ENGINEERING HYDROLOGY :

RUNOFF

Prepared by:SUZILAWATIE BT ABDUL GHANI

P 60832

RUNOFF

Drought

Surface Water Resources of India

DROUGHT

Definition Result from

• Subnormal rainfall over large region

Causing

• Below normal natural availability of water over long periods of time

A climatic anomaly characterized by deficit supply of moisture

Characteristic

Consequence

Develop in a region over a length of time

Agricultural productionHydropower generation

Regional economyQuality of available water

Highly degradedEnvironment

alHealth

Cla

ssifi

cati

on

Meteorological drought

Hydrological drought

Agricultural drought

DROUGHT

Meteorological DroughtIt is a situation where there is

more than 25 % decrease in precipitation

from normal over an area

actual rainfall less than

climatological mean of that

area

Moderate : seasonal

deficiency between 26% and

50%

Severe : seasonal deficiency above

50%

Drought year : affected by moderate or

severe more than 20% of the total

area of the country

Drought prone area : drought

occur in an area with probability 0.2 < P < 0.4

Classification

DROUGHT

Hydrological DroughtDrought mean below average

values of stream flow, contents in tanks and reservoir,

groundwater and soil moisture

Magnitude

Duration

Severity

Frequency of occurance

COMPONENT

End of drought : adequate rainfall saturates the soil mass and restores the

stream flow and reservoir contents to normal values is relatively easy to

determine

Importants of hydrological studies: Design and operation of reservoir

Diversion of stream flow for :- Irrigation

Power Drinking water

DROUGHT

Agricultural DroughtInadequate soil moisture

resulting in acute crop

stress and fall in agricultural productivity

Principal criteria :

deficiency of rainfall

Aridity Index (AI)

Palmer Index (PI)

Moisture Availability Index (MAI)

An indicator of possible moisture stress experinced by cropAI = ( PET – AET ) x 100 PET Normal value = AI anormaly (moisture shortage)

PET = potential evaporation

AET = actual evaporation

AI anomalySeverity ClassZero or negative Non-arid1 - 25 Mild arid26 - 50 Moderate arid> 50 Severe arid

Used to characterize agricultural drought IM

D

Produce AI anomaly maps of INDIA on bi-weekly basis based on data from 210 station

Represent different agro-climate zone in the country

Aridity is the Thornthwaites’

s concept to describe water

deficiency experienced

by plant

DROUGHT

DROUGHT

DROUGHT

Drought ManagementCAUSETemporal and spatial

aberrations in the rainfall

Improper management of available water

Lack of soil and water conversation

Short-term

strategies

Long-term strategies

Early warning

MonitoringAssessmen

t

of the drought

Drought mitigating measures

Proper soil and water

conservation Irrigation scheduling

Cropping pattern

DROUGHTCloud Seeding

Cloud seeding is the process of spreading chemical into the upper part of clouds to try to stimulate the precipitation process and form rain

The most common chemicals used for cloud seeding include silver iodide and dry ice (solid carbon dioxide)

Cloud seeding chemicals may be dispersed by aircraft or etc. For release by aircraft, silver iodide flares are ignited and dispersed as an aircraft flies through the inflow of a cloud

The formation of ice particles in supercooled clouds allows those particles to grow at the expense of liquid droplets. If sufficient growth takes place, the particles become heavy enough to fall as precipitation from clouds

DROUGHT

Drought Management

Creation of water storage through appropriate water resource development

Inter-basin transfer of surface water from surplus water areas to drought prone areas

Development and management of ground water potential

Development of appropriate water harvesting practices

Economic use of water in irrigation through practices such as drip irrigation and sprinkler irrigation

POSSIBLE MEASURE

FOR MAKING

DROUGHT PRONE

AREAS LESS VULNERABL

E TO DROUGHT ASSOCIATES PROBLEM

DROUGHT

Water Harvesting

Water Harvesting

DROUGHT

The productive utilization of rain water falling in roof-tops of structures Urban area :- roof tops are impervious and occupy considerable land area Water supply :- inadequate , inefficient , unreliable

Economic

• Definition

• Factor

• Advantage

Micro Catchment System (Within The Field) of Rainwater

System :- the catchment is small area - not put for any productive purpose Length :- between 1 – 30 metres During storm :- overland flow is harvested by collecting and delivering it to a small cultivated area Ratio :- catchment to cultivated area = 1:1 to 3:1 Overflow :- no provision

• Characteristic

Roof Top Water Harvesting (RTWH)

DROUGHTMicro Catchment System (Within The Field) of Rainwater

Dividing the catchment into a large number of micro catchment in a diamond pattern along the slope

Each micro catchment is of square shape with a small earthen bunds at its boundary and an infiltration pit is provided at the lowest corner

The pit is the cultivated area and usually a tree is grown in the pit

The arrangement of micro catchment of sizes 10m^2 to 100m^2

Negarim Micro Catchment

DROUGHTMacro Catchment System (Within The Field) of Rainwater

The system is designed for slightly larger catchment area where overland flow and rill flow is collected behind the bund allow to be stored in the soil profile through infiltration

• Definition

Length :- 30 to 200 m long Ratio :- catchment to cultivated area = 2:1 to 10:1 Arrangement :- one row or two staggered rows of trapezoidal bunds with

wing wall - contour bunds made a piled up stones

Overflow :- for disposing of the excess runoff water Infiltration area :- use to grow crop

Characteristic

DROUGHTFloodwater Farming ( Floodwater Harvesting )

Length :- several kilometres long Ratio :- catchment to cultivated area = larger than 10:1

• Characteristic

Storage Structure SystemSmall structures are built

across the drainage to store part of the runoff

Store water : utilisable for community Infiltration :

recharge to the ground waterAdvantages :- arresting erosion from the catchment - prevent the deep

and widen of gullies

Check Dams :- masonry overflow spillway - flanks

: masonry / earthen embankment - lower

stream (up to 3) with median slope

Nalabunds :- across streams for impounding

runoff flow to cause a small storage - objective ~

improve water percolation ~ improve of soil

moisture regime - material ~ earthen

embankment - spillway ~ stone lined/rock cut steep channel - construct ~ flat reach of a stream with slopes less than

2 %

Check Dam

Nalabund

Cement Nalabund

Earthen Nalabund

DROUGHT Water Spreading

Spreading of WaterDiversion across the drainage would cause the runoff to flow on the adjacent land. The water is forced to leave its natural course and conveyed to nearby cropping fields

Appropriates bund cause spreading the water over the command

Spread water infiltrates into the soil and is retained as soil moisture

Provision for overflow spillway at the diversion structure, to pass excess water

onto the downstream side of the diversion structure, IMPORTANT component of

diversion structure

Drought in INDIA

Faced 29 drought

year since 1875 -2004

1918 – the worst year

(70% effected)

Affect –agriculture production - economy

SURFACE WATER RESOURCES OF INDIA

Surface Water Resource

Total Catchment Area (all river) = 3.05 mil km

Large : larger than 20,000 km^2

Medium : between 20,000 to 2,000 km^2

Small : less 2,000 km^2

SURFACE WATER RESOURCES OF INDIA

Utilizable Water Resource

the quantum of water withdrawable from its place of natural occurrence

topographic conditions availability of land

Not be possible to utilize entire surface water resource because:- - topography - environmental consideration - non-availability of suitable location - technology shortcoming - evaporation - percolation

• Definition

• Depend

Limitation

SURFACE WATER RESOURCES OF INDIA

Utilizable Water Resource

CWC in 1988

Utilizable surface water resource = 690.32 km^3

SURFACE WATER RESOURCES OF INDIA

Utilizable Dynamic Groundwater Resource

CGWB

Total replenish-able water groundwater resources is 431.89 km^3/year Utilizable dynamic groundwater potential is 396 km^3/year

• Estimate by

Water Available from Return Flow

retu

rned

back

s Due to economic, technology constraints and diminished water

quality part of return flow is recoverable for

re-use

SURFACE WATER RESOURCES OF INDIA

Total Water Requirement

Estimated by NCIWRD

Highest Irrigation (68%)

Evaporation

Evaporation losses

NCIWRD adopted - 15% of the live storage capacity of major project- 25% of the live storage capacity of minor project

Demand and Available Water Resources

The return flow contributes 20-25% in reducing the demand

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