Post on 02-Jun-2018
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LESSON 2 – RESERVOIRS
8/10/2019 Lesson 2 Reservoirs.pdf
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Why Reservoirs?To stabilize the flow of water, either by regulating a varying supply
in a natural stream or by satisfying a varying demand by the ulti
mate consumers
LESSON 2 – Reservoirs
Storage, or conservation reservoir can retain excess
water from periods of high flow for use during periods
of drought Storage of floodwater may reduce flood damage below
the reservoir
Distribution reservoir to provide the varying rate of
demand for water during the day
Stock tanks or farm ponds may conserve the intermittent
flow from small creeks for useful purposes
8/10/2019 Lesson 2 Reservoirs.pdf
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Physical Characteristics of Reservoirs
Area – elevation curve
is constructed by
planimetering thearea enclosed within
each contour within
the reservoir site
STORAGE CAPACITY
Elevation – storage and elevation –area
curves for Cherokee Reservoir on the
Holston River, Tennessee
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
NORMAL POOL LEVELmaximum elevation to which the reservoir surface will r ise during
ordinary operating condi tions
determined by the elevation of the spillway crest or the top of the
spillway gates
MINIMUM POOL LEVELlowest elevation to which the pool is to be drawn under normal
conditionsmay be fixed by the elevation of the lowest outlet in the dam or,
in the case of hydroelectric reservoirs, by conditions of operating
the efficiency of the turbines
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
USEFUL STORAGEstorage volume between the minimum and normal pool levels
for multipurpose dams, these may be subdivided into conservation
storage and flood- mitigation storage
DEAD STORAGEwater held below the minimum pool level
SURCHARGE STORAGEdischarge over the spillway; normally uncontrolled; it exists only
while a flood is occurring and cannot be retained for later use
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
BANK STORAGEincreases the capacity of the reservoir above that indicated by the
elevation-storage curve
VALLEY STORAGEa variable volume occupied by water in natural stream channel
LESSON 2 – Reservoirs
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Physical Characteristics of Reservoirs
LESSON 2 – Reservoirs
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Reservoir Yield
is the amount of water that can be supplied from the reservoirduring a specified interval of time; it is dependent on inflow
and wil l vary from year to year
YIELD
SAFE or FIRM YIELD is the maximum quantity of water thatcan be guaranteed during a critical dry period
SECONDARY YIELD water available in excess of safe yieldduring periods of high flow
LESSON 2 – Reservoirs
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Selection of Distribution Reservoir
Capacity for a Given YieldExample 1. The water supply for acity is pumped from wells to a dis
tribution reservoir. The estimated
hourly water requirements for the
maximum day are as fo llows. If
the pumps are to operate at auniform rate, what distribution
reservoir capacity is required?
Hour
ending
Demand
(m³/h)
Pumpingrate
(m³/h)
Hour
ending
Demand
(m³/h)
Pumpingrate
(m³/h)
0100 273 529.3 1300 759 529.3
0200 206 529.3 1400 764 529.3
0300 256 529.3 1500 729 529.3
0400 237 529.3 1600 671 529.3
0500 257 529.3 1700 670 529.3
0600 312 529.3 1800 657 529.3
0700 438 529.3 1900 612 529.3
0800 627 529.3 2000 525 529.3
0900 817 529.3 2100 423 529.31000 875 529.3 2200 365 529.3
1100 820 529.3 2300 328 529.3
1200 773 529.3 2400 309 529.3
LESSON 2 – Reservoirs
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Hour endingDemand
(m³/h)
Pumping rate
(m³/h)
Required from
reservoir (m³)Hour ending
Demand
(m³/h)
Pumping rate
(m³/h)
Required from
reservoir (m³)
0100 273 529.3 1300 759 529.3
0200 206 529.3 1400 764 529.3
0300 256 529.3 1500 729 529.3
0400 237 529.3 1600 671 529.3
0500 257 529.3 1700 670 529.3
0600 312 529.3 1800 657 529.3
0700 438 529.3 1900 612 529.3
0800 627 529.3 2000 525 529.3
0900 817 529.3 2100 423 529.3
1000 875 529.3 2200 365 529.3
1100 820 529.3 2300 328 529.3
1200 773 529.3 2400 309 529.3
TOTAL TOTAL
LESSON 2 – Reservoirs
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GRAPHICAL SOLUTION
∫ −b
a
I O )(
where:
O = Outflow (demand)
I = Inflow pumping rate
RRC =
LESSON 2 – Reservoirs
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Selection of Capacity for a River
Reservoir
Sequent – Peak Algori thm - values of cumulative sum of inflow
minus withdrawals
LESSON 2 – Reservoirs
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Selection of Capacity for a River
Reservoir
Mass Curve (Rippl Diagram) –
a cumulative plotting of
net reservoir inflow
LESSON 2 – Reservoirs
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Selection of Capacity for a River
ReservoirExample 2. What reservoir capacityis required to assure a yield of
75,000 acre-ft/yr for the inflows
shown?
LESSON 2 – Reservoirs
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Selection of Capacity for a River
ReservoirExample 3. What yield will be availableif a reservoir of 30,000 acre-ft
capacity is provided at the site for which
the mass curve of Fig. 7.7 applies?
LESSON 2 – Reservoirs
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Reservoir Reliability
RELIABILITY of the reservoir is defined as the probabil ity that
will deliver the expected demand throughout its li fetime without
incurring a deficiency
LESSON 2 – Reservoirs
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LET LEARNING CONTINUE….