Water flowing through a traditional channel system (acequia) towards almond terraces (Joris de Vente)
Water shortage is one of the most limiting factors for sustainable agriculture in large parts of SE-Spain. Part of the solution of this problem may come from the restoration of traditional water harvesting structures. Many of these structures were widely used in SE-Spain already during Arab and Roman times, and are also widespread in N-Africa and the Middle East. However, nowadays in Spain many of them are abandoned and forgotten. Here, we describe the technology of a small earthen- or stone- built bund that diverts flood water from intermittent streams towards cultivated fields with almond orchards and/or cereals. The diverted water will temporarily flood the fields and provide the crops with water. Depending on the slope gradient and the amount of water to be harvested, the fields are organised as single terraces, or as a staircase of terraces. On fields with gradients above ~3%, terraces are necessary to reduce the gradient and to retain the floodwater as long as possible. Water is diverted from one terrace to the next through small spillways in the terrace. The spillways can best be fortified with stones to prevent bank gully formation. The extra input of surface water can double the almond yield. The use of these water harvesting structures is only possible under certain environmental and topographic conditions. The cultivated fields should be at a relatively short distance from an intermittent stream (<~50m), and the stream should have a sufficiently large upstream contributing area to provide significant amounts of runoff water during rainfall events. With these systems, water can be harvested up to 8 times per year, mostly in spring and autumn during high intensity rainfall events. A well designed Boquera system may provide up to 550 mm of additional water, in areas with an average annual rainfall of 300 m.
Purpose of the Technology: The goal of this technology is to increase crop yield. In addition, these structures help to reduce the intensity of floods and reduce the damage caused by them by reducing runoff volume in intermittent streams.
Establishment / maintenance activities and inputs: Water harvesting requires the identification of a suitable location for the construction of a diversion structure. This requires assessment of expected water inflow, which can usually be based on simple field observation during rainfall events and based on local knowledge of land users. It is, however, important to consider whether there are activities upstream that possibly affect the water quality (e.g. farm animals) and to assess the implications the water harvesting might have downstream. Permission is required from the water authorities to construct any type of water harvesting structure. Such structures are built by creating a small bund (<1m height) in the centre or to the side of a stream. Depending on the size, the bund can be built with a shovel or a tractor. The water harvesting structure will require control and some maintenance after each important runoff event. When strengthened with concrete, maintenance will be reduced to approximately once every 5 years.
Natural / human environment: Soils are mostly of shallow to medium depth (20-60 cm), and slopes are gentle to moderate (5-15%). The climate is semi-arid with a mean annual rainfall around 300 mm. Droughts, centred in summer commonly last for more than 4-5 months. Annual potential evapotranspiration rates larger than 1000 mm are common.
ទីតាំង: Guadalentin catchment, Murcia, ប្រទេសអេស្ប៉ាញ
ចំនួនទីកន្លែងបច្ចេកទេស ដែលវិភាគ:
ការសាយភាយនៃបច្ចេកទេស: ត្រូវបានផ្សព្វផ្សាយត្រឹមតំបន់មួយ (approx. < 0.1 គម2 (10 ហិកតា))
តើស្ថិតក្នុងតំបន់ការពារអចិន្ត្រៃយ៍?:
កាលបរិច្ឆេទនៃការអនុវត្ត: ច្រើនជាង 50 ឆ្នាំមុន (ប្រពៃណី)
ប្រភេទនៃការណែនាំឱ្យអនុវត្តន៍៖
| បញ្ជាក់ពីធាតុចូល | ឯកតា | បរិមាណ | ថ្លៃដើមក្នុងមួយឯកតា (EURO) | ថ្លៃធាតុចូលសរុប (EURO) | % នៃថ្លៃដើមដែលចំណាយដោយអ្នកប្រើប្រាស់ដី |
| កម្លាំងពលកម្ម | |||||
| Labour | 5 meter dyke | 1,0 | 150,0 | 150,0 | 100,0 |
| សម្ភារៈ | |||||
| Machine use | 5 meter dyke | 1,0 | 350,0 | 350,0 | 100,0 |
| សម្ភារៈសាងសង់ | |||||
| Concrete | 5 meter dyke | 1,0 | 400,0 | 400,0 | 100,0 |
| ថ្លៃដើមសរុបក្នុងការបង្កើតបច្ចេកទេស | 900.0 | ||||
| ថ្លៃដើមសរុបក្នុងការបង្កើតបច្ចេកទេសគិតជាដុល្លារ | 1'428.57 | ||||
| បញ្ជាក់ពីធាតុចូល | ឯកតា | បរិមាណ | ថ្លៃដើមក្នុងមួយឯកតា (EURO) | ថ្លៃធាតុចូលសរុប (EURO) | % នៃថ្លៃដើមដែលចំណាយដោយអ្នកប្រើប្រាស់ដី |
| កម្លាំងពលកម្ម | |||||
| Labour | 5 meter dyke | 1,0 | 4,0 | 4,0 | 100,0 |
| សម្ភារៈ | |||||
| Machine use | 5 meter dyke | 1,0 | 12,0 | 12,0 | 100,0 |
| សម្ភារៈសាងសង់ | |||||
| Concrete | 5 meter dyke | 1,0 | 25,0 | 25,0 | 100,0 |
| ថ្លៃដើមសរុបសម្រាប់ការថែទាំដំណាំតាមបច្ចេកទេស | 41.0 | ||||
| ថ្លៃដើមសរុបសម្រាប់ការថែទាំដំណាំតាមបច្ចេកទេសគិតជាដុល្លារ | 65.08 | ||||
Depending on the amount of water harvested yield may be the same or increase slightly
Implementation of dykes is considered relatively expensive
Water extraction by a water harvesting may cause less water at downstream locations, whihc may cause conflicts
during Roman and Arab times when most structures were operative they increased significantly the production. Nowadays, most of them are abandoned. However, those that are operational do cause increased crop yields.
For small flood events only
Possibly a small effect
If various structures are present in a stream and only for relatively low intensity events
