RAIN WATERHARVESTINGINRURAL AREA WATER MANAGEMENT FORUMThe Institution of Engineers (India) http://www.wmf-iei.org/index.php/
What is Rain Water Harvesting (RWH)?• Process of arresting and storing rain water forefficient application and conservation• An effective way of utilising large quantum ofwater which otherwise goes as surface runoff.• RWH has 2 components: 1) Rain water collection for storage 2) Recharging groundwater What is artificial recharge to ground water?• Process of enhancing ground water storageartificially at a rate exceeding natural rate of recharge• Possible by putting up small structure enablingstorage and infiltration
What are the advantages of RWH & recharge? Improvement in ◦ ground water levels ◦ water availability in wells/ tube-wells ◦ the quality of ground water through dilution ◦ living conditions in rural areas Saving energy in lifting ground water – one meter rise in level saves 0.40 KWH Reduction in soil erosion due to reduced surface water runoff Prevention of sea water ingress in coastal areas
Aspects to be considered for designing RWHsystem• Hydrogeology of the area including • nature & extent of aquifer, •soil cover, •topography, •depth to water level, • ground water quality• Availability of source i.e. surplus runoff• Hydro-meteorological characters – rainfall duration, pattern, intensity• Area contributing runoff like roof top area, etc
CATCH RAIN WHERE IT FALLSWhat are the Rain water Harvesting techniques for Ruralareas? Recharge Shaft -- 2 meter diameter or more, ends in permeable strata - If unlined, backfilled with filter medium - If lined, small conductor pipe leads recharge water to• Useful for village ponds having top impermeable clay filter• Shaft top projects above bed-level of pond and is takenupto half the full water depth• Top one or two m done with brick masonry for stabilityof shaft• Half of water collected in pond recharges groundwater.The other half used for domestic purposes.
DUG WELLS•Abandoned and existing dug wells can be put to useafter removing silt• Periodic chlorination required• Recharge water taken through delivery pipe via siltchamber to well bottom to avoid scouring.
CHECKDAMS/NALA PLUGGING• Constructed across streams with gentle slopes.• Should have sufficient thickness of permeable bed• Water confined within the bank of stream• Height not to exceed 1.5 to 2 meter in general• Excess water flows above wall• May be constructed with masonry/ concrete• Downstream water cushion chamber required toprevent scouring.
Underground Checkdam/ Subsurface dyke • Constructed below ground to retard movement of water. • Site to have shallow impervious layer with wide valley, narrow outlet • One or two meter wide trench dug across streambed with depth extending to impervious layer.• Trench can be filled with clay or concrete wall upto 0.5meter below ground level• PVC sheet of 3000 psi tearing strength at 400 to 600gauge or LDPE film 200 gauge can also be used alongexcavated face of the trench
Percolation Tanks • Located on highly permeable soil so as to allow water stored above to percolate and effect recharge • Normal storage capacity 0.1 to 0.5 million cubic meter • Tanks created by earthen bund with masonry spillway Built along hilly slopes Gully Plug across gullies/ small streams using locally available stones, clay etc. Better selection where slope breaks so as to have some storage behind Prevents soil erosion and conserves soil moisture
Contour Bunds • Suited for lands with moderate slopes without involving terracing • Suited for low rainfall area where runoff can be stored on slope all along contour of equal elevation.• Prevents soil erosion and conserves soil moisture• Spacing between two contour bunds depends uponslope and soil permeability.