Republic of the Philippines
NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY
Cabanatuan City, Nueva Ecija, Philippines
CIVIL ENGINEERING DEPARTMENT
HYDROLOGY
(CE 332)
GROUP 2 (BSCE - 3B)
Advincula, Jhosua F.
Abillon, Aiko Bulanadi
Besa, Dan Robert A.
Butic, Lenih Jade
Capricho, Lesner
Cuaresma, Earl Kenneth E.
Cunanan, Reggie Mae A.
Dela Cruz, Janna Marie
Dela Peña, David SanGabriel
Desiderio, Jeremy
Requintel, Jurist Magnate
Sanqui, Andrei Ruiz
Seminiano, Benjamin jr. L.
Table of Contents
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
Introduction to Reservoir
Types of Reservoirs
Types of Dams
Classification of Reservoirs through Dams
Factors Affecting Selection of Dam for Reservoir
Advantages and Disadvantages of Building a Dam
Storage Zones of a Reservoir
Determination of Reservoir Storage Capacity
Volume of Reservoirs
UNIT V: STORAGE OF RESERVOIR
I.
Introduction to Reservoir
Reservoir
● Water can be stored in three main places: the atmosphere, on the surface of the Earth, and
underground. Specifically, these water storage areas are known as reservoirs.
● Natural reservoirs include oceans, glaciers and ice sheets, groundwater, lakes, soil
moisture, wetlands, living organisms, the atmosphere, and rivers. A reservoir can also be
formed from a natural lake whose outlet has been dammed to control the water level and
this is known as an artificial reservoir. Most reservoirs are formed by constructing dams
across rivers.
Why are Reservoirs important?
● Reservoirs are designed to store the rain that falls during the wetter parts of the year so
that there is a continuous supply of water for the drier periods.
● The most critical purpose of reservoirs is flood risk management.
Popular Reservoirs in the Philippines
Magat Dam
La Mesa Watershed
and Eco-park
San Roque Dam
Angat Dam
Lake Lanao
Pantabangan Dam
II.
Types of Reservoirs
Depending upon the purposes served, the reservoirs may be classified into the following types.
1. Storage or conservation reservoirs
2. Flood control reservoirs
3. Distribution reservoirs
4. Multipurpose reservoirs.
1. Storage or Conservation Reservoirs
● These reservoirs are primarily used to maintain minimum supplies of water for irrigation,
hydroelectric generation, domestic and industrial water supply schemes, etc.
● The storage reservoir is constructed to store the excess water of floods and released
gradually as and when required.
2. Flood Control Reservoirs
● A flood control reservoir is generally called a flood-mitigation reservoir or retention
basin. Flood control reservoirs are designed to manage, control, and store excess water
temporarily. The stored water will then be released- in a controlled manner to minimize
the impact of flooding downstream.
Flood control reservoirs may be further classified into two categories.
(i) Detention reservoirs.
● Detention reservoirs are designed to detain and control the stormwater runoff
temporarily during heavy rain or snowmelt.
● The water is stored for a short period and then released at a controlled rate which
prevents downstream flooding and erosion.
(ii) Retention reservoirs
● Unlike detention reservoirs, retention reservoirs are intended to retain water for a
longer period.
● Retention reservoirs store excess water during storms and release it gradually,
providing a more sustained flow downstream.
● They are often designed to optimize the use of stored water for various purposes.
3. Distribution Reservoir
● It is a small-capacity reservoir that is mainly constructed to meet the water supply
requirements of a particular city.
● It is made of masonry or cement concrete and may be covered from the top to prevent
contamination and evaporation.
● This reservoir is filled with treated water and ensures a steady and reliable supply of
water.
● Since demand for water remains fluctuating during the day, water may have to be drawn
from this reservoir at times at much more than the inflow rate.
4. Multipurpose Reservoirs
● The reservoir designed and constructed keeping only one purpose in view is known as a
single-purpose reservoir.
● A reservoir designed to serve more than one purpose simultaneously is called a
Multipurpose reservoir. It provides more flexibility and versatility in managing water
resources for various purposes.
● For example, a reservoir designed to protect the downstream areas from floods and also
to conserve water for irrigation, water supply, hydroelectric purposes, etc. shall be called
a multi-purpose reservoir.
III.
Types of Dams
A dam is a man-made barrier usually built across a river to hold back water and raise its
level, creating a lake or a reservoir behind it to generate electricity or as a water supply.
Classification of dams can be two types:
1. Based on Function
a. Storage Dam - Storage dams are the most common types of dams which are
constructed to store water during the rainy seasons, supply water to the local
wildlife, and store water for hydroelectric power generation, and irrigation.
b. Diversion Dam - Diversion dam is used to divert water. They provide pressure to
push water into ditches, canals, or other areas used for conveyance. It is typically
lower in height and has a small water storage area in its upstream.
c. Detention Dam - Detention dams are typically constructed for flood control by
retarding flow downstream, helping reduce flash floods. The water is retained in a
reservoir to be later gradually released.
d. Debris Dam - Debris dams are a form of detention dam that collects material to
keep it from flowing into locations where a substantial deposit of debris could be
harmful.
e. CofferDam - A temporary structure enclosing all parts of the construction area so
that construction can proceed in a dry working environment.
2. Based on Structure and Design
a. Gravity Dam - Made from concrete or masonry, or sometimes both. It is called a
gravity dam because gravity holds it down to the ground stopping the water in the
reservoir and pushing it over.
Wawa Dam
b. Arch Dam - Arch dams are made from concrete, usually constructed in narrow,
steep-sided valleys. They are curved in the shape of an arch, with the top of the
arch pointing back into the water. An arch is a strong shape for resisting the
pushing force of the water behind the dam.
Idukki Dam
c. Buttress Dam - Made from concrete or masonry. They have a watertight
upstream side supported by triangular-shaped walls, called buttresses. The
buttresses are spaced at intervals on the downstream side. They resist the force of
the reservoir water trying to push the dam over.
Magballo-Balicotoc-Canlamay Buttress Dam
d. Embankment Dam - Made mainly from natural materials. The two main types
are earthfill dams and rockfill dams. Earthfill dams are made up mostly of
compacted earth, while rockfill dams are made up mainly of dumped and
compacted rockfill. The materials are usually excavated or quarried from nearby
sites, preferably within the reservoir basin.
Pantabangan Dam
IV. Classifications of Reservoir through Dams
Reservoirs created by dams play a crucial role in water resource management, providing
water for irrigation, drinking, industrial use, and power generation. Reservoirs vary in size,
purpose, and characteristics, leading to the need for classification.
Three (3) Classifications of Reservoir through Dams
● Major dams – (reservation capacity dams (1x106to6x107 m3) are designed to withstand
the maximum probable flood.
● Intermediate–sized dams (intermediate than 1x106m3) the dams are designed to handle
the discharge from the most severe storm considered to be reasonably characteristic of the
watershed.
● Minor reservoirs – (less than (1x106 m3) The dams are designed to handle floods with
return periods of 50 to 100 years.
V. Factors Affecting Selection of Dam for Reservoir
1. Topography
The natural topography of the area, including the shape of the valley and the type of foundation
material, influences dam selection.
2. Geological Condition
Surveying geological and foundation conditions is imperative as
the foundations bear the dam's weight. Different types of
foundations include solid rock, like granite, which provides
robust support for various dam types.
3. Hydrology
In essence, hydrology provides the foundational data needed to make informed decisions about
dam design, operation, and management, contributing to the overall success and sustainability of
reservoir projects.
4. Seismicity
Dam sites must be evaluated for seismic risk, and structures designed accordingly to withstand
potential earthquakes. In earthquake-prone areas, the design of a dam must consider the impact
of seismic forces.
5. Environmental Impact
Assessments consider the ecological impact on flora, fauna, and ecosystems in the reservoir area,
as well as downstream effects. Prioritizing environmental impact in dam selection promotes
sustainable development, reduces negative consequences on ecosystems, and enhances the
overall social and ecological resilience of the project.
6. Hydraulic Consideration
The rate at which sediment is transported into the reservoir affects its lifespan and functionality,
requiring consideration during site selection. The hydraulic characteristics of the river or stream,
including flow rates and sediment transport, influence dam design.
7. Construction and Economic Viability
Construction and maintenance costs, as well as the economic benefits of the reservoir, play a role
in decision-making. Another key consideration in choosing a dam type is the availability of
materials. To ensure cost-effective dam construction, materials must be available locally or
within a short distance of the construction site.
8. Land Use and Resettlement
The impact on local communities, land use, and the need for resettlement are important social
factors to be considered. The height of a dam is a multifaceted factor that influences its
functionality, efficiency, cost, and impact on the environment and surrounding communities.
9. Legal and Regulatory Consideration
They ensure that dams are planned, constructed, and operated in a manner that safeguards public
safety, respects environmental concerns, and adheres to established legal standards.
VI. Advantages and Disadvantages of Building a Dam
Advantages
● Flood control
Flood control involves ways to lessen
flood damage. A reservoir for flood control
stores water during floods and lets it out
slowly, protecting areas downstream from too
much harm.
● Hydroelectric power
Hydroelectric energy, also known as
hydroelectric power or hydroelectricity, is a
type of energy that uses moving water, like
from a waterfall, to make electricity. People
have been using this water power for a very
long time.
● Irrigation
Irrigation means adding water to the soil using
pipes, pumps, and sprays. It's often used in places
with little rain or during dry periods. Different
systems are used to spread water evenly across the
entire field.
● Water supply
Getting water to people through pipes and
pumps is called water supply. It's done by
public groups, businesses, communities, or
individuals. Having good water systems is
important for societies to work well,
providing drinking water to people
worldwide.
● Presentation of aquatic life
Aquatic" is about things connected to water, like
living in or near water, or activities happening in
water. It doesn't include underground water. It
can also mean an animal, with or without a
backbone, that lives in water for most or all of its
life.
● Recreation
Recreational uses of domestic water supply
reservoirs and the land-based infrastructure
necessary to support such uses can add microbial,
physical, and chemical contaminants to the
drinking water produced from the reservoirs.
Disadvantages
● Environmental impact.
Dams can cause significant ecological disruption,
including the alteration of river flow, sedimentation,
and the destruction of habitats
● People and animals' lives are disrupted.
Disturbance and habitat modification by
humans can alter animal movement, leading to
negative impacts on fitness, survival, and population
viability.
● Cost: Dams can be costly to construct and
maintain, and their failure can lead to devastating outcomes.
● Greenhouse gas emissions: Reservoirs behind a
dam can lead to higher greenhouse gas emissions
and have a large impact on aquatic systems.
● Maintenance challenges
Dams require regular maintenance to ensure their safety and longevity
● Potential failure
Dams can fail, leading to catastrophic consequences such as flooding
and loss of life
VII. Storage Zones of a Reservoir
The storage capacity of a reservoir is conceptually divided into different zones based on the
useful purpose that a reservoir is required to serve.
1. Dead Storage
● The dead storage zone is the bottom-most zone of a reservoir.
● This storage is not useful in reservoir operation.
● It is provided to accommodate the still trapped in the reservoir.
A reservoir provides dead storage primarily to suit two purposes:
a) The river, during its course to the reservoir, picks up a sizable amount of sediment that carries
it along either as a suspended load or bed load. Upon entering the reservoir the velocity of flow
becomes zero that’s why its carrying capacity is lost. The sediment settles down and continues to
accumulate over time. As a result of this buildup, the reservoir's effective storage capacity and
hence its reliability continues to deteriorate with time. Dead storage is the zone where these
sediments primarily settle (they settle in other zones also).
b) Most of the time the water that is released from the reservoir passes through the turbines of
power stations located downstream of the dam to create hydroelectric electricity. For the turbines
to efficiently work or operate it is necessary that head variation stays within a range and a
minimum head is always available. This minimum head corresponds to the top of the dead
storage zone.
2. Useful Storage
● The total amount of water between the minimum pool level and the normal pool level is
called useful storage.
● This water is very useful for irrigation and power generation purposes.
3. Surcharge Storage
● The volume of water stored between the normal pool level and the maximum pool level
is known as surcharge storage.
● In hydrologic terms, the volume of a reservoir between the maximum water surface
elevation for which the dam is designed and the crest of an uncontrolled spillway, or the
normal full-pool elevation of the reservoir with the crest gates in the normally closed
position.
4. Bank Storage
● Bank storage can be defined as water that is absorbed and stored in the bed and banks of
a lake, river, or reservoir during periods of high groundwater and later returned to the
water body during periods of low groundwater.
5. Valley Storage
● The volume of water stored between any two specified points along a stream, including
both the channel and the flood plain.
VIII. Determination of Reservoir Storage Capacity
The storage capacity of a reservoir is conceptually divided into several zones based on
the useful purposes that a reservoir is required to serve. Fig. 1.1 gives a schematic of various
storage zones of a reservoir.
FRL: Full reservoir level
MWL: Maximum water level
Surcharge storage
-it is the storage between the full reservoir level (FRL) and the maximum water level (MWL) of
a reservoir which may be attained with capacity exceeding the reservoir at FRL to start with.
-designed to reduce maximum discharge through the hydro system during spring flood and
rainfall flood
Flood Control Storage
- the area within an elevation range on a reservoir that is reserved for the storage of floodwater.
-designed to reduce the peak flood flow passed downstream, spreading the overall volume passed
downstream over a longer period
Conservation Zone
-This is the storage section of a reservoir that is dedicated to the long-term water supply needs of
various stakeholders, such as domestic, industrial, agricultural, and environmental purposes
Dead storage
- Also called inactive storage, dead storage represents the portion of a reservoir that is
permanently submerged and cannot be utilized for any practical purposes.
Reservoir Capacity
● Depends upon the inflow available and the demand.
● If the inflow in the reservoir is always greater than the demand, there is no
reservoir capacity required.
● If the inflow in the reservoir is smaller than the demand, a large reservoir capacity
is required.
Determining the Required Reservoir Capacity
Mass Inflow Curve - a curve that represents the cumulative flow in a reservoir at any
particular instance. It is a plot between cumulative inflow in the reservoir with time. It can be
prepared with the help of a hydrograph of the river for the dam site for a large number of years.
Procedure in determining the Required Reservoir Capacity using Mass Inflow Curve
1. Gather Data:
- Collect historical data on precipitation, streamflow, and any other relevant hydrological
parameters for the area of interest. This data is crucial for developing the Mass Inflow Curve.
2. Hydrological Analysis:
- Conduct a hydrological analysis to understand the patterns of precipitation and runoff.
Identify the duration and intensity of rainfall events, as well as the corresponding streamflow
response.
3. Calculate Mass Inflow:
- Use the collected data to calculate the mass inflow (or volume of water) entering the reservoir
for each time step. This involves integrating the streamflow over time.
4. Develop the Mass Inflow Curve:
- Plot the calculated mass inflow values against time to create the Mass Inflow Curve. This
curve provides a graphical representation of the variation in water input to the reservoir.
5. Define Design Criteria:
- Determine the design criteria for the reservoir, including the desired storage duration, safety
margins, and any specific requirements related to the intended purpose of the reservoir (e.g.,
water supply, flood control).
6. Calculate Required Storage:
- Analyze the Mass Inflow Curve to identify the periods of maximum inflow and estimate the
corresponding required storage in the reservoir. This involves integrating the area under the
curve during critical periods.
7. Consider Safety Margins:
- Incorporate safety margins into the calculations to account for uncertainties in the data,
changes in hydrological patterns, and unexpected events. This ensures that the reservoir can
handle variations in inflow and meet its objectives under different scenarios.
8. Check Regulatory Requirements:
- Verify that the calculated reservoir capacity meets any regulatory requirements or standards
applicable to the project. Different regions may have specific guidelines for reservoir design and
safety.
9. Engineering Design:
- Based on the calculated required storage capacity, proceed with the detailed engineering
design of the reservoir. Consider factors such as dam height, spillway design, and environmental
impact mitigation measures.
10. Integrate Sedimentation Analysis:
- If sedimentation is a concern in the area, integrate sedimentation analysis into the design
process. Consider the rate of sediment deposition and its impact on reservoir capacity over time.
11. Review and Iteration:
- Review the design calculations and, if necessary, iterate the process to refine the reservoir
capacity estimate. Consider feedback from relevant experts and stakeholders.
12. Documentation and Reporting:
- Document the methodology, assumptions, and results of the reservoir capacity determination.
Prepare a comprehensive report for internal and regulatory review.
IX. Volume of Reservoirs
Volume of Reservoirs
● The techniques for determining the storage volume required for a reservoir are dependent
both on the size and use of the reservoir. The simplest procedure which is quite
satisfactory for small water-supply impoundments, stormwater retention ponds, and
wastewater equalization basins is called the mass diagram or Ripple method.
● The main disadvantage of the Ripple method is that it assumes that the sequence of
events leading to the drought or flood will be the same in the future as it was in the past.
More sophisticated techniques have been developed to overcome this disadvantage, but
the techniques are left for more advanced classes.
The Ripple procedure for determining the storage volume is an application of the mass balance =
approach. In this case, it is assumed that the only input is the flow into the reservoir (Qout).
By cumulatively summing the storage terms, we can estimate the size of the reservoir. If
the reservoir design is for water supply, then Qout is the demand, and the zero or positive values
of storage (Δs) indicate there is enough water to meet the demand. If the storage is negative, then
the reservoir must have a capacity equal to the absolute value of cumulative storage to meet the
demand. If the reservoir design is for flood protection, then Qout is the capacity of the
downstream river to hold water. And zero or negative values indicate the river is below the flood
storage. If the storage is positive, then the reservoir must have a capacity equal to the cumulative
storage to prevent flooding.
Example:
Using the date in Table 2-4, determine the storage required to meet a demand of 2.0 m3/s for the
period from August 1976 through December 1978.
GIVEN:
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