Mamadou Abdou Sani
Programme d’Appui à l’agriculture Productive (PROMAP)/GIZ
有助于对技术进行记录/评估的项目名称（如相关）Manual of Good Practices in Small Scale Irrigation in the Sahel (GIZ )
有助于对技术进行记录/评估的机构名称（如相关）Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) - 德国
有助于对技术进行记录/评估的机构名称（如相关）Misereor - 德国
Permeable rock dams serve to restore seriously degraded farmland and forest/rangeland and are used to fill in gullies and control water flow.
The permeable rock dam is a structure built in gullies using loose rocks and stones and sometimes reinforced with gabions. A filtering layer (blanket of gravel or small stones) is laid in a foundation trench. Further layers of medium-sized and large stones and rocks are laid on top. They are between 0.50 and 3 metres high, and the width of the foundation and the crest depends on the estimated volume of water flow. The structure built across the gully is extended to the sides with the construction of wingwalls that spread the water over a larger area to the sides of the dam. The total width of the structure is generally at least three times its height. The dams can be constructed with or without a spillway. A spillway is required when flood water flow is stronger.
Purpose of the Technology: Permeable rock dams are used to fill in gullies and control water flow. They slow the flow of floodwaters and spread the water over adjacent land. This improves infiltration, and sediment builds up behind the dams. In time, the sediment fills in the gully. This stops lateral drainage from the land on either side, increasing its productivity. High infiltration upstream of the dam contributes to recharging the groundwater system. These structures are therefore also effective in raising the water table in wells and in protecting the bottom-lands from sand filling and gully erosion. They are used in combination with other measures, such as reforestation and stone bunds, to protect and improve the surrounding area, and to increase the area of land that can be used for growing crops.
By dissipating the flow of floodwaters, they ensure better use of rainwater and are therefore important in dry periods. The conservation of water for longer periods and the fine particles of earth trapped by the structure favour the establishment of natural vegetation along it, which helps to stabilise the dam. Seeds are also trapped, favouring the spontaneous growth of grass and trees upstream and downstream, which contributes to restoring and conserving biodiversity.
Establishment / maintenance activities and inputs: The sustainability of permeable rock dams depends on the quality of construction and whether they are maintained regularly. A certain amount of expertise and good community organisation is required to repair any cracks in
the dam. Biological measures (sowing grass and planting trees) increase the stability of the structure.
The size of a permeable rock dam can vary considerably from one site to another. The cost is also affected by the distance of the site from the quarry, the topography of the terrain and the actual amount of rock carried in each lorryload. It costs less to construct this type of structure with loose stones and rocks than with gabions.
developed, implemented and disseminated as part of projects and programmes undertaken from the 1980s onwards to combat desertification and improve natural resource management. Implemented by GIZ (German Federal Enterprise for International Cooperation), and PATECORE (project for land development and resource conservation in Plateau Central Burkina Faso)
Major land use problems (compiler’s opinion): soil erosion, surface runoff, unfertile land
Constraints of common grazing land
Constraints of forested government-owned land or commons
Longest growing period in days: 120, Longest growing period from month to month: August to October
Main causes of degradation: soil management (Unadapted land use methods, reduced or abandoned fallow periods), floods, droughts, population pressure (rapidly growing population increasing pressure on land), land tenure (insecure access to land)
Permeable rock dam with spillway
Technical knowledge required for field staff / advisors: moderate
Technical knowledge required for land users: low
Main technical functions: control of dispersed runoff: retain / trap, control of dispersed runoff: impede / retard, control of concentrated runoff: retain / trap, control of concentrated runoff: impede / retard, control of concentrated runoff: drain / divert, stabilisation of soil (eg by tree roots against land slides), increase in nutrient availability (supply, recycling,…), increase of infiltration, increase / maintain water stored in soil, increase of groundwater level / recharge of groundwater, water harvesting / increase water supply, sediment retention / trapping, sediment harvesting
Dam/ pan/ pond
Depth of ditches/pits/dams (m): 0.5-3
Width of ditches/pits/dams (m): 9
The size of a permeable rock dam can vary considerably from one site to another. The cost is also affected by the distance of the site from the quarry, the topography of the terrain and the actual amount of rock carried in each lorryload. The use of gabions also increases the cost considerably.
- Topographical surveying
- supply of quarry rock/stones: 113 m3 per 100 linear metres.
- Labour: depends on the size of the dam.
- Transportation by lorry: 23 lorryloads (skip loader – 4.5 m3 per load).
Other costs: Equipment (pickaxes, shovels, wheelbarrows, water-tube level, etc.).
- < 250毫米
- > 4,000毫米
Thermal climate class: subtropics
- 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.
Slopes on average: Also moderate (6-10%), rolling (11-15%)
Landforms: Also valley floors
Altitudinal zone: Also 1000-1500 m a.s.l.
- 非常深（> 120厘米）
Soil fertility: Medium and low
Soil drainage/infiltration: Medium and poor
Soil water storage capacity: Medium and low
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
- < 0.5 公顷
- 0.5-1 公顷
- 1-2 公顷
- > 10,000公顷
traditional land use rights on fields, common lands on pasture and forest land
Improved livelihoods and human well-being
As these dams are used in valley bottoms and the beds of seasonal streams to increase infiltration, they can also contribute to raising the water table. Such sites are particularly suitable for horticulture and market gardening, which is important in the off-season. The produce supplements the food available and is an extra source of income.
Physical structures can be biologically stabilized through planting of grass, bushes or trees. Damages are generally small but need to be repaired quickly.
There is a little trend towards spontaneous adoption of the Technology
Comments on adoption trend: The potential for replication depends on the type of terrain and whether there is a supply of rocks nearby.
|Permeable rock dams are used to fill in gullies and control water flow. They slow the flow of floodwaters and spread the water over adjacent land. This improves infiltration, and sediment builds up behind the dams. In time, the sediment fills in the gully which favours the establishment of natural vegetation along it, which helps to stabilise the dam. Seeds are also trapped, favouring the spontaneous growth of grass and trees upstream and downstream, which contributes to restoring and conserving biodiversity.|
|By dissipating floodwater flow, they also contribute to reducing sand filling in valleys further downstream.|
|As these dams are used in valley bottoms and the beds of seasonal streams to increase infiltration, they can also contribute to raising the water table. Such sites are particularly suitable for horticulture and market gardening, which is important in the off-season. The produce supplements the food available and is an extra source of income.|
|increase the area of land that can be used for growing crops|
|Depending on the size of the dam, the construction of this type of structure may require a high level of engineering expertise (topographical surveying, calculation of floodwater flow).It also requires a large amount of quarry rocks, which means that the cost of the structure and the labour and transport required is significantly higher than for structures made with stones. As the data required for calculating floodwater flow is often unavailable, the dams must be observed during the first few years, so that they can be reinforced and repaired if necessary.||It is important for farmers to have access to partners providing the necessary know-how, means of transport and support for community organisation. The community must be trained to carry out repair work.|
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.