Water and Wastewater Engineering
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3-34 WATER AND WASTEWATER ENGINEERING
Physical barrier screens are the most widely accepted and successful approach. The screens
are fine mesh with openings of 1.75 mm. The inlet velocity is designed to be a maximum of 12
cm/s (Foellmi, 2005).
Behavioral guidance may be accomplished with either electric
shock (Bosserman et al.,
2006) or, for submerged intakes, a velocity cap (Foellmi, 2005). The velocity cap on top of a
submerged intake, such as shown in Figure 3-20 , forces water to enter horizontally. Fish tend to
swim against horizontal currents.
Frazil ice complicates the fish protection issu
e because fine mesh systems are very suscep-
tible to clogging (Bosserman et al., 2006). As noted above, air burst systems with 1,000 kPa pres-
sure have been used to alleviate this problem. For T-screens at shore-based fac ilities, mounting
the screen on a boom that can be rotated out of the water for mechanical cleaning has also been
use as a method to alleviate the frazil icing problem.
3-5 OPERATION AND MAINTENANCE
With a well designed and constructed intake system, very little operation and maintenance (O&M)
is required. O&M tasks include regular preventive maintenance of the mechanical equipment
such as the fine sc reens, pumps, and gates. The tasks include removal of large floating objects
on the racks, dei
cing, lubrication and adjustment of the moving parts on the screens and pumps,
and exercising the port gates to prevent them from freezing up because of corrosion. Periodically,
divers must be employed to examine the condition of underwater structures.
For installation
s with multiple level ports, regular chemical analysis of the water at various
port levels will allow for adjustment of the intake level to reduce treatment costs. This is particu-
larly important when algal blooms and taste and odor problems are evident.
Velocity cap
Horizontal inflow
Bottom of lake
or reservoir
FIGURE 3-20
Velocity cap.
INTAKE STRUCTURES 3-35
Hints from the Field. Operation and maintenance personnel who have to live with the results
of the engineer’s design have offered the following suggestions:
• The overhead crane supplied to facilitate maintenance of the pumps and motors should also
provide a means to move the equipment outside of the building to facilitate replacement
of equipment that has rea
ched its life expectancy. Alternatively, a hatch in the roof with a
means of positioning the equipment to be removed below the hatch should be provided. In
the second instance, a crane can be rented to remove the old equipment and transfer the new
equipment into the building. The hatch should be sized to cons ider the likelihood that the
replacement equipment will be larger than the equipment being removed.
• For zebra mussel control, a chlorine feed line s hould be supplied to the screen/bar rack of
the intake. The feed line is commonly located inside the conduit carrying water from the
intake structure to the low-lift pump station. Sodium hypochlorite solution is
used to sup-
ply the chlorine. Care should be taken in selecting the pipe material and joining cements
because s odium hypochlorite m ay adversely affect the material and/or the cement. This
includes polyvinyl chloride (PVC) cements.
• In hard water, with high concentrations
of calcium and magnesium carbonate, the addition
of commercial sodium hypochlorite may cause precipitation of carbonates on the interior
of the pipe. Operators call this “plating out” of the hardness. Over time this will limit the
capacity of the supply pipe. The addition of sodium hexametaphosphate to the hypochlorite
feed
will help to mitigate the precipitation.
• The conduit from the intake to the low-lift pump station should be inspected regularly (pref-
erably annually). For large conduits (1.5 m or large in diameter) a diver is employed to
“swim” the conduit and make the inspection. For small pipes, a TV camera inspection may
be used. The inspection should include such items as structural integrity of the pipe, build-
up of zebra mussels and slime layers, and the condition of the chlorine supply line (both the
pipe and the hangers).
• Because the air supply used by divers will be relea
sed inside of the conduit during the inspec-
tion, some means must be provided to release the gas; otherwise the gas “bubble” that accu-
mulates in the pipe will limit the flow rate. This is particularly true if the discharge into the wet
well is through a downward facing bell. One solution is to provide a small (5 cm diameter) tap
at the ter
minus to the pipe just above the bell and use it to release the accumulated air.
3-6 CHAPTER REVIEW
When you have completed studying this chapter, you should be able to do the following without
the aid of your textbook or notes:
1 . For a client, sketch a diagram of a lake intake structure and a river intake structure.
Identify the following features: bar screen, sluice gate, fine screen, pump, operating
floor, water level in surface water supply relative to the intake structure vertical profile.
2. List and discuss the key
requirements of intake structures.
Visit the text website at www.mhprofessional.com/wwe for supplementary materials
and a gallery of photos.
3-36 WATER AND WASTEWATER ENGINEERING
3. Select the appropriate screen type (coarse or fine) for a given scenario, that is, place-
ment in the intake structure or type of material to be removed.
4 . Select the appropriate type of pump from a pump catalog for a deep low-lift pump station.
5. Explain the advantages and disadvantages of an adjustable frequency drive for a pump
to a client.
6. Explain, to a client, what frazil ic
e is and how its buildup on the intake structure may
be minimized.
7. Explain, to a news media person, why zebra mussels are an operational problem and
list two control techniques.
W ith the use of this text, you should be able to do the following:
8 . For a given scenario (river or lake) with appropriate data on depth, sediment, and cli-
mate, select an acc
eptable type of intake structure.
9. Design an intake port given the seasonal flow rates and climate conditions.
10. Design a bar rack for an intake port given the seasonal flow rates and climate conditions.
11. Design the conduit to carry water from an offshore intake structure to a low-lift pump station.
12. Construct a system head curve given the elevations
, pipe dimensions, and identification
of the fittings.
13. Given a system head curve and a set of head-discharge curves, select an appropriate
pump and specify (1) BEP, (2) number of stages, (3) efficiency at BEP, (4) the operat-
ing range of flow rate, and (5) motor power.
14. Design the wet well for a low-lift pump station including specifications
of (1) the depth
of the wet well and (2) the location of the pump intake given the surface water level,
intake conduit specifications, and pump NPSH.
3-7 PROBLEMS
3-1. Design a tower intake to be placed in a reservoir in a warm climate. Provide the mini-
mum number of ports. The design conditions are:
S ummer design fl ow rate 38,000 m
3
/ d
M a ximum reservoir elevation 499.0 m
Minimum reservoir elevation 480.7 m
Lake bottom elevation 477.7 m
Bar rack bars: 1 cm diameter; 8 cm between bars
Specify the following:
N umber and location of intake ports
Spacing of the ports
Depth of lowest port
Depth of top port
D i mensions of a port
Provide a sketch of the following:
Intake tower with elevations of ports, reservoir elevations, and lake botto
m
elevation
INTAKE STRUCTURES 3-37
3-2. Design a shore river intake system in a cold climate. Provide the minimum number
of ports. The design conditions are:
Winter design fl ow rate 4,300 m
3
/ d
Minimum river elevation held constant by lock and dam system 99.0 m
500-year fl ood elevation 113.3 m
River bottom elevation 90.4 m
A ssume a muck bottom
T r a sh rack: 2 cm diameter; 8 cm between bars
Specify the following:
N umber and location of intake ports
Spacing of the ports
Depth of lowest port
Depth of top port
D i mensions of a port
Provide a sketch of the following:
Intake tower with elevations of ports, reservoir elevations, and lake bottom elevation
3-3. Design a conduit to carry water from a submerged intake structure to the wet well of
a low-lift pump station. The design conditions are:
Low water surface elevation 353.5 m
Elevation of lake bottom 306.6 m
Length of pipe from intake structure to wet well 1,500 m
M a ximum demand at design life 53,000 m
3
/ d
Concrete pipe
A ssume the lake bottom is fl at
Specify the following:
Wet well drawdown elevation
Minimum slope of energy grade line required to carry the maximum demand
Diameter of the conduit
Velocity in the conduit
Depth of soil cover at the intake structure and at the wet well
Provide a sketch showing the following:
Low water s
urface elevation
S urface elevation of water in the wet well at maximum fl ow rate
Pipe profi le from the intake structure to the low-lift pump station
Elevation of bottom of conduit at the intake structure and at the wet well
Note: Because both the slope of the energy grade line and the diameter are unknown,
a trial and error solution is required. A spreadsheet solution for the trial and error cal-
cu
lation is recommended.
3-4. Design a conduit to carry water from a submerged intake structure to the wet well of
a low-lift pump station. The design conditions are:
Low water surface elevation 153.5 m
Elevation of lake bottom 106.6 m
3-38 WATER AND WASTEWATER ENGINEERING
Length of pipe from intake structure to wet well 2,500 m
M a ximum demand at design life 26,000 m
3
/ d
Concrete pipe
A ssume the lake bottom is as shown in Figure P-3-4
S p e cify the following:
Wet well drawdown elevation
Minimum slope of energy grade line required to carry the maximum demand
Diameter of the conduit
Velocity in the conduit
Depth of soil cover at the intake structure and at the wet well
Provide a
sketch showing the following:
Low water surface elevation
S urface elevation of water in the wet well at maximum fl ow rate
Pipe profi le from the intake structure to the low-lift pump station
Elevation of bottom of conduit at the intake structure and at the wet well
Note: Because both the slope of the energy grade line and the diameter are unknown,
a trial and error solution is required. A spreadsheet s
olution for the trial and error cal-
culation is recommended.
3-5. Show by calculation that losses for valves, fittings, and velocity head are negligible
compared to the static head at the maximum flow rate for Example 3-5.
3-6. Develop the system head curves for the low-lift pump station to the water treatment plant
pumping system shown in
Figure P-3-6 . The minimum flow rate is 9,500 m
3
/ d. The av-
erage flow rate is 19,000 m
3
/ d. The maximum flow rate is 38,000 m
3
/ d. You may ignore
losses from valves, fittings, and velocity head.
3-7. Develop the system head curves for the low-lift pump station to the water treatment
plant pumping system shown in Figure P-3-7 . The minimum flow rate is 4,500 m
3
/ d.
The average flow rate is 9,000 m
3
/ d. The maximum flow rate is 18,000 m
3
/ d. You
may ignore losses from valves, fittings, and velocity head.
Low water surface elevation = 153.5 m
Intake
Con
duit
106.6 m
FIGURE P-3-4
INTAKE STRUCTURES 3-39
Elev. = 1,379.2 m
450 mm Ø DIP
Elev.
= 1,408.2 m
Total pipe length = 3,200 m
Conduit
Elev. = 1,371.6 m
Elev. = 1,420.4 m
FIGURE P-3-7
Elev. = 321.1 m
Total pipe length 1,600 m
675 mm Ø DIP
Elev. = 335.1 m
Intake
conduit
Elev. = 307.3 m
FIGURE P-3-6
3-40 WATER AND WASTEWATER ENGINEERING
3-8. For the system head curve shown in Figure P-3-8 , select a pump. Specify the fol-
lowing at the average flow rate of 9,000 m
3
/ d: (1) BEP, (2) number of stages,
(3) efficiency at BEP, (4) the operating range of flow rate, and (5) motor power.
Sketch and label (1) the depth of the wet well and (2) the location of the pump intake.
M
a
x
i
m
u
m
t
o
t
a
l
h
e
a
d
M
i
n
i
m
u
m
t
o
t
a
l
h
e
a
d
5,000
30
Total dynamic head, m
50
40
10,000
Flow rate, m
3
/d
15,000 20,000
FIGURE P-3-8
3-9. For the system head curve shown in Figure P-3-9 , select a pump. Specify the fol-
lowing at the average flow rate of 24,000 m
3
/ d: (1) BEP, (2) number of stages,
FIGURE P-3-9
21
20
19
18
17
16
15
10,000 20,000 30,000 40,000 50,000
Total dynamic head, m
Flow rate m
3
/d
Maximum total head
Minimum total head
INTAKE STRUCTURES 3-41
(3) efficiency at BEP, (4) the operating range of flow rate, and (5) motor power.
Sketch and label (1) the depth of the wet well and (2) the loc ation of the pump
intake.
3-8 DISCUSSION QUESTIONS
3-1. A city council member has suggested that the council would avoid having to comply
with surface water rules for water treatment if an infiltration gallery was used instead
of a shoreline intake structure on the river water supply for their community. Explain
to the council mem
ber why this statement may not be true.
3-2. Given a choice of a sluice gate or butterfly valve for controlling the flow into an in-
take port, which would you select? Explain why.
3-3. What design data must you have to establish the depth of the wet well?
3-4. Which of the following depths for a submerged intake structure is the bes
t to mini-
mize the formation of frazil ice:
• 5 m
• 10 m
• 15 m
3-5. What chemical(s) would you recommend in setting up a zebra mussel control system?
3-9 REFERENCES
ASCE (1990) Water Treatment Plant Design, 2nd ed., American Society of Civil Engineers and American
Water Works Association, McGraw-Hill, NY, pp. 27–56.
Bosserman, B. E., R. J. Ringwood, M. D. Schmidt, and M. G. Thalhamer (2006) in G. M Jones et al.
(eds.) Pump Station Design, Elsevier, Boston, pp. 18.5–18.16.
Cooper, P. and G. Tchobanoglous (2006) “Performance of Centrifugal Pimps,” in G. M. Jones (ed.),
Pump Station Design, Elsevier, New York, pp. 10.1–10.44.
Foellmi, S. N. (2005) “Intake Facilities,” in E. E Baruth (ed.), Water Treatment Plant Design, M cGraw-Hill,
NY, pp. 4.1–4.35.
Honeycutt, F. G. and D. E. Clopton (1976) “Water Supply,” in I. J. Karassik et al. (eds.), Pump Handbook,
McGraw-Hill, NY, p. 10–6.
Jones, G. M. and R. L. Sanks (2006) “Pumps: Intake Design, Selection, and Installation,” in G. M. Jones
(ed.), Pump Station Design, Elsevier, New York, pp. 12.2–12.82.
Kawamura, S. (2000) Integrated Design and Operation of Water Treatment Facilities, 2n
d ed., John
Wiley & Sons, NY, pp. 409–412.
Richardson, W. H. (1969) “Intake Construction for Large Lakes and Rivers,” Journal of American Water
Works Association, vol. 61, no. 8, p. 365.
Sanks, R. L. (2006) “Flow in Conduits,” in G. M. Jones (ed.), Pump Station Design, Elsevier, NY,
pp. 3.1–3.37.
Williams, G. S. and A. Hazen (1905) Hydraulic Tables, John Wiley, New York.
4-1
4-5 CHAPTER REVIEW
4-6 PROBLEMS
4-7 DISCUSSION QUESTIONS
4-8 REFERENCES
WELLS
4-1 INTRODUCTION
4-2 DESIGN ELEMENTS
4-3 WELL PROTECTION
4-4 WELL DESIGN
4
CHAPTER
4-2 WATER AND WASTEWATER ENGINEERING
4-1 INTRODUCTION
The design of a well field and/or individual wells begins after the completion of the evaluation
of the groundwater source to establish that a safe yield is available to meet the demand and that
water quality standards can be met. These issues were discussed in Chapter 2. The d esign must
provide for protection of the well from
contamination, and it must conform to the hydraulic and
hydrogeologic constraints of the aquifer.
4-2 DESIGN ELEMENTS
The key requirements of wells are that they are:
• L o cated in an aquifer that has adequate long-term capacity (see Chapter 2 for a detailed
discussion).
• Protected from contamination.
• Reliable.
• Of adequate size and/or number to provide the required quantity of water.
• Located to obtain the best quality water.
• Not located where they
will cause an adverse resource impact.
Protection from Contamination
A significant effort is made to protect wells from contamination because of their vulnerability to
numerous sources of contamination. Aquifers lack the inherent protection of replenishment that
is afforded to surfac e water supplies. Unlike surface waters that are replenished in hours, days,
weeks, or even year
s, contaminated groundwater may only be replenished over geologic time
scales—lifetimes in the shortest instances and centuries in most cases.
Reliability
Reliability is an essential requirement of groundwater supplies. The water supply system ceases
to function when the well system fails. Sm all systems are particularly vulnerable because they
typically have only a few wells.
Capacity
Unlike surface water systems, well systems may be expanded relatively inexpensively as c om-
munities grow. However, the ability of the aquifer to yield adequate water is not infinite. The
geologic structure of the aquifer limits both the total quantity of water and the rate at which it can
be withdrawn.
Quality
All groundwater is not equal in quality. Contact with geologic minerals guarantees an abundance
of chemical constituents in the water. While most groundwater may be treated to meet water