Drought management and water harvesting m5

Drought Management and Water Harvesting

Prepared by Bibhabasu Mohanty

Dept. of Civil EngineeringSALITER, Ahmedabad

MODULE- V

Contents

Definition of drought, Causes of drought, measures for water conservation and augmentation, drought contingency planning.

Water harvesting: rainwater collection, small dams, runoff enhancement, runoff collection, ponds, tanks.

Introduction Normal, recurrent feature of climateOccurs everywhere, vary from

region to region.Originates from deficiency of

precipitation.Impact on ecosystem and

agricultural of affected region.Drought leads to food insecurity,

famine, malnutrition, epidemics and displacement of populations.

Types of drought

Meteorological drought

Agricultural drought

Hydrological drought

Socioeconomic drought

Causes of droughtReduced rainfall results in drought.Occurs because water vapour not

brought by air currents to right areas at right times.

Unusual currents of cold and warm water in oceans creates high pressure. El Nino causes drought in Asia.

Mountain prevent wind from blowing moisture to needy region.

In India when water vapour moves from east to west, water vapour does not leave Indian ocean causes drought.

Human activity directly trigger over farming, excessive irrigation, deforestation.

Global warming result in rainfall in some areas and drought in some areas.

Drought contingency planning

To provide contingency plans to manage drought and emergency conditions.

To continue to deliver a cost effective, adequate, safe and reliable supply of water.

The provision of credit or cash/food for work

Maintaining water supply for animals and humans

Maintaining cereal availabilityHuman and livestock health service

provisionSupport for private sectorProvide fodder for affected stockFlexible taxation systems for

affected people

Drought contingency planning allow for implementation of :

Mitigation

Relief

Rehabilitation

Drought contingency planning for implementation:

Overall drought policy, setting out plans objectives of minimizing the impact of drought

Set plans for specific mitigation, relief and rehabilitation measures

Construction of dams and additional reservoirs for supply of water.

Cloud seeding- artificial rain

Desalination of sea water for irrigation or consumption.

Drought monitoring by total rainfall levels and total usage levels

Land use by carefully planned crop rotation

Outdoor water use restrictionRainwater harvestingRecycled waterRelief worksDisease prevention and control

• Contingency planning done by Govt. Policy issues, national, regional and

district level rural development infrastructure input supply, marketing and farm

advisory services• Non- Govt.NGO’SRural institutionsPrivate sectors

Augmentation of water

It includes methods for providing an entirely new supply of fresh water and techniques for increasing utility of available supplies of water.

New supply of water include weather modification.

Weather modification done to increase precipitation and decrease Evapotranspiration.

Cloud seeding done to increase precipitation.

Available water supplies increased by conservation of available water supplies.

Agricultural water requirements can be reduced by reducing conveyance losses, and discouraging wasteful irrigation techniques.

Technique should be developed to reduce water consumption in home and industry.

Evaporation losses from small reservoirs can be reduced by providing roofs.

Reclamation and reuse of waste water can be encouraged.

Evaporation loss in ground water is less. Use of ground water storage reservoir in conjunction with surface storage reservoirs.

Infiltration losses can be reduced by sealing the soil surface useful in arid regions.

Water harvesting done by collecting from roof top, pavements, constructing small storage.

Measures for water conservation

Goals of water conservation efforts include:

Sustainability- ensure availability for future generations

Energy conservation- world 15% energy production dependent on water management.

Habitat conservation- preserve fresh water habitat, migrating waterfowl.

Benefits of water conservation:

Save water save money.Reduction in excess water use

reduce waste water generation, reduce overflowing of gutter.

Ecosystem and habitat protection.Helps in improving quality of

drinking water.

Water conservation measures by:

Domestic conservation

Industrial conservation

Agricultural conservation

Domestic conservation

Repair all leaks quicklyTurn off water when not in useUse conserving appliance which use

low volume water for domestic useLocal bodies should install water

meter and encourage water pricing.

Industrial conservation

Use cooling system which use less water.

Reuse of cooling water for irrigation or other purposes.

Install in plant treatment measures for treating the waste water or effluent.

Agricultural (irrigation) conservation

Improved irrigation methods such as sprinklers or drip irrigation.

Water required for agricultural considerably reduced by reducing conveyance loss.

Evaporation losses from small reservoirs can be reduced by providing roofs over them.

Use of lined canals which reduce seepage and evaporation.

Use of ground water storage reservoir in conjunction with modern surface storage reservoirs to reduce evaporation loss, in arid regions.

Price agricultural water to encourage conservation.

Infiltration losses reduced by sealing soil surface.

Water harvesting in arid regions.

For conservation of water the following structures can be constructed:

Earthen bundGully pluggingCheck damKhet talawadi

Earthen bund

Gully plugging

Check dam

Khet Talawadi

Water harvestingCollection of rain water called water

harvesting.Rainwater harvesting is

accumulation and storing of rainwater for reuse, before it reaches aquifer.

Water collected from roofs of houses, schools, local institutions make important contribution.

Water collected from ground, called storm water harvesting.

Benefits of rainwater harvesting

Increase water availabilityChecks declining water tableEnvironmental friendlyImproves water quality of ground

waterSurface water runoff conservationPrevents soil erosion and flooding in

urban area

Rainwater harvesting technique

Rainwater collection – Roof top rainwater harvesting

Runoff collection – Surface runoff harvesting

Recharge to ground waterRunoff enhancement

Roof top rain water harvesting

Rainwater captured from roof catchments and stored in sub surface ground water reservoir.

Objective is to make water available for future use.

Useful in dry land, hilly, urban and costal areas.

Components of roof top rainwater harvesting

a collection area a conveyance system storage facility a delivery system

Storage reservoir expensive part, careful design and construction required.

First rainwater should be flushed or diverted.

Surface runoff harvesting

Surface runoff harvesting is traditional technique.

Small dams, ponds, tanks are used.

Used for irrigation, domestic, livestock use.

Small damsSmall dams/check dams constructed

in natural channel to impound the runoff water up to certain depth.

Impounded water slowly infiltrate into soil and recharge ground water.

Ponds and reservoirsImpounding type and dug-cut type

ponds constructed.In impounding type, a retaining wall

or dam is constructed to block the flow of water in a natural storm.

In dug-cut type area is excavated to store the runoff.

Reservoirs requires water storage area, spillways and earth embankment.

Storage tankSurface or above ground tankSubsurface or underground tankStorage tanks requireSolid secure coverCoarse inlet filterOverflow pipeManhole, sump and drain to

facilitate cleaningOutlet system, tap or pump

Recharge to ground waterThe structures generally used:PitsTrenchesDug wellHand pumpsRecharge wellSpreading techniquesUnderground reservoirs

Runoff enhancement Can be done by increase

precipitation.Seeding generally done to increase

precipitation.Precipitation can be increased by

10% by cloud seeding.Lumb demonstrated that increase in

annual runoff (∆R) due to small increase in precipitation (∆P) is given by∆R= ∆P (0.29+1.2 R/P)

R= mean runoff, P= mean precipitation

Methods for runoff enhancement:Cloud seedingEnhancement by paved surfaces.Surface of drainage basin effect on

runoff. Bare surface give more runoff.

Drainage basin located on windward side of mountain produce more runoff.

Runoff affected by geology of drainage basin. Pervious soil yield less runoff.

Drainage basin has larger no of natural depressions, which deposited by other material then runoff at basin increases.

More Human activity, more load on soil, reduce infiltration, hence increase runoff.

ASSIGNMENT

1. Discuss various causes of drought2. Discuss drought contingency

planning and its importance.3. Explain augmentation of water and

its various methods.4. Explain water conservation and its

various methods.5. Discuss importance of rainwater

harvesting and explain various techniques used for it.