1.2 参与该技术评估和文件编制的资源人员和机构的联系方式

有助于对技术进行记录/评估的项目名称（如相关）

Book project: Water Harvesting – Guidelines to Good Practice (Water Harvesting)

1.3 关于使用通过WOCAT记录的数据的条件

（现场）数据是什么时候汇编的？:

08/03/2012

编制者和关键资源人员接受有关使用通过WOCAT记录数据的条件。:

是

2.1 技术简介

技术定义:

Water-spreading weirs are structures that span the entire width of a valley to spread floodwater over the adjacent land area.

2.2 技术的详细说明

说明:

Over the last 12 years water-spreading weirs have been introduced and improved as a new rehabilitation technique for degraded dry valleys in Burkina Faso, Niger and Chad. In Chad 104 water-spreading weirs were constructed in the scope of the two development projects, initiated by the German Technical Cooperation (GIZ) and the Swiss Development Cooperation (SDC) in the 1990s. Water-spreading weirs are made of natural stones and cement, and 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 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 groundwater table also rises in a few years.

Purpose of the Technology: In dry valleys in which water flows in the rivers for only a few days a year, the weirs serve to distribute the incoming runoff over the valley floor and allow as much water as possible to infiltrate the soil. The aquifer is thus replenished and is then available for agricultural use. In contrast to the various types of dams, the goal of water-spreading weirs is not to create reservoirs for later use. What water-spreading weirs do is cause a temporary flooding of the adjacent land area above and below the weir. Depending on user preferences, the primary goal may be 1) agricultural use, 2) sylvo-pastoral use or 3) the replenishment and rising of the water table.

Establishment / maintenance activities and inputs: Water-spreading weirs require detailed technical planning and experienced engineering and construction firms. The bulk of the work is performed using local materials and by village craftsmen and helpers.

Natural / human environment: Compared to small impoundment dams, retention basins and microweirs, water-spreading weirs are especially well-suited for shallow, wide valleys that, due to severe gully erosion, are no longer inundated by small and medium
volume floodwaters. The flooding no longer takes place because the actual riverbed has been deeply eroded and enlarged. However, water-spreading weirs are also suitable for improving agricultural productivity in more or less intact valley floors. Water-spreading weirs are successful in regions where precipitation during the growing season is erratic and where the weirs ensure a more evenly distributed water supply for crops, as well as in zones in which water enrichment makes one or two additional growing seasons possible. At the present time they are in use in a broad area where annual rainfall ranges from 50 to 1,200 mm/year.

2.3 技术照片

2.5 已应用该技术的、本评估所涵盖的国家/地区/地点

2.6 实施日期

如果不知道确切的年份，请说明大概的日期:

• 10-50年前

2.7 技术介绍

详细说明该技术是如何引入的:

• 通过项目/外部干预

注释（项目类型等）:

The first water-spreading weirs were introduced during the 1990s in Chad through Swiss cooperation

3.1 该技术的主要目的

• 改良生产
• 减少、预防、恢复土地退化

3.2 应用该技术的当前土地利用类型

注释:

Major land use problems (compiler’s opinion): Substantial degradation of drainage basins in the Sahel due to population growth and intense land-use pressure has been observed since the 1960s. Climate change has further amplified this trend. 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. 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.

3.3 有关土地利用的更多信息

其它（比如洪水后）:

• Post-flooding

注释:

Water supply: Also mixed rainfed - irrigated and rainfed

3.4 该技术所属的SLM组

• 横坡措施
• 灌溉管理（包括供水、排水）
• 引水和排水

3.5 技术传播

具体说明该技术的分布:

• 均匀地分布在一个区域

如果该技术均匀地分布在一个区域上，请注明覆盖的大致区域。:

• 10-100 平方千米

注释:

Total area covered by the SLM Technology is 20 m2.

The technology has been applied in 22 different valleys in Eastern Chad. The total area that profits from the installation of one such structure is therefore somewhere between 10 and 100 ha.

3.6 包含该技术的可持续土地管理措施

3.7 该技术强调的主要土地退化类型

注释:

Main type of degradation addressed: Wt: loss of topsoil / surface erosion, Wg: gully erosion / gullying, Hg: change in groundwater / aquifer level

Main causes of degradation: soil management (abandonment of fallow periods), deforestation / removal of natural vegetation (incl. forest fires) (for agricultural expansion), over-exploitation of vegetation for domestic use, droughts, population pressure

Secondary causes of degradation: overgrazing

3.8 防止、减少或恢复土地退化

具体数量名该技术与土地退化有关的目标:

• 减少土地退化
• 修复/恢复严重退化的土地

注释:

Main goals: rehabilitation / reclamation of denuded land

Secondary goals: mitigation / reduction of land degradation

4.1 该技术的技术图纸

4.2 技术规范/技术图纸说明

Water-spreading weir with spillway, lateral abutments and wing walls.

Technical knowledge required for field staff / advisors: high

Main technical functions: control of dispersed runoff: retain / trap, control of dispersed runoff: impede / retard, increase of groundwater level / recharge of groundwater, water harvesting / increase water supply, water spreading, sediment retention / trapping, sediment harvesting

Secondary technical functions: increase of infiltration, spatial arrangement and diversification of land use

Dam/ pan/ pond
Height of bunds/banks/others (m): 0.75
Width of bunds/banks/others (m): 5
Length of bunds/banks/others (m): 500

4.4 技术建立活动

	活动	措施类型	时间
1.	Excavating the steps	结构性的
2.	Excavating the wall foundations	结构性的
3.	Pouring the foundations	结构性的
4.	Building the walls	结构性的
5.	Finishing the walls and filling the stilling basin	结构性的

4.5 技术建立所需要的费用和投入

	对投入进行具体说明	单位	数量	单位成本	每项投入的总成本	土地使用者承担的成本%
劳动力	Labour	ha	1.0	750.0	750.0	100.0
设备	Total costs for equipment	ha	1.0	750.0	750.0
施工材料	Stone	ha	1.0	750.0	750.0
技术建立所需总成本					2250.0

4.7 维护/经常性活动所需要的费用和投入（每年）

	对投入进行具体说明	单位	数量	单位成本	每项投入的总成本	土地使用者承担的成本%
劳动力	Labour	ha	1.0	50.0	50.0	100.0
设备	Total costs for equipment	ha	1.0	50.0	50.0
施工材料	Stone	ha	1.0	50.0	50.0
技术维护所需总成本					150.0

注释:

The costs were calculated per structure (one diversion weir). The length of the weir varies depending on the width of the valley it is constructed in. The weir has to span the whole valley which is usually between 100 and 1000 m wide.

5.1 气候

5.2 地形

5.3 土壤

如有可能，附上完整的土壤描述或具体说明可用的信息，例如土壤类型、土壤酸碱度、阳离子交换能力、氮、盐度等。:

Soil fertility: High
Soil drainage/infiltration: Medium (ranked 1) and good (ranked 2)
Soil water storage capacity: Medium

5.4 水资源可用性和质量

关于水质和水量的注释和进一步规范:

Availability of surface water: excess (during heavy rainfalls in the rainy season) or poor/ none (in the dry season)

5.5 生物多样性

5.6 应用该技术的土地使用者的特征

说明土地使用者的其他有关特征:

Population density: < 10 persons/km2
70% of the land users are poor.
Market orientation: Mixed (rainfed crops are for subsistence, post-rainy season crops and irrigated crops (vegetables) mainly for market)

5.7 应用该技术的土地使用者拥有或租用的平均土地面积

5.8 土地所有权、土地使用权和水使用权

土地所有权:

• 社区/村庄

土地使用权:

• 租赁

注释:

In Chad, only the rainfed fields are in private family ownership and inheritable. Reclaimed irrigated fields and vegetable production fields go back to the community and can be redistributed.

6.1 该技术的现场影响

社会经济效应

生产

收入和成本

其它社会经济效应

社会文化影响

生态影响

水循环/径流

土壤

生物多样性:植被、动物

6.2 该技术的场外影响已经显现

6.3 技术对渐变气候以及与气候相关的极端情况/灾害的暴露和敏感性（土地使用者认为的极端情况/灾害）

渐变气候

渐变气候

	季节	气候变化/极端天气的类型	该技术是如何应对的？
年温度		增加	好

气候有关的极端情况（灾害）

气象灾害

	该技术是如何应对的？
局地暴雨	好
局地风暴	好

水文灾害

	该技术是如何应对的？
比较和缓的（河道）洪水	好

6.4 成本效益分析

技术收益与技术建立成本相比如何（从土地使用者的角度看）？

技术收益与技术维护成本/经常性成本相比如何（从土地使用者的角度看）？

注释:

Depending upon the users' experience and the availability of labour, it may take anywhere from 2 to 10 years before the rehabilitated land area reaches its optimum use potential.

6.5 技术采用

在所有采用这项技术的人当中，有多少人是自发地采用该技术，即未获得任何物质奖励/付款？:

• 0-10%

注释:

100% of land user families have adopted the Technology with external material support

6000 land user families have adopted the Technology with external material support

Comments on acceptance with external material support: Between 4000 and 8000 households are direct beneficiaries of the construction of water-spreading weirs in Eastern Chad.

There is no trend towards spontaneous adoption of the Technology

Comments on adoption trend: It is unlikely that communities will be able to adopt this technology without external funding. Even for maintenance activities it remains to be seen if the communities will be capable of funding more extensive maintenance work with their low budgets.

6.7 该技术的优点/长处/机会

编制者或其他关键资源人员认为的长处/优势/机会
Through the construction of water-spreading weirs, soils are regularly flooded and supplied with water and sediment. Thus, the arable land area and the yields of the rainy season crops serving as staple food increase. How can they be sustained / enhanced? Ensure proper maintenance of the system.
The more frequent flooding of the soils results in increased infiltration, and the groundwater level rises substantially.
Prior to rehabilitation, in most of the sites, it was only possible to grow a rainfed crop and perhaps an irrigated crop on some small areas of land. After, in addition to the rainfed crop grown on larger areas of land, it became possible to grow a post-rainy season crop (culture de contresaison) and, once the water table had risen, an irrigated crop (culture de décrue) as well. How can they be sustained / enhanced? Upscale water-spreading weirs to increase the number of people benefitting.
Post-rainy season crops and irrigated crops diversify agricultural production. They are used as a means of earning cash income. How can they be sustained / enhanced? Improve access to markets.
With their capacity to regulate annual floodwaters and harness them to stabilise production, water-spreading weirs are an effective measure for adapting to climate change in regions experiencing increasing variability in rainfall.

6.8 技术的弱点/缺点/风险及其克服方法

编制者或其他关键资源人员认为的弱点/缺点/风险	如何克服它们？
It can be assumed that one third of the weirs will require complete renovation every 20 years	The renovation of these weirs can be done for approximately 10% of the initial construction costs
Maintenance of the weirs by the management committees is still a weak area. Funds expected from user fees for the plots are often inadequately collected and too low to cover costs. Some management committees lose their drive and neglect their duties.	New fundings sources have to be found and tapped.
In spite of the great potential for the use of water-spreading weirs and the very promising results, implementation will continue to depend in the medium term on outside funding, as it is unlikely that the communal budgets will be able to fund investments of this size.	The existing knowledge hast to be spread.
Know-how and experience for the construction of water-spreading weirs are still concentrated among a few countries.

7.2 参考可用出版物

标题、作者、年份、ISBN:

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) (2011). Water-spreading weirs for the development of degraded dry river valleys. Experience from the Sahel. Frankfurt and Eschborn, GIZ and KFW.

可以从哪里获得?成本如何?

http://www.gtz.de/de/dokumente/giz2012-en-water-spreading-weirs-sahel.pdf

标题、作者、年份、ISBN:

Direction du développement et de la coopération DDC (2012). Gestion des eaux de ruissellement dans le Tchad sahélien. Bern, DDC.

可以从哪里获得?成本如何?

http://www.gopa.de/uploads/tx_bdojobopps/PRODOC_Tchad.pdf