Page 47 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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10 Chapter 1 Introduction to Water Systems

2
3. For an average consumption of 150 gpcd, the drainage area of 100 mile and impoundage
of 13.5 BG will supply a population of 100 750,000>150 500,000 persons.
4. For water supply by continuous draft, low water flows rather than average annual yields
govern.
2
3
In well-watered sections of North America, these approximate 0.1 ft /s or 64,600 gpd/mile .
2
A catchment area of 100 mile , therefore, can supply without storage:
100 64,600>150 43,000 people
This is compared against 500,000 people in the presence of proper storage.
Solution 2 (SI System):
1. The following conversion factors and approximations are being employed:
2
1 cm/km 67.12 ML (million liters)
2
Hence, 19.6 cm/km annually 19.6 67.12 1,315.6 ML annually 3.6 MLD.
2
2. A stream flow of about 1.46 MLD/km is a good average for the well-watered sections of
North America. Not all of it can be adduced economically by storage.
2
For 75% development (0.75 1.46 MLD/km ), about half a year’s supply must
generally be stored.
2
For a catchment area of 259 km , therefore:
2
2
Storage 0.75(1.46 MLD/km )(259 km )(0.5 365) 51,758 ML 51.758 BL
(billion liters)
In semiarid regions storage of three times the mean annual stream flow is not uncommon,
that is, water is held over from wet years to supply demands during dry years.
2
3. For an average consumption of 567.8 Lpcd, the drainage area of 259 km and impoundage
of 51.758 BL will supply a population of:
2
2
(0.75 1.46 MLD/km )(259 km )(1,000,000 L/ML)>(567.8 Lpcd) 500,000 persons
4. For water supply by continuous draft, low water flows rather than average annual yields
govern. In well-watered sections of North America these approximate 28.32 L/s, or
2
0.094316 MLD/km .
2
A catchment area of 259 km , therefore, can supply without storage:
2
2
(259 km )(0.094316 MLD/km )(1,000,000 L/ML)>(567.8 Lpcd) 43,000 people
This is compared against 500,000 people in the presence of proper storage.

1.6 GROUNDWATER
Smaller in daily delivery, but many times more numerous than surface water supplies,
are the municipal and private groundwater supplies of North America. Groundwater is
drawn from many different geological formations: (a) from the pores of alluvial (water-
borne), glacial, or aeolian (windblown) deposits of granular, unconsolidated materials
such as sand and gravel, and from consolidated materials such as sandstone; (b) from
the solution passages, caverns, and cleavage planes of sedimentary rocks such as lime-
stone, slate, and shale; (c) from the fractures and fissures of igneous rocks; and (d) from
combinations of these unconsolidated and consolidated geological formations.