Engineering Hydrology chapter one for bachelor

hydrology chapter 1

1. eH did means Waker Introduction

“Logy” means Science
Hence, Hydrology means the science of water

Definition:- Hydrology is the applied science which deals about
occurrence, distribution, and movement of water of the earth.

Practical applications of hydrology are found in such tasks as the
design and operation of hydraulic structures, water supply,
wastewater treatment and disposal, irrigation, drainage, hydropower
generation, flood control, navigation, erosion and sediment control,
salinity control, pollution reduction, recreational use of water, and
fish and wildlife protection.

_ The role of applied hydrology is to help analyze the problems involved

in these tasks and to provide guidance for the planning and
management of water resources”. |

2. HYDROLOGY | applications

\ Predicting
floods

3. Hydrological Cycle

Moisture over land Le

Precipitation
on Tand

Evaporation from land
Precipitation

; pi
Evapotranspiration
ww 9 5

Infiltration Evaporation from ocean

Surface outflow $ $

Groundwater outflow

—

Groundwater flow

5. 1)

2)

3)

4)

Hydrological Cycle

Evaporation of water from the (a) surface sources like
river, lakes, oceans, (b) from the surface of soil (c) plants
through transpiration. By this process water is converted
into vapour.

Condensation :- It is the process by which vapour is
converted into solid form. (Clouds)

Precipitation in the form of rain, snow, sleet, drizzle etc.
Interception :- When precipitation occurs it is intercepted
by vegetation . So, this part do not contribute to the

urface water.

6. 6)

7)

8)

9)

Infiltration :- After water reaches the ground it infiltrates
into the ground.

Surface Detention :- Some part of the water is stored in
depression present on the ground.

Surface runoff :- The remaining water which flows on
ground or surface and joins channel is called surface
runoff.

Ground water flow or inter flow :- The water which
infiltrated into the ground joins the stream on the later

stage is called inter flow.

7. Global water balance (mm/yr)

Precipitation Atmospheric moisture flow 316 _ Precipitation Evaporation
800 1270 1586
Evaporation
484
Outflow
ts

Land (148.7 M km’) Ocean (361.3 M Ocean (3613M im?)
(29% of earth area) (71% of earth area)

8. Global Water Resources

105,000 km? or
0.0076% of total
water

Source: Igor A. Shiklomanoy, State Hydrological Institute (SHI, St. Petersburg) and United Nations Educational, Scientifie and
Cultural Organisation (UNESCO, Paris), 1999.

9. Global Water Availability

Average River Flows and Groundwater Recharge <0)

> “e, ho? 1350

3850
10000
37500

325000

Countries with
the least freshwater resources

Egypt : 2

United Arab Emirates: 61

Countries with

the most freshwater resources À
‘Suriname :479 000

Iceland 605 000

© © 1000 1700 5000 15000 50000 605.000 m’ per capita per year

‘Source: Word Resources 2000-2001, People and Ecosystems: The Fraying Web of Life, World Resources Institute (WAI), Washington DC, 2000.

10. Watershed system

Precipitation / (t)

oe

m — no

Watershed surface 7 System boundary

~

TA

Watershed
divide |
| Streamflow Q(t)
| TI |
Ms — mm
FIGURE 1.2.3

The watershed as a hydrologic system.

a

11. Water Balance
The water balance defines the conservation of mass across the different

compartments of the hydrological cycle (atmosphere, water bodies, soil
and ground, vegetation, snowpack and ice, ...)

The concept of conservation of mass implies the identification of an
incoming and an outgoing flux, and of a storage variation over a given

unit of time.
The water balance equation for a basin states that all the

water that enter in a system in specified period of time
must be consumed, stored or go out as surface or sub-
surface flow.
Inflow = Outflow + Change in storage

I = [0] + AS

l= Inflow in system
O= Outflow in system

AS= Change in storage

12. v

The inflow into the system includes: > The change in storage includes :

a Precipitation a Change in soil moisture storage
à Surface inflow .
a Subsurface inflow a Change in groundwater storage
> The outflow from the system includes à Snow cover
E
a Surface outflow à Surface Storage P ;
a Subsurface outflow . Î
a Evaporation a Depression storage
a Transpiration a Channel storage
a Evapo -transpiration
Water Budget Equation
G
- Fora specified area and for specified period of time , the
p id p Where, | \
water balance equation can be written as, R

P= Precipitation

P-(R+G+E+T)=AS

Q = Runoff

P=Q+E+AS o
E= Evapotranspiration

(Sen AS = Change in storage

13. Q. A small catchment of area 150 ha received a rainfall of 10.5 cm
in 90 minutes due to a storm. At the outlet of the catchment, the
stream draining the catchment was dry before the storm and
experience a runoff lasting for 10 hours with an average discharge
value of 2 m? /s. The stream was again dry after the runoff event.(a)
what is the amount of water which was not available to runoff due to
combined effect of infiltration, evaporation, transpiration? (b) what
is the ratio of runoff to precipitation?

Q. The Catchment area of a reservoir is 10.5 km?. A uniform
precipitation of 0.5 cm/hr for 2h was observed on a particular day.
50% of the rainfall reached the reservoir. A canal carrying a flow of
1 m?/s is taken from the reservoir. The rate of evaporation was
0.7mm/h/m?. Assuming seepage loss to be 50% of evaporation loss,
find the change in reservoir level for 8 hours in the next, if the water
spread of the reservoir was 0.45 km?

a,

14. Development of hydro-meteorological study in Nepal

project

an Hydrological study in Nepalese river started with initiation of Koshi

947

> Establishment of hydrological station at Barahachhetra, Kampughat

(sunkoshi), and mulghat(Tamor)

| Meteorological observation stations were established with the help of

the Government of India

> Started hydrological and meteorological study of Karnali basin under

Department of Electricity

1988

|, Establishment of Department of Hydrology and Meteorology and

starting of publication of Hydro-meteorological data

=> Started nationwide hydro-meteorological data management was started

2002

|». Water Resources Strategy was prepared

2005

I, National Water Plan was published

15. “Sa Hydro-meteorological Network
À Legend
[ District
e Hydrological_ Station

+ Meteorological_station