Canals and conservation

The three major food-producing countries - the United States, the Union of Soviet Socialist Republics (USSR), and China - face water shortages by the end of the century that threaten their food production. To meet their water needs these countries are now planning massive water diversion projects that will cost billions of dollars and pose serious threats to the environment.

There are better ways to increase water supplies than building new dams, reservoirs, and canals. Using water more efficiently, particularly by improving existing irrigation systems, will cost a fraction of what it takes to move large amounts of water from one place to another. Conservation efforts must begin now, however, before political pressure for large-scale water diversion projects becomes overwhelming.

Irrigation already plays a pivotal role in world food production. The US, USSR, and China account for nearly half of total world food production and two-fifths of the world's irrigated area. As these countries attempt to grow more food to keep pace with demand, they face serious water constraints.

In the US, agriculture on the High Plains depends on a shrinking underground water reservoir known as the Ogallala Aquifer. This body of water, underlying the High Plains from South Dakota to Texas, is being drained faster than rainfall can replenish it. The Ogallala has already shrunk 40 percent, and best estimates are that irrigated agriculture in the region will be reduced by two-fifths within a few decades.

The specter of water shortages has created an ''import or perish'' mentality among farmers. The Army Corps of Engineers has prepared four separate plans for canals to bring water from the Missouri or Mississippi Rivers to the High Plains. The cost of these projects ranges from $13.4 billion to $40 billion each. Pumping water through these canals would be at least 10 times more expensive than what farmers in the region currently pay for water. The prospective drying-up of irrigated agriculture with attendant job and population losses are putting pressure on elected officials to build one of those canals.

Farmers in the Soviet Union face even more pressing water problems than those in the US. According to Soviet agriculture specialist Thane Gustafson of the Rand Corporation, ''The entire irrigation program is threatened because the southern half of the country is running short of water.'' This area is the Soviet breadbasket, where improved harvests are desperately needed to stem rising food imports from the US.

After decades of debate, the Kremlin approved a plan this past spring to reverse several northward flowing Siberian rivers, bringing water to parched farmlands in Central Asia. The Irtysh and Ob Rivers will be dammed and their waters pumped south for 1,400 miles. The initial investment for the Siberian canal will be $41.6 billion. More important, reducing the flow of fresh water into the Arctic Ocean could change weather patterns over the entire Northern Hemisphere.

The Chinese have the Soviet agricultural water problem in reverse; adequate supplies in the south but not enough water in the north. To increase food production in the North China Plain near Beijing, the Chinese are building two canals to divert water from the Chang Jiang (Yangtze) River. These two 750-mile canals will eventually cost $13.2 billion. Without adequate water management, this new irrigation could lead to waterlogging and overly salty soils, taking land out of production even as irrigation is expanding. Moreover, there has been no adequate assessment of the political and social costs of relocating nearly 250,000 people who now live in the path of the canals.

The apparent choice facing the major food-producing countries is stark indeed: invest in major water projects or expect food shortages. Although some interbasin transfers of water may be necessary in the long run, the true demand for such projects cannot be fairly judged until more has been done to improve the efficiency of current water use.

Waste accounts for a significant portion of agricultural water demand. The US General Accounting Office estimates that half the water used in American agriculture is lost before it can be absorbed by crops. In the Soviet Union water losses of 40 to 50 percent from seepage and evaporation are typical. Similar inefficiency has been recorded in China.

In most parts of the world, it will be cheaper to save water than to develop new sources. A US study recently estimated that a $5 billion investment in simple water conservation measures on the farm could save nearly two trillion gallons of water per year.

Much of these savings can come through upgrading traditional irrigation methods. Capturing excess water at the end of fields and recycling it can cut losses in half. Lining dirt-walled irrigation canals or installing sprinkler and drip irrigation systems can achieve even greater savings.

Unfortunately, farmers have little incentive to improve irrigation efficiency , because water today is underpriced. US farmers pay only about one-fifth of the cost of the water they use. Government subsidies cover the rest. As more users compete for limited water supplies, higher water prices will be necessary to help society make decisions about how water is allocated and used.

Just as wasted energy became a fuel resource when supplies tightened, a similar reserve of wasted water exists on nearly every farm. Tapping that reserve will require a fundamental change in agricultural water policies. The huge earthmoving projects of the past were designed to mobilize water supplies They reflected assumptions that water resources were infinite and the consequences of their development were negligible. In a financially strapped world increasingly aware of the limits on water supplies and of the fragility of the environment, water conservation is a far more prudent if less heroic approach to increasing food production.