System simulation and modeling

1. Simulation of water reservoir
system
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Case Study:

2. Simulation of water reservoir
system
 A water reservoir is an enclosed area for the storage of water to be used at a
later date.
 It can also serve to catch floods to protect valleys downstream of it, to establish
an aquatic environment, or to change the properties of the water.
 A reservoir can be created by building a dam across a valley, or by using natural
or man-made depressions.
 The main parameters of the reservoir are the volume, the area inundated and
the range that the water level can fluctuate.
 The basic function of an artificial reservoir is to change the rate of flow in the
stream or to store water for more expedient use.
 Reservoirs are among the more useful means of controlling the natural
character of water flows, instead of depending on nature.
 There is significant interaction between reservoirs and the environment: the
reservoirs affect the environment and vice versa
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3. Simulation of water reservoir
system
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4. Simulation of water reservoir
system
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5. Simulation of water reservoir
system
 Reservoir storage is essential to regulate highly variable water flows for
more steady uses like municipal and industrial water supply, irrigation,
hydroelectric power generation, and navigation.
 Usually, the water drawn from a reservoir is used at a much slower (and
constant) rate than the rate and constancy of the water flowing into the
reservoir (see Figure below).
 Reservoir modelling has naturally been employed to assist size reservoir
storage capacities, launching operating policies, assessing operating
plans, administering water allocations, developing management
strategies, and real-time operations.
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6. Simulation of water reservoir system
Inflow and Outflow Hydrograph
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7. Simulation of water reservoir system
 The basic prerequisite for adequate illustration of a reservoir is
employment of the continuity equation, or conservation of volume over
a period of time.
 This is a function that communicates dynamically with the existing state
of the reservoir.
 The foundational equation for preservation of volume is:
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8. Simulation of water reservoir system
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equation for preservation of volume

9. Simulation of water reservoir
system
 The term “Reservoir System Operations” points to the practice of
preserving and supervising a reservoir for multiple purposes, under
dynamic conditions.
 The state of the reservoir system is frequently in flux, requiring dynamic
methods of simulation to estimate and model them.
 The term “Reservoir System Operations Model” refers to a computer
program used for simulating and optimizing changes in storage, water
deliveries, and flood control for one or numerous reservoirs.
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10. Simulation of water reservoir
system
 Time and again, the purpose of the reservoir operation is to balance
the control of flood storage and preserve reliable water supply.
 Operational procedures are diverse for flood events than what are
employed under water scarce conditions and thus, the model must be
tailored for these changing conditions.
 To better administer potential changes to reservoir operations given
worries or changes in circumstances, it is helpful to build up a
calibrated simulation model of the reservoir
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11. Simulation of water reservoir
system
 Let us consider the following proposal for constructing a dam across a
river to create a reservoir.
 The reservoir is to be constructed at a specified site.
 The curve of the projected demand for the water from the reservoir
has been determined (from the expected growth pattern and the
seasonal fluctuations).
 The input to the reservoir is from the river inflow and from the rainfall
directly over the reservoir.
 The output consists of the seepage and evaporation losses, in addition
to the water supplied to meet the projected demand.
 This system (called a simple run-of-river storage demand system) is
represented symbolically in Figure below.
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12. Simulation of water reservoir
system
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13. Simulation of water reservoir
system
 Example Your water flow is insufficient to compensate for the total water requirements
(filling plus water losses).
 The volume of your pond is 2 073 m3.
 You have calculated that the water losses will average, during the culturing period (240
days), the following: seepage 34.56 m3 /day and evaporation 8.64 m3 /day.
 Total water losses will therefore be 34.56 + 8.64 = 43.2 m3 /day.
 During this period, your water source supplies only 0.25 l/s or 21.6 m3 /day (see Table
2). But much more water is available outside this period to fill your reservoir in 60-80
days.
 You will need to store in this reservoir the water needed for pond filling (2 073 m3) plus
the water required to compensate for the losses during 240 days.
 Water losses each day: 43.2 m3 Water available each day: 21.6 m3 Stored water used
each day: 43.2 - 21.6 = 21.6 m3 For 240 days, your storage will need to be 21.6 m 3 x
240 = 5184 m3 Total water volume to be stored: 2 073 m3 + 5184 m3 = 7257 m3.
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14. Simulation of water reservoir
system
 The amount of seepage loss is not a constant but depends on the volume of
the water stored.
 We have been given a curve (converted into a table) showing the seepage
loss as a function of volume for the proposed reservoir.
 Likewise, the evaporation loss depends on the area of the exposed surface
and the coefficient of evaporation.
 We are given another curve showing the surface area as a function of volume
as well as the seasonal variation of the coefficient of evaporation.
 Therefore, for a given volume of water in the reservoir at a particular time of
the year we can calculate the two losses.
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15. Simulation of water reservoir
system
 In reality no reasonable finite-sized reservoir can provide an absolute
guarantee of meeting the demand 100 % of the time because the river
inflow, the rainfall, the losses, the demand are all random variables.
 To build such a large dam which will never fail (to meet the demand)
through its entire life will generally be uneconomical.
 Therefore, in practice one determines the reservoir size which will meet the
demand with a specified risk of failure (of water shortage).
 For example, a 2 % failure means that once in 50 years the reservoir would
become empty before meeting the demand for water.
 The objective of the study is to determine the size of the reservoir with a
specified risk of failure.
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16. Simulation of water reservoir
system
 There is a single state variable in this system, namely, the volume of water
in the reservoir.
 Since the volume varies continuously with time, we are dealing with a
continuous system.
 It is reasonable to take one month as the basic time interval for the
simulation study.
 Thus, for example, if we wish to simulate the system for 100 years, the
simulation run length will be 1200.
 The simulation will be repeated assuming several different capacities of
the reservoir.
 The output will be in series of ranked shortages for each capacity.
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17. Simulation of water reservoir
system
 The basic procedure, to be repeated for each
time step, may be expressed in terms of the
following steps:
1. For the current month M of the current year IY
determine the total amount of river inflow and the
total rainfall directly over the reservoir.
 Let the sum of two inputs be denoted by
VIN (= RAIN + RFLOW).
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18. Simulation of water reservoir
system
2. Add the input volume VIN to the volume left over in the reservoir at the end
of the last month, VOL (m – 1).
This gives us the gross volume, GROSSV = VIN + VOL(m – 1).
3. On the basis of the last month's volume VOL (m – 1) calculate this month's
seepage and evaporation losses and add them as total loss TLOSS = SEEP +
EVAP
.
4. From the demand curve (stored as a table in the computer memory)
determine the demand of water for the current month DEM.
5. If the TLOSS >GROSSY, then the reservoir runs dry without supplying any
water and therefore shortage, SHORT = DEM.
The volume of water left at the end of the current month VOL (m) = 0. Spillage
SPILL = 0 and go co Step 8; else if TLOSS < GROSSY then the net water volume
available to satisfy the demand is YNET = GROSSV – TLOSS.
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19. Simulation of water reservoir system
6. If DEM > VNET the reservoir runs dry and the shortage is
given by SHORT = DEM – VNET, and SPILL = 0.
Go to Step 8; else if DEM < VNET, then the difference
DIFF = VNET – DEM is the water left over.
7. If this leftover water exceeds the capacity CAP of the
reservoir there will be a spill over, i.e., if DIFF > CAP then SPILL
= DIFF – CAP and VOL (m) = CAP; else if DIFF > CAP then
SPILL = 0 and VOL (m) = DIFF.
8. Print out SPILL and SHORT for this month, and move to the
next month. If the period exceeds the intended simulation
length stop, else go to Step I.
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