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)?

30/12/2008

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 technology of check dam is a technique consisting of binding different gabion cages filled with small stones together to form a complete flexible gabion unit.

2.2 Detailed description of the Technology

Description:

In order to slow down the water flow in the wadi courses and improve its infiltration into deeper soil layers and geologic formations, small check dams are installed on the wadi beds. They are usually positioned in series, with a spacing of 100-500m. These dams are made of gabion.
The gabion technique has been first introduced in the civil engineering domain. They are largely used since then and found many applications.
A gabion is a cage which has a cubic shape filled with stony material of suitable diameter enclosed in metal grating keeping the stones together and stops them from moving under the pressure of water. The gabion is normally the name of the cage only but it is also used frequently for the whole structure itself. The technique of gabion check dam consists in binding different cages together to form a complete gabion unit. The average height varies from 1 to 4 m and its length is a function of the width of the wadi bed (Royet, 1992).

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

Comments (type of project, etc.):

In the provinnce of Medenine, the first gabion check dams used for groudwater recharge and spreading have been constructed starting from 1985.

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

Comments:

Major land use problems (compiler’s opinion): -Degradation of soil and land cover
-Loss of water and soil ressources
-Flooding

Major land use problems (land users’ perception): Loss of water resources by flow out from the watershed

Future (final) land use (after implementation of SLM Technology): Cropland: Ct: Tree and shrub cropping

Constraints of wadi beds: floods

If land use has changed due to the implementation of the Technology, indicate land use before implementation of the Technology:

Grazing land: Ge: Extensive grazing land

3.3 Further information about land use

Number of growing seasons per year:

• 1

Specify:

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

3.4 SLM group to which the Technology belongs

• water harvesting
• irrigation management (incl. water supply, drainage)

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

Comments:

This technique is practiced in the Jeffara plain as well as in the mountain region.

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: Wg: gully erosion / gullying

Secondary types of degradation addressed: Wt: loss of topsoil / surface erosion, Wr: riverbank erosion, Wo: offsite degradation effects

Main causes of degradation: deforestation / removal of natural vegetation (incl. forest fires) (intensity)

Secondary causes of degradation: over-exploitation of vegetation for domestic use, overgrazing (degradation of land cover), Heavy / extreme rainfall (intensity/amounts)

3.8 Prevention, reduction, or restoration of land degradation

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

• prevent land degradation
• restore/ rehabilitate severely degraded land

Comments:

Main goals: rehabilitation / reclamation of denuded land
Secondary goals: prevention of land degradation
Third goal: mitigation / reduction of land degradation

4.1 Technical drawing of the Technology

4.2 Technical specifications/ explanations of technical drawing

Gabion check dam is made of galvanised blocks filled with stones.

Location: Jeffara plain. Medenine, Tunisia

Date: January 2009

Technical knowledge required for field staff / advisors: high

Technical knowledge required for land users: moderate

Main technical functions: increase of groundwater level / recharge of groundwater

Secondary technical functions: increase of infiltration, increase / maintain water stored in soil, water harvesting / increase water supply, water spreading, sediment retention / trapping, sediment harvesting

Dam/ pan/ pond
Vertical interval between structures (m): 3-5
Spacing between structures (m): 100-500
Height of bunds/banks/others (m): 1-4
Width of bunds/banks/others (m): 4-6
Length of bunds/banks/others (m): 30-100

Construction material (stone): The average length varies between 15 and 30 cm

Construction material (other): Gabion: Galvanised cages of 1 to 3 m3.

Slope (which determines the spacing indicated above): 3-8%

Lateral gradient along the structure: <1%

Specification of dams/ pans/ ponds: Capacity 5000-15000m3

Catchment area: 1-3 ham2

Beneficial area: 30-100ham2

Other specifications: The whole structure has the form of a spillway.

4.3 General information regarding the calculation of inputs and costs

other/ national currency (specify):

Tunisian Dinars

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

1.3

4.4 Establishment activities

	Activity	Type of measure	Timing
1.	Topographic survey and selection of the site	Structural
2.	Digging of the basement	Structural
3.	Gabion installation	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	Dam	1.0	5000.0	5000.0	100.0
Construction material	Construction material	dam	1.0	5000.0	5000.0	100.0
Construction material	Gabion cages	dam	1.0	10000.0	10000.0	100.0
Total costs for establishment of the Technology					20000.0

Comments:

Duration of establishment phase: 1.5 month(s)

4.6 Maintenance/ recurrent activities

	Activity	Type of measure	Timing/ frequency
1.	Repair of breaks	Structural	each 1 to 2 years
2.	Reconstruction	Structural	After heavy floods (once in 5-10 years)

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	dam	1.0	500.0	500.0	100.0
Construction material	construction material	dam	1.0	500.0	500.0	100.0
Construction material	Gabion cages	dam	1.0	1000.0	1000.0	100.0
Total costs for maintenance of the Technology					2000.0

Comments:

Machinery/ tools: Generally, the work is manual but tractors can be used too.

4.8 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

construction materials

5.1 Climate

5.2 Topography

5.4 Water availability and quality

Comments and further specifications on water quality and quantity:

Availability of surface water: excess, medium, poor/ none (The wadi is almost always dry)
Water quality (untreated): Poor drinking water (treatement required) (from cisterns and wells) but good drinking water if pumped in the deep aquifer (100-300m)

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: Historically, the hard work is done by men.

Population density: 10-50 persons/km2

Annual population growth: < 0.5%

30% of the land users are rich and own 50% of the land.
60% of the land users are average wealthy and own 30% of the land.
10% of the land users are poor and own 20% of the land.

Off-farm income specification: Off-farm incomes come from migration, construction works, commerce, tourism sector, administration or informal activities.

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:

• state

Land use rights:

• communal (organized)

Water use rights:

• communal (organized)

Comments:

Generally, this technology is applied in the wadi beds which is considered as state owned but the local community can have access.

5.9 Access to services and infrastructure

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

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)

Climate-related extremes (disasters)

Meteorological disasters

	How does the Technology cope with it?
local rainstorm	well

Hydrological disasters

	How does the Technology cope with it?
general (river) flood	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)?

Comments:

Gabion chech dams are financed by the State

6.5 Adoption of the Technology

Comments:

Comments on acceptance with external material support: This technology is supposed to be implemented solely by the government agencicies but in some cases the farmers can make use of it.

Comments on spontaneous adoption: This technology is supposed to be implemented solely by the government agencicies but in some cases the farmers can make use of it.

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
Efficient structures How can they be sustained / enhanced? Regular and good maintenance

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
Robust and flexible structures How can they be sustained / enhanced? Regular and good maintenance

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?
They can not be fully exploited by the farmers	Change regulations.
Very expensive and cost not affordable by normal farmers	Continue subsidising by the government.

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be overcome?
Accumulation of sediments	Desilting

7.2 References to available publications

Title, author, year, ISBN:

Yahyaoui, H., Chaieb, H., Ouessar, M. 2002. Impact des travaux de conservation des eaux et des sols sur la recharge de la nappe de Zeuss-Koutine (Sud-est tunisien). TRMP paper n° 40, Wageningen University, The Netherlands, pp: 71-86.

Available from where? Costs?

IRA - Medenine; DGRE - Tunis

Title, author, year, ISBN:

Boufelgha et al. 1998. Comportement des ouvrages CES dans le bassin versant d’oued Koutine lors de la crue d'Octobre 1998. Rapport interne, CRDA, Médenine

Available from where? Costs?

CRDA Médenine

Title, author, year, ISBN:

Chniter et al. 2007. Comportement des ouvrages CES dans le bassin versant d’oued Oum Zessar lors de la crue de 22 Février 2007. Rapport interne, CRDA, Médenine

Available from where? Costs?

CRDA Médenine

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:

Mahdhi, N., Sghaier, M, Ouessar, M. 2000. Analyse d’impacts des aménagements de CES en zone aride: cas du bassin versant d’Oued Oum Zessar. Technical report, WAHIA project, IRA, Tunisia.

Available from where? Costs?

IRA

Title, author, year, ISBN:

Yahyaoui, H., Ouessar, M. 2000. Abstraction and recharge impacts on the ground water in the arid regions of Tunisia: Case of Zeuss-Koutine water table. UNU Desertification Series, 2: 72-78.

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 - Médenine;