Chapter 5 runoff


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Chapter 5 runoff

  2. 2. DroughtSurface Water Resources of India
  3. 3. A climatic anomaly characterized by deficit Definition supply of moisture Result from Causing • Subnormal rainfall over large • Below normal natural region availability of water over long periods of timeCharacteristic Develop in a region over a Meteorological drought length of time Classification Agricultural production Hydrological drought Hydropower generationConsequence Regional economy Quality of available water Agricultural drought Highly degraded Environmental Health
  4. 4. Meteorological Drought ClassificationIt is a situation where there is more than 25 % decrease in precipitation from normal over an area Moderate : seasonal Severe : seasonal  actual rainfall less than deficiency between deficiency aboveclimatological mean of that 26% and 50% 50% area Drought year : affected by Drought prone area : moderate or severe drought occur in an more than 20% of the area with probability total area of the 0.2 < P < 0.4 country
  5. 5. Hydrological Drought Drought mean below average values of End of drought : adequate rainfall saturates the stream flow, contents soil mass and restores the stream flow and in tanks and reservoir contents to normal values is relatively reservoir, groundwater easy to determine and soil moisture Importants of hydrological studies:C Design and operation of reservoir MagnitudeO Diversion of stream flow for :-M IrrigationP Duration PowerO Drinking waterN SeverityENT Frequency of occurance
  6. 6. Agricultural Drought An indicator of possible moisture Aridity Index stress experinced by crop Inadequate soil moisture (AI) AI = ( PET – AET ) x 100 PET = potential evaporation resulting in acute crop PET AET = actual evaporation stress and fall in Aridity is the Normal value = AI anormaly agricultural productivity Thornthwaites’s (moisture shortage) Principal criteria : concept to describe water AI anomaly Severity Class deficiency of rainfall deficiency Zero or negative Non-arid experienced by 1 - 25 Mild arid plant 26 - 50 Moderate arid > 50 Severe arid Produce AI anomaly maps of INDIA on bi-weekly basis based Palmer Index on data from 210 station (PI) Used to characterize agriculturalIMD Moisture drought Represent different agro- Availability climate zone in the country Index (MAI)
  7. 7. Drought Management Temporal and spatial aberrations in the rainfallCAUSE Improper management of available water Lack of soil and water conversation Short-term Long-term strategies strategies Drought mitigating Early measures warning Proper soil Monitoring and water Assessment conservation Irrigationof the drought scheduling Cropping pattern
  8. 8. Cloud SeedingCloud seeding is the process ofspreading chemical into the upper partof clouds to try to stimulate theprecipitation 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
  9. 9. Drought Management Creation of water storage through appropriate water resource development POSSIBLE MEASURE Inter-basin transfer of surface water from surplus water areas to drought prone areas FOR MAKING DROUGHT PRONE Development and management of ground water potential AREAS LESSVULNERABLE TO DROUGHT Development of appropriate water harvesting practicesASSOCIATES PROBLEM Economic use of water in irrigation through practices such as drip irrigation and sprinkler irrigation
  10. 10. Water Harvesting DEFINITION (FOA)The process of collecting and concentrating runoff waterfrom a runoff area into a run-on area, where the collected water is either directly applied to the cropping area and stored in soil profile for immediate use by the crop (runoff farming or stored in an on-farm water reservoir) for future productive uses (domestic use, livestock watering, aquaculture and irrigation)
  11. 11. Roof Top Water Harvesting (RTWH) Definition  The productive utilization of rain water falling in roof-tops of structures  Urban area :- roof tops are impervious and occupy considerable land area Factor  Water supply :- inadequate , inefficient , unreliable Advantage  Economic 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 toCharacteristic a small cultivated area  Ratio :- catchment to cultivated area = 1:1 to 3:1  Overflow :- no provision
  12. 12. Micro Catchment System (Within The Field) of Rainwater Negarim Micro CatchmentDividing the catchment into alarge number of microcatchment in a diamondpattern 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
  13. 13. Macro Catchment System (Within The Field) of Rainwater The system is designed for slightly larger catchment area where overland Definition flow and rill flow is collected behind the bund allow to be stored in the soil profile through infiltration  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 withCharacteristic wing wall - contour bunds made a piled up stones  Overflow :- for disposing of the excess runoff water  Infiltration area :- use to grow crop
  14. 14. Floodwater Farming ( Floodwater Harvesting )  Length :- several kilometres long Characteristic  Ratio :- catchment to cultivated area = larger than 10:1 Small structures are built across the drainage to Check Dam Nalabund store part of the runoff Store water : utilisable for communityStorage Structure System Infiltration : recharge to the ground water Advantages :- arresting erosion from the catchment - prevent the deep and widen of gullies Check Dams :- masonry overflow spillway Cement Nalabund - 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 % Earthen Nalabund
  15. 15. Water Spreading Diversion across the drainage would cause the runoff to flow on theSpreading of Water 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 1918 Affect drought year – the worst –agriculture since year production 1875 -2004 (70% effected) - economy
  16. 16. Surface Water ResourceIn most of the basin of the country, the surface water resource have been develop Utilize through diversion structure and reservoir Utilization produce return flow Definiton : non-comsumptive part of any diversion returned back 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
  17. 17. Utilizable Water ResourceDefinition  the quantum of water withdrawable from its place of natural occurrence  topographic conditions Depend  availability of land  Not be possible to utilize entire surface water resource because:- - topography - environmental considerationLimitation - non-availability of suitable location - technology shortcoming - evaporation - percolation
  18. 18. Utilizable Water Resource CWC in 1988Utilizable surface waterresource = 690.32 km^3
  19. 19. Utilizable Dynamic Groundwater Resource Estimate by  CGWB  Total replenish-able water groundwater resources is 431.89 km^3/year  Utilizable dynamic groundwater potential is 396 km^3/year Water Available from Return FlowWater Resource Surface flow Consumptive Due to economic, technology returned backs constraints and diminished Groundwater system water quality  part of Non-Consumptive return flow is recoverable for re-use Soil moisture
  20. 20. Total Water Requirement Estimated by NCIWRDHighest  Irrigation (68%) Evaporation Evaporation losses NCIWRD adopted - 15% of the live storagecapacity of major project - 25% of the live storagecapacity of minor project
  21. 21. Demand and Available Water ResourcesThe summary of NCIWRD study relating to national level assessment of demand and available water resource The return flow contributes 20-25% in reducing the demand
  22. 22. THANK YOU