Dinámica de inundaciones del río Colorado e impacto en Turrialba, Costa Rica

Abstract

La investigación tiene como objetivos contribuir al conocimiento de riesgos y daños producidos por inundaciones y desviaciones del cauce del río Colorado, caracterizar los factores determinantes asociados con las inundaciones, estimar costos sociales y económicos derivados y proponer un diseño de estrategias para aliviar posibles impactos. El estudio se realizó en la ciudad de Turrialba, Cartago, Costa Rica. En 1992, la ciudad era asiento de 30561 y el cantón de 65792 habitantes (DGEC, 1992). El uso de la tierra es principalmente agrícola (café y caña de azúcar). La cuenca del río Colorado se halla dentro de la cuenca del río Turrialba. La información provino de publicaciones meteorológicas, urbanísticas, de salubridad, censos, anuarios, legislación, documentos y registros de instituciones nacionales. Se utilizaron encuestas prediseñadas para obtener información por parte de la población turrialbeña aledaña al cauce principal del río Colorado. Se consideraron 50 m a ambas márgenes. La investigación se ha centrado en factores causales principales que determinan las inundaciones en Turrialba: precipitación máxima y crecimiento poblacional, éste último como expansión de urbanización, deforestación, manejo del cauce y ubicación de las viviendas, ya que no se dispone de información cronológica de estos últimos. Los resultados indican que la precipitación máxima diaria necesaria para causar inundaciones va de 242 a 31 mm. El mes de mayor ocurrencia es diciembre (37,5 por ciento), le sigue febrero (25 por ciento).

The city of Turrialba is exposed to floods from the surrounding rivers and creeks. The Colorado river constitutes one of the main menaces and its floods summing eleven in this century. The most important factors favoring floods are: intense rains at the basin area, increasing urban pressure due to population expansion, land use and above all the city's foundation on top of the Colorado riverbed. The river was limited to bridges and tunnels with deficient dimensions for proper evacuation in case of strong floods. The objectives of this research were to contribute to the knowledge of risks and damages produced by the floods and deviations of the Colorado riverbed to estimate social and economical costs of floods and with that information to assist in designing strategies to alleviate possible impacts. The study was conducted in the city of Turrialba, Cartago Province, Costa Rica. In 1992, the city was inhabited by 30561 persons and the country by 65792 (DGEC, 1992). The land use is basically agricultural (coffee and sugarcane cultures). The Colorado river basin is located within the Turrialba river basin. Data was collected from two main sources: primary and secondary. The first refer to meteorological, urban and health publications, census, annual reports, national legislation, documents and records from national institutes. Pre-designed surveys were applied to obtain data from Turrialba's population near the main stream of the Colorado river. For this purpose, fifty meters from each river margin were considered and aleatory sampling was utilized. This research emphasized two main causal factors, which determined floods in the city of Turrialba: maximum precipitation and population increase. Factor like urban development, deforestation, stream management and houses location, are included within the population growth. Regarding the precipitation needed to cause floods, this varies from 242 to 31 mm in an average day. The month with the highest floods occurrence is December (37,5 percent), followed by February (25 percent). Floods during February show the biggest precipitation values with 183,7 mm and 242 mm. The years recorded for floods do not necessary coincide with the highest total annual or monthly rainfalls, excepting the year of 1970. The harmonic series (Fourier series) analysis allowed to find two main periods in the years as a whole, cut approximately in 1970. From that year on, the maximums have been more frequent. It is difficult to estimate a clear return period for strong maximums, though its occurrence could be at any time as this phenomenon has become unpredictable. The relationship between population growth through time and the accumulated average precipitation shows a lineal tendency toward decreasing of extreme rainfalls necessary to produce floods as the population increases.