Environmental Management

, Volume 38, Issue 6, pp 910–920 | Cite as

A Water Quality Index Applied to an International Shared River Basin: The Case of the Douro River

  • Adriano A. BordaloEmail author
  • Rita Teixeira
  • William J. Wiebe


A Water Quality Index (WQI) is a numeric expression used to evaluate the quality of a given water body and to be easily understood by managers. In this study, a modified nine-parameter Scottish WQI was used to assess the monthly water quality of the Douro River during a 10-year period (1992–2001), scaled from zero (lowest) to 100% (highest). The 98,000 km2 of the Douro River international watershed is the largest in the Iberian Peninsula, split between upstream Spain (80%) and downstream Portugal (20%). Three locations were surveyed: at the Portuguese–Spanish border, 350 km from the river mouth; 180 km from the mouth, where the river becomes exclusively Portuguese; and 21 km from the mouth. The water received by Portugal from Spain showed the poorest quality (WQI 47.3 ± 0.7%); quality increased steadily downstream, up to 61.7 ± 0.7%. In general, the water quality at all three sites was medium to poor. Seasonally, water quality decreased from winter to summer, but no statistical relationship between quality and discharge rate could be established. Depending on the location, different parameters were responsible for the episodic decline of quality: high conductivity and low oxygen content in the uppermost reservoir, and fecal coliform contamination downstream. This study shows the need to enforce the existing international bilateral agreements and to implement the European Water Quality Directive in order to improve the water quantity and quality received by the downstream country of a shared watershed, especially because two million inhabitants use the water from the last river location as their only source of drinking water.


Water quality index Discharge Residence time Reservoir Dam Douro River 



This article was partially funded by the grant POCTI/MSG/45533/2002 from the Portuguese Fundação Ciência e Tecnologia awarded to AAB. We also thank the two reviewers, one anonymous and Mr. Curtis Cude, for their valuable comments and suggestions.

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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Adriano A. Bordalo
    • 1
    Email author
  • Rita Teixeira
    • 1
  • William J. Wiebe
    • 2
    • 3
  1. 1.Laboratory of HydrobiologyInstitute of Biomedical Sciences (ICBAS) and CiimarPortoPortugal
  2. 2.Department of Marine SciencesUniversity of GeorgiaAthensUSA
  3. 3.PortoPortugal

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