Water management improvements in irrigated valleys save water, enhance environment
provided by Colorado State University
retired Colorado State University agricultural engineer and his colleague believe a decades-old concept that improving water management cannot save water in an irrigated valley is wrong.
Wayne Clyma of Colorado State and M. S. Shafique, both water management consultants, will present a paper at the forthcoming 94th Annual International ASAE Meeting asserting that improving water management practices in irrigated valleys can save water. Their presentation counters a long-accepted but unproven concept to the contrary.
Improving irrigation efficiencies saves water by using less to irrigate an area. Water not needed for irrigation remains in the reservoir for other uses and is the water saved. This water is available to replace legally required return flows (excess water that returns to the river) because improved irrigation efficiency reduces the return flows. Meanwhile, the remaining water saved is available for reallocation to other uses additional irrigation, and municipal, industrial or environmental needs.
In their paper, Clyma and Shafique explain as erroneous assumptions the contention that all the water from excess irrigation will come back to a river as return flow and all the return flows will subsequently be diverted again and used for irrigation until 100 percent is used. Proponents have never tested the concept, Clyma said. Yet many people working in irrigation believe low irrigation efficiencies mean the water is recycled by return flows and that this multiplies the water supply. Thus, bad water management is good, they believe. Proponents of 100 percent return flows do not believe that water saved by improving water management could be put to additional good uses.
Clyma, who spent years on field projects in Pakistan and Egypt, and Shafique decided to define more carefully the concepts for improving water management and saving water in an irrigated valley. Current applications, based upon an assumption that you cannot save water, have continued practices that increased waterlogging and salinity in an irrigated valley.
Clyma and Shafique discovered the concept was in error and the assumptions in the applications of the concept were even more inappropriate. Assumptions included exceptionally high irrigation efficiencies and amounts of return flow recovered and reused. Backers of this proposition provided no measurements or data to support these assumptions. Clyma and Shafique say their better understanding of water management in an irrigated valley gave them the means to define their concept for saving water.
Significantly increasing the valley's water supply by saving water and reducing the impact of irrigation on the environment are both major benefits from the new concept, says Shafique.
Basically, we say that improving water management saves water to replace return flows and provides water for other uses, Clyma said. This contradicts the beliefs of many professionals in irrigation. But their erroneous beliefs are based on two incorrect assumptions.
One is that there are a sufficient number of diversions small dams across rivers that divert water for irrigation below any given diversion to make all return flows available for irrigation. This isn't so irrigated agriculture does not have an infinite number of diversions to capture all the return flows.
The second error lies in the belief that 100 percent of water not beneficially consumed by crops appears in the river as return flow. It doesn't.
Instead, Clyma said, high water tables and poor drainage systems cause large amounts of water to be lost (evaporated from the fields and channels or used by vegetation and not crops).
Water saved and not previously used for irrigation is less saline. It would decrease, not increase, the salinities of the water found even here in Colorado on the Arkansas and Cache La Poudre rivers. The water released to replace the return flows increases the flow and reduces the salinity of the river. Both actions improve the environment of the river.
Instituting improved water management in irrigated valleys depends on farmers' willingness to cooperate and on the level of benefits they receive. Clyma and Shafique propose that the water available for reallocation be used by the farmers, rented to other users annually or sold as a water right that would consider the future value of the water. The income would enhance the value of making water management improvements.
Based on his experiences in water management, technical and organizational change in irrigation is hard to achieve, Clyma said. Nevertheless, change is possible and has been achieved under a variety of circumstances over three decades of experience, he said.
Clyma and Shafique do not believe that the complete recapture of all irrigation water is possible, and this sets them apart from the beliefs and policies that have been in place for decades. The assumption was that capturing all return flows were possible and that this multiplied the water supply, resulting in continuing bad water management practices. This usually results in increased waterlogging and salinity, they suggest, to the detriment of farming and the environment in irrigated valleys.
Irrigation water management is important from the smallest unit for managing the irrigation of a field to an entire irrigated valley, they write in conclusion. 'The reasons include increasing the productivity of water and the incomes of farmers, increasing food production, saving water for other uses, reducing the salinity impacts of irrigation and improving the environment in an irrigated valley. Saving water is a new, urgent emphasis. Major water shortages already exist.
We expect shortages to become critical in many irrigated valleys of the world in the next 25 years. Reducing the environmental impacts of irrigation and improving the water quality of river flows and water for other uses, including irrigation, is an additional major benefit.
Water management improvements in irrigated valleys in Egypt or Pakistan could, they believe, result in water savings that would equal between 25 and 50 percent of the supply currently used for irrigation. In those water-short countries, reallocating that water to irrigation units in the valley or to other uses would provide major benefits.