Brève description de la meilleure pratique

Water-spreading weirs are structures that span the entire width of the
valley. They consist of a spillway in the actual riverbed and lateral abutments and wings.
Floodwaters are spread over the adjacent land area above the structure, where they eventually overflow the lateral wings and then slowly flow back towards the riverbed below the structure.
As a result the land area below the waterspreading weir is flooded. The lateral spreading of the water causes the land area above and below the structure to be flooded and supplies it with sediment. Water infiltrates, gullies in the valley are filled and the riverbed is raised.
Thanks to the infiltration, the water table also rises in a few years.
Water-spreading weirs alter the basic runoff and sedimentation processes in the valley.
Specific adaptation to the various alterations of natural processes and agricultural optimisation of the water-spreading weirs are frequently beyond the scope of a single construction campaign,
and subsequent adaptations may be required. In constructing water-spreading weirs, the first step is to identify basically suitable valleys in a region and inform the respective villages, communities and technical services about the possibilities and prerequisites for rehabilitation. Interested communities then submit a written request to the project in charge, which is examined by an approval committee. The socioeconomic conditions and structures in the valley and the willingness of the local people to cooperate are assessed in the subsequent feasibility study. Then the basic construction parameters are defined and the anticipated
costs are estimated in a preliminary technical study. The information delivered by these studies provides the basis for the final approval of the construction.

Site

Sahel, project has been implemented in Burkina Faso, Niger and Chad |

Brève description de l’environnement naturel du site

Sahel region, arid climate with unregular rainfall|
The expansion of agriculture and intensification of grazing and logging have caused the natural vegetation cover to decline.
This process has been accelerated by severe droughts and has led to the degradation of the soils. Sparse vegetation cover and structurally damaged soils reduce rainfall infiltration into the soil, resulting in more runoff and soil erosion on plateaus and slopes|
wide and shallow dry valleys

Conditions socio-économiques dominantes des personnes vivant sur ou à proximité du site

communal areas are used as pasture and individual plots for agriculture
subsistence farming, animal husbandry|
GDP ranging between 626$ per capita in Niger to 1078$ in Burkina Faso and 1181$ in Chad.

Sur la base de quel critère/indicateur(s) (sans relation avec la stratégie) la pratique proposée et technologie correspondante ont-elles été considérées comme « meilleures »?

no comment

Principaux problèmes abordés par la meilleure pratique

1. degradation of drainage basins in the Sahel due to population growth and intense land-use pressure
2. structurally damaged soil with reduced rainfall infiltration into the soil resulting in more runoff and soil erosion on plateaus and slopes
3. Runoff is concentrated in the valleys, in which heavy floodwaters wash away fertile soils and lead to deep erosion of the riverbed
4.less infiltration in the valley leads to droping water table which harms the vegetation and limits the agricultural use|

Décrivez les principaux problèmes liés à la dégradation des terres abordés par la meilleure pratique

Sparse vegetation cover and structurally damaged soils reduce rainfall infiltration into the soil, resulting in more runoff and soil erosion on plateaus and slopes. Runoff is concentrated
in the valleys, in which heavy floodwaters wash away fertile soils and lead to deep erosion of the riverbed. The annual, recurrent small and medium-size floods that normally cause temporary inundation of the valleys and deposition
of fertile sediments no longer occur. Due to the rapid runoff of the water, there is also less infiltration in the valley and the water table there drops. This in turn harms the natural vegetation and limits agricultural use. Within a few years
fertile valleys turn into desert-like landscapes.|

Précisez les objectifs de la meilleure pratique

1. sustainable improvement of economic situation and living conditions through higher crop yields which leads to higher income
2. the local population improves their nutritional base
3. ecological improvements: reclamation of soil and reduced soil erosion, more natural vegetation and biodiversity

Brève description des principales activités, par objectif

The activities can not be separated and allocated to only one objective. All objetives are reached through the described best practice measure.  

Brève description et caractéristiques techniques de la technologie

A series of preparatory steps is necessary before construction of the weirs can start. The technical planning starts with a preliminary technical study once the people of a valley on an extensive area of the valley floor have agreed to the rehabilitation work. In the scope of the preliminary technical study, the approximate sites of the weirs, the weir type and the rough dimensions are determined, wherein it is necessary to gauge how the individual weirs will interact. This ultimately leads to the overall design of the planned series of water-spreading weirs. The inundation area to serve as potential production area is determined, and the cost of the entire system is estimated using per hectare cost values derived from experience. The soil quality and the depth of the water table are assessed and the anticipated impact of the weirs on the groundwater level is estimated. Groundwater levels that can be raised rapidly and clayey soils are indicative of valleys with a high production potential of up to three possible harvests. After a valley is selected, the next step is the detailed technical study, which is necessary for preparing the tender documents. In this study the type of weirs and the dimensions of the structures are established and the exact sites of the individual water-spreading weirs are marked on the landscape. The cross-section of the valley at the height of each weir is measured. The individual plans of the water-spreading weirs are drawn. Next steps are the construction of the water-spreading weirs and supplemental erosion protection measures Agricultural, providing of consultancy Support and monitoring of the implementation of the master plan.|

Nom et adresse de l’institution développant la technologie

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH|Dag-Hammarskjöld-Weg 1-5
65760 Eschborn
Friedrich-Ebert-Allee 40
53113 Bonn

La technologie a-t-elle été développée en partenariat ?

Oui

Dressez la liste des partenaires :

Swiss Development Cooperation

Précisez le cadre de promotion de la technologie

• Initiative locale
• Initiative nationale – gouvernementale
• Initiative basée sur un programme/projet

La participation des parties prenantes locales, y compris des OSC, a-t-elle été recherchée au cours du développement de la technologie ?

Oui

Dressez la liste des parties prenantes locales:

management committee consisting of village representatives and the municipal authority
local engineering and construction firms
local craftsmen
local authorities

Précisez le rôle des parties prenantes ci-dessus dans la conception, l’introduction, l’utilisation et la maintenance de la technologie, le cas échéant.

The management committee serves as the contact partner for the project, government agencies and construction companies. It is responsible for establishing rules of use and for organising the people during the construction, use and maintenance of the weirs. Diverse organisational-administrative training sessions on topics such as rights and duties, planning and administration, and also technical training sessions on the use and maintenance of weirs are provided to the committees. The committees collect and administer the plot fees paid by all users and organise minor maintenance and repair work. Local Craftsmen and masons are trained by experienced professionals. Engineering firms are contracted to conduct the planing and hire local craftsmen.  |

La population vivant sur ou à proximité du site a-t-elle été impliquée dans le développement de la technologie?

Oui

Par quels moyens?

• Consultation
• Approches participatives
• Autre (précisez)

Précisez:

Intensive involvement through on-site discussion and problem solving to transfer the responsibility for the weirs to the local level which shall ensure the long-term effect of the project.

Décrivez les impacts sur site (les deux principaux impacts par catégorie)

Less use pressure on other land areas
More soil moisture availableto plants
"More groundwater, More and longer-lasting
bodies of surface water"
More nutrients, reclamation of soil
"The economic situation is improved through higher crop yields: An additional irrigated crop is possible,
Higher productivity of rainfed and postrainy season crops,
More arable land available, Reduced costs for well construction,  Diversification in crops, Temporary income
improvement (HIMO)
"Greater and secure production
of staple foods, Market crop production improved,
Easier access to valley plains (vegetable production), Additional income, Year-round employment, Creation of new activities/jobs
"In Niger the total land area farmed during the dry season increased from an average of 0.15 ha to 0.49 ha per user.18
Assuming 20% increases in vegetable crop yields
(by a factor of 1.2) and an expansion of the land
area by a factor of 3.3.
Water-spreading weirs increase and diversify
production by expanding the arable land,
increasing per hectare yields, and enabling
2 to 3 harvests per year. Water-spreading weirs increase per hectare yields through the better water supply and
the annual deposition of fine soil and organic
matter. |
social component: improvement of living conditions of local people through higher crop yields: Capacity-building
Year-round acces to the village, Easier access to water for
drinking and watering livestock,  Workload of women
(fetching water) eased, Food security assured
through crop and livestock |
"Distribution of water
over the valley plain, Reduced soil erosion"
Runoff rate slowed, Deposition of fertile sediments
Greater water infiltration, Filling in of gullies
More natural vegetation and greater biodiversity

Décrivez les deux principaux impacts hors site (dans les environs)

The waterspreading wears reduce the erosion by the reduced rate of runoff.
The waterspreading wears rise the groundwater level which has positive effects on the productivity of grown plants.

Impact sur la biodiversité et le changement climatique

Décrivez:

According to current climate change projections,
the temperature in West Africa, including
Burkina Faso, Niger and Chad, is expected to be
2.5 to 3.5 °C higher by the end of the century.
Depending on the region, absolute precipitation
will increase or decrease slightly, but the
variability in precipitation within and between
years is expected to increase in every country.20
The evaporation of water will also increase
due to the higher temperatures. Furthermore,
intense precipitation events and hence surface
runoff will continue to increase, whereas
the duration and consistency of the rainy
seasons will decrease. Water management in
arid regions will therefore become more critical.
Water-spreading weirs effectively buffer
peak runoffs from the drainage basins, reduce
erosion and improve the availability of water
for people, livestock, agriculture and nature.
The ecological improvement of alluvial plains
protects against changes in environmental
conditions and stabilises the food supply and
the living conditions of the local population.
Water-spreading weirs are therefore effective
measures for adapting to climate change.

Une analyse coût-avantage a-t-elle été réalisée?

Une analyse coût-avantage a-t-elle été réalisée? :

Non

La technologie a-t-elle été diffusée/introduite sur d’autres sites?

La technologie a-t-elle été diffusée/introduite sur d’autres sites? :

Oui

Où?

Chad, Burkina Faso, Niger|

Des mesures d’incitation ont-elles été mises en place pour faciliter le lancement de la technologie?

Des mesures d’incitation ont-elles été mises en place pour faciliter le lancement de la technologie?

Oui

Précisez le type de mesure d’incitation:

• Mesures d’incitation financières (telles que des taux préférentiels, aide d’État, subventions, dons, prêts, etc.)

Pouvez-vous identifier les trois principales conditions ayant favorisé la réussite de la meilleure pratique/technologie présentée?

"The ongoing funding and improvement of the
initial approach by a long-term project as key factors in the development of water-spreading weirs."

Réplication

Selon vous, la meilleure pratique/technologie proposée peut-elle reproduite, y compris avec un certain degré d’adaptation?

Oui

Si oui, à quel niveau?

• Local
• National
• Régional

Liées aux ressources humaines

1. The participatory approach, with all stakeholders involved as much as possible, generates a greater sense of ownership and lays the foundations for successful future use and (within limits) maintenance
2. The fact that the measures were implemented in regions where the local people had already been organised and trained to some extent in land-use planning and selfhelp measures in the scope of a previous project(PDRT) helped in Niger

Liées aux aspects techniques

1. technical measures and the ‘software’ (advisory and organisational components) were improved through financial
and technical cooperation, respectively, thus enabling initial weaknesses in the approach to be remedied
2. important were the professional skills of all parties involved and the personnel continuity of the participating international and national engineering firms, as well as their willingness of the latter to share acquired know-how