River response to environmental changes: monitoring of geoindicators in representative reaches of Chocancharava and Achiras-del Gato streams, Córdoba, Argentina
by
Susana Degiovanni
Dpto. de Geología, F. Cs. Exactas, Físico-Químicas y Naturales. Universidad Nacional de Río Cuarto, Argentina

The fluvial systems in the south of Córdoba Province have torrential hydrological regimes. They drain the southeastern slopes of the Comechingones range, cross the agro-ecosystems of the Pampean plains, ending in the eastern–southeastern depressions (Saladillo and Tigre Muerto wetlands). In the last century, rivers discharge increased because of the increasing precipitations, changes in land use and management, and channelizations in the lower basins, inducing important rejuvenation processes.

Taking into account that fluvial systems have a high sensitivity to show environmental changes, a set of pressure-state geoindicators was chosen. The monitoring of geoindicators will improve the knowledge of the complex nature of adjustment mechanisms involved in approaching a new equilibrium. Besides, monitoring actions will allow to establish environmental change tendencies and to explain cause-effect relationships

The selected areas to monitor geoindicators are the reaches of Chocancharava and Achiras-del Gato streams, since they present a very active morphodynamic related to natural and antrophic causes. The latter, such as land use, straightening, channeling and mining, are considered pressure geoindicators. In these areas, the state geoindicators that are being monitored are those of morphological, sedimentologycal, climatic and hydrological characteristics, such as sinuosity, planform pattern, lateral erosion rate, streambed degradation, streambed datum line, headward erosion rate, cross-section changes, bed-material changes (1, 50, 84 percentile, mean size and sorting variations), precipitation and flow and sediment discharge.

The monitored geoindicators showed different sensibility for detecting changes in a wide space-temporal scale. Thus, the magnitude and distribution of rainfall excess in the water balance caused by the increasing trend of rainfalls in the last decades, are positive correlated with the most important floods and consequently with the highest lateral and headward erosion rates. Furthermore, increasing in channel downcutting is a good indicator of channelization and transvasses. The slope channel and sorting and fine grains percentage of bed material are suitable geoindicators to show fast response for local interventions (mining, straightening). The sinuosity variations were not significant except for regulated reaches. The suspended load is the best geoindicator for land use and management changes.

Date received: December 14, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caod-63.