Page 176 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch04_118-153.qxd 8/2/10 9:18 PM Page 138

138 Chapter 4 Quantities of Water and Wastewater Flows

EXAMPLE 4.2 DETERMINATION OF CAPACITIES OF WATERWORKS SYSTEMS
The four typical waterworks systems shown in Fig. 4.4 supply a community with an estimated future
population of 120,000. Determine the required capacities of the constituent structures for an average
consumption of 150 gpcd (568 Lpcd) and a distributing reservoir so sized that it can balance out dif-
ferences between hourly and daily flows, fire demands, and emergency requirements. Assume a re-
quirement for fire protection that is needed to control two simultaneous fires in two unprotected
2
2
wood-frame construction, multistory buildings having a 12,000-ft (1,115-m ) area per floor.

Conduit
Conduit to service reservoir to city
I III
Service
Impounding reservoir
reservoir Distribution system
(A)
Conduit
Conduit to filters to city
I III
Impounding Filters Service
reservoir Distribution system
reservoir
(B)
Treatment Conduit to city Conduit to and
Conduit plant 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 (U.S. 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
Area of three floors 3 12,000 ft /floor 36,000 ft 2
Flow for one fire 5,000 gpm
Flow or two simultaneous fires 2 5,000 10,000 gpm 14.4 MGD