Page 177 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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4.4 Variations or Patterns of Water Demand 139

Coincident draft plus fire flow 36 14.4 50.4 MGD
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.

Table 4.14 Capacities of the Four Systems of Example 4.2
Capacity of system, MGD
Structure Required capacity A B C D
1. River or well field Maximum day 36.0 36.0
2. Conduit I Maximum day 36.0 36.0 36.0 36.0
3. Conduit II Maximum day . . . . . . } 36.0
4. Conduit III Maximum hour 81.1 81.0 81.0 81.0
5. Low-life pumps Maximum day plus reserve . . . . . . 48.0 48.0
6. High-life pumps Maximum hour plus reserve . . . . . . 108.0 108.0
7. Treatment plant Maximum day plus reserve . . . 48.0 48.0 48.0
8. Distribution system
high-value district Maximum hour 81.0 81.0 81.0 81.0
Conversion factor: 1 MGD 3.785 MLD.

Solution 2 (SI System):
Required capacities for waterworks systems of Fig. 4.4:
6
Average daily draft Q avg day (568 Lpcd) (120,000)>10 68.2 MLD
Maximum daily draft Q max day coincident draft 2 Q avg day 2 68.2 136.4 MGD
Maximum hourly draft Q max h 4.5 Q avg day 4.5 68.2 306.9 MLD
Fire flow from Table 4.13:
2
2
Area of three floors 3 12,000 ft /floor 36,000 ft 3,344.4 m 2
Flow for one fire 5,000 gpm 18,925 Lpm
Flow or two simultaneous fires 2 18,925 37,850 Lpm 54.5 MLD
Coincident draft plus fire flow 136.4 54.5 190.9 MLD
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) 136.4 181.9 MLD
High-lift pumps: 4>3 maximum hourly draft (4>3) 306.9 409.2 MLD
Treatment works: 4>3 maximum daily draft 181.9 MLD
The resultant capacities of systems components are summarized in Table 4.14.

EXAMPLE 4.3 ESTIMATION OF WATER DEMAND TO A RESIDENTIAL AREA
For management and design purposes, find the expected maximum day and peak hour demand and
daily rates of water to be supplied to a residential area of 200 houses with a gross housing density