According to the report of FAO AQUASTAT report on Yemen[1], there are over a thousand hydraulic structures including dams, spate water diversion structures and small water harvesting structures. : this category includes cisterns, pits and reservoirs with a storage capacity ranging from 500 m3 to 50 000 m3
Dams
In general, dams function to recharge groundwater, irrigation, as well as domestic uses; indeed, a recovery of the water level of shallow wells was observed inside the Sanaa basin. However, the National Water Sector Strategy and Investment Plan (NWSSIP) points out that in spite of the tremendous efforts to construct dams, they have not stopped the continuously declining levels of groundwater or helped replenish the depleted aquifers in many basins.
Based on the AQUASTAT report [2], there are 347 in Yemen. According to the capacity, the dams are divided into three categories:
- large dams with a capacity larger than 500 000 m3
- medium dams with a variable capacity from 200 000 to 500 000 m3
- small dams with a capacity of less than 200 000 m3.
Table 1 shows the major dams along with their capacities.
Table 1: Overview of major dams in Yemen [3]
| Name of the Dam | Location | Basin | Operation/ completion year | Height (m) | Capacity (MCM) |
| Semnah | Sana’a | Sana’a Basin | 1985 | 16 | 0.6 |
| Ma’areb | Marib | Arabian Sea Basin | 1987 | 40 | 400 |
| Raya’an | Sana’a | Sana’a Basin | 1993 | 22 | 1.02 |
| Al-Amerah | Taizz | Taiz Siham Basin | 1996 | 25 | 0.785 |
| Arishah | Sana’a | Sana’a Basin | 1997 | 13 | 0.5 |
| Bait Al-Khardal | Sana’a | Ma’areb BasinSana’a basin | 1999 | 20.5 | 2 |
| Ghayman | Sana’a | Sana’a Basin | 2001 | 15 | 0.73 |
| Al-Gargoor | Sana’a | Sana’a Basin | 2001 | 16 | 1 |
| Muogif | Al Mahwit | Tehama Surdud Basin | 2002 | 18 | 0.5 |
| Al-Wakr- AlHaythem | Sana’a | Sana’a Basin | 2002 | 17.2 | 0.54 |
| Al-Hajar | S,adah | Sa’ada Basin | 2004 | 23 | 0.777 |
Marib dam
Marib dam is the first water harvesting system in history built in the Arab region. Recent archaeological excavations discovered ruins of irrigation structures around Marib city dating from some 4,000 years ago. In the mountainous areas, villagers use harvested water for drinking, watering their animals and supplementary irrigation, particularly in the drier seasons. They mainly build cisterns to collect runoff from clear and carefully selected catchment areas well away from the villages to prevent pollution. Terraces are an ancient distribution system by which rainwater is diverted to basins where it is used to irrigate crops and feed drinking-water ponds, serve forest and grazing land and recharge local aquifers.[4]
An indigenous water knowledge project conducted at the Water and Environment Centre showed that traditional urban storm water collection in Sanaa’s Old City is considered the primary source of water for irrigating gardens growing crops, which are the main income source for the Old City’s farmers.[5]
Spate water diversion structures (Flood water harvesting)
Spate irrigation is an ancient water harvesting system by which floodwater is diverted from its river bed and channelled to basins where it is used to irrigate crops and feed drinking-water ponds, serve forest and grazing land and recharge local aquifers. In Yemen, large traditional spate systems consisting of numerous individual intakes and canals irrigating areas of up to 30 000 ha were developed in individual wadis. Sophisticated water sharing arrangements were formalized, with rules relating to water rights that exist in written records dating back at least 600 years. [6]
The spate irrigation areas in Yemen varies and difficult to measure, depending on the availability of the rainfall and floods water. The name of the diversion structures of the traditional spate irrigation system differ from area to area. The terms used depend on the size, order length, type of building material, shapes, way of built and position in the wadi. Examples of names are: Oqmas, Obars, Atm (in the coastal area), Saqiya (in Hadhramout and Shabwa) and Rozzum (in some parts of the highlands). The ‘Ogma’ is as earthen dyke (bund) constructed across the main stream of the wadi to divert the entire low stage flow of flood to be used in upper part of the wadis. While, the ‘Obar’ is a temporary bunds or spurs (a small earth fill embankment), it is used at wadis middle part, and the ‘Atum’ is a temporary earth spurs surrounding the field. [7]
Cistern system
Cistern system, locally called as Karif or Majel, in the mountainous area of Yemen, it is generally underground tank, constructed from masonry or concretes and usually covered and used for the collection and storage of surface run-off. [8]
Sanitation and wastewater treatment network
As mentioned above, Yemen has more than 17 urban and more than 15 rural wastewater treatment plants (WWTPs) in operation. Several others are under construction. It has been reported that waste stabilization ponds as a means of treating wastewater are underutilized, with more than 80% placed in nine urban and rural areas (Aden, al-Hodeidah, Bajil, Thamr, Yarim, al-Baidha, Radaa, Amran and Baitalfaqih). The other WWTPs are either activated sludge in Sanaa and Ibb, Imhoff tanks or trickling filters in Hajjah or a combination of more than one technology, such as Imhoff tanks followed by stabilization ponds as in Zabid, or septic tanks followed by stabilization ponds as in al-Mahwet [9]. Stabilization ponds are considered the best treatment process, with the potential to reduce pathogens in effluent to make it suitable for irrigation.[10] Furthermore, the WWTPs receive industrial and hospital wastewater from different facilities.
[1] FAO AQUASTAT, 2008, Country file -Yemen.
[2] IBID
[3] Available at: http://www.fao.org/aquastat/en/countries-and-basins/country-profiles/country/YEM. Accessed on: 27 November 2019
[4] Guidelines on Spate irrigation ,2010, FAO Irrigation and drainage paper. Available at: http://www.fao.org/3/i1680e/i1680e.pdf. Accessed on : 27 November 2019.
[5]Noman A.A., El-Din Saleh S.A (2009). Flood water uses in Yemen.
[6]Noman A.A., Indigenous knowledge for using and managing water harvesting techniques in Yemen
[7] Ministry of Water and Environment, 2010. Baseline Survey for Future Impact Evaluation. Sanaa Basin Water Management Project. MWE: 107.
[8]Al-Nozaily F.A., Al-Sabri A., Bola F., Al-Hakimi A., Al-Haddad A. (2014). Promotion of Indigenous knowledge in water Demand management for the historical Old Sana’a gardens (Maqashem). Journal of Engineering Sciences, 3 (1): 35-57, June 2014. ISSN 2312-9999.
[9] Al-Nozaily F et al., 2019. Sanitary Engineering 2, Sana’a university, College of Engineering. Lectures book, Aljeel Al-Jadeed publishers, third edition, Sana’a, Yemen
[10] Veenstra, S., Al-Nozaily, F. A. and Alaerts, G. J. (1995). Purple non-sulfur bacteria and their influence on waste stabilization ponds performance in the Republic of Yemen. Wat. Sci. Tech. Vol. 31 (12) pp. 141-149.