HomeMy WebLinkAbout13.0 Water System Summary Report 11.1979• •
SUMMARY REPORT
WESTBANK RANCH/HILLVIEW P.U.D. WATER SYSTEM
NOVEMBER 1979
PREPARED
FOR
WESTBANK DEVELOPMENT COMPANY INCORPORATED
JOB NO. 9036
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WESTBANK RANCH/HILLVIEW P.U.D.
WATER SYSTEM
I. SCOPE AND PURPOSE OF REPORT
The Westbank Ranch currently comprises 101 single-family residential
units. Westbank Ranch #1 Ltd. has filed an application to develop an
additional 98 residential units south of the existing development.
Concurrently, an application has been filed for the Hillview P.U.D.,
east of the existing Westbank Ranch, consisting of 50 townhouse units.
Westbank Ranch #1 Ltd. and the developer of the Hillview P.U.D. plan
to establish an integrated water system to serve existing Westbank
residences, the 98 additional Westbank units proposed for development,
and the 50 townhouse units in Hillview. The water system will provide
water for in-house use and for fire protection.
The purposes of this report are 1) to identify the water supply available
to the system; 2) to estimate water demand; and 3) to discuss storage
requirements for peak demand and fire flow service.
Irrigation water is supplied through ditch rights into a separate system,
and water for irrigation purposes is not included in the following
discussion.
II. WATER SUPPLY
The existing Westbank development is served by four wells producing a
total of 205 gallons per minute (gpm), adjudicated. The Hillview
- 2
property includes two wells with total adjudicated capacity of 55 gpm.
Total adjudicated capacity of the six wells, then, is 260 gpm. Assuming
a .75 pump reliability factor, the dependable yield of the six wells is
195 gpm, or 280,800 gallons per day.
III. WATER DEMAND
Water demands for the existing
mated based on the following:
Population:
3.2 persons
2.8 persons
and planned development can be esti-
per single-family dwelling unit
per townhouse unit
Domestic Water Demand:
150 gallons per person per day
Fire Flow Requirements:
500 gallons per residential unit
Water demand for the service area is calculated based on the above cri-
teria, as follows:
Domestic Demand:
Existing:
Planned:
Fire Flow:
Existing:
Planned:
101 units X 3.2 persons
98 units X 3.2 persons
50 units X 2.8 persons
TOTAL DOMESTIC DEMAND
X 150 gallons
X 150 gallons
X 150 gallons
48,400 gpd
= 47,040 gpd
21,000 gpd
= 116,440 gpd
101 units X 500 gallons = 50,500 gallons
148 units X 500 gallons = 74,000 gallons
TOTAL FIRE FLOW
= 124,500 gallons
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IV. STORAGE REQUIREMENTS
Even though the dependable yield of the six wells which will serve the
system exceeds the demand estimated for domestic use and fire flow, an
economical and reliable water system requires storage to equalize high
and low demand periods, to provide water for fire protection, and to
ensure a supply of water in case of well pump outages. Storage should
be developed to at least equal fire flow requirements plus an average
day's water demand. As the calculations above show:
Average Day Demand = 116,440 gallons
Fire Flow Demand = 124,500 gallons
Total = 240,940 gallons
Thus, the combined Westbank/Hillview water system should provide a little
over 240,000 gallons of storage. Currently, about 100,000 gallons of
storage is available at Westbank Ranch. Therefore, an additional 140,000+
gallons of storage should be added to adequately serve the entire area.
Seventy-nine of the proposed Westbank units are situated on an elevated
bench above existing storage facilities and wells. This area will be
served by water pumped from lower elevations. Therefore, a storage reser-
voir above the bench is proposed to ensure that fire flow and average day
demand for the 79 units can be met by gravity flow in the event of pump
failure.
Demands for the area are calculated at:
domestic fireflow
(79 X 3.2 X 150) + (79 X 500)
37,920 + 39.500 = 77,420 gallons
Therefore, an 80,000 gallon capacity reservoir would provide adequate
protection.
As mentioned above, existing storage is about 100,000 gallons. Westbank
Ranch now utilizes two storage reservoirs: one steel tank at 20,000
gallons, and a concrete tank with a theoretical capacity of 100,000 gallons.
However, the 100,000 gallon tank actually stores an estimated 80,000+
gallons, due to hydraulics of the existing system. The developers propose
to improve storage capacity at that reservoir by changes to the water
system, and to add an additional 60,000 gallon storage reservoir near the
site of the existing concrete tank. Depending upon the degree to which
existing capacity can be improved, storage below the elevated bench will
total 160,000+ to 180,000 gallons. Total storage for the system will be
240,000+ to 260,000 gallons. This level of storage will meet or exceed
calculated fire flow plus average day demands.
It should be noted that due to large local elevation differences, the
water system will constitute three separate pressure zones. The zones
will be interconnected with pumps and pressure regulators to maintain
adequate pressure in all areas for both domestic and fire flow use.