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

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1.3 Conditions regarding the use of data documented through WOCAT

When were the data compiled (in the field)?

05/07/2011

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

Yes

2.1 Short description of the Technology

Definition of the Technology:

The tabia earthen dyke is a water harvesting technique used in the foothill and piedmont areas.

2.2 Detailed description of the Technology

Description:

The tabia technology is similar to the jessour system but is used in the gently-sloping foothill and piedmont areas. It is considered to be a relatively new technique, developed by mountain dwellers who migrated to the plains. Tabias, like jessour, comprise an earthen dyke (50-150 m in length, 1-2 m in height), a spillway (central and/or lateral) and an associated water harvesting area. The ratio between the area where water is applied (cropped area) and the total area from which water is collected varies from 1:6 to 1:20. The differences between the tabia and the jessour systems are that the former contains two additional lateral bunds (up to 30 m long) and sometimes a small flood diversion dyke (mgoud). Small tabia are constructed manually using shovels, pickles and carts. Larger constructions are done mechanically using tractors and bulldozers.

Purpose of the Technology: Tree products and annual crops are commonly grown using tabia. Besides their water harvesting qualities, tabias also have a positive effect on soil erosion and groundwater recharge.

Natural / human environment: The tabia runoff-water harvesting technique is widely practised in central Tunisia. Tabias are usually installed on the piedmont, where the slope does not exceed 3% and where the soil is relatively deep. Ancient remnants of tabias have been found in the region of Gafsa (south west Tunisia). The system has been adopted by people living in the neighbouring foothills and plains of the central and southeastern regions (Jeffara) of the country, following the transformation of their pasture to cultivated fields.

2.3 Photos of the Technology

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

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

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

Comments:

Major land use problems (compiler’s opinion): soil erosion by water, runoff and soil loss

Major land use problems (land users’ perception): overgrazing

3.3 Further information about land use

Comments:

Water supply: rainfed, mixed rainfed - irrigated

Number of growing seasons per year:

• 1

Specify:

Longest growing period in days: 180Longest growing period from month to month: Oct - Apr

3.4 SLM group to which the Technology belongs

• water harvesting

3.5 Spread of the Technology

Specify the spread of the Technology:

• evenly spread over an area

If the Technology is evenly spread over an area, indicate approximate area covered:

• 10-100 km2

3.6 SLM measures comprising the Technology

Comments:

Main measures: structural measures

3.7 Main types of land degradation addressed by the Technology

Comments:

Main type of degradation addressed: Wt: loss of topsoil / surface erosion

Secondary types of degradation addressed: Wg: gully erosion / gullying

Main causes of degradation: Heavy / extreme rainfall (intensity/amounts), land tenure

Secondary causes of degradation: overgrazing, population pressure

3.8 Prevention, reduction, or restoration of land degradation

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

• prevent land degradation
• reduce land degradation

Comments:

Main goals: prevention of land degradation

Secondary goals: mitigation / reduction of land degradation

4.1 Technical drawing of the Technology

4.2 Technical specifications/ explanations of technical drawing

Tabia with natural water collection area (upper) and tabia on an expanded system with additional flood water diversions (lower). (Adapted from Alaya et al. 1993)
Found in flatter areas, tabia can accommodate more trees on the terrace especially when it can receive additional water from floods.

south east Tunisia

Date: January 2009

Technical knowledge required for field staff / advisors: moderate

Technical knowledge required for land users: moderate

Main technical functions: control of concentrated runoff: retain / trap

Secondary technical functions: increase of infiltration, water harvesting / increase water supply, water spreading

Diversion ditch/ drainage
Height of bunds/banks/others (m): 2
Width of bunds/banks/others (m): 2-5
Length of bunds/banks/others (m): 10-30

Spillway
Height of bunds/banks/others (m): 1
Width of bunds/banks/others (m): 5
Length of bunds/banks/others (m): 2-4

Bund/ bank: graded
Vertical interval between structures (m): 3
Spacing between structures (m): 100
Height of bunds/banks/others (m): 2
Width of bunds/banks/others (m): 2-5
Length of bunds/banks/others (m): 50-150

Construction material (earth): Main dyke

Construction material (stone): Spillway

Construction material (concrete): Spillway

Construction material (other): Gabion: Diversion dyke

Lateral gradient along the structure: 1%

For water harvesting: the ratio between the area where the harvested water is applied and the total area from which water is collected is: 1:4

4.3 General information regarding the calculation of inputs and costs

other/ national currency (specify):

TND

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

1.3

4.4 Establishment activities

	Activity	Type of measure	Timing
1.	Diversion channel	Structural	in the case of tabia on spreading system
2.	Plantation	Structural
3.	Spillway construction	Structural
4.	Terracing	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	500.0	500.0	100.0
Construction material		ha	1.0	170.0	170.0	100.0
Total costs for establishment of the Technology					670.0

Comments:

Duration of establishment phase: 1 month(s)

4.6 Maintenance/ recurrent activities

	Activity	Type of measure	Timing/ frequency
1.	Dyke and spillway maintenance	Structural	Annually
2.	Reconstruction	Structural

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	150.0	150.0	100.0
Construction material		ha	1.0	50.0	50.0	100.0
Total costs for maintenance of the Technology					200.0

Comments:

The technology establishment and maintenance costs met by the land users are 100% if executed on a private basis, but it can range from 10 to 50% when the site is part of a publicly-funded programme.

4.8 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

Labour is the most determining factor affecting the costs.

5.1 Climate

5.2 Topography

5.3 Soils

If available, attach full soil description or specify the available information, e.g. soil type, soil PH/ acidity, Cation Exchange Capacity, nitrogen, salinity etc.

Soil fertility is: very low
Soil drainage/infiltration is: medium
Soil water storage is: medium

5.4 Water availability and quality

Comments and further specifications on water quality and quantity:

Water quality (untreated): Poor drinking water (treatement required/medium quality)

5.5 Biodiversity

5.6 Characteristics of land users applying the Technology

Indicate other relevant characteristics of the land users:

Land users applying the Technology are mainly common / average land users

Difference in the involvement of women and men: Outdoor hard works are generally performed by men.

Population density: 10-50 persons/km2

Annual population growth: 0.5% - 1%

10% of the land users are rich and own 10% of the land.
70% of the land users are average wealthy and own 75% of the land.
20% of the land users are poor and own 15% of the land.

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

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

Land ownership:

• individual, not titled
• individual, titled

Land use rights:

• individual

Water use rights:

• individual

5.9 Access to services and infrastructure

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

Income and costs

Other socio-economic impacts

Socio-cultural impacts

Ecological impacts

Water cycle/ runoff

Soil

6.2 Off-site impacts the Technology has shown

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
local windstorm	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	not well

Other climate-related consequences

Other climate-related consequences

	How does the Technology cope with it?
reduced growing period	well

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?

6.5 Adoption of the Technology

Of all those who have adopted the Technology, how many have did so spontaneously, i.e. without receiving any material incentives/ payments?

• 50-90%

Comments:

35% of land user families have adopted the Technology with external material support

65% of land user families have adopted the Technology without any external material support

There is a strong trend towards spontaneous adoption of the Technology

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
Improved production and expansion of cropping land.

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
This technique allows a rapid expansion of cropping lands in the piedmont and flat areas How can they be sustained / enhanced? encourage maintenance of existing structure.
Allows crop production in very dry environments (with less than 200 mm of rainfall) How can they be sustained / enhanced? encourage maintenance of existing structure.
Collects and accumulates water, soil and nutrients behind the tabia and makes it available to crops How can they be sustained / enhanced? encourage maintenance of existing structure.
Reduced damage by flooding How can they be sustained / enhanced? encourage maintenance of existing structure.

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?
Expansion is done at the expense of natural grazing land.

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be overcome?
Risks related to the climatic changes	it needs to be combined with supplementary irrigation.
Drought spells	Supplemental irrigation.
Land ownership fragmentation	new land access / agrarian reform.
Productivity of the land is very low	development of alternative income generation activities.
Risk of local know-how disappearance	training of new generations.

7.2 References to available publications

Title, author, year, ISBN:

Alaya, K., Viertmann, W., Waibel, Th. 1993. Les tabias. Imprimerie Arabe de Tunisie, Tunis, Tunisia. 192 pp.

Available from where? Costs?

IRA

Title, author, year, ISBN:

Ben Mechlia, N., Ouessar, M. 2004. Water harvesting systems in Tunisia. In: Oweis, T., Hachum, A., Bruggeman, A. (eds). Indigenous water harvesting in West Asia and North Africa, , ICARDA, Aleppo, Syria, pp: 21-41

Available from where? Costs?

IRA, ICARDA

Title, author, year, ISBN:

Ennabli, N. 1993. Les aménagements hydrauliques et hydro-agricoles en Tunisie. Imprimerie Officielle de la République Tunisienne, Tunis, 255 pp.

Available from where? Costs?

IRA, INAT

Title, author, year, ISBN:

Genin, D., Guillaume, H., Ouessar, M., Ouled Belgacem, A., Romagny, B., Sghaier, M., Taamallah, H. (eds) 2006. Entre la désertification et le développement : la Jeffara tunisienne. CERES, Tunis, 351 pp.

Available from where? Costs?

IRA, IRD

Title, author, year, ISBN:

Nasri, S. 2002. Hydrological effects of water harvesting techniques. Ph.D. thesis, Lund University, Sweden, 104 pp.

Available from where? Costs?

IRA, INRGREF

Title, author, year, ISBN:

Sghaier, M., Mahdhi, N., De Graaff, J., Ouessar, M. 2002. Economic assessment of soil and water conservation works: case of the wadi Oum Zessar watershed in south-eastern Tunisia.TRMP paper n° 40, Wageningen University, The Netherlands, pp: 101-113.

Available from where? Costs?

IRA

Title, author, year, ISBN:

Ouessar M. 2007. Hydrological impacts of rainwater harvesting in wadi Oum Zessar watershed (Southern Tunisia). Ph.D. thesis, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium, 154 pp.

Available from where? Costs?

IRA