Core Concepts for the Civil PE Exam Water Resources and Environmental Depth

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Civil PE Exam Water Resources and Environmental  Depth

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Civil PE Exam Water Resources Online Study Guide
Click below to expand each topic. All of this is included in the paperback version of the Water Resources Depth

Analysis and Design

Storm Characteristics


A design storm must be specified when performing any calculations. The design storm is defined by its recurrence interval which is the given amount of time it is likely to see a storm of a certain intensity. Design storms are often 10, 20, 50, or 100-year storms meaning a storm of a certain intensity would only occur once within the given duration.




Runoff Analysis


The rational method can be used to determine the flow rate from runoff of a drainage area. The equation is:

Q = ACi

Q = Flow Rate (cfs)

A = Drainage Area (Acres)

C = Runoff Coefficient

i = Rainfall Intensity (in/hr)

NRCS/SCS Runoff Method

This is an alternative method for determining runoff:

S = Storage Capacity of Soil (in.)

CN = NRCS Curve Number

Q = Runoff (in.)

Pg = Gross Rain Fall (in.)




Hydrographs


Hyetographs – Graphical representation of rainfall distribution over time

Hydrograph – Graphical representation of rate of flow vs time past a given point often in a river, channel, or conduit. The area under the hydrograph curve is the volume for a given time period

Parts of a Hydrograph are shown graphically:

Unit Hydrographs can be determined by dividing the points on the typical hydrograph by the average excess precipitation.

Synthetic Hydrographs are created if there is insufficient data for a watershed. This method uses the NRCS curve number and is a function of the storage capacity.

To develop the synthetic hydrograph, you must calculate the time to peak flow:

tR = Storm duration (time)

Lo = Length overland (ft)

SPercentage = Slope of land

The equation for peak discharge from a synthetic hydrograph then is:




Rainfall


Storm characteristics include duration, total volume, and intensity

Duration: The length of time of a storm. Often measured in days and hours.

Total Volume: The entire amount of precipitation throughout the duration of the storm in a defined area.

Storm Intensity: Total volume of the storm divided by the duration of the storm event. Intensities can be averaged over the entire storm or at shorter intervals to provide instantaneous high intensity portions of the storm. Hyetographs are bar graphs used to measure instantaneous rainfall intensities over time and are covered below.




Stormwater Management


Detention and retention ponds are often used to collect water for flood control and stormwater runoff treatment.

Detention Ponds: Also known as dry ponds. These are ponds which are often kept dry except during flood events. The pond will fill up during increased precipitation to control the flow intensity. This is common in dry, arid, or urban areas to prevent excessive flooding. The ponds typically will be designed to hold water for about 24 hours. Detention ponds also control the amount of sediment since it is captured in the pond and then typically becomes accessible after the pond has dried.

Retention Ponds: Also called wet ponds since they contain a volume of water at all times. The elevation of the water will vary depending on precipitation but will always maintain a permanent amount of water based on low flow conditions. This allows sediment control since the deposits will settle to the bottom and allow for collection.

Infiltration is the rate of which water seeps into the ground. The Horton equation can be used to approximate this rate. This assumes that the water supply is infinite and the ground is saturated:




Time of Concentration





Depletions


The change in storage for a body of water can be approximated from the following equation:

ΔS=P+R+GI-GO-E-T-O

S = Storage

P = Precipitation

R = Runoff

GI = Groundwater inflow

GO = Groundwater outflow

E = Evaporation

T = Transpiration

O = Surface water release




Stream Gauging


Stream gauging is the measurement of a stream channel to determine the discharge by obtaining the depth and velocity of the channel over time. The channel can be approximated by areas created by connected the dots of the measured depths. The discharge can be calculated by the following:

w = Width of cross section (ft)

y = Height of cross section (ft)

v = Velocity at indicated cross section (ft/s)





Hydraulics-Closed Conduit

Bernoulli Continuity Equation


The Bernoulli equation for the conservation of energy states that the total energy is equal to the sum of the pressure + kinetic energy + potential energy of a system and is conserved at any point in the system. Therefore:




Pressure Conduit


Pressure conduits refer to closed cross sections that are not open to the atmosphere such as pipes:

The Darcy Equation is used for fully turbulent flow to find the head loss due to friction. The equation is:

hf = Head Loss due to friction (ft)

f = Darcy friction factor

L = Length of pipe (ft)

v = Velocity of flow (ft/sec)

D = Diameter of pipe (ft)

g = Acceleration due to gravity, (Use 32.2 ft/sec2)

The Hazen-Williams equation is also used to determine head loss due to friction. Be aware of units as this equation may be presented in different forms. The most common is the following:

hf = Head Loss due to F\friction (ft)

L = Length (ft)

V = Velocity (gallons per minute)

C = Roughness coefficient

d = Diameter (ft)

In addition to these losses, there is also what is called minor losses of energy due to friction

Minor Losses – Friction losses due to geometric changes such as fittings in the line, changes in the dimensions of the pipe, or changes in direction:

  • Minor losses can be calculated as per the Method of Loss coefficients.
  • Each change in the flow of a pipe is assigned a loss coefficient, K
  • Loss coefficients for fittings are most often determined and provided by the manufacturer

Loss coefficients for sudden changes in area can be determined:

For Sudden Expansions: For Sudden Contractions:

D1=Smaller diamter pipe

D2=Larger diamter pipe

Loss coefficients are then multiplied by the kinetic energy to determine the loss:




Pump Application and Analysis


A pump is a machine which adds energy to the flow of water or other fluids. A pump is often used to oppose the effects of gravity to transport a fluid to a position up grade.

The head added by a pump can be determined from the following equation as a function of the total energy:




Pipe Network Analysis


A system of pipes can be arranged in different configurations to be able to appropriately transport water. There are a few types of common arrangements that can be used. Each has certain principles to follow when determining the flow through the system. It is important to remember the conservation of mass or flow principle when analyzing these systems:

Series Pipe System: Pipes of different areas connected along the same line.

In a series pipe, the total friction loss is the sum of the loss in all the individual pipes. Therefore, in a pipe such as the one shown above the total head loss can be determined as follows: Parallel Pipe Systems: As the name suggests, this is a pipe system with flow separating into parallel pipes.

There are three concepts which are important to keep in mind during the analysis of parallel pipes:

  1. The head loss in parallel pipes is equal
  2. The head loss between the inlet and outlet is equal to that of each pipe individually
  3. The flow rate at the outlet is equal to the sum of the flow rates from the parallel pipes

Pipe Networks: These are more complicated systems of pipes which have flow breaking off in multiple directions.

Often pipe networks are very complicated and left to iterative analysis on computers. It is important to note the two concepts which govern the analysis however:

  1. The flow entering the system is equal to the flow leaving the system (conservation of flow)
  2. The sum of head losses in any closed loop is equal to zero





Hydraulics-Open Channel

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Hydrology

Storm Characteristics


A design storm must be specified when performing any calculations. The design storm is defined by its recurrence interval which is the given amount of time it is likely to see a storm of a certain intensity. Design storms are often 10, 20, 50, or 100-year storms meaning a storm of a certain intensity would only occur once within the given duration.




Runoff Analysis


The rational method can be used to determine the flow rate from runoff of a drainage area. The equation is:

Q = ACi

Q = Flow Rate (cfs)

A = Drainage Area (Acres)

C = Runoff Coefficient

i = Rainfall Intensity (in/hr)

NRCS/SCS Runoff Method

This is an alternative method for determining runoff:

S = Storage Capacity of Soil (in.)

CN = NRCS Curve Number

Q = Runoff (in.)

Pg = Gross Rain Fall (in.)




Hydrographs


Hyetographs – Graphical representation of rainfall distribution over time

Hydrograph – Graphical representation of rate of flow vs time past a given point often in a river, channel, or conduit. The area under the hydrograph curve is the volume for a given time period

Parts of a Hydrograph are shown graphically:

Unit Hydrographs can be determined by dividing the points on the typical hydrograph by the average excess precipitation.

Synthetic Hydrographs are created if there is insufficient data for a watershed. This method uses the NRCS curve number and is a function of the storage capacity.

To develop the synthetic hydrograph, you must calculate the time to peak flow:

tR = Storm duration (time)

Lo = Length overland (ft)

SPercentage = Slope of land

The equation for peak discharge from a synthetic hydrograph then is:




Rainfall


Storm characteristics include duration, total volume, and intensity

Duration: The length of time of a storm. Often measured in days and hours.

Total Volume: The entire amount of precipitation throughout the duration of the storm in a defined area.

Storm Intensity: Total volume of the storm divided by the duration of the storm event. Intensities can be averaged over the entire storm or at shorter intervals to provide instantaneous high intensity portions of the storm. Hyetographs are bar graphs used to measure instantaneous rainfall intensities over time and are covered below.




Stormwater Management


Detention and retention ponds are often used to collect water for flood control and stormwater runoff treatment.

Detention Ponds: Also known as dry ponds. These are ponds which are often kept dry except during flood events. The pond will fill up during increased precipitation to control the flow intensity. This is common in dry, arid, or urban areas to prevent excessive flooding. The ponds typically will be designed to hold water for about 24 hours. Detention ponds also control the amount of sediment since it is captured in the pond and then typically becomes accessible after the pond has dried.

Retention Ponds: Also called wet ponds since they contain a volume of water at all times. The elevation of the water will vary depending on precipitation but will always maintain a permanent amount of water based on low flow conditions. This allows sediment control since the deposits will settle to the bottom and allow for collection.

Infiltration is the rate of which water seeps into the ground. The Horton equation can be used to approximate this rate. This assumes that the water supply is infinite and the ground is saturated:




Time of Concentration





Depletions


The change in storage for a body of water can be approximated from the following equation:

ΔS=P+R+GI-GO-E-T-O

S = Storage

P = Precipitation

R = Runoff

GI = Groundwater inflow

GO = Groundwater outflow

E = Evaporation

T = Transpiration

O = Surface water release




Stream Gauging


Stream gauging is the measurement of a stream channel to determine the discharge by obtaining the depth and velocity of the channel over time. The channel can be approximated by areas created by connected the dots of the measured depths. The discharge can be calculated by the following:

w = Width of cross section (ft)

y = Height of cross section (ft)

v = Velocity at indicated cross section (ft/s)





Groundwater and Wells

Bernoulli Continuity Equation


The Bernoulli equation for the conservation of energy states that the total energy is equal to the sum of the pressure + kinetic energy + potential energy of a system and is conserved at any point in the system. Therefore:




Pressure Conduit


Pressure conduits refer to closed cross sections that are not open to the atmosphere such as pipes:

The Darcy Equation is used for fully turbulent flow to find the head loss due to friction. The equation is:

hf = Head Loss due to friction (ft)

f = Darcy friction factor

L = Length of pipe (ft)

v = Velocity of flow (ft/sec)

D = Diameter of pipe (ft)

g = Acceleration due to gravity, (Use 32.2 ft/sec2)

The Hazen-Williams equation is also used to determine head loss due to friction. Be aware of units as this equation may be presented in different forms. The most common is the following:

hf = Head Loss due to F\friction (ft)

L = Length (ft)

V = Velocity (gallons per minute)

C = Roughness coefficient

d = Diameter (ft)

In addition to these losses, there is also what is called minor losses of energy due to friction

Minor Losses – Friction losses due to geometric changes such as fittings in the line, changes in the dimensions of the pipe, or changes in direction:

  • Minor losses can be calculated as per the Method of Loss coefficients.
  • Each change in the flow of a pipe is assigned a loss coefficient, K
  • Loss coefficients for fittings are most often determined and provided by the manufacturer

Loss coefficients for sudden changes in area can be determined:

For Sudden Expansions: For Sudden Contractions:

D1=Smaller diamter pipe

D2=Larger diamter pipe

Loss coefficients are then multiplied by the kinetic energy to determine the loss:




Pump Application and Analysis


A pump is a machine which adds energy to the flow of water or other fluids. A pump is often used to oppose the effects of gravity to transport a fluid to a position up grade.

The head added by a pump can be determined from the following equation as a function of the total energy:




Pipe Network Analysis


A system of pipes can be arranged in different configurations to be able to appropriately transport water. There are a few types of common arrangements that can be used. Each has certain principles to follow when determining the flow through the system. It is important to remember the conservation of mass or flow principle when analyzing these systems:

Series Pipe System: Pipes of different areas connected along the same line.

In a series pipe, the total friction loss is the sum of the loss in all the individual pipes. Therefore, in a pipe such as the one shown above the total head loss can be determined as follows: Parallel Pipe Systems: As the name suggests, this is a pipe system with flow separating into parallel pipes.

There are three concepts which are important to keep in mind during the analysis of parallel pipes:

  1. The head loss in parallel pipes is equal
  2. The head loss between the inlet and outlet is equal to that of each pipe individually
  3. The flow rate at the outlet is equal to the sum of the flow rates from the parallel pipes

Pipe Networks: These are more complicated systems of pipes which have flow breaking off in multiple directions.

Often pipe networks are very complicated and left to iterative analysis on computers. It is important to note the two concepts which govern the analysis however:

  1. The flow entering the system is equal to the flow leaving the system (conservation of flow)
  2. The sum of head losses in any closed loop is equal to zero





Wastewater Collection and Treatment

Storm Characteristics


A design storm must be specified when performing any calculations. The design storm is defined by its recurrence interval which is the given amount of time it is likely to see a storm of a certain intensity. Design storms are often 10, 20, 50, or 100-year storms meaning a storm of a certain intensity would only occur once within the given duration.




Runoff Analysis


The rational method can be used to determine the flow rate from runoff of a drainage area. The equation is:

Q = ACi

Q = Flow Rate (cfs)

A = Drainage Area (Acres)

C = Runoff Coefficient

i = Rainfall Intensity (in/hr)

NRCS/SCS Runoff Method

This is an alternative method for determining runoff:

S = Storage Capacity of Soil (in.)

CN = NRCS Curve Number

Q = Runoff (in.)

Pg = Gross Rain Fall (in.)




Hydrographs


Hyetographs – Graphical representation of rainfall distribution over time

Hydrograph – Graphical representation of rate of flow vs time past a given point often in a river, channel, or conduit. The area under the hydrograph curve is the volume for a given time period

Parts of a Hydrograph are shown graphically:

Unit Hydrographs can be determined by dividing the points on the typical hydrograph by the average excess precipitation.

Synthetic Hydrographs are created if there is insufficient data for a watershed. This method uses the NRCS curve number and is a function of the storage capacity.

To develop the synthetic hydrograph, you must calculate the time to peak flow:

tR = Storm duration (time)

Lo = Length overland (ft)

SPercentage = Slope of land

The equation for peak discharge from a synthetic hydrograph then is:




Rainfall


Storm characteristics include duration, total volume, and intensity

Duration: The length of time of a storm. Often measured in days and hours.

Total Volume: The entire amount of precipitation throughout the duration of the storm in a defined area.

Storm Intensity: Total volume of the storm divided by the duration of the storm event. Intensities can be averaged over the entire storm or at shorter intervals to provide instantaneous high intensity portions of the storm. Hyetographs are bar graphs used to measure instantaneous rainfall intensities over time and are covered below.




Stormwater Management


Detention and retention ponds are often used to collect water for flood control and stormwater runoff treatment.

Detention Ponds: Also known as dry ponds. These are ponds which are often kept dry except during flood events. The pond will fill up during increased precipitation to control the flow intensity. This is common in dry, arid, or urban areas to prevent excessive flooding. The ponds typically will be designed to hold water for about 24 hours. Detention ponds also control the amount of sediment since it is captured in the pond and then typically becomes accessible after the pond has dried.

Retention Ponds: Also called wet ponds since they contain a volume of water at all times. The elevation of the water will vary depending on precipitation but will always maintain a permanent amount of water based on low flow conditions. This allows sediment control since the deposits will settle to the bottom and allow for collection.

Infiltration is the rate of which water seeps into the ground. The Horton equation can be used to approximate this rate. This assumes that the water supply is infinite and the ground is saturated:




Time of Concentration





Depletions


The change in storage for a body of water can be approximated from the following equation:

ΔS=P+R+GI-GO-E-T-O

S = Storage

P = Precipitation

R = Runoff

GI = Groundwater inflow

GO = Groundwater outflow

E = Evaporation

T = Transpiration

O = Surface water release




Stream Gauging


Stream gauging is the measurement of a stream channel to determine the discharge by obtaining the depth and velocity of the channel over time. The channel can be approximated by areas created by connected the dots of the measured depths. The discharge can be calculated by the following:

w = Width of cross section (ft)

y = Height of cross section (ft)

v = Velocity at indicated cross section (ft/s)





Water Quality

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Drinking Water Distribution and Treatment

Drinking Water Distribution Systems


As the name suggests, systems are developed so that drinking water can be safely and efficiently distributed to the populations. These systems may consist of many components such as pipes, reservoirs, pumps, storage tanks and many others. These components carry water from a centralized distribution plant which maintains regulated levels of safe drinking water.




Drinking Water Treatment Process


There is a large number of processes which can be performed to get water meeting quality standards. The selection of which processes are performed depends heavily on the characteristics of the water specific to a certain plant. The procedure can be divided into 3 components: Pretreatment, Treatment, and Special Treatment. Here we will provide a breakdown of what may be involved in each portion depending on the type of water that needs to be treated.

Pretreatment

Screening: As the name suggests suspended solids which are large enough to be physically removed by allowing water to flow through fine screens is an initial process that is necessary to remove any debris.

Microstraining: A second level of screening used to remove the more finer debris. This process is very effective in the removal of algae.

Plain Settling: A removal of sediment by allowing the water to sit and the natural movement of sediments to fall to the bottom to occur.

Aeration: The rapid moving of water to allow mixing or the infusion of oxygen into the water. Aeration can have many benefits depending on the desired result. It can increase dissolved oxygen, decrease dissolved gases, reduce iron and manganese, or decrease odor and taste compounds.

Treatment

Lime Softening: As the name suggests this is the process of adding lime water (calcium hydroxide) to soften water. This additive will react with the calcium and manganese to form precipitates.

Coagulation and Sedimentation: This process is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. This process is essential to the treatment of water and is covered in greater detail later on.

Rapid Sand Filtration/Pressure Sand Filtration: See section on filtration.




Demands


Water demands need to be measured and analyzed so that distribution systems may be properly designed. Water demand is most often specified as gallons per capita per day (gpcd). It can also be expressed as Average Annual Daily Flow (AADF) which as the name suggests is the average daily use of water per person averaged over a year time period. A common value used for basic design purposes is often taken as 165 gpcd but should be adjusted based on the intended water use whether it be residential, commercial, or industrial.

Besides the average flow demand throughout a day, there may be increased demands instantaneously which systems must have adequate capacity for. The average annual daily flow times a specified multiplier is often used to determine the instantaneous demand:

Qinstant=M(AADF)

It is also important to note that per capita demand needs to account for the entire population but it must often be specified at what time period. Because of growth, a distribution system should meet some future predicted growth of population.




Storage


Water supplies need to be stored for a variety of uses and as well as to ensure adequate supply in times of growth or emergency. Water can be distributed from storage either through gravity or pumping. Gravity is available when there is a sufficiently high point in elevation relative to the population. Otherwise pumping is necessary. Water is most often stored in surface or elevated tanks. Within these tanks the elevation of the surface water is monitored to determine the appropriate distribution pressure. These are often monitored by altitude valves.




Rapid Mixing


This process as mentioned above is the addition of chemicals, called coagulates, to form together contaminants into solids which can then be removed. Coagulates form together precipitate which is called floc. For this reason we have combined two of the NCEES syllabus items since it is most appropriate to discuss these topics together. The most common type of coagulates are aluminum sulfate commonly referred to simply as alum. Others include ferrous sulfate and chlorinated copperas. Alum is often provided in doses in the range of 5-50 mg/L. There are three requirements for Alum to be effective:

  1. A large enough quantity of Alum must be present to neutralize the negative particles present in the water
  2. Enough alkalinity must be present to facilitate the reaction of aluminum sulfate to aluminum hydroxide
  3. The PH must be within the acceptable range which is a function of the type on contaminant. Typically it is taken between 6-7

The amount of coagulate to successfully form floc must be determined. The equation for the feed rate is:

F = Feed Rate

D = Dose

Q = Flow Rate

P = Purity

G = Availability (1.0 is not specified)




Taste and Odor Control


There are many processes which can aid in the elimination of undesirable taste and odor in water. Some include chlorination, aeration and micro straining. To identify the presence of taste or order, the threshold odor number (TON) is established and can be calculated as per below:

TON= (V Raw Sample+V Dilution Water)/VRaw Sample

Typically, a TON of less than 6 is desirable




Sedimentation


A plain sedimentation tank is used to allow water which includes suspended sediments to settle out. The time and velocity for the particles to settle is a function of the temperature of the water, the particle size and the specific gravity of the particles (however this is often taken as 2.65 for analysis). Assumed settling velocities can be taken as the following to calculate the actual settling velocities:

Gravel: 3.28 ft/s

Coarse Sand: 0.328 ft/s

Fine Sand: 0.0328 ft/s

Silt: 0.000328 ft/s

Then the approach to determining the settlement time can be determined by first calculating the Reynolds number:




Filtration


Filtration is used to remove excess floc, precipitates from softening, algae, debris and any other suspended byproducts remaining in the treated water. The most common is rapid sand filtration. Rapid Sand Filtration is the filtering of water through a bed of sand and gravel as a medium for removing suspended particles. Water moves through a layer of sand in which the suspended particles will be held back by the sand. Depending on the type of filter, the loading rate can be anywhere from 2 – 10 gpm/ft2. The loading rate can be determined by the following equation:

Load Rate= Flow Rate/Area

Filters often need to be cleaned and therefore there is a high maintenance cost. The pores between the filters will become clogged and need to get washed out. To counteract this is a process called back washing. This is where water is pumped slowly in the reverse direction of the water to be filtered so that the pores in the sand can be expanded to release any trapped material. It is important during backwashing to monitor the rise rate of the water to ensure it does not exceed the settling velocity of the smallest particle intended to be left in the filter. These rates are often taken as about 1-3 ft/min. The amount of backwash needed can be determined by:

V= Area Filter(Rise Rate)(t Backwash)




Hardness and Softening


Hardness is a measure of the presence of calcium and magnesium ions expressed as calcium carbonate (CaCO3). Practically, hardness in water does not provide any health concerns but does have an effect on the usefulness of the water. One of the main concerns is often that hardness in water will greatly reduce the effectiveness of soap. It also has a detrimental effect on the pipes and storage facilities of a water distribution system.

There are two types of hardness:

Carbonate Hardness: Water containing Bicarbonate (HCO3-)

Noncarbonate Hardness: Remaining hardness not carbonate due to sulfates, chlorides, and nitrates.

Hardness can also be expressed as total hardness which is the sum of carbonate and noncarbonate hardness in mg/L as CaCO3. There is a clear connection between the alkalinity of water and the hardness. The following assumptions can be made:

  • If Total Hardness = Alkalinity, all hardness is carbonate and there are no sulfates, chlorides, or nitrates present
  • If Total Hardness > Alkalinity, noncarbonate hardness is present
  • If Total Hardness < Alkalinity, all hardness is carbonate and the remainder of the bicarbonate is from additional sources

Water softening is the removal of hardness through the use of lime and soda ash in mg/L as CaCO3. It is important to note that lime will attack any carbon dioxide in water first and then begin with the removal of any carbonate hardness before the noncarbonate.




Disinfection


Disinfectants were defined earlier in the wastewater section. Here we will discuss by products.

Chlorine in water produces the following chemical reaction depending on PH

PH > 4: Cl2+ H2O →HCl+HOCl

PH > 9: HOCl → H++ OCl-

HCl and HOCL are hydrochloric and hypochlorous acids respectively. You can see that at PH greater than 9, the hypochlorous acid becomes hydrogen and hypochlorite ions.





Engineering Economics

Bernoulli Continuity Equation


The Bernoulli equation for the conservation of energy states that the total energy is equal to the sum of the pressure + kinetic energy + potential energy of a system and is conserved at any point in the system. Therefore:




Pressure Conduit


Pressure conduits refer to closed cross sections that are not open to the atmosphere such as pipes:

The Darcy Equation is used for fully turbulent flow to find the head loss due to friction. The equation is:

hf = Head Loss due to friction (ft)

f = Darcy friction factor

L = Length of pipe (ft)

v = Velocity of flow (ft/sec)

D = Diameter of pipe (ft)

g = Acceleration due to gravity, (Use 32.2 ft/sec2)

The Hazen-Williams equation is also used to determine head loss due to friction. Be aware of units as this equation may be presented in different forms. The most common is the following:

hf = Head Loss due to F\friction (ft)

L = Length (ft)

V = Velocity (gallons per minute)

C = Roughness coefficient

d = Diameter (ft)

In addition to these losses, there is also what is called minor losses of energy due to friction

Minor Losses – Friction losses due to geometric changes such as fittings in the line, changes in the dimensions of the pipe, or changes in direction:

  • Minor losses can be calculated as per the Method of Loss coefficients.
  • Each change in the flow of a pipe is assigned a loss coefficient, K
  • Loss coefficients for fittings are most often determined and provided by the manufacturer

Loss coefficients for sudden changes in area can be determined:

For Sudden Expansions: For Sudden Contractions:

D1=Smaller diamter pipe

D2=Larger diamter pipe

Loss coefficients are then multiplied by the kinetic energy to determine the loss:




Pump Application and Analysis


A pump is a machine which adds energy to the flow of water or other fluids. A pump is often used to oppose the effects of gravity to transport a fluid to a position up grade.

The head added by a pump can be determined from the following equation as a function of the total energy:




Pipe Network Analysis


A system of pipes can be arranged in different configurations to be able to appropriately transport water. There are a few types of common arrangements that can be used. Each has certain principles to follow when determining the flow through the system. It is important to remember the conservation of mass or flow principle when analyzing these systems:

Series Pipe System: Pipes of different areas connected along the same line.

In a series pipe, the total friction loss is the sum of the loss in all the individual pipes. Therefore, in a pipe such as the one shown above the total head loss can be determined as follows: Parallel Pipe Systems: As the name suggests, this is a pipe system with flow separating into parallel pipes.

There are three concepts which are important to keep in mind during the analysis of parallel pipes:

  1. The head loss in parallel pipes is equal
  2. The head loss between the inlet and outlet is equal to that of each pipe individually
  3. The flow rate at the outlet is equal to the sum of the flow rates from the parallel pipes

Pipe Networks: These are more complicated systems of pipes which have flow breaking off in multiple directions.

Often pipe networks are very complicated and left to iterative analysis on computers. It is important to note the two concepts which govern the analysis however:

  1. The flow entering the system is equal to the flow leaving the system (conservation of flow)
  2. The sum of head losses in any closed loop is equal to zero





 
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