Technologies

Roof rainwater harvesting system [Botswana]

Lekidi

technologies_1417 - Botswana

Completeness: 86%

1. General information

1.2 Contact details of resource persons and institutions involved in the assessment and documentation of the Technology

Key resource person(s)

SLM specialist:
Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)
DESIRE (EU-DES!RE)
Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)
Book project: Water Harvesting – Guidelines to Good Practice (Water Harvesting)
Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)
University of Botswana (University of Botswana) - Botswana

1.3 Conditions regarding the use of data documented through WOCAT

When were the data compiled (in the field)?

03/06/2011

The compiler and key resource person(s) accept the conditions regarding the use of data documented through WOCAT:

Yes

1.4 Declaration on sustainability of the described Technology

Is the Technology described here problematic with regard to land degradation, so that it cannot be declared a sustainable land management technology?

No

2. Description of the SLM Technology

2.1 Short description of the Technology

Definition of the Technology:

Roof rainwater catchment system using galvanised iron roof material, feeding underground water tank.

2.2 Detailed description of the Technology

Description:

A roof of galvanised iron (corrugated iron) with the dimensions 7 x 6m is constructed on a support of gum poles (see photos). The roof catches the rain. The rain water flows over the roof into pipes at the rear end of the roof (sloping side) into an underground conical water tank. The tank is made of bricks and mortar. The underground tank serves two key roles: i) it stores water for use during the dry spells or times of no rain; and ii) the tank keeps the water cool in this hot environment. The technology is most preferred for so-called ‘lands’ areas, to provide household drinking water. On average, these lands are distant from water sources (e.g. 2-15 km). Other benefits of storing rainwater include less pressure on natural water ponds, but this would be a secondary concern

Water is critical for human consumption and needed around the home. The cool water is effective in quenching the thirst; it reduces labour time to collect water thus freeing time to concentrate on other farm activities. The water is mainly for household drinking and household chores like washing. Some is used as drinking water for chickens and for the animals used for draught power (e.g. donkeys during ploughing). The units are for use by individual farmers and thus restricted to individual households. The owner or the farmer has exclusive rights to the use of the water. Some farmers indicated that, in times of no rain, or before the first rains, they collect water from the village in drums, and pour it into this underground water tank, thus using it as a reservoir. They especially like the persistent coolness of water stored in the underground tank.

The technology is for rainwater collection in four villages. Rainwater that flows over the roof is collected, for example, on galvanised iron roofs. The water then runs through gutters and a pipe to the underground water tank. To build the underground tank, the ground is excavated, to about 2m deep and about 3m wide. Within this hole, a drum-like feature is built with concrete bricks and mortar. After the wall of the tank is complete, it is then lined with mortar from the inside, and the base is also lined to form the completed tank. It is then sealed at over most of the surface leaving an opening with a lid. This opening is large enough for a man to enter for occasional cleaning of the groundwater tank. Thus the system comprises a roof, for collecting rainwater, and an underground tank for storing it.

The environment is semi-arid and seasonal rainfall dominates during the summer months of October to April. People depend on nearby boreholes for water in the lands areas or have to travel to the village (about 2-5km away on average, but can be up to 15km) to fetch water. Most boreholes are either privately owned or communal and water is rationed to about two drums per week or even fortnightly. Most of the borehole water in the area is brackish. Thus roof rainwater (which is fresh) acts as the preferred alternative source of water. The underground tank, once full, is equivalent to 110 drums. Most normal rain events fill the tank, and the water remains in use till the next rainy season, which was found to be the case at all four pilot sites visited. Thus the rainwater catchments systems offer water security in the lands areas; water of very good drinking quality (sweet taste, cooler).

2.3 Photos of the Technology

2.5 Country/ region/ locations where the Technology has been applied and which are covered by this assessment

Country:

Botswana

Region/ State/ Province:

Boteti area, in Central District of Botswana

Further specification of location:

Central District

2.6 Date of implementation

If precise year is not known, indicate approximate date:
  • 10-50 years ago

2.7 Introduction of the Technology

Specify how the Technology was introduced:
  • through projects/ external interventions
Comments (type of project, etc.):

This is an ALDEP (arable lands development project) which is specifically for arable lands areas, to ascertain water provision and it started in the 1980-1990s, then up to mid 2008.

3. Classification of the SLM Technology

3.1 Main purpose(s) of the Technology

  • reduce risk of disasters

3.2 Current land use type(s) where the Technology is applied

Cropland

Cropland

  • Annual cropping
Grazing land

Grazing land

Extensive grazing land:
  • Semi-nomadism/ pastoralism
  • Ranching
Comments:

Major land use problems (compiler’s opinion): The water harvesting system is critical in a semi-arid environment, where water shortages are common. To augment water supplies, storage is needed especially in arable land areas where there are no coordinated water distributions like standpipes, as is the case in villages. People at the lands eke a living out of the arable fields, and assured water availability enables families to remain longer close to the fields for essential crop management, hence increased yields.
Major land use problems (land users’ perception): Water shortage and poor water quality.
Type of cropping system and major crops comments: Very little in a way of cash crops as the production system is subsistence based.
Type of grazing system comments: Free range grazing
Constraints of settlement / urban: piped water is cheap

3.3 Further information about land use

Water supply for the land on which the Technology is applied:
  • rainfed
Comments:

Water supply: rainfed, rainfed

Number of growing seasons per year:
  • 1
Specify:

Longest growing period in days: 197, Longest growing period from month to month: Oct - Mar

Livestock density (if relevant):

1-10 LU /km2

3.4 SLM group to which the Technology belongs

  • water harvesting

3.5 Spread of the Technology

Comments:

Total area covered by the SLM Technology is 0.01 m2.
This is a roof rainwater catchment system which is about 7m by 6m = 42 m2. The collection tank has a capacity of 10 000 litres.

3.6 SLM measures comprising the Technology

structural measures

structural measures

  • S5: Dams, pans, ponds

3.7 Main types of land degradation addressed by the Technology

water degradation

water degradation

  • Hs: change in quantity of surface water
  • Hg: change in groundwater/aquifer level
Comments:

Main causes of degradation: droughts (Reduced water/moisture due to droughts), land tenure (livelihoods depending on fragile ecosystem)
Secondary causes of degradation: overgrazing (high stocking rates in dry areas), population pressure, poverty / wealth (limited access to water and saline water)

3.8 Prevention, reduction, or restoration of land degradation

Specify the goal of the Technology with regard to land degradation:
  • reduce land degradation

4. Technical specifications, implementation activities, inputs, and costs

4.1 Technical drawing of the Technology

Author:

Atlhopheng Julius, Botswana

4.2 Technical specifications/ explanations of technical drawing

The top lid of the underground tank:
Rain water falls onto the corrugated roof surface, which usually measures 7 x 6m. This water flows down into the gutters, then down through the pipe into an underground water storage tank (built from concrete blocks which are lined with a coating of mortar, or mortar is applied to wire mesh. Most storage tanks, when full, have a capacity of about 110 drums (a drum holds 200 litres). Without this system, a farmer usually only has about 2 drums per week.

Technical knowledge required for field staff / advisors: moderate (Easy strycture or system to explain)
Technical knowledge required for land users: low (Needs professional builder to construct, but easy to run)
Main technical functions: water harvesting / increase water supply
Secondary technical functions: is used as open storage for farm equipment, offers shade against the heat, as well as temporary shelter

Structural measure: Roof rainwater system (roof)
Width of ditches/pits/dams (m): 6
Length of ditches/pits/dams (m): 7

Structural measure: Tank specifications (conical)
Depth of ditches/pits/dams (m): 2.7
Width of ditches/pits/dams (m): 1.75
Length of ditches/pits/dams (m): 3.5

Construction material (earth): To mix with cement
Construction material (wood): gum poles, rafters for supporting iron roof
Construction material (concrete): To build tank foundation
Construction material (other): iron
Lateral gradient along the structure: 5%
Specification of dams/ pans/ ponds: Capacity 10m3
Catchment area: 42m2
Beneficial area: 5m2

4.3 General information regarding the calculation of inputs and costs

other/ national currency (specify):

Pula

Indicate exchange rate from USD to local currency (if relevant): 1 USD =:

8.0

Indicate average wage cost of hired labour per day:

5.00

4.4 Establishment activities

Activity Type of measure Timing
1. Digging pit Structural
2. Transporting sand, cement and concrete blocks Structural
3. Construction Structural

4.5 Costs and inputs needed for establishment

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour labour ha 1.0 12.5 12.5 100.0
Labour labour by gov (8 person days) ha 1.0 500.0 500.0
Construction material sand, cement, concrete block ha 1.0 1500.0 1500.0 100.0
Total costs for establishment of the Technology 2012.5
Comments:

Duration of establishment phase: 1 month(s)

4.6 Maintenance/ recurrent activities

Activity Type of measure Timing/ frequency
1. Cleaning roof Structural once a year, before onset of rains
2. Cleaning storage tank Structural once a year, before onset of rains

4.7 Costs and inputs needed for maintenance/ recurrent activities (per year)

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour labour ha 1.0 12.5 12.5 100.0
Total costs for maintenance of the Technology 12.5
Comments:

Machinery/ tools: Stock bricks, corrugated iron sheets, meshwire, gutters, wire nails. No machinery, just broom and bucket to collect sediment and dispose of it.
Prices of construction material for the roof rainwater system, fitted with the underground water storage system. All prices and exchange rates were calculated for 29 September 2008. The government subsidy was such that, men pay 30% of all costs, while women pay 20%. The 20-30% could be paid through labour (i.e. digging the pit, transporting sand and cement and serving as a labour hand during construction. Thus if the farmer offers labour, then he does not pay anything. The costs are calculated with labour input and its price or the local wage.

4.8 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

Cost of building materials, specifically iron sheets, timber, bricks, concrete and the professional builder from the government.

5. Natural and human environment

5.1 Climate

Annual rainfall
  • < 250 mm
  • 251-500 mm
  • 501-750 mm
  • 751-1,000 mm
  • 1,001-1,500 mm
  • 1,501-2,000 mm
  • 2,001-3,000 mm
  • 3,001-4,000 mm
  • > 4,000 mm
Agro-climatic zone
  • semi-arid

Thermal climate class: subtropics. sub-tropical thermal climate (hot summers, cool winters)

5.2 Topography

Slopes on average:
  • flat (0-2%)
  • gentle (3-5%)
  • moderate (6-10%)
  • rolling (11-15%)
  • hilly (16-30%)
  • steep (31-60%)
  • very steep (>60%)
Landforms:
  • plateau/plains
  • ridges
  • mountain slopes
  • hill slopes
  • footslopes
  • valley floors
Altitudinal zone:
  • 0-100 m a.s.l.
  • 101-500 m a.s.l.
  • 501-1,000 m a.s.l.
  • 1,001-1,500 m a.s.l.
  • 1,501-2,000 m a.s.l.
  • 2,001-2,500 m a.s.l.
  • 2,501-3,000 m a.s.l.
  • 3,001-4,000 m a.s.l.
  • > 4,000 m a.s.l.

5.3 Soils

Soil depth on average:
  • very shallow (0-20 cm)
  • shallow (21-50 cm)
  • moderately deep (51-80 cm)
  • deep (81-120 cm)
  • very deep (> 120 cm)
Soil texture (topsoil):
  • coarse/ light (sandy)
  • fine/ heavy (clay)
Topsoil organic matter:
  • medium (1-3%)
  • low (<1%)

5.4 Water availability and quality

Ground water table:

5-50 m

Availability of surface water:

poor/ none

Water quality (untreated):

poor drinking water (treatment required)

5.5 Biodiversity

Species diversity:
  • high

5.6 Characteristics of land users applying the Technology

Market orientation of production system:
  • subsistence (self-supply)
Off-farm income:
  • less than 10% of all income
Relative level of wealth:
  • very poor
  • very rich
Individuals or groups:
  • individual/ household
Level of mechanization:
  • animal traction
Gender:
  • women
  • men
Indicate other relevant characteristics of the land users:

Land users applying the Technology are mainly disadvantaged land users
Population density: < 10 persons/km2
Annual population growth: 2% - 3%
10% of the land users are very rich and own 50% of the land (rich cattle barons).
60% of the land users are average wealthy and own 30% of the land (most inhabitants).
30% of the land users are poor and own 20% of the land (subsistence farmers).
Off-farm income specification: Saves labour time to fetch water. Very limited off-farm income opportunities for everyone, including non-adopters of the technology

5.7 Average area of land owned or leased by land users applying the Technology

  • < 0.5 ha
  • 0.5-1 ha
  • 1-2 ha
  • 2-5 ha
  • 5-15 ha
  • 15-50 ha
  • 50-100 ha
  • 100-500 ha
  • 500-1,000 ha
  • 1,000-10,000 ha
  • > 10,000 ha
Is this considered small-, medium- or large-scale (referring to local context)?
  • small-scale

5.8 Land ownership, land use rights, and water use rights

Land ownership:
  • communal/ village
  • individual, not titled
Land use rights:
  • open access (unorganized)
  • individual
Water use rights:
  • communal (organized)
  • individual
Comments:

Communal grazing and individual land ownership for ploughing. Water availed through communal boreholes in lands and cattle posts, but with individual standpipes in villages. Open access to surface water resources for livestock e.g. pans after rains. Dual grazing rights problem, whereby private ranchers graze in the commons, but the opposite not possible.

5.9 Access to services and infrastructure

health:
  • poor
  • moderate
  • good
education:
  • poor
  • moderate
  • good
technical assistance:
  • poor
  • moderate
  • good
employment (e.g. off-farm):
  • poor
  • moderate
  • good
markets:
  • poor
  • moderate
  • good
energy:
  • poor
  • moderate
  • good
roads and transport:
  • poor
  • moderate
  • good
drinking water and sanitation:
  • poor
  • moderate
  • good
financial services:
  • poor
  • moderate
  • good

6. Impacts and concluding statements

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

crop production

decreased
increased
Quantity before SLM:

0.15 t/ha/y

Quantity after SLM:

0.195 t/ha/y

Comments/ specify:

30% increase due to more time to manage crops better e.g. weeding

animal production

decreased
increased
Comments/ specify:

mainly chickens and small stock

risk of production failure

increased
decreased
Quantity before SLM:

40%

Quantity after SLM:

10%

Comments/ specify:

more time on farm

Water availability and quality

drinking water availability

decreased
increased
Comments/ specify:

water year round

Income and costs

expenses on agricultural inputs

increased
decreased
Quantity before SLM:

5%

Quantity after SLM:

90%

Comments/ specify:

at construction phase only

diversity of income sources

decreased
increased
Quantity before SLM:

3%

Quantity after SLM:

25%

Comments/ specify:

from horticulture, chickens etc

economic disparities

increased
decreased
Quantity before SLM:

5%

Quantity after SLM:

90%

Comments/ specify:

poor cannot afford it

workload

increased
decreased
Comments/ specify:

no time lost in collecting water afar

Socio-cultural impacts

food security/ self-sufficiency

reduced
improved
Quantity before SLM:

5%

Quantity after SLM:

35%

Comments/ specify:

better yields with more on-farm time

health situation

worsened
improved
Quantity before SLM:

5%

Quantity after SLM:

40%

Comments/ specify:

the water is better than in region

community institutions

weakened
strengthened
Quantity before SLM:

6%

Quantity after SLM:

50%

Comments/ specify:

uplifting of the disadvantaged

SLM/ land degradation knowledge

reduced
improved
Quantity before SLM:

4%

Quantity after SLM:

50%

conflict mitigation

worsened
improved
Comments/ specify:

conflicts exist over boreholes

situation of socially and economically disadvantaged groups

worsened
improved
Comments/ specify:

improved water provision, not affordable for the poor (unless subsidized)

contribution to human well-being

decreased
increased
Comments/ specify:

Many educational tours made on these demonstration sites. Fresh rainwater is good for health compared to borehole (salty) water.

Ecological impacts

Water cycle/ runoff

water quantity

decreased
increased
Quantity before SLM:

5%

Quantity after SLM:

80%

Comments/ specify:

water year round

water quality

decreased
increased
Comments/ specify:

not salty/saline, to clean roof and tank annually (temporarily)

harvesting/ collection of water

reduced
improved
Quantity before SLM:

1%

Quantity after SLM:

90%

Comments/ specify:

resource from previous year used

evaporation

increased
decreased
Quantity before SLM:

1%

Quantity after SLM:

90%

Comments/ specify:

underground water tank, sealed

Climate and disaster risk reduction

emission of carbon and greenhouse gases

increased
decreased
Quantity before SLM:

1%

Quantity after SLM:

90%

Comments/ specify:

clean technology

6.2 Off-site impacts the Technology has shown

water availability

decreased
increased
Quantity before SLM:

2 drums/we

Quantity after SLM:

42drums/we

Comments/ specify:

all this water saved due to technology

6.3 Exposure and sensitivity of the Technology to gradual climate change and climate-related extremes/ disasters (as perceived by land users)

Gradual climate change

Gradual climate change
Season Type of climatic change/ extreme How does the Technology cope with it?
annual temperature increase well

Climate-related extremes (disasters)

Meteorological disasters
How does the Technology cope with it?
local rainstorm well
Climatological disasters
How does the Technology cope with it?
drought not well
Hydrological disasters
How does the Technology cope with it?
general (river) flood well

Other climate-related consequences

Other climate-related consequences
How does the Technology cope with it?
reduced growing period well
Comments:

The roof area is such that, some limited amounts of rain do fill or add some water into the storage tank

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?
Short-term returns:

very negative

Long-term returns:

very positive

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?
Short-term returns:

very negative

Long-term returns:

very positive

Comments:

Very costly to set up, if no government aid. It is however, very good for long term water provision.

6.5 Adoption of the Technology

Comments:

1% of land user families have adopted the Technology with external material support
1 land user families have adopted the Technology with external material support
There is one such structure per village in Boteti sub-district - and they are all demonstration schemes. There was no public uptake following demonstration, as government subsidy changed and was later stopped.
It is too costly e.g. building materials, hiring of professional builder and cement to set up in lands areas.
There is no trend towards spontaneous adoption of the Technology
High capital or start-up costs. The area has low income groups who get water from communal boreholes, while rich cattle owners obtain water from their private boreholes, and hence desalination is favoured rather than rainwater systems.

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
Useful as shelter or storage
Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
Provides cool water in hot summers
Provides water in lands areas, where it is most needed
Farmers appreciate the good water quality and clean system annually
It has low maintenance costs, it is easy to use

6.8 Weaknesses/ disadvantages/ risks of the Technology and ways of overcoming them

Weaknesses/ disadvantages/ risks in the land user’s view How can they be overcome?
Costly to set up, due to price of building materials Government subsidies, priviate sector, NGOs
Fear that their land would be taken away by the government after financial assistance Education about subsidies to allay fears
Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view How can they be overcome?
Costly to set up subsidies by government, NGOs, private sector
Seen as dependent on rains, thus fails during droughts research, information dissemination to stakeholders
Water quality issues (concerns) education on keeping storage clean and boiling water for human consumption

7. References and links

7.1 Methods/ sources of information

  • field visits, field surveys
  • interviews with land users

7.2 References to available publications

Title, author, year, ISBN:

Ministry of Agriculture Headquarters, Department of Crop Production, Engineering Division, Water Development Section,

Available from where? Costs?

P/Bag 003, Gaborone,

Title, author, year, ISBN:

en.wikepedia.org/wiki/rainwater-harvesting

Available from where? Costs?

website

Title, author, year, ISBN:

www.harvesth2O.com

Available from where? Costs?

website

Title, author, year, ISBN:

www.rainwaterharvesting.org/index.htm

Available from where? Costs?

website

Title, author, year, ISBN:

www.rainwaterharvesting.co.uk

Available from where? Costs?

website

Title, author, year, ISBN:

cgwb.gov.in/Ground Water/roof-top.htm

Available from where? Costs?

website

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