that the first part of a rainfall event goes to initial wetting of surfaces and filling depression storage.
The depth assumed to be lost is usually related to the surface type and condition. Rain water can be intercepted by vegetation or can be trapped in depressions on the ground surface. Depression storage can occur on any surface, paved, or otherwise. Estimation of depression storage based on data from catchments in the UK Price As rainfall increases so does depression storage. The values of a and b depend in part on the surface type. Evaporation, another source of initial loss, is generally considered to be relatively unimportant.
Continuing losses are often separated into two parts: evapotranspiration and infiltration. These processes are usually assumed to continue throughout and beyond the storm event as long as water is available on the surface of the ground. Losses due to vegetation transpiration and general evaporation are not particularly an issue for single events, but can be during the interevent periods where catchment drying takes place.
This is applicable to models where time-series data are used and generated. Infiltration is usually assumed to account for the remaining rainfall that does not enter into the drainage system.
Effect of catchment wetness on runoff Q over time t Price It is impractical to take full account of the variability in urban topography, and surface condition. Impervious paved surfaces are often dominant in an urban catchment and the loss of rainfall prior to runoff is usually relatively small. Runoff routing is the process of passing rainfall across the surface to enter the drainage network. This process results in attenuation and delay.
These are modeled using routing techniques that generally consider catchment area size, ground slope, and rainfall intensity in determining the flow rate into the network. The topography and surface channels and even upstream parts of the sewer system are usually lumped together into this process and are not explicitly described in a model.
The runoff routing process is often linked to catchment surface type and empirical calibration factors are used accordingly. Various models for rainfall—runoff and routing are available and are used in different parts of the world. Overland runoff on catchment surfaces can be represented by the kinematic wave equation.
However, direct solution of this equation in combination with the continuity equation has not been a practical approach when applied to basins with a large number of contributing subcatchments. Simpler reservoir-based models, that are less computationally and data demanding, represent the physical processes almost as accurately as the more complex physically based approaches Price In practice, models applied to catchments typically assume an average or combined behavior of a number of overland flow planes, gutters, and feeder pipes.
Therefore, the parameters of a physically based approach for example, the roughness value as applied would not relate directly to parameters representative of individual surfaces and structures.
In municipal water systems, water is withdrawn from the water source and treated before it is pumped to our homes and businesses. The quality of the source water determines the type of treatment method. Most systems will include several stages of filtration to remove suspended particles, debris and algae and disinfection to remove bacteria and viruses and purify the water.
Disinfection methods include chlorination and treatment with UV ultra violet light. After treatment, municipal water systems distribute water to homes and businesses in large pipes called water mains that are usually buried under our roads and sidewalks.
Water mains are maintained by our local governments, and paid for by water rates and property taxes. Water lines are smaller pipes that transport the water from water mains to individual homes, apartments and businesses. Water lines are the responsibility of the property owner. Water in municipal systems is required to meet strict water quality standards established in provincial regulations, and is tested regularly to ensure that it is safe to drink.
Stormwater is the result of rain or melting snow. Some of this water is absorbed by the earth and percolates down into underground aquifers, and some finds its way through ditches to streams and rivers that flow into lakes and oceans.
In urban areas, where the ground is covered by sealed surfaces such as roads, parking lots, or buildings, stormwater systems prevent flooding of our homes and businesses by collecting the water in storm drains and piping it to lakes, rivers and the ocean.
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