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Sustainability of Engineered Rivers in Arid Lands
Modern river engineering is just a century old. It started in two rivers: Nile and Rio Grande. British engineers closed the first Aswan Dam in 1902. The U.S. Corps of Engineers closed Elephant Dam, an hour’s drive north of El Paso, Texas, in 1916. Engineered rivers are the lifeblood of irrigated agriculture, produce electricity and supply water for industry and cities in the river basins. By now most large rivers in the world have been engineered—equipped with multiple dams, bypass canals, and distribution channels. River engineering brings large benefits to farmers and cities.
It also creates risks. In this project we study the most important ones in order to find out how the rivers will do in 2040 and 2060. We look at both physical and social drivers of change: climate change/variation, reservoir sedimentation, surface-to-groundwater connection, and environmental flow on nature’s side; population and land use changes, as well as options for more efficient water use and better policies, on the social side.
SERIDAS stands for Sustainability of Engineered Rivers in Arid Lands. We assembled a team of river experts to project water supply and demand for a group of heavily engineered rivers worldwide. We also invited a second group of team members who can advise the river experts on how to deal with future risks.
How we got started: Rio Grande/Río Bravo
Back in the 1990s EPA and NSF ran a program called “Science to produce results”. HARC received a grant to work with colleagues from Mexico to study the future of the Rio Grande/Río Bravo. We spent several years on the project and found that the river would be dramatically changed by 2030. Most importantly, there would be 1/3 less river water:
- Each decade the Rio Grande loses 5 percent of reservoir storage to sediment buildup behind reservoir dams
- Early impact of climate change is already measurable: the mountain snowpack which is responsible for the bulk of river water is diminishing
- The basin population will double by 2030 requiring a larger share of river water
- Environmental flow, already low, will decline even more
There was one good piece of news: we found that farmers might be able to maintain the value of current harvests while using less water—provided they adopted more efficient irrigation methods and shifted to less water demanding crops. And both agriculture and cities could make much progress with water conservation.
For a detailed summary of the study results see, J. Schmandt, Bi-national water issues in the Rio Grande//Rio Bravo, Water Policy 4 (2202) 137-155. The full report is available at http://mitchell.harc.edu/archive/RioGrandeBravo/Report. An abstract is available on the EPA website (http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstrac...).
The Rio Grande results gave us pause: were they representative of rivers elsewhere? What are the prospects for engineered rivers in arid lands worldwide? We started SERIDAS to find answers.
2040 and 2060 Scenarios
Scenarios describe plausible futures. All of our scenarios include projections for reservoir sedimentation, environmental flow and changes in population and land use. In addition to those variables 2040 and 2060 scenarios use data and projections as follows:
- Business as usual: current water use + climate change
- Worst case: Business as usual + drought of record + climate change
- Seeking sustainability: More efficient water use + climate change + ecological restoration
Water budgets account for water supply and demand. They are the main tools for the quantitative assessment of past, current and future hydrological conditions in each river. We will construct water budgets for the past (1970, 1990, 2010) and the future (2040 and 2060). There will be three water budgets each for 2040 and 2060, using Scenarios A, B and C.
We will use the water budget results to assess likely river and basin conditions in 2040 and 2060. We will use these criteria to determine whether river basins will be more or less sustainable than now: agricultural productivity, economic well-being of the basin population, ecological health and sound basin management. In a final step we will take all of SERIDAS basins together and ask what the future holds for global food security.