Water-spreading weir (Axel Brückmann)
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.
Местоположение: Mali, Niger, Burkina Faso, Chad, Ethiopia, Мали
Число исследованных участков, где применяется Технология:
Пространственное распространение Технологии:
На постоянно охраняемой территории?:
Продолжительность применения Технологии: 10-50 лет назад
Тип внедрения/ применения
| Опишите затраты | Единица | Количество | Затраты на единицу (CFA Franc) | Общая стоимость на единицу (CFA Franc) | % затрат, оплаченных землепользователями |
| Другие | |||||
| total construction | ha | 1,0 | 2901,0 | 2901,0 | 100,0 |
| Общая стоимость запуска Технологии | 2'901.0 | ||||
| Общие затраты на создание Технологии в долларах США | 5.61 | ||||
Thanks to the weirs, water flowing through the valleys can be used for crop growing, livestock raising and forestry. 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.
