Module 1 provides an introduction to hydrology and precipitation. It defines hydrology as the science dealing with the occurrence, circulation and distribution of water on Earth. The hydrologic cycle and water budget equation are introduced. Applications of hydrology in engineering include estimating water resources, studying processes like precipitation and runoff, and addressing problems like floods and droughts. Precipitation is also defined and different types and measurement methods are discussed.

1. Module 1:
Introduction to
Hydrology and
Precipitation
1

2. • Hydrology: Introduction,
• Hydrologic Cycle (Horton’s) qualitative and engineering representation,
• Water Budget Equation,
• Applications of Hydrology in Engineering.
• Precipitation: Definition, Forms and types of precipitation,
• Measurement of rain fall using Symon’s and Syphon type of rain gauges,
• Optimum number of rain gauge stations,
• Computation of mean rainfall,
• Estimation of missing data,
• Presentation of rainfall data: Mass Curve and Rainfall Hyetographs.
CONTENT

3. Basic Hydrology Concept
• 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".

4. WATER SCENARIO
IN 2025
TODAY
AND
BEFORE

5. IN 2025
Today
and
before

6. Today and before By 2025

7. Today and before By 2025

11. These satellite images from June 15, 2018, (left) and June 15, 2019,
show the diminishing size of the Puzhal Lake reservoir in Chennai, India.

13. • 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.

14. • 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

15.  Hydrology is basically an applied science.
To further emphasize the degree of applicability, the
subject is sometimes classified as
1. Scientific hydrology – The study which is
concerned chiefly with academic aspects.
2. Engineering or applied hydrology – study
concerned with engineering applications.

16. Hydrologic Cycle
• Water exists on the earth in all its three states,
viz. liquid, solid, gaseous and in various degrees
of motion.

20. North-East, Very high
Rainfall > 2,500 mm
Rajasthan
Rainfall < 100 mm
Western Ghats
High Rainfall Area
Shadow area
Low rainfall
Central India
Moderate rainfall
SPATIAL DISTRIBUTION OF RAINFALL
Eastern
Coast
High rainfall

22. • Watershed – area of land
draining into a stream at
a given location

24. Water Budget Equation
• For a given catchment, in an interval of time ∆t, the
continuity equation for water in its various phases
can be given as:
Mass inflow – Mass outflow = change in mass storage
• If the density of the inflow, outflow and storage
volumes are the same:
Vi - Inflow volume in to the catchment, Vo - Outflow volume
from the catchment and ∆S - change in the water volume
S
o
i 





25. • Therefore, the water budget of a catchment for a time
interval ∆t is written as:
P – R – G – E – T = ∆S
P = Precipitation, R = Surface runoff, G = net ground water flow out of the
catchment, E = Evaporation, T = Transpiration, and ∆S = change in storage
• The above equation is called the water budget
equation for a catchment
NOTE: All the terms in the equation have the dimension of
volume and these terms can be expressed as depth over the
catchment area.
Water Budget Equation…

26. Application in Engineering
• Hydrology finds its greatest application in the design and
operation of water resources engineering projects
• The capacity of storage structures such as reservoir.
• The magnitude of flood flows to enable safe disposal of
the excess flow.
• The minimum flow and quantity of flow available at
various seasons.
• The interaction of the flood wave and hydraulic
structures, such as reservoirs, barrages and bridges.
• Municipal and Industrial water supplies.