Ancient irrigation systems

Agriculture and irrigation in ancient civilizations

The first people to grow plants had to learn three main tasks: how to concentrate desirable plants in a manageable area: how to prevent weeds from growing there, and how best to encourage the plants to flourish. In short, people have learned to plant crops, weeds, and water or drain. In the climate of England, there is enough natural rainfall to staple crops. But in a dry climate, most crops need water, and must be submitted by the grower. Irrigation was the technology behind many of the greatest civilizations of the world.

But irrigation is not easy. Usually, irrigation systems require a large investment of money or work or both. The water supply must be safe and reliable. In each growing season, water of good quality must be delivered at the right time and place in the right quantity at the right price, and irrigation water must then be evacuated cultures. Even within one growing season, irrigation systems require ongoing maintenance.

Benefits and risks of irrigation

The long-term risks of irrigation are even greater. Investment in irrigation projects pays better in dry areas where evaporation is high. The water is never pure, but has dissolved mineral salts. Evaporation will therefore be even saltier. Rivers flowing through dry or desert areas lose water by evaporation, and become salty. For example, the water in the lower part of Colorado contains more than one tonne of salt per acre foot of water.

Many areas in dry climates have natural lakes of brackish or salt, or salt marshes, even dry. Soils are often loaded with lime (calcium carbonate) or salt (sodium chloride), and many sedimentary rocks contain natural salts. Irrigation areas may therefore be promising natural salts in rocks or soils that are easily transferred into the fields as soon as irrigation water is applied, and even that water can come from rivers that have become more saline through evaporation along their course.

As water is used on crops, it spreads into a thin sheet, exposed at the surface. Much of it can evaporate, making it saltier. It can dry up completely, leaving a thin layer of salt and soil. Even under normal circumstances, plants absorb soil moisture, leaving behind the excess salts. Finally salts accumulate in the soil surface until they become sterile. Over time, therefore, dry soils in irrigated areas tend to become salinized.

The only way to solve this problem is to apply enough water so that the salt is rinsed or flushed through the soil. Rinsing should remove salts from the area altogether, along natural or artificial drainage. In well-drained areas with a dry season and wet season, a natural blush is held annually. But in poorly drained areas, overwatering simply mobilizes the salt while the water table rises to ground level.

Capillary action draws the salt water on the surface, where dry salt as a surface deposit, and the problem has worsened rather than improved. Once the soil is saturated with water to the surface, there is no way to salts leaching through soil, and fertility of the region is destroyed, except the main drainage channels are constructed to remove salt.

Even rinsing may not be a net benefit of the environment: hot flashes simply provides salt elsewhere, perhaps to downstream users, or in groundwater. Flushing also leach away nutrients from the soil with salt.Therefore, irrigation can not be maintained over a long term basis under the following conditions.

Water is applied so that the salt is not allowed to develop in the ground. Usually, this means that lots of good quality water is applied, and that drainage is fast and efficient. Soils need a large infusion of fertilizer, to balance the hunt that is required to keep them without salt.

The first means of irrigation and for the most basic of irrigation used by the Egyptians. Along the River Nile, there are several recesses formed naturally in the earth. During the annual flooding of these depressions would fill with water. The Egyptians of that time came with the idea of surrounding these depressions with mud dams in order to retain water.

Cannals were dug from the river to farmers' fields. As technology has increased, the tanks were surrounded by stone dams to retain more water and keep water in the basin for long periods. Later, the ponds were man made to move them to where they were needed. This method was replaced when the system was designed cannal.