Water c h_2020_t_c1

Water Conservation and
Harvesting
08-03-2020 Water_Conservation_Harvesting_T_C1
Introduction
1

Overview
• Goals of Water Conservation
• Definition and the Basics of Water Harvesting
• WHY Rain Water Harvesting?
• Where to Use RWH Techniques?
• Benefits of Rainwater Harvesting
• Advantages and Disadvantages of Water Harvesting
• Overview of Main WH Systems
• Factors Need to be Considered in WH Technology
• Site Selection for Water Harvesting Technology
• Limitations of Water Harvesting08-03-2020 Water_Conservation_Harvesting_T_C1 2

Goals of Water Conservation
• 1) Sustainability: To ensure availability for future generations, the
withdrawal of fresh water from an ecosystem should not exceed its
natural replacement rate.
• 2) Energy conservation: Water pumping, delivery, and wastewater
treatment facilities consume a significant amount of energy. In some
regions of the world over 15% of total electricity consumption is
devoted to water management.
• 3) Habitat conservation: Minimizing human water use helps to
preserve fresh water habitats for local wildlife and migrating water
flow, as well as reducing the need to build new dams and other water
diversion infrastructure.
08-03-2020 Water_Conservation_Harvesting_T_C1 3

Water conservation: refers to reducing the usage of water and recycling
of waste water for different purposes like domestic usage, industries,
agriculture …
Methods of Water Conservation:
• 1. Protection of Water from Pollution;
• 2. Redistribution of Water
• 3. Rational Use of Groundwater
• 4. Renovation of Traditional Water
Sources
• 5. Use of Modern Irrigation Methods
• 6. Increasing Forest Cover
• 7. Change in Crop Pattern
• 8. Flood Management
• 9. Conserving Water in Industries
• 10. Conservation of water by Municipal
authorities
• 11. Use rainwater effectively
• 12. Make effective use of soil water
reserves
• 13. Take measures to avoid run off
• 14. Avoid wasting water through
evaporation
• 15. Reduce water losses through drainage
• 16. Plan your irrigation
• 17. Contour Farming & Contour Ploughing
• 18. Recycle & desalination
• 19. Groundwater recharge

Water harvesting for crop production
• Is the collection and concentration of runoff water
• Can produce crops in areas with insufficient rain for rainfed agriculture
• Can improve pasture and crop yield
• Is suited for arid, semi-arid and semihumid regions
• Has positive side effects on: water and soil conservation
• Consists of a runoff area and a runon area
• The water is stored in the soil, in cisterns, ponds or reservoirs
• Has been used traditionally in many (semi-)arid areas of the world
• Its use is still far below its potential !

1.1. Definition and the Basis of Water Harvesting
The Basis of Water Harvesting
• Water is essential to all life – human, animal and vegetation. It is
therefore important that adequate supplies of water be
developed to sustain such life.
• As land pressure rises, more and more marginal areas in the
world are being used for agriculture.
• Much of this land is located in the arid or semi-arid belts where
rainfall is irregular and much of the precious water is soon lost as
surface runoff.

Cont…
• Recent droughts have highlighted the risks to human beings and livestock,
which occur when rains falter or fail.
• While irrigation may be the most obvious response to drought, it has proved
costly and can only benefit a fortunate few.
• There is now increasing interest in the low cost alternative generally
referred to as ‘water harvesting’.
• Water harvesting is the collection of runoff for productive purposes. Instead
of runoff being left to cause erosion, it is harvested and utilized.
• In the semi-arid drought-prone areas where it is already practiced, water
harvesting is a directly productive form of soil and water conservation.
• Both yields and reliability of production can be significantly improved with
this method.

Definition of Water Harvesting
• Water harvesting in its broadest sense can be defined as the "collection of
runoff for its productive use". Includes the gatherin, accumulating and
storing.
 crops, pastures and trees production
 livestock consumption
 domestic consumption
 (fish and duck ponds)
• Runoff may be harvested from roofs and ground surfaces as well as from
intermittent or temporary watercourses.
• Water harvesting techniques, which harvest runoff from roofs or ground
surfaces fall under the term ‘Rainwater Harvesting’ while all systems which
collect discharges from watercourses are grouped under the term
‘Floodwater Harvesting’.

Unit 1 - Introduction 9
WHAT ARE THE BENEFITS OF WATER HARVESTING ?
WATER
HARVESTING
Pasture improvement
= more livestock
[= more desertification ?]
Soil conservation
(for macrocatchments
on cropping area only)
= less soil erosion
Higher productivity
(higher yields
and less risk)
Water conservation
(tapping unused water)
Suppression of salinity in soil
= more productive land
Improved re-/afforestation
= less desertification
Groundwater recharge
= more water available
Crop production in
areas where it is
normally not feasible

• Where water demand of crops is higher than supply
because of
x low rainfall and / or
x uneven seasonal distribution of rainfall and / or
x high temperatures (high evapotranspiration)
FOR WHICH AREAS IS WATER
HARVESTING SUITABLE ?
• Arid, semi arid and semihumid areas
• Where rainfall exceeds 150 mm / a, if rain falls in the cool season
• Where rainfall exceeds 200 mm / a, if rain falls in the hot season and if no
storage in ponds or reservoirs is provided

WHERE WAS WATER HARVESTING
USED TRADITIONALLY ?
ASIA
• Jordan ( since 7000 BC)
• Mesopotamia (4500 BC)
• Palestine (2000 BC-1200 AD)
• Yemen (since 1000 BC)
• Pakistan
• India
• Sri Lanka
• China etc.
AMERICA
•Arizona and New-Mexico (1000
AD)
AFRICA
•Tunisia : `Meskat´, ´M´goud´ and
`Jessours´
•Somalia : `Caag´ and `Gawan´
systems
•Sudan : `Haffire´; `Teras´ etc.
•Burkina Faso: Pits

Rain Water Harvesting Classification
Broadly there are two ways of harvesting rain water
 surface runoff harvesting
 Roof top runoff harvesting
1. Surface runoff harvesting
Mostly surface runoff harvesting used for recharging aquifers and
agriculture
Less applicable for drinking as compared to roof runoff due to some
dissolved materials on the surface
Characterized by topography, soil type and land use

Cont…
2. Roof harvesting
By guiding runoff through
gutter to the storage tank

Cont…
Roof harvesting
Commonly practiced in urban areas for domestic use and gardening
Relatively clean as compared to surface one
Depends on roof size and type
Corrugated iron roofs are the most suitable
Grass roofs neither the quality nor quantity of runoff from them is
suitable and also difficult to gutter08-03-2020 Water_Conservation_Harvesting_T_C1 14

The Principle Of Water Harvesting
• Taking rain water from a run off area and convey to run on area.
Run-on area/
cropping area
Runoff area/
catchment
Macrocatchment Floodwater harvesting
Microcatchments

Components of Water Harvesting Technology
Basic components of RWH system:
•A catchment surface (Roof tops, streets, public squares, small ground
surfaces, large catchment areas
•A storage reservoir (surface and subsurface tanks, rock catchment
dams, earth dams, etc.)
•A delivery system(Gutters , Surface drains , Channels )
• Filtration/ silt trap system

1.2 WHY Rain Water Harvesting?
• RWH can boost water supply in all sectors.
• RWH increases food production and hence forms the foundation of
many development projects that promote agriculture and land
management.
• RWH minimizes the risk of crop failure during droughts, intra
seasonal droughts and floods.
• RWH reduces women's burden of collecting water for domestic use,
leaving time for other productive activities.

Cont…
• RWH gives opportunity for the girl child to attend school and
• provides a relatively safe and clean source of drinking water,
minimizing incidences of water borne diseases.
• When applied at watershed level, it improves the environment and
minimizes the effects of drought and floods.
• RWH is a decentralized water supply system encouraging community
participation and self reliance.

1. 3 Where to Use RWH Techniques?
• Rainwater harvesting techniques can be applicable in all agro
climatic zones.
• However, it is more suitable in arid and semi-arid areas where
the average annual rainfall is from 200 to 800 mm (rarely
exceeding 800 mm) and the average annual mean temperature
is high enough to enhance evapotranspiration demand of
crops.
• In such an environment, rain fed crop production is usually
difficult without using rainwater harvesting techniques.

Cont…
Generally, the RWH techniques can be applicable in the following
circumstances:
• In dry environment with erratic and poorly distributed rainfall for crop
production.
• In the area where other permanent water sources like rivers, springs, lakes,
etc. are not available or economically not feasible to develop and use.
• In arid and semi arid areas where the potential for crop production is
diminishing due to environmental degradation and shortage of rainfall.
Providing water to these areas through rainwater harvesting can improve the
vegetative cover and enhance resource conservation.
• In rain-fed areas where crops can be produced, but with low yield and with
high risk of total crop failure.
• In areas where the water supply for both domestic and livestock is not
sufficient.

1.4 Benefits of Rainwater Harvesting
• Rainwater harvesting in urban and rural areas offers several
benefits including:
 provision of supplemental water,
increasing soil moisture levels for urban greenery,
increasing the groundwater table via artificial recharge,
mitigating urban flooding and
improving the quality of groundwater.
In homes and buildings, collected rainwater can be used for
irrigation, toilet flushing and laundry.
With proper filtration and treatment, harvested rainwater can
also be used for showering, bathing, or drinking.

1.5 Advantages and Disadvantages of Water Harvesting
The advantages of rainwater harvesting are summarized below:
• rainwater is a relatively clean and free source of water
• rainwater harvesting provides a source of water at the point where
it is needed
• it is owner-operated and managed
• it is socially acceptable and environmentally responsible
• it promotes self-sufficiency and conserves water resources

Cont…
• rainwater is friendly to landscape plants and gardens
• it reduces storm water runoff and non-point source pollution
• it uses simple, flexible technologies that are easy to maintain
• offers potential cost savings especially with rising water costs
• provides safe water for human consumption after proper treatment
• low running costs
• construction, operation and maintenance are not labor-intensive.

Disadvantages
• The main disadvantages of rainwater harvesting technologies
are the limited supply and uncertainty of rainfall.
• Rainwater is not a reliable water source in times of dry
periods or prolonged drought.
• Low storage capacity which will limit rainwater harvesting,
whereas, increasing the storage capacity will add to the
construction and operating costs making the technology less
economically feasible.

Cont…
• Possible contamination of the rainwater with animal wastes and
organic matter which may result in health risks if rainwater is not
treated prior to consumption as a drinking water source.
• Leakage from cisterns can cause the deterioration of load-
bearing slopes.
• Cisterns and storage tanks can be unsafe for small children if
proper access protection is not provided.

1.6. Overview of Main WH Systems
• In crop production systems, RWH is composed of a runoff producing
area normally called the catchment area (CA) and a runoff utilization
area normally called cropped basin (CCA).
• Therefore RWH systems for crop production are divided into different
categories basically determined by the distance between CA and CCA
as follows:
In-situ rain water harvesting,
Internal (Micro) catchment RWH,
External (Macro) catchment RWH and
Flood water harvesting.

1.6.1. In-situ rain water harvesting
• In-situ rain water harvesting, also called water conservation, involves
the use of methods that increase the amount of water stored in the
soil profile by trapping or holding the rain where it falls.
• In this application there is no separation between the collection area
and the storage area, the water is collected and stored where it is
going to be utilized.

Cont…
• In-situ rainwater harvesting involves small movements of rainwater as
surface runoff, in order to concentrate the water where it is wanted
most.
• It is basically a prevention of net runoff from a given cropped area by
holding rain water and prolonging the time for infiltration.
• This system works better where the soil water holding capacity is
large enough and the rainfall is equal or more than the crop water
requirement.
• In-situ RWH is achieved mainly by the following means: Deep tillage,
Contour farming and ridging, and agronomic practices.

1.6.2 Internal (Micro) catchment RWH
• This is a system where there is a distinct division of CA (catchment
area, which collects runoff ) and CCA (crop cultivated area, which
receives and concentrates runoff from the catchment area for crop
water supply) but the areas are adjacent to each other.
• This system is mainly used for growing medium water demanding
crops such as maize, sorghum, groundnuts and millet.
• Micro-catchment water harvesting is a method of collecting surface
runoff from a small catchment area and storing it in the root zone of
an adjacent infiltration basin.
• This infiltration basin may be planted with a single tree, bush or with
annual crop.

Cont…
The major characteristics of the system include:
• Overland flow/run-off harvested from short catchment length
• Catchment length between 1-30 meters
• Runoff stored in soil profile
• Ratio catchment: cultivated area (CCA) usually 1:1 to 3:1
• Since handling normally only small flows, no provision for overflow.
• Plant growth is even
• Use to replenish soil moisture, increase crop production and soil conservation.
• Examples: Negarim Microcatchments (for trees), Contour Bunds (for trees),
Contour Ridges (for crops), Semi-Circular Bunds (for range and fodder).

Cont…
37
Figure : a typical Micro catchment

Cont…
WHAT IS MICROCATCHMENT WATER HARVESTING ?
• Collection of surface runoff (sheet and rill flow)
• Small dimension of catchment (1 - 1000 m²) and cropping area
• Catchment and cropping area adjacent to each other
• Storage of water in the soil (root zone)
• Plantation of a single tree, bush or of annual crops
• No provision for overflow
• Microcatchments are mostly aligned in a series of units
• Typical ratio of catchment : cropping
area = 1 : 1 - 10 : 1

Cont…
CONSTRUCTION :
• mainly by handwork
WHERE IS MICROCATCHMENT WH IMPLEMENTED?
> 200 mm annual rainfall for tree planting (summer rainfall areas)
> 300 mm annual rainfall for production of annual crops
Three types of microcatchment water
harvesting; Source: Rocheleau 1988
= 1 : 1 to 10 : 1
< 1000 m²
< 100 m²
DIMENSIONS :

Water_Conservation_Harvesting_T_C1 40
MICROCATCHMENTS
Example of a typical microcatchment
Cropping
area
A= 5 m²
Catchment area
A = 10 m²
Slope = 2 %
Plan
view
Cross-
section
Bund
Run-off
Ratio =
10 m²
5 m²
= 2 : 1
catchment area
cropping area
08-03-2020

1.6.3 External (Macro) catchment RWH
• Water harvesting from medium-sized catchments (1,000 m2 - 200 ha)
is also known as “water harvesting from long slopes”, as “macro-
catchment water harvesting” or as “harvesting from external
catchment systems”.
• This is a system that involves the collection of runoff from large areas
which are at an appreciable distance from where it is being used.
• This is sometimes used with intermediate storage of water outside
the CCA for later use as supplementary irrigation.
• The catchment areas usually have slopes ranging from 5-50%, while
the harvested water is used on cropped areas which are either
terraced or on flat lands.

Cont…
• The various characteristics of this type of system are:
• Overland flow or runoff harvested from catchments of areas ranging from 0.1
ha to thousands of hectares
• Diverted from farms land, hill side, pasture, or even roads
• Runoff stored in soil profile or even stored in ponds, tanks or groundwater
aquifers.
• Catchment 30 - 200 meters in length
• Ratio catchment: cultivated area (C:CA) usually 2:1 to 10:1
• Provision for overflow of excess water
• Uneven plant growth unless land leveled.
• Use to replenish soil moisture, increase or ensure crop production.
• Typical Examples: Trapezoidal Bunds (for crops), Contour Stone Bunds (for
crops)08-03-2020 Water_Conservation_Harvesting_T_C1 42

Cont…
43
Figure : Macro catchment

Cont…
WHAT IS MACROCATCHMENT WATER HARVESTING ?
• Collection of surface runoff
• Large catchment outside of arable area
(“external catchment”)
• Catchment untreated or treated
• Storage of water mostly in the soil
• Provision for overflow (spillway)
• Slope of catchment area 5 - 50%
• Cropping area either terraced or
in flat terrain (< 10% slope)

Cont…
WHERE IS MACROCATCHMENT WH IMPLEMENTED?
CONSTRUCTION :
• Handwork or mechanized
 300 mm annual rainfall (in summer rainfall areas)
= 10 : 1 to 100 :1
= 1000 m² - 200 ha
SIZES :

1.6.4. Flood water harvesting
• Flood water harvesting (Often referred to as “Water Spreading" and sometimes
"Spate Irrigation").
Main Characteristics:
• turbulent channel flow harvested either (a) by diversion or (b) by spreading
within channel bed/valley floor
• runoff stored in soil profile
• catchment long (may be several kilometers)
• ratio catchment: cultivated area above 10:1
• provision for overflow of excess water
• Typical Examples: Permeable Rock Dams (for crops), Water Spreading Bunds (for
crops)
• Floodwater harvesting comprises two different techniques: Floodwater
harvesting within the stream-bed and floodwater diversion.

Floodwater harvesting within the stream bed
• Floodwater harvesting within the stream bed” means blocking the
water flow to inundate the valley bottom of the entire flood plain, to
force the water to infiltrate and use the wetted area for crop
production or pasture improvement.
• This is a system that uses barriers such as permeable stone dams to
block the water flow and spread it on the adjacent plain and enhance
infiltration.
• The wetted area is then used for crop production (Figure).

Cont…

WHAT IS FLOODWATER HARVESTING ?
FLOODWATER HARVESTING
• Collection of turbulent channel flow from a major
seasonal river channel
• Provision for overflow (spillways)
• Storage of water in soil (root zone),
ponds or reservoirs
• Large catchment upstream
• Complex structures of dams
and distribution networks
08-03-2020

WHERE IS FLOODWATER WH IMPLEMENTED?
FLOODWATER HARVESTING
300 mm / a  150 mm / a in case of storage facilities)
= 200 ha - 50 km²
= variable
= 100 : 1 to 10,000 :1
SIZES :
What are the special benefits of floodwater harvesting ?
Supply of soil moisture for crop production
Recharge of ground water
Reduction of damage caused by flash floods08-03-2020

1.7 Factors Need to be Considered in WH Technology
• The following factors must be considered while applying a water
harvesting technology:
• If other renewable water sources are not available in the required
quantity and quality
• If it is cheaper than other water resources
• If it is easier to develop than other water resources
• If the risk of crop failure can be reduced.

1.8. Site Selection for Water Harvesting Technology
52
Slope > 5%Slope < 5%
Irrigation not viableIrrigation viable
Not suitable soilsSuitable soils
Semi-arid and arid areas
Water harvesting Not recommendedWater harvesting possible
Flood water farming
Trees
Runoff farming
Rangeland fodder Crop production
-Planting pits
-Contour bunds
-Semi-circular bunds
-Contour stone bunds
Stones available No stones available
-Contour bunds
-Closed microcatchment
-Infiltration pits
-Contour stone bunds
-Earth bunds with stone spillways
-Contour bunds
-Planting pits

Cont…
Technical factors include those related to crop, soil and
topography characteristics.
Socio-economic factors include the preferences of the local
community, the quantities of earthwork or stonework that
will be needed in construction and the costs, especially labor,
that may be involved.
The long-term rights to use of land may be a major
consideration
The availability of land must be considered.
Where a farmer has a limited area of land he or she will be
reluctant to adopt a water harvesting system, which involves
leaving some of the arable land idle.

1.9 Limitations of Water Harvesting
 Climatic risks still exist
 No guarantee for high yields
 Methods scientifically not well established Very often limited
experience of extension service
 Possible conflicts between people upstream and downstream
 Possible harm to fauna and flora
 Larger schemes and structures are difficult to implement (need
acceptance by people, political backing and financial support)

Cont…
• Climatic risks still exist
• No guarantee for high yields
• Methods scientifically not well established
• Very often limited experience of extension service
• Possible conflicts between people upstream and downstream
• Possible harm to fauna and flora
• Larger schemes and structures are difficult to implement
(need acceptance by people, political backing and financial support)

WATER HARVESTING AND PRECIPITATION
Annual precipitation ranges for different types of water harvesting
in summer rainfall areas; Source: Prinz 1994, altered
Microcatchment WH
Macrocatchment WH
Floodwater harvesting
100 200 300 400 500 600
annual precipitation
(mm)

OVERVIEW OF THE MAIN TYPES OF WATER HARVESTING
Type of WH Kind of
flow
Annual
rainfall
Treatment of
catchment
Size Ratio
Micro-
catchment
sheet and
rill flow
> 200 -
> 300 mm
treated or
untreated
- 1000 m² 1:1-10:1
Macro-
catchment
turbulent
runoff +
channel flow
> 300 mm treated or
untreated
1000 m² -
200 ha
10:1-100:1
Floodwater
harvesting
flood water > 150 mm untreated 200 ha -
50 km²
100:1-
10,000:1
Overview over the main types of water harvesting for crop production

Water c h_2020_t_c1

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