chapter 5 runoff
TRANSCRIPT
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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