BFC 32002 Hydrology

Chapter 1. Basic Concept of Hydrology

Prepared by:

Siti Nazahiyah Rahmat

Learning Outcomes

At the end of this chapter, students should be able to:

• define hydrology.

• apply fundamental knowledge of hydrology particularly use in civil andenvironmental engineering.

• apply water balance equation as the base of a modeling of hydrologywhich covers processes of precipitation, evaporation, infiltration, runoffand groundwater.

Hydrology

• Hydrology is a science that studies the availability (sources ofwater) and movement of water in the earth.

• Hydrology is also defined as a science related to the occurrenceand distribution of natural water on the earth.

• As general, hydrology covers many types of water, includingtransformation among liquid, solid and gas in atmosphere, surfaceand subsurface land

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Tahan River, Pahang Hot spring, Sungai Klah, Sungkai, Perak

Importance in managing:

1) Water resources

2) Water supply management

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3) Managing floods/droughts, drainage & urban stormwater problems

Stormwater Management and Road Tunnel (SMART), Kuala Lumpur, Malaysia

Global Water StatisticsTotal water = 1.36 x 1018 m3

• Oceans and lakes (saltwater) 97.2%

• Ice and glaciers (fresh water) 2.15%

• Groundwater (fresh water) 0.64%

• Lakes and rivers (fresh water) 0.0085%

• Atm and biosphere (moisture) 0.00015%

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Malaysia Water Statistics Total water = 990 x 109 m3

• Lakes and rivers 566 x 109 m3

• Atm and biosphere(moisture) 360 x 109 m3

• Groundwater 64 x 109 m3

Definition

Hydrologic cycle is a continues process in which water is evaporated fromwater surfaces and oceans, moves inland as moist air masses, and produceprecipitation if the correct vertical lifting conditions exist. Theprecipitation that falls from clouds onto the land surface of the earth isdispersed to the hydrologic cycle via several pathways.

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Catchment/Watershed areasLand area that topographically drains to a particular point

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Main River

River

River

River

River

Catchment boundary

Lake

Spring

Spring

Spring

H

I

G

H

L

A

N

D

A

R

E

A

C

O

A

S

T

A

L

A

R

E

A

Sketch of Movement of Water on the Land Surface

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Typical Watershed Areas

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Outlet

Outleta. Elongated shape b. Concentrated shape

Typical watershed areas

Water balance

• In quantitative terms, hydrology cycle can be represented by a closedequation which represents the principle of conservation of mass, oftenreferred to in hydraulics as the continuity equation. And many forms ofthis expression, called the water balance.

• Water balance equation is the base of a modeling of hydrology.

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Water budget

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Conceptual• The same concept can be applied to small basins or

large watersheds𝑃 − 𝑅 − 𝐺 − 𝐸 − 𝑇 = ∆𝑆

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where: P = precipitation,R = surface runoff ,G = groundwater flow,E = evaporation, T = transpiration,ΔS = change in storage in a specified time period.

Example 1.1

In April 2017, a 121 ha lake has 0.43 m3/s of inflow, 0.37m3/s of outflow, and total storage increase of 1.97 ha-m. AUSGS gage next to the lake recorded a total of 3.3 cmprecipitation for the lake for the month. Assuming thatinfiltration loss is insignificant for the lake, determine theevaporation loss, in cm, over the lake for the month.

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• Solving the water balance for inflow I and outflow Q in a lake gives, for evaporation,

E = I – O + P – ΔS

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( )cmm 9292.0 ==

=

1ha

10,000m121ha

1hour

3,600sec

1day

24hr

1month

30day1month

sec

m0.43

2

3

I

( )

( )mm 7979.0 ==

=

1ha

10,000m121ha

1hour

3,600sec

1day

24hr

1month

30day1month

sec

m0.37

2

3

Q

P = 3.3 cm

E = 92 – 79 + 3.3 – 1.63 = 14.67 cm

( )( )

cm63.10163.0 ==−

=121ha

m1.97haΔS

Example 1.2

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A reservoir has the following inflow and outflows (in cubicmeters) for the first three months of the year. If the storageat the beginning of January is 65 m3, determine the storage atthe end of March.

( I1 + I2 + I3 )/3 - (O1 + O2 + O3)/3 = S3 – S1 /3 months(3.5 + 5.7 + 8.3)/3 – (6.4 + 7.1 + 5.5 )/3 = (S3-65)/3

months(17.5-19) = S3 – 65 m3

-1.5 = S3 – 65 m3

S3 = 63.5 m3

Month January February Mac

Inflow (m3) 3.5 5.7 8.3

Outflow (m3) 6.4 7.1 5.5

Example 1.3

Day Evaporation(mm)

Rainfall(mm)

Measured Level(mm)

123456789

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12.70

12.70

12.712.7

012.712.712.7

-25.4

-50.8

--

101.6---

1,524

1,321

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A swimming pool (6 m 6 m 1.5 m) has a small leak atthe bottom. Measurements of rainfall, evaporation, andwater level are taken daily for 10 days to determine whatshould be done for repair. Estimate the average dailyleakage out of the swimming pool in cm3/day. Assume thepool is exactly 1.5 m deep at the end of day 1.

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Example 1.4

The storage capacity in a reservoir at certain period is given as9.5 ha-m. The inflow and outflow of reservoir is recorded as25 m3/s and 16.5 m3/s, respectively. However, the inflow andoutflow is changed to 20 m3/s and 22 m3/s, respectively afterfour (4) hours.

(a) Calculate change of storage capacity in the reservoir duringthe four hours period.

(a) Calculate total storage at the end of four hoursGive answers in cubic-meter.

BFC32002_Ch1/ZARINA'S 21

Example 1.5

An amount of 6 cm of water evaporates over a period of two

days from a vertical walled reservoir in a 250 ha catchment

area. The reservoir also receives storm water at a flow rate of

6 m3/s during this period. Compute the volume of water

released in ha-cm during the 2 days period assuming the

water level in the reservoir remains the same. (Conversion

unit: 1 ha = 10,000 m2).

Hydrological Data

Includes rainfall depth, streamflow, evaporation,temperature, wind speed, moisture, sunlight (solarradiation), groundwater level, land use, topography,land slope.

• Rainfall depth - Department of Irrigation and DrainageMalaysia (DID) and Malaysian Meteorological Department

• Meteorological data (evaporation, temperature, wind speedand direction, solar radiation, and moisture content) -Malaysia Meteorological Department (MMD) and DID

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Hydrological Data • Stream-flow and water level - Department of Irrigation and

Drainage Malaysia (DID) and Department of Environment(DOE) Malaysia

• Groundwater level - Minerals and Geoscience DepartmentMalaysia of Ministry of Natural Resources and Environment

• Landuse - Forestry Departments or Department of Surveyand Mapping Malaysia

• Physical characteristics of development area - Departmentof Survey and Mapping Malaysia or Malaysian RemoteSensing Agency

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Conclusion

• Hydrology is the science of water.

• It embraces the occurrence, distribution, movement and properties ofthe waters of the earth.

• A mathematical accounting system may be constructed for the inputs,outputs and water storages of a region so that a history of watermovement over time can be estimated.

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