Managing Water Irrigation and Drainage

Shortages and surpluses of water are key factors that limit crop yields globally. It’s estimated that over half of the world’s food supply relies on some form of water management. Indeed, the earliest major civilizations and population hubs arose when farmers began to regulate water, leading to more reliable yields and steady food supplies. This includes Mesopotamia, literally “the land between the rivers” (the Tigris and Euphrates), the lower Nile Valley, and China. High yields in drained and irrigated areas facilitated the growth of trade specialization, as not everyone had to secure their own food supply. This spurred significant advancements like markets, writing, and the wheel. Furthermore, new water management strategies compelled societies to organize, collaborate on irrigation and drainage systems, and establish laws on water distribution. However, failures in water management also led to the downfall of societies. Notably, the salinization of irrigated lands in Mesopotamia and the accumulation of sediments in ditches—cleared by enslaved Israelites among others—resulted in lost soil fertility and the inability to maintain large, centrally governed civilizations.

In the present day, many of the most fertile agricultural regions depend on some form of water management. In the United States, the average crop yields of irrigated farms surpass those of dryland farms by 118% for wheat and 30% for corn. Globally, irrigation is employed on 18% of cultivated lands, but these lands contribute to 40% of the world’s food production. The vast majority of agricultural lands in the western U.S. and other arid climates worldwide would not be productive without irrigation water, and the majority of the U.S. horticultural crop.

Farmland, particularly in California, relies heavily on intricate irrigation systems. Even in humid regions, irrigation is used for most high-value crops during dry periods to ensure product quality and consistent supply for market outlets, partly because the soils have become less resistant to dehydration due to intensive use.

To tackle the issue of excess water, the finest fields in the U.S. corn belt have had drainage systems installed, making those soils even more productive than they naturally were. Draining wet fields allows for an extended growing season as farmers can access those fields earlier in the spring and harvest later in the fall without causing severe compaction.

The advantages of irrigation and drainage are clear. They are vital for food security and the agricultural intensification required to preserve natural areas. Concerns about climate change, which is leading to more frequent deficits and surpluses of precipitation, will intensify the demand for more irrigation and drainage. However, they also impose a cost on the environment. Drainage systems create hydrological shortcuts and contribute to increased chemical losses to water resources. Some irrigation systems have led to dramatic changes in river and estuarine ecosystems, as well as land degradation through salinization and sodium accumulation, and have been the cause of international disputes. In the case of the Aral Sea, previously the fourth largest inland freshwater body globally, the diversion of rivers for irrigated cotton farming in the former USSR resulted in a 50% reduction in the sea’s area. It also became severely polluted with drainage water from agricultural fields.

There are various types of irrigation systems, which depend on the source of water, the size of the system, and the method of water application. The three primary sources of water are surface water, groundwater, and recycled wastewater. Irrigation systems range from small on-farm setups that use a local water supply to extensive regional schemes involving thousands of farms and managed by government authorities. Water application methods include traditional flood or furrow irrigation, which relies on gravity flow, and pumped water for sprinkler and drip irrigation systems.

Historically, streams, rivers, and lakes have been the primary source of irrigation supplies. Early efforts involved diverting river waters and then developing storage ponds. Small-scale systems, like those used by the Anazasi in the southwestern U.S. and the Nabateans in present-day Jordan, involved cisterns filled by small stream diversions.

Nowadays, small-scale irrigation systems tend to pump water directly from streams or farm ponds. These water sources are generally adequate for situations where supplemental irrigation is used—in humid regions where rainfall and snowmelt provide most of the crop water needs, but limited amounts of additional water may be needed for good yields or high-quality crops. Such systems, typically managed by a single farm, have limited environmental impacts. Most states require permits for such water diversions to prevent excessive impacts on local water resources.

Large-scale irrigation schemes have been developed worldwide with significant involvement from state and federal governments. The U.S. government invested $3 billion to create the complex Central Valley project in California, which has provided a hundredfold return on investment. The Imperial Irrigation District, located in the arid desert of Southern California, was developed in the 1940s with the diversion of water from the Colorado River. Even today, large-scale irrigation systems, like the GAP project in southeastern Turkey, are being implemented. Such projects often drive major economic development efforts in the region and serve as a significant source for national or international food or fiber production. However, large dams also often have detrimental effects, displacing people and flooding productive farmland or important wetlands.

When good aquifers are available, groundwater is a relatively inexpensive source of irrigation water. A significant advantage is that it can be pumped locally and does not require large government-sponsored investments in dams and canals. It also has less impact on regional hydrology and ecosystems, although pumping water from deep aquifers requires energy. Center-pivot overhead sprinklers are often used, and individual systems, irrigating from 120 to 500 acres, typically draw from their own well. A good source of groundwater is critical for the success of such systems, and low salt levels are especially critical to prevent the buildup of soil salinity. Most of the western U.S. Great Plains—much of it part of the former Dust Bowl area—uses center-pivot irrigation systems supported by the large (174,000-square-mile) Ogallala aquifer, which is a relatively shallow and accessible water source. However, it is being used faster than it is recharging from rainfall—clearly an unsustainable practice. Deeper wells that require more energy—plus, more expensive energy—to pump water will make this mining of water an increasingly questionable practice.

In recent years, water scarcity has forced governments and farmers to seek alternative sources of irrigation water. Since agricultural water does not require the same quality as drinking water, recycled wastewater is a good alternative. It is being used in regions where densely populated areas generate a significant amount of wastewater