Page 122 - Water Engineering Hydraulics, Distribution and Treatment

100
Chapter 4
Quantities of Water Demand
Conduit
to city
I
Service
Impounding
reservoir
(A)
Conduit
Conduit to filters
to city
I
Filters
Impounding Conduit to service reservoir reservoir III III Distribution system
Service
reservoir Distribution system
reservoir
(B)
Treatment
Conduit to city Conduit to and
plant
Conduit and service from service
to filters reservoir reservoir
I II III
Well field
Low-lift High-lift
pumps pumps Distribution system
(C)
Intake Filters Conduit to Conduit
conduit service reservoir to city
I II III
Service
Low-lift High-lift reservoir
River pumps pumps Distribution system
(D)
Figure 4.4 Required capacities of four typical waterworks systems. The service reservoir is assumed to
compensate for fluctuations in draft and fire drafts and to hold an emergency reserve.
Solution 1 (US Customary System):
Required capacities for waterworks systems of Fig. 4.4:
6
5
Average daily draft = 150 × 1.2 × 10 ∕10 = 18 MGD.
Maximum daily draft = coincident draft = 2 × 18 = 36 MGD.
Maximum hourly draft = 4.5 × 18 = 81 MGD.
Fire flow from Table 4.13:
2
2
Area of three floors = 3 × 12,000 ft ∕floor = 36,000 ft .
Flow for one fire = 5,000 gpm.
Flow for two simultaneous fires = 2 × 5,000 = 10,000 gpm = 14.4 MGD.
Coincident draft plus fire flow = 36 + 14.4 = 50.4MGD.

Provision for breakdowns and repair of pumps and water purification units by installing one reserve unit, as shown in Table 4.14,
assuming total units = 3 + 1 = 4:

Low-lift pumps: 4∕3 × maximum daily draft = (4∕3) × 36 = 48 MGD.
High-lift pumps: 4∕3 × maximum hourly draft = (4∕3) × 81 = 108 MGD.
Treatment works: 4∕3 × maximum daily draft = 48 MGD.

The resultant capacities of systems components are summarized in Table 4.14.