Summary

Studying the global history of irrigation shows that virtually every irrigation society, with three notable exceptions, has failed after some 200 years primarily due to salinity.

Irrigation is like a natural evaporation system which concentrates salts.  The enduring societies have had the luck of natural rain or cyclic flooding which has flushed the salt to the sea, the rest simply failed.

Modern irrigation is highly managed and could easily avoid salinity but there has been generally little consideration of the need for flushing.  The financial benefits of irrigation are immediate, the accumulation of salt in the soil is insidious and long term, so generally most rivers are over allocated.

The problems water managers face are more than technical; with water already allocated they face major political resistance in clawing back the water for the necessary flushing.  This requires a paradigm shift in both technology and adoption.

The theme of the book is about the process of innovation, how to develop the needed technology and how to ensure its adoption.  It shows how significant water can be saved without any loss of agricultural output; the problem is to persuade the irrigators to adopt these practices and reallocate the water saved for flushing.

One key to saving water is to ensure that no water passes the root zone for the majority of the irrigations.  The water saved can then be used for periodical flushing flows, with irrigators applying extra water to flush water from their land while simultaneously extra water is flushed down the river to carry the salt to the sea.

The book describes how irrigators can determine exactly how much water has to be applied to reach the specified depth by using a self learning approach which determines their soil characteristics. ‘Self learning’ software has been developed which is both efficient and easy for the average farmer to use.

With this technology controlling irrigation depth is relatively easy with modern drip and sprinkler systems however it is generally impossible to control irrigation depth using flood irrigation, which used by far the bulk of water.

The book describes a low cost method where flood irrigation can be modified to increase efficiency and control irrigation depth.

While the technology exists to ensure our water use is sustainable the biggest problem is one of adoption.  The book shows how to bring about the required changes in attitudes of both the traditional managers of our water system and the public.