SPATE irrigation is a system for management and use of rainwater and hill torrents that is unique to semi-arid environments. Under this system, earthen diversion weirs are constructed across the hill torrents to regulate water for various uses including agriculture and groundwater recharging through field channels. These field channels are constructed at appropriate places and sides of the spate river. These channels carry floodwater to command areas for irrigation. The weir sites on steep gradient of hill torrent are usually not constructed in order to avoid uncontrollable flows.Communities using traditional technology usually build these diversion structures and weirs and the water conveyance systems. Their labour contribution is proportional to the size the land on the spate river, command area or their water share.
Embankments around agricultural lands to store floodwater are also constructed by these communities. These embankments are 4-8 feet high based on kind of soil and water share.
Water is stored in fields for moisture which is conserved using various techniques. Crops are sown on moist soils which are the only source and no further irrigation is applied except for the rain, if any occurs. Application of 600-1000 mm of water in a single irrigation before planting is sufficient to produce all spate crops provided the soil has good moisture holding capacity. It is also assumed that an irrigation application results 400mm water stored in soils.
Spate irrigation practices are prevalent in various arid parts of the world under various names. Traditional knowledge of Yemen mentions that Queen Saba made Sadds (literally, walls in Arabic) many centuries ago for bringing more and more area under irrigation. Spate irrigation and agriculture is also found in arid parts of the Middle East, North Africa, West Asia, East Africa and parts of Latin America. The British colonial authorities during land settlements in 1872 in the Indian sub-continent had used the term Sadd for what is locally known as Gandha.
An area of 1.2 million hectares out of total irrigated area of 17.6 million hectares in Pakistan is under this system of irrigation which is eight per cent of the area under different irrigation systems in the country. The area under this irrigation in Pakistan, in absolute terms, is highest in the world. . Spate irrigation is used in large tracts of land in hilly districts of Balochistan province including Kachi, Sibi, Loralai, Turbat, Panjgoor, Guwadar, Awaran, Pishin, Qila Saifullah, Dera Bugti, Mastung, Lasbela and Khuzdar districts. Dera Ghazi Khan and Rajanpur districts of Punjab, Dera Ismail Khan and Tank districts in NWFP. Malir, Larkana and Dadu districts in Sindh also do farming under this system of irrigation.
The spate areas depend upon hill torrents during monsoon (mostly June to September) from the adjoining mountain ranges.
The spate river flows depend upon the rains. The cropping system, pattern and agronomical practices on spate are highly dependent of timings of rain and magnitude of floods.
For example, farmers in spate areas grow sorghum, millet, gowar and melon with intercropping of pulses in case of a good rainfall in June or July. Whereas, if spate rivers flow after mid September due to late season rains, farmers prefer growing barley, gram, mustard with sorghum as fodder.
The local populations and communities have developed substantial wisdom to organise and manage spate river water and the heavy sediment loads. Framers, traditionally, construct one to three meters high dykes/structures locally known as bund or lath to manage the spate (flood) irrigation network in Sindh, southern Punjab and Balochistan.
The life of lath/band is only one flooding season; thus, it is rebuilt after every flood season in most cases. The rebuilding of lath/bund depends on the frequency and flow of spate river (nae) and the availability of labour and bullock power.
There are three types of spate irrigation structures in the traditional system. The first one is dhoro which is the source of water for the main spate river. Dhoro transports the runoff from highland towards main spate river irrigating agricultural fields on its way. Muhaga is subdivided into smaller channels called roonoon , at the third level in the system bringing water to each farm plot.
Spate faming in climate change and global food crises scenario is a potential source for food security and livelihood to a large number of communities living in the areas having spate potential.
The state policy for spate irrigation is the need of the time so that water rights are defined and regulation is put in place. Institutional and human resource capacity building programmes and development of material are also areas for attention. Piloting innovative ideas would also help the areas for livelihood of people and to compliment the national requirements for food and ecological balance.
Both agriculture and livestock are the major source of people living in the arid areas (mountainous and desert areas) of country, thus, agricultural and livestock extension and support services may also be initiated.