Water Water Harvesting for Harvesting for Groundwater Groundwater

RechargeRecharge

Is it effective?Is it effective?

INTRODUCTIOININTRODUCTIOIN

Water scarcity is becoming an increasing Water scarcity is becoming an increasing problem worldwide.problem worldwide.

35% of global land surface is semi-arid35% of global land surface is semi-arid

In 1997 it was reported that 80% of In 1997 it was reported that 80% of countries suffered from serious water countries suffered from serious water shortage, which encompasses 40% of the shortage, which encompasses 40% of the worlds populationworlds population

Main reason due to a shift in water management Main reason due to a shift in water management across the world.across the world.

Individuals/communities have given over the role Individuals/communities have given over the role of water management to the State/Government.of water management to the State/Government.

Increasing exploitation of rivers and groundwater – Increasing exploitation of rivers and groundwater – these are now the key sources of water supply these are now the key sources of water supply across the world.across the world.

However, it is generally believed that enough However, it is generally believed that enough precipitation falls on the worlds land surfaces to precipitation falls on the worlds land surfaces to supply the global population.supply the global population.

Use of water harvesting to capture the water that Use of water harvesting to capture the water that falls before it gets chance to be evaporatedfalls before it gets chance to be evaporated

WATER HARVESTINGWATER HARVESTING

Term was 1Term was 1stst used by the Australian HJ used by the Australian HJ Geddes to denote:Geddes to denote:

‘ ‘the collection and storage of any farm the collection and storage of any farm waters, either runoff or creek flow, for waters, either runoff or creek flow, for irrigation use.’irrigation use.’

Idea has been around since early civilization, Idea has been around since early civilization, beginning about 4000years ago in the beginning about 4000years ago in the Bronze AgeBronze Age

Desert dwellers smoothed hillsides to increase Desert dwellers smoothed hillsides to increase runoff and built ditches to collect the water and runoff and built ditches to collect the water and convey it to lower lying fieldsconvey it to lower lying fields

Also included collection from rooftops and Also included collection from rooftops and courtyardscourtyards

There has been an increasing interest in the redevelopment There has been an increasing interest in the redevelopment and implementation of water harvesting systems, and implementation of water harvesting systems, especially of water harvesting for groundwater rechargeespecially of water harvesting for groundwater recharge

Groundwater is a more favourable source of water for Groundwater is a more favourable source of water for several reasonsseveral reasons

It provides ready made storage reservoirsIt provides ready made storage reservoirs It helps reduce the problems of evaporationIt helps reduce the problems of evaporation It protects against pollution due to the filtering action of It protects against pollution due to the filtering action of

the aquiferthe aquifer It helps keep saline waters from intrudingIt helps keep saline waters from intruding It helps convert/dispose of floodwatersIt helps convert/dispose of floodwaters It helps to prevent subsidence of the ground above the It helps to prevent subsidence of the ground above the

depleted aquiferdepleted aquifer

WATER HARVETSING TECHNIQUES FOR WATER HARVETSING TECHNIQUES FOR GROUNDWATER RECHARGEGROUNDWATER RECHARGE

Artificial recharge of groundwater as Artificial recharge of groundwater as define by UNEP isdefine by UNEP is

‘‘The planned human activity of The planned human activity of augmenting the amount of augmenting the amount of groundwater available through the groundwater available through the works designed to increase the natural works designed to increase the natural replenishment or percolation of surface replenishment or percolation of surface waters into the groundwater system, waters into the groundwater system, resulting in a corresponding increase resulting in a corresponding increase the amount of groundwater available the amount of groundwater available for abstraction.’for abstraction.’

2 main techniques have been described for 2 main techniques have been described for increasing groundwater recharge in arid areasincreasing groundwater recharge in arid areas

The planting of treesThe planting of trees Estimates have been suggested that the Estimates have been suggested that the

planting of trees can increase precipitation planting of trees can increase precipitation by over 300% and therefore more water is by over 300% and therefore more water is available for recharge to the aquiferavailable for recharge to the aquifer

The construction of water harvesting devicesThe construction of water harvesting devices Include the use of both floodwater and Include the use of both floodwater and

rainfallrainfall• Increasing surface runoff into storage/collection areas by Increasing surface runoff into storage/collection areas by

decreasing infiltrationdecreasing infiltration• Increasing infiltration into the aquifer along the route of Increasing infiltration into the aquifer along the route of

travel of surface watertravel of surface water• Use of engineering structures to collect and pump the Use of engineering structures to collect and pump the

water into the deep aquiferwater into the deep aquifer

Floodwater harvesting for groundwater Floodwater harvesting for groundwater rechargerecharge

There are several methods by which There are several methods by which floodwater harvesting can be carried out for floodwater harvesting can be carried out for aquifer rechargeaquifer recharge

Check damsCheck dams Percolation tanksPercolation tanks Groundwater damsGroundwater dams

These are amongst the cheapest and most These are amongst the cheapest and most widely used methods for groundwater widely used methods for groundwater recharge for 2 main reasonsrecharge for 2 main reasons

Relatively low construction costsRelatively low construction costs Easy to operate and maintainEasy to operate and maintain

Check damsCheck dams

Temporary structures constructed from Temporary structures constructed from locally available material such as locally available material such as brushwood, loose rock or woven wirebrushwood, loose rock or woven wire

Aim to impede the soil and water removed Aim to impede the soil and water removed from the catchment – the impeded water from the catchment – the impeded water collects behind the dam and infiltrates the collects behind the dam and infiltrates the soil, recharging the aquifersoil, recharging the aquifer

Cheap to construct costing approx. US Cheap to construct costing approx. US $200-400 depending on the material used, $200-400 depending on the material used, size of the gully and the height of the damsize of the gully and the height of the dam

Life span of 2-5 yearsLife span of 2-5 years More permanent dams constructed using More permanent dams constructed using

stones, brick and cement, but costs stones, brick and cement, but costs increase to US $1000-2000increase to US $1000-2000

Percolation tanksPercolation tanks

This is a dam built on permeable ground so This is a dam built on permeable ground so that floodwater is held back long enough to that floodwater is held back long enough to percolate into the groundpercolate into the ground

More permanent and larger than check More permanent and larger than check damsdams

Constructed by excavating a depression to Constructed by excavating a depression to form a small reservoir or by constructing an form a small reservoir or by constructing an embankment in a natural ravine or gullyembankment in a natural ravine or gully

Cost is estimated to be approx. US $5,000-Cost is estimated to be approx. US $5,000-10,00010,000

Capacity varies from 10,000-15,000mCapacity varies from 10,000-15,000m33

2-3 filling expected per wet season (30,000-2-3 filling expected per wet season (30,000-45,000m45,000m33))

Enough to irrigate 4-6 ha of irrigated dry crop Enough to irrigate 4-6 ha of irrigated dry crop (maize) and 2-3 ha of paddy crop(maize) and 2-3 ha of paddy crop

Groundwater damsGroundwater dams

Structures that intercept or obstruct Structures that intercept or obstruct the natural flow of groundwaterthe natural flow of groundwater

Often built within river beds to Often built within river beds to obstruct and detain groundwater flow obstruct and detain groundwater flow so as to sustain the storage capacity so as to sustain the storage capacity of the aquifer and meet demands of the aquifer and meet demands during high periodsduring high periods

Used in many areas such as India, Used in many areas such as India, Africa and BrazilAfrica and Brazil

2 main types2 main types Sub-surface damSub-surface dam Sand storage/silt trapping damsSand storage/silt trapping dams

Sub-surface damSub-surface dam

Constructed within the aquifer itselfConstructed within the aquifer itself Dam reduces variation of the level of the Dam reduces variation of the level of the

groundwater upstreamgroundwater upstream

Sand storage damSand storage dam Constructed above groundConstructed above ground Sand and silt particles transported in floodwater and Sand and silt particles transported in floodwater and

get deposited behind the damget deposited behind the dam Constructed in layers to trap the sand with each floodConstructed in layers to trap the sand with each flood

Important considerationsImportant considerations

Material used must be impermeable for the Material used must be impermeable for the permanent structurespermanent structures

Dam must be strong enough to withstand Dam must be strong enough to withstand the build up of the sediment behind itthe build up of the sediment behind it

Aquifer should be confined beneath to Aquifer should be confined beneath to prevent seepageprevent seepage

Bitumen/plastic liningBitumen/plastic lining

Rainwater harvesting for groundwater Rainwater harvesting for groundwater rechargerecharge

More related to the ‘micro-catchment’More related to the ‘micro-catchment’ RoofsRoofs Artificial surfaces at ground level e.g. Artificial surfaces at ground level e.g.

courtyardscourtyards Slopes less than 50-150m in lengthSlopes less than 50-150m in length

Contour trenchesContour trenches Excavations made parallel to contours on Excavations made parallel to contours on

slopesslopes Rainwater ponds and infiltrateRainwater ponds and infiltrate Helps to prevent eroding soil migrating Helps to prevent eroding soil migrating

down-slopedown-slope Gully plugsGully plugs

Stone barriers built across gullies and Stone barriers built across gullies and deep rillsdeep rills

Traps sediment eroded from higher up Traps sediment eroded from higher up slope and impound runoff encourage slope and impound runoff encourage encouraging infiltrationencouraging infiltration

Rooftop harvestingRooftop harvesting Can be adopted by individualsCan be adopted by individuals Relatively easy to construct, operate and Relatively easy to construct, operate and

maintainmaintain

Several techniques in useSeveral techniques in use• Abandoned dug wellAbandoned dug well• Abandoned/running hand pumpAbandoned/running hand pump• Gravity head rechargeGravity head recharge• Recharge pitRecharge pit

Recharge by injection wellRecharge by injection well Direct sub-surface recharge technique Direct sub-surface recharge technique

conveying water directly into the aquiferconveying water directly into the aquifer Can be used in conjunction with rooftop Can be used in conjunction with rooftop

harvestingharvesting Concerns that groundwater may get Concerns that groundwater may get

contaminatedcontaminated Potential for clogging from suspended Potential for clogging from suspended

solid, biological activity or chemical solid, biological activity or chemical impuritiesimpurities

Expensive to construct and harder to Expensive to construct and harder to maintain and operate than the other maintain and operate than the other methodsmethods

Is water harvesting for groundwater Is water harvesting for groundwater recharge effective?recharge effective?

Important initial considerationsImportant initial considerations Only suitable for areas where aquifers existOnly suitable for areas where aquifers exist Simpler with unconfined aquifersSimpler with unconfined aquifers Thorough survey of the area is necessaryThorough survey of the area is necessary

Climatic records (ppt, humidity, evaporation rates)Climatic records (ppt, humidity, evaporation rates) Topographical maps (drainage networks, Topographical maps (drainage networks,

ephemeral streams)ephemeral streams) Soil data (type, distribution and thickness)Soil data (type, distribution and thickness) Distribution of rock types, esp. surface featuresDistribution of rock types, esp. surface features Definition of pore networksDefinition of pore networks Recognition of recharge/discharge areas, direction Recognition of recharge/discharge areas, direction

of groundwater flowof groundwater flow

Once a suitable site has been foundOnce a suitable site has been found Essential to involve the local communityEssential to involve the local community

Once the structure has been builtOnce the structure has been built Important that the system is managed Important that the system is managed

properlyproperly Unnecessary consumption of waterUnnecessary consumption of water

Groups of locals need to be put in charge of Groups of locals need to be put in charge of the systemthe system

Ensure adequate distribution amongst the Ensure adequate distribution amongst the villagersvillagers• Poor farmers/owners of small farmsPoor farmers/owners of small farms

Potential problemsPotential problems

Contamination from direct injectionContamination from direct injection Contaminate water already stored in the aquiferContaminate water already stored in the aquifer Lower the value of the water (drinking water)Lower the value of the water (drinking water)

Water quality problems from rooftop Water quality problems from rooftop harvestingharvesting

Dust/faeces washed off the roofDust/faeces washed off the roof Large evaporative lossesLarge evaporative losses SiltingSilting

politicspolitics

SUMMARYSUMMARY

Many potential problemsMany potential problems

If planned and managed properly can be a If planned and managed properly can be a great successgreat success

More effective for shallow aquifersMore effective for shallow aquifers More accessible for farmersMore accessible for farmers Cheaper to extract the waterCheaper to extract the water Recharged more effectively with little high-tech Recharged more effectively with little high-tech

equipmentequipment