SURFACE-WATER QUALITY IN PORTUGAL DURING A DROUGHT PERIOD

A severe drought starting during the hydrological year 1991/92 has been affecting water resource availability in Portugal with 1993 being one of the driest in the last 60 years. The accumulated precipitation for 1992/93 was 70-50% of the mean of previous years with values lower than 40% in some areas in the south of the country. River flow was below normal mean values, with minimums of 1 and 7% in some watersheds in the south, where total storage volumes of only 20% of maximum capacity were registered. Since water quality could be seriously affected by reduced flow and storage, a study to ascertain possible relationships was undertaken. As part of this study, based upon the existing Water Quality Network, fifteen reservoirs, representative of different regions were selected, and analytical data on water quality parameters that are significant for each station collected since 1989 were evaluated. In addition to considering the variability of specific parameters, a water quality index was also used. A significant correlation between water quality parameters and storage volume was not established. Preventive measures on point sources of pollution, no irrigation of agricultural crops and reduction of transported pollution from upstream may in part explain these findings.