INVOLVING
PROCESSES
HYDROLOGICAL
CYCLE
CONCEPT
OF HYDROLOGY
1.
2.
3.
4.
5.
6.
7.
8.
Evaporation
Condensation
Precipitation
Surface Runoff
Interception
Transpiration
Infiltration
Sub-surface Runoff
TOPIC 1
BASIC OF
HYDROLOGY
water
balance
calculate
THE HYDROLOGY
CONTINUITY EQUATION
THE EFFECT OF SOILS
USE TOWARD
HYDROLOGICAL CYCLE
Basic Hydrology Concept
Introduction
• Water is vital for all living organisms on Earth.
• For centuries, people have been investigating
where water comes from and where it goes, why
some of it is salty and some is fresh, why
sometimes there is not enough and sometimes too
much. All questions and answers related to water
have been grouped together into a discipline.
• The name of the discipline is hydrology and is
formed by two Greek words: "hydro" and "logos"
meaning "water" and "science".
CONCEPT OF HYDROLOGY
• Discusses the hydrologic cycle, it’s processes,
water balance, precipitation types, estimation of
precipitation, and analysis of precipitation data.
Also methods of measurement of stream flow,
stage discharge relation, unit hydrograph theory,
Transposition of Hydrograph, Synthesis of
hydrograph from basin characteristics, stream
flow routing, flood frequency analysis and
attenuation of flood flows. Emphasis is given
towards the calculation of rain fall data and
urban drainage concept in developing new
areas.
What Is Hydrology?
– It is a science of water.
– It is the science that deals with the
occurrence, circulation and distribution of
water of the earth and earth’s atmosphere.
• A good understanding of the hydrologic
processes is important for the assessment
of the water resources, their management
and conservation on global and regional
scales.
What Is Hydrology?
1. The study of water on, under, and over
the Earth’s surface, and from its origins
to all its destinations on the earth is
called hydrology.
2. The scientific study of water, seeking to
explain the water balance equation in
terms of time and space, and assessing
the impact of physical and chemical
processes and their role in ecosystems.
• In general sense engineering
hydrology deals with
– Estimation of water resources
– The study of processes such as
precipitation, evapotranspiration, runoff
and their interaction
– The study of problems such as floods
and droughts and strategies to combat
them
Uses of Engineering Hydrology
• Hydrology is used to find out maximum probable flood at
proposed sites e.g. Dams.
• The variation of water production from catchments can
be calculated and described by hydrology.
• Engineering hydrology enables us to find out the
relationship between a catchment’s surface water and
groundwater resources
• The expected flood flows over a spillway, at a highway
Culvert, or in an urban storm drainage system can be
known by this very subject.
• It helps us to know the required reservoir capacity to
assure adequate water for irrigation or municipal water
supply in droughts condition.
• It tells us what hydrologic hardware (e.g. rain gauges,
stream gauges etc) and software (computer models) are
needed for real-time flood forecasting
Uses of Engineering Hydrology
• Used in connection with design and operations
of hydraulic structure
• Used in prediction of flood over a spillway, at
highway culvert or in urban storm drainage
• Used to assess the reservoir capacity required
to assure adequate water for irrigation or
municipal water supply during drought
• Hydrology is an indispensable tool in planning
and building hydraulic structures.
• Hydrology is used for city water supply design
which is based on catchments area, amount of
rainfall, dry period, storage capacity, runoff
evaporation and transpiration.
Branches of Hydrology
HYDROLOGY
Surface Water
Hydrology
Ground Water
Hydrology
Ice and Snow
Hydrology
Limnology
Hydrology
Hydrologic Cycle
• Water exists on the earth in all its three
states, viz. liquid, solid, gaseous and in
various degrees of motion.
Hydrologic cycle….
• Water, irrespective of different states,
involves dynamic aspect in nature.
• The dynamic nature of water, the
existence of water in various state with
different hydrological process result in a
very important natural phenomenon
called Hydrologic
cycle.
Hydrological Cycle
•
Evaporation of water from water bodies, such as oceans and lakes, formation and
movement of clouds, rain and snowfall, stream flow and ground water movement
are some examples of the dynamic aspects of water.
Hydrologic cycle….
• Evaporation from
water bodies
• Water vapour
moves upwards
• Cloud formation
• Condensation
• Precipitate
• Interception
• Transpiration
• Infiltration
• Runoff–streamflow
• Deep percolation
• Ground water flow
Hydrological Cycle
• The hydrologic cycle is the continuous, unsteady
circulation of water from the atmosphere to and
under the land surface and back to the
atmosphere by various processes. It is dynamic
in that the quantity and quality of water at a
particular location may vary greatly with time.
Temporal variations may occur in the
atmosphere, on land surface, in surface waters,
and in the groundwater of an area. Within the
hydrologic cycle, water may appear in all three
of its states; solid, liquid, and gas.
How The Water Cycle Works
Solar energy heats up
the oceans water surface, lake, river etc.
Water falls as rain, snow
Water vapour condenses into clouds
Some of rain infiltrates in soil
Water evaporates and rises into the air
Water returns to the sea
Surface runoff makes its way into rivers and streams.
Rivers flow back into the ocean due to the force of gravity.
The cycle starts all over again.
Hydrologic cycle….
• The hydrologic cycle has importance
influence in a variety of fields agriculture,
forestry, geography, economics, sociology,
and political scene.
• Engineering application of the knowledge are
found in the design and operation of the
projects dealing with water supply,
hydropower, irrigation & drainage, flood
control, navigation, coastal work, various
hydraulic structure works, salinity control and
recreational use of water.
Evaporation
• Evaporation is the process by which water is
converted from its liquid form to its vapor
form and thus transferred from land and
water masses to the atmosphere.
• The rate of evaporation depends upon:
– Wind speed: the higher the wind speed, the more
evaporation
– Temperature: the higher the temperature, the
more evaporation
– Humidity: the lower the humidity, the more
evaporation
Evapotranspiration
Condensation
The change of water from its
gaseous form (water vapor)
into liquid water.
Condensation generally
occurs in the atmosphere
when warm air raises, cools
and looses its capacity to hold
water vapor. As a result,
excess water vapor
condenses to form cloud
droplets.
Precipitation
• Precipitation occurs when so much water has condensed
that the air cannot hold it anymore. The clouds get
heavy and water falls back to the earth in the form of
rain, hail, sleet or snow.
• Precipitation can occur primarily as rain. Annual amounts
of precipitation are unpredictable and variable, ranging
from approximately 1500 mm to 4000 mm in various
locations in Malaysia. In essence, precipitation is the
most important process in the hydrologic cycle because
it is the 'driving force' providing water that must be
accommodated in the urban environment.
Surface runoff
• Sometimes referred to as overland flow, is
the process whereby water moves from
the ground surface to a waterway or water
body. Urbanisation usually dramatically
increase surface runoff volume and rates.
Interception
• Interception is the amount of precipitation that
wets and adheres to aboveground objects
(primarily vegetation) until it is evaporated back
into the atmosphere. The annual amount of
interception in a particular area is affected by
factors such as the amount and type of
precipitation, the extent and type of vegetation,
and winds. Interception is not likely to be an
important process in urban stormwater
management programs.
Transpiration
• When plants absorb water from the ground and
exhale it into the air as water vapour (Pielou,
1998).
• Transpiration is the process by which moisture is
carried through plants from roots to small pores
on the underside of leaves, where it changes to
vapor and is released to the atmosphere.
Transpiration is essentially evaporation of water
from plant leaves. Transpiration also includes a
process called guttation, which is the loss of
water in liquid form from the uninjured leaf or
stem of the plant, principally through water
stomata.
Environmental factors that affect the rate of transpiration:
1. Light
Plants transpire more rapidly in the light than in the dark. This is largely because light
stimulates the opening of the stomata (mechanism). Light also speeds up
transpiration by warming the leaf.
2. Temperature
Plants transpire more rapidly at higher temperatures because water evaporates more
rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as
it does at 20°C.
3. Humidity
The rate of diffusion of any substance increases as the difference in concentration of
the substances in the two regions increases.When the surrounding air is dry, diffusion
of water out of the leaf goes on more rapidly.
4. Wind
When there is no breeze, the air surrounding a leaf becomes increasingly humid thus
reducing the rate of transpiration. When a breeze is present, the humid air is carried
away and replaced by drier air.
5. Soil water
A plant cannot continue to transpire rapidly if its water loss is not made up by
replacement from the soil. When absorption of water by the roots fails to keep up with
the rate of transpiration, loss of turgor occurs, and the stomata close. This
immediately reduces the rate of transpiration (as well as of photosynthesis). If the
loss of turgor extends to the rest of the leaf and stem, the plant wilts.
Infiltration
• Infiltration is defined as the passage of water
through the air-soil interface. Infiltration rates are
affected by factors such as time since the rainfall
event started, soil porosity and permeability,
antecedent soil moisture conditions, and
presence of vegetation. Infiltration is a very
important process in urban stormwater
management and, therefore, essentially all
hydrologic methods explicitly account for
infiltration. Urbanisation usually decreases
infiltration with a resulting increase in runoff
volume and discharge.
Sub-surface runoff.
• Interflow, sometimes referred to as subsurface
stormflow, is the process whereby water moves
laterally beneath the land surface, but above the
groundwater table. Interflow occurs until water
enters a waterway or water body, or is
evapotranspired. Interflow is affected by the
same factors as those for surface runoff.
Interflow is rarely explicitly analysed; it is usually
considered part of the surface runoff. Surface
runoff, interflow, and precipitation falling directly
on water bodies are sometimes lumped together
and called direct runoff.
The Effect of Soils Use Toward
Hydrological Cycle.
 When development occurs, the resultant alterations to the
land can lead to dramatics changes to the hydrology or the
way water is transported and stored,
 Impervious man-made surfaces (asphalt, concrete, rooftops)
and compacted earth associated with development create a
barrier to percolation of rainfall into the soil, increasing
surface runoff and decreasing ground water infiltration.
Watershed
Urbanization
Relationships between impervious cover
and surface runoff
Natural Ground Cover
0% Impervious Surface
Urban Residential
35%-50% Impervious Surface
Low Density Residential
10%-20% Impervious Surface
Commercial Industrial
75%-100% Impervious Surface
This disruption of the natural water
cycle leads to a number of
changes, including:
Impacts on Stream Form and Function
1. Increased volume and velocity of
runoff
2. Increased frequency and severity
of flooding
3. Peak (storm) flows many times
greater than in natural basins
4. Loss of natural runoff storage
capacity in vegetation, wetlands,
and soil
5. Reduced groundwater recharge
6. Decreased base flow (the ground
water contribution to stream
flow). This can result in streams
becoming intermittent or dry, and
also affects water temperature.
The Effect of Soils Use Toward Hydrological Cycle.
Rainwater runs off the land into water
bodies. It also percolates into the soil.
Percolation recharges groundwater
and filters pollutants. Through both
pathways, water makes its way into
our creeks, ponds, wetlands, rivers,
and oceans.
Development puts impervious
surfaces, roads, sidewalk, and roofs,
that prevent percolation. Most of the
rainwater runs off the land carrying
pollutants into water bodies. Without
percolation, flooding is more frequent
and severe.
THE HYDROLOGY CONTINUITY EQUATION
Inflow – Outflow
=
I–O
=
I–O
=
P – DRO – E – T- G
@
P – ( R + ET + G)
Change in Storage
ds/dt
∆S
=
∆S
=
∆S
Abbreviations:
G
= Ground water
P
= Precipitation
R
= Runoff or excess rainfall
DRO
= direct runoff
B
= Subsurface flow
I
= Infiltration
ET
= Evapotranspiration
E
= Evaporation
T
= Transpiration
S
= Change in storage in the saturated zone - soil or groundwater
Exercise 1:
•
Kelantan's river catchment's expected to
accept rain as much as 350 mm from the
beginning October 2003 to December
2003. Evaporation and infiltration
respectively was estimated at 35 mm
and 25 mm in that time period. The
catchment’s area was 90 km2. There is a
reservoir in these catchments. Estimate
runoff volume in m3 if level of reservoir
unchanged.
Exercise 2:
•
Hydrology record for a catchment's as wide as
500 km2 show excess rainfall annual and
average the surface runoff annual respectively
was 90 cm and 33 cm. One reservoir as wide
1700 km2 had planned the construction in the
outlet part of catchment area. The annual
evaporation average to that reservoir was
expected as much as 150 mm. Determine
storage values that occur in that reservoir.
Exercise 3:
•
In period three months, Ketereh district are
expected to receive rain as much as 245 mm.
evapotranspiration were estimate as 80 mm
and diffusion to sub surface as much as 20
mm. Wide of basin was 36 km2. Estimate :
i. Excess rain depth
ii. Calculate direct runoff volume
iii. If direct runoff may be stored in a reservoir, determine
population of people which can accept water supply for
now if per-capita daily utilizability was 200 liters.
Exercise 4:
•
Catchment area in Kuala Krai has area 1720
km2. Annual average rainfall data is 3200 mm.
There are two rivers which flowed to that
catchment area, namely Sungai Kuala Nal and
Sungai Krai. Discharge from Sungai Kuala Nal
is 23m3/s while data from Sungai Krai not
obtained. Record that made to show loss result
condensation process and bypass is 12% from
average annual rainfall. Calculate discharge
value for Sungai Krai.
References:
• http://arrowsmithwatersheds.org/links/Definitions.html
• http://www.bbc.co.uk/schools/ks2bitesize/science/materi
als/changing_states/read5.shtml
• http://www.planningwithpower.org/pubs/id-257.htm
• http://lincoln.ne.gov/city/pworks/watrshed/educate/runoff/
index.htm