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

Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)

Good Practices in Soil and Water Conservation - A contribution to adaptation and farmers ́ resilience towards climate change in the Sahel (GIZ)

Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH (GIZ) - Germany

1.3 Conditions regarding the use of data documented through WOCAT

When were the data compiled (in the field)?

01/07/2012

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

Ja

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?

Nee

2.1 Short description of the Technology

Definition of the Technology:

Water-spreading weirs slow the flow of water, spread it over a wider area, increase infiltration and reduce erosion.

2.2 Detailed description of the Technology

Description:

The water-spreading weir technique was developed in Burkina Faso, Niger and Chad in the late 1990s and early 2000s. They are suitable as a land improvement measure for 90% of valleys in the Sahel area. These weirs regulate floodwater in medium-sized watercourses and in wider degraded valley bottoms with a pronounced low-water channel. They are constructed with local materials and have a spillway in the middle, abutments on either side and long wingwalls to spread the water over a large area.
In order to reverse the degradation process in a valley, it is necessary to ensure the comprehensive rehabilitation of the degraded parts of the valley. This is why the technique requires an overall assessment of the valley in order to identify the causes of degradation. In order to restore the water system in a degraded valley, a series of weirs is generally required.

Water-spreading weirs slow the flow of water in valleys and spread it over a wider area where it can infiltrate into the soil. In this way, they control river floodwater, and this reduces erosion and the loss of water. At the same time, sediments improve soil fertility and replenish the water table. When water flow is low in the valley, all the water passes over the spillway. When floodwater flow is stronger, the water is channelled towards the sides and flows over the outer lower wingwalls. When the floodwaters are at their heaviest, the water flows over even the higher walls. Downstream, the waters rejoin the low-water channel. Water-spreading weirs permit the reclamation and rehabilitation of degraded land and the restoration of vegetation cover. Thanks to the weirs, water flowing through the valleys can be used for crop growing, livestock raising and forestry.
Thanks to the infiltration of considerable amounts of water, water-spreading weirs contribute to raising the water table by several metres and improving ecological conditions in adjacent areas. As a result, vegetation cover is restored, which has a positive effect on biodiversity. By 2010, German cooperation had established water-spreading weirs in Niger to improve 10,000 hectares of land in valleys. Sorghum yields increased by between 50% and 100% per ha, from 400 kg to 800 kg per ha. The production of sorghum was 10 to 15 times higher in the improved areas than it had been before. As water-spreading weirs raise the water table, areas can be developed (or abandoned farmland restored) for market gardening and horticulture, with two or three crop harvests a year. The produce is used to supplement the food available and can also be sold (especially market garden produce).
The amount of time spent by women and girls fetching water is reduced by several hours a day. Horticulture generates extra income to cover family expenses, such as education and health care. Growing crops outside the rainy season generates work all year round, which reduces temporary migration.

This technique requires accurate preliminary studies to design the system. The more degraded the valley, the more complex the work is. Improving severely degraded valleys requires extensive experience, and any necessary technical adjustments must be made when flaws are detected.
If the weirs are built to a high standard, with a certain amount of upkeep, they will last. Major repairs are beyond the means of the communities, which is why commune authorities are often assigned the role of project owner. However, this is not yet a satisfactory solution, as in most countries in the Sahel, commune authorities are still weak.

This technique has great potential for climate change adaptation in two scenarios: 1) Water-spreading weirs distribute the watershed’s water over wide areas of land in the valley bottom. This enables water resources to be used more efficiently in low-rainfall periods, during dry spells and when the rainy season ends early. 2) In high-rainfall periods and/or in the event of heavy downpours, water-spreading weirs slow the flow of water, thereby preventing or reducing gully and river bank erosion and protecting areas downstream.

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.):

The water-spreading weir technique was developed in Burkina Faso, Niger and Chad in the late 1990s and early 2000s.
By 2010, German cooperation had established water-spreading weirs in Niger to improve 10,000 hectares of land in valleys.

3.1 Main purpose(s) of the Technology

• reduce, prevent, restore land degradation

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

Comments:

Major land use problems (compiler’s opinion): soil erosion by water and wind erosion, surface runoff, lack of infiltration, fertility decline
Constraints of common grazing land
Constraints of forested government-owned land or commons

3.3 Further information about land use

Water supply for the land on which the Technology is applied:

• mixed rainfed-irrigated

Number of growing seasons per year:

• 1

Specify:

Longest growing period in days: 120, Longest growing period from month to month: August to October

3.4 SLM group to which the Technology belongs

• irrigation management (incl. water supply, drainage)
• water diversion and drainage
• surface water management (spring, river, lakes, sea)

3.5 Spread of the Technology

Comments:

By 2010, German cooperation had established water-spreading weirs in Niger to improve 10,000 hectares of land in valleys

3.6 SLM measures comprising the Technology

Comments:

Specification of other structural measures: water-spreading weirs

3.7 Main types of land degradation addressed by the Technology

Comments:

Main causes of degradation: crop management (annual, perennial, tree/shrub) (Unadapted landuse methods, reduced or abandoned fallow periods), floods, droughts, population pressure (rapidly growing population increasing pressure on land), land tenure (insecure access to land)

3.8 Prevention, reduction, or restoration of land degradation

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

• restore/ rehabilitate severely degraded land

4.1 Technical drawing of the Technology

4.2 Technical specifications/ explanations of technical drawing

Water-spreading weirs are constructed with local materials and have a spillway in the middle, abutments on either side and long wingwalls to spread the water over a large area.

Technical knowledge required for field staff / advisors: high
Technical knowledge required for land users: low
Main technical functions: control of dispersed runoff: impede / retard, control of concentrated runoff: impede / retard, control of concentrated runoff: drain / divert, increase of infiltration, increase / maintain water stored in soil, increase of groundwater level / recharge of groundwater, water harvesting / increase water supply, water spreading
Secondary technical functions: improvement of ground cover

Dam/ pan/ pond
Depth of ditches/pits/dams (m): 1
Length of ditches/pits/dams (m): 50-100

4.3 General information regarding the calculation of inputs and costs

other/ national currency (specify):

CFA Franc

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

517.0

4.4 Establishment activities

	Activity	Type of measure	Timing
1.	accurate preliminary studies to design the system	Structural
2.	transport of stones	Structural
3.	construction of water-spreading weir	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
Other	total construction	ha	1.0	2901.0	2901.0	100.0
Total costs for establishment of the Technology					2901.0

4.6 Maintenance/ recurrent activities

	Activity	Type of measure	Timing/ frequency
1.	upstream watershed development to prevent sand filling of the bottomlands	Structural
2.	any necessary technical adjustments must be made when flaws are detected	Structural

4.8 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

The cost of improving land with water-spreading weirs is 0.25 to 1.5 million CFA francs per hectare (2901 US Dollar per ha). Labour:
• team formed by 25 people for 2 to 3 months, depending on the size of the structure.
Lorries to transport stones:
• 150 to 200 lorryloads (skip loader – 4.5 m3 per load) at a rate of 10 to 15 lorryloads a day.
Cost of construction:
• 1 medium-sized weir 50 m long and 1 m high with 200 m long wingwalls plus basin: 15 million CFA francs
• 1 weir 100 m long and 1 m high with basin: 30 to 32 million CFA francs
• stonework: 25,000 CFA francs/m3
• basin: 15,000 CFA francs/m3.

5.1 Climate

5.2 Topography

5.3 Soils

5.4 Water availability and quality

5.5 Biodiversity

5.6 Characteristics of land users applying the Technology

Indicate other relevant characteristics of the land users:

Population density: 10-50 persons/km2
Annual population growth: 3% - 4% (mostly poor households below poverty line).
Off-farm income specification: men migrate temporarily or permanently to cities for off-farm income
Growing crops outside the rainy season generates work all year round, which reduces temporary migration.

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:

traditional land use rights on fields, communal land on pasture and forest land

5.9 Access to services and infrastructure

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

Water availability and quality

Socio-cultural impacts

Ecological impacts

Water cycle/ runoff

Soil

Other ecological impacts

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	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

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

Comments:

There is a little trend towards spontaneous adoption of the Technology
In most countries in the Sahel, commune authorities are still weak. Without external support, the potential for replication is very low.

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
Growing crops outside the rainy season generates work all year round, which reduces temporary migration.
The amount of time spent by women and girls fetching water is reduced by several hours a day
If the weirs are built to a high standard, with a certain amount of upkeep, they will last

Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
Water-spreading weirs permit the reclamation and rehabilitation of degraded land and the restoration of vegetation cover. Suitable as a land improvement measure for 90% of valleys in the Sahel area.
Slow the flow of water in valleys and spread it over a wider area where it can infiltrate into the soil. The control of river floodwater reduces erosion and the loss of water.
sediments improve soil fertility and replenish the water table, vegetation cover is restored
As water-spreading weirs raise the water table, areas can be developed (or abandoned farmland restored) for market gardening and horticulture, with two or three crop harvests a year. The produce is used to supplement the food available and can also be sold (especially market garden produce).
Horticulture generates extra income to cover family expenses, such as education and health care.

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

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view	How can they be overcome?
The evaluation carried out by the FICOD (investment fund for local authorities) in 2010 highlighted the serious problem of sand filling siltation in valleys when additional measures are not implemented in a watershed’s upstream areas to ensure the overall development of the whole watershed area.	To ensure that the effectiveness of water-spreading weirs is long-lasting, upstream watershed development is essential to prevent sand filling of the bottomlands.
Major repairs are beyond the means of the communities, which is why commune authorities are often assigned the role of project owner. However, this is not yet a satisfactory solution, as in most countries in the Sahel, commune authorities are still weak.

7.1 Methods/ sources of information

7.2 References to available publications

Title, author, year, ISBN:

Good Practices in Soil and Water Conservation. A contribution to adaptation and farmers´ resilience towards climate change in the Sahel. Published by GIZ in 2012.

Available from where? Costs?

http://agriwaterpedia.info/wiki/Main_Page