HYDROLOGY

Science of water that deals with the occurrence, circulation and distribution of water of the earth and earth’s atmosphere

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Hydrological data

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5. Engineering Hydrology by K Subramanya6. Hydrology by H M Raghunath

Lectures_ 1 &2

Definitions

Hydrological Cycles and Water Distribution

Water Budget

Space-time Scales

Catchment Area

History of Hydrology

Applications

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1.0 Hydrologic Cycle

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A global schematic of the hydrologic cycle

ET=evapotranspiration; SF = surface runoff ; TF=tidal flow; SR = sea rise; GW int. = ground water intrusion

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A schematic of the hydrologic cycle in the earth system

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A schematic of the hydrologic cycle in land system

More complete cycle

Water Distribution

Land and Water Resources of India

Source-CWC, India

Source-CWC, India

Water Resources Potential (km3) in Major River Basins of India

2. Hydrologic Budget

The water budget represents the inventory of water for a specific water body (or hydrologic region) during a certain time interval.

It can be estimated using the mass conservation equation, which expresses the balance between the inflows, outflows and change of storage in any water body / hydrologic region over a period of time. For a drainage basin

P - R - G - E - T = ΔS (1)

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P=precipitation; R= runoff; G= ground water flow; E=evaporation; T= Transpiration; S = storage

For a drainage basin

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Subscripts s=surface storage; m = soil moisture storage; g = ground water storage; i = interception storage

Ir = rainfall intensity; Isn = rate of snowfall; Osr= surface runoff; Osb= subsurface runoff; Og = ground water runoff; e = rate of evaporation; et = rate of transpiration; f = infiltration rate

feeOOOIISSSSdt

d

OIdt

dS

tgsbsrsnrigms

3. Space-Time scales

Depending on the hydrologic problem under consideration, the hydrologic cycle or its component can be treated at different scales of time and space.

The global scale is the largest spatial scale and the drainage basin, the smallest spatial scale.

The time scales used in hydrologic studies range from a fraction of an hour to a year or perhaps many years. The time scale used in a hydrologic study depends on the purpose of the study and the problem involved.

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4. Catchment Area (drainage area, drainage basin, Watershed in USA) The area of land draining into a stream or water course at a given location is known as catchment areaRidge line is also called Divide in USA and Watershed in UK

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The line of the ground water table from which the water table slopes downward away from the line on both sides, is called the ground water divide.

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Catchment boundary of the Kosi river Almora

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Stream Drainage Pattern

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Dendritic Drainage: A stream drainage pattern that resembles the veins of a leaf in map view. Occurs mainly where the rocks below have a uniform resistance to erosion.

Trellis Drainage: A drainage pattern in which streams intersect at right angles. This forms in areas of long parallel valleys such as in folded mountain belts. Rivers occupy the valleys and tributary streams .

Radial Drainage: A system of streams running in a radial pattern away from the center of a circular elevation, such as a volcano or dome.

Characteristics of the drainage

1.The number of streams

2.The length of streams

3.

4. Drainage density

Stream density, 2-km area Catchment

streams ofNunmber

A

ND ss

A

LD sd

nt)intermitte and (perennial channels streams all of length Total

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Drainage density varies inversely as the length of overland flow and indicates the drainage efficiency of the basin.

A high value indicates a well-developed network and torrential runoff causing intense floods while a low value indicates moderate runoff and high permeability of the terrain.

The shape of a drainage basin can generally be expressed by:

Form factor, 1 2

bb

bf L

A

L

WF

Wb=axial width of basin

Lb=axial length of basin, i.e., the distance from the measuring point to the most remote point on the basin.

Compactness coefficient, 1 2

A

PC bc

Pb=perimeter of the basin

A2 =circumference of circular area having area equal to the area of the basin

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Shape factor, 1 2

A

LB bs

Elongation ratio , 1 length Watershed

area watershedof circle ofDiameter

Circularity ratio, 1 perimeter watershedof circle ofArea

area Watershed

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Basin slope = difference in elevation between farthest point and outlet/ distance from farthest point to outlet

Stream slope

1. Average stream slope=total fall of the longest water course/length of the entire longest water course.

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1

1

2/1

N

ii

N

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m

L

SLS

2. The channel is divided into N number of reaches each having Slope Si, and length Li. (Johnstone and Cross, 1949)

The equivalent stream slope

History of Hydrology

It is not easy to answer the question “How and where the science of hydrology began?”.

In ancient times various hydrologic principles were successfully applied in practice.

Early Chinese irrigation and flood control works and Greek and Roman aqueducts are worth mentioning.

The Roman engineer Marcus Vitruvius (1st century B.C.) developed an early theory of the hydrologic cycle in his treatise 'On Architecture'.

During the Middle Ages, Vitruvius's work was the standard reference book on Hydrology.

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15th century: Leonardo da Vinci and Bernard Palissy gave, independently of each other, an accurate explanation of the hydrologic cycle.

17th century: the modern science of hydrology was established by Perrault, Mariotte and Halley. Perrault measured the rainfall and runoff in the Seine River and proved that rainfall contributes significantly to river flow. He also measured evaporation and capillarity. Mariotte recorded the velocity of flow in the Seine River and made measurements of the cross section, estimating the discharge. Halley measured evaporation of the Mediterranean Sea.

18th century: The Bernoulli piezometer and theorem, the Pitot tube and Chezy's formula are representative achievements

19th century: experimental hydrology made considerable progress: Darcy's law of flow in porous media and Dupuit-Thiem's well formula were elaborated.

Early 20th century: governmental agencies developed their own programs of hydrologic research. Sherman's unit hydrograph, Horton's infiltration theory and Theis's non-equilibrium approach to well hydraulics were based on their analyses and were the results of research programs.

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Chow classifies the history of hydrology into eight periods as:

• Period of Speculation – prior to AD 1400

• Period of Observation – 1400 – 1600

• Period of Measurement – 1600 – 1700

• Period of Experimentation – 1700- 1800

• Period of Modernization – 1800 – 1900

• Period of Empiricism – 1900 – 1930

• Period of Rationalization – 1930 – 1950

• Period of Theorization – 1950 – to date

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Applications In Engineering

Hydrology finds its greatest application in the design and operation of water resources engineering, such as those for

(i)Irrigation,

(ii) Water supply,

(iii) Flood control,

(iv) Hydropower, and

(v) Navigation

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1. Scientific Hydrology-a study concerned with academic aspects.2. Engineering or applied Hydrology- a study concerned with

engineering applications

Hydrological Data

The basic hydrological data required are:

1.Precipitation and climatological data - IMD

2.Topographic maps - SOI

3.Stream-flow records - CWC

4.Ground water data – Central Ground Water Board

5.Evaporation and transpiration data -IMD

6.Cropping pattern, crops and their consumptive use – Irrigation Dept

7.Soil map

8.Water quality data of surface streams and groundwater 9.Geological maps - GSI

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