Spate Irrigation

As spate irrigation uses seasonal floods for irrigation, it is akin but different from the other categories of flood-based irrigation systems. In spate irrigation water is diverted from normally dry river beds (wadi’s) when the river is in spate. The flood water is then diverted to the fields. This may be done by free intakes, by diversion spurs or by bunds, that are build across the river bed. The flood water – typically lasting a few hours or a few days – is channeled through a network of primary, secondary and sometimes tertiary flood channels. Command areas may range from anything between a few hectares to over 25,000 hectares.

Where does one find Spate irrigation?

Spate irrigation occurs in areas as varied as South Asia, the Middle East, West Africa, North Africa, the Horn of Africa, Central Asia and Latin America. Estimates for the area under flood irrigation are not easy to make, as the area under spate irrigation changes from year to year and as spate irrigation has never had the amount of attention from development agencies or tax authorities, that perennial irrigation has had. Spate irrigation is typically found in arid and semi-arid regins, where highlands border plains. It uses seasonal floods for irrigation – but as the floods differ from year to year the area served by it fluctuates widely.

The most comprehensive information on how much spate irrigation there is comes from FAO.

Country Year Area under Spate Irrigation in Hectares
Algeria 2008 53,000
Eritrea 2004 16,000
Ethiopia 2007 140,000
Iran 2008 450,000 – 800,000
Morocco 2008 79,000
Pakistan 1999 640,000 – 1,280,000
Somalia 1984 150,000
Sudan 2007 132,000
Tunisia 1991 30,000
Yemen, Rep. of 1999 117,000
Mongolia 1993 27,000
Kazakhstan 1994 0
Tajikistan 2002 0
Turkmenistan 1994 0
Uzbekistan 1996 0

Sources: FAO Aquastat and “Spate Irrigation, Livelihood Improvement and Adaptation to Climate Change Variability.

The figures for these selected countries indicates an order of magnitude. Some figures are debatable. The area under spate irrigation in Eritrea is also quoted as 90,000 ha. For Pakistan – where spate irrigation is found in all four provinces – an estimate of 3.250,000 has been mentioned by other sources. Further spate irrigation is reported from North Chile and Bolivia, Iran, Afghanistan, Mauretania and Senegal, Ethiopia, Kenya and the Northwest coast of Egypt.

How are spate irrigation systems managed?

Some of the larger spate irrigation rank among the largest farmer managed irrigation systems in the world. The structures are sometimes spectacular: earthen bunds, spanning the width of a river, or extensive spurs made of brushwood and stones. Spate systems are made in such a way that ideally the largest floods are kept away from the command area. Very large floods would create considerable damage to the command area. They would destroy flood diversion channels and cause rivers to shift. This is where the ingenuity of many of the traditional systems comes in. Spurs and bunds are generally made in such a way that the main diversion structures in the river break when floods are too big. Breaking of diversion structures also serves to maintain the flood water entitlements of downstream land owners.

Repairing a brushwood spur (Eritrea)

Wadi Al Ain, Yemen

What is the history of spate irrigation?

Spate irrigation has a long history. Several sources assume that in Yemen spate irrigation started when the wet climate of the Neolithic gave way to more arid circumstances and that spate irrigation thus has been in use for five thousand years. Similarly, archeologists have discovered the remains of checkdams for spate rivers in Tauran, Iran and Balochistan, Pakistan. In Yemen spate irrigation witnessed its zenith during the Shebean period in the first millenium BC. The great Mar’ib Dam, constructed on Wadi Dhana, irrigated two oases on either banks, estimated to cover 9600 ha.

One can only speculate how the technique spread across the world. The intense development of trade after the Islamic period may have helped spread innovations from the Yemen area. The recent development of spate irrigation in Eritrea is for instance traced back to the arrival of Yemeni migrants 80-100 years ago. Yet it is likely that spate irrigation techmology has sprung up independently in several areas – particularly as it is found in areas as diverse and remote as West Africa, Arabia, Central Asia and Latin America.