Methods of irrigation

In my previous blog post, I discussed the economics of irrigation development in Africa. The aim of that blog was to identify the factors influencing the feasibility of irrigation in a given area. Today, in this blog, I would like to explore the various types of irrigation that exist in Africa with reference to case studies.

Irrigation by definition is the artificial application of water to land to produce crops[1]. Although irrigation has developed over the years due to modernisation and advances in technology, some farmers still use traditional approaches. This is due to these methods being reliable and relatively inexpensive. Examples of traditional irrigation methods include water harvesting, flood plain irrigation, swamp irrigation and groundwater irrigation.

Water harvesting is a method that has been used extensively for centuries. Rainwater is collected and channelled into a small growing area. An area where water harvesting is heavily used in the lowlands of Tanzania where rainfall is between 600 – 900mm and run off naturally collects at the bottom of the valleys. This provides optimal conditions for paddy rice cultivation and research shows that this system contributes to 35% of the total rice production in Tanzania [FAO,2001]. Figure 1 shows the tanks used for rainwater harvesting in Tanzania.

 

Figure 1 shows the tank used for rainwater harvesting in Tanzania. [Source]

Groundwater irrigation, unlike water harvesting, uses water within the Earth, in the form of medium to deep aquifers. It is believed that the use of groundwater will alleviate seasonal water scarcity as it is a reliable water resource that is less susceptible to evaporation and contamination in comparison to surface water resources.

In areas such as southwest Egypt, groundwater irrigation is ideal due to the region’s aridity and lack of surface water. The Nubian Sandstone Aquifer System within this region has a reasonable amount of groundwater that is being heavily exploited by surrounding inhabitants. Results from research conducted by Ebraheem, 2003 indicate that large-scale irrigation cannot be supported in this area as the annual recharge of the aquifer is too low. Ebraheem further stated that the present value of extraction must decrease from 203 million m³ yr^-1 to 93 million m³ yr^-1 to avoid depletion.

In contrast to traditional methods of irrigation, modern technologies are costly and usually require the presence of a specialist upon construction and installation which may incur additional charges. The High Aswan Dam is an example of a full control dam built to provide sufficient water for agricultural and other purposes. The dam was built on the border between Egypt and Sudan, successfully ceasing floods and droughts in regions around the Nile River. Figure 2 shows the location of the dam along the Nile River. The dam supplies Egypt’s annual quota of 55.5 milliard cubic meters of water and has been effective in doing so since 1970. However, the cost of construction neared $1 billion which cannot be afforded by rural farmers and smaller countries with lower GDP.

Figure 2 shows the location of the High Aswan Dam along the Nile River. [Source]

Although modern technologies may seem disadvantageous, the benefits in some cases outweigh the negatives. For example, modern technology such as motor-driven pumps can be used to reduce the drudgery of lifting water. This is will increase the efficiency of farming thus, allowing more plants to be grown over a larger area. In addition, distribution technologies such as trickle sprinkle irrigation and piped water supplies will aid the reduction of water wastage. Water can be fed directly to the root of the plant at regular intervals, allowing optimal root moisture to be maintained. This will reduce the stress on the plant, enabling the maximum growth rate, therefore increasing the profits made by farmers. Despite perennial irrigation providing new opportunities for more intensive crop cultivation, issues may build up in the long run, reducing the efficiency of production. These include waterlogging, salt builds up in the soil and fluctuations in the water table [El Gamal F, 2000].

Due to the global market, the prices of cereal crops have dropped over the years, meaning it would be unreasonable for a small-holder farmer to invest in costly, large-scale irrigation infrastructure. I believe it would be more ideal to use modern technology that has been modified to become low-cost such as a treadle pump. This compromise will ensure the farmer makes enough money for a living as well as increasing the efficiency of their food production.

Overall, I think the use of irrigation for crop production is beneficial, especially in areas with variable rainfall and an arid climate. However, the type of irrigation used must be suited to the growing area and the farmers income.