5th UF Water Institute Symposium Abstract

Submitter's Name Alice Alonso
Session Name Poster Session - Coastal Waters
Poster Number 8
Author(s) Alice  Alonso,  University of Florida (Presenting Author)
  Arnoldo Valle-Levinson,  University of Florida
  Rafael Muñoz-Carpena, University of Florida
  Can Upstream Anthropogenic Activities Reshape the Tidal Influence on a Downstream Wetland? A case study in NW Costa Rica.
  Alice Alonso; Rafael Muñoz-Carpena; Arnoldo Valle-Levinson; Carolina Murcia. The Tempisque river surrounding the internationally recognized Palo Verde wetland in NW Costa Rica is influenced by tidal propagation from the Gulf of Nicoya. The discharge in this river has decreased as a consequence of an uncontrolled water withdrawal for irrigation purpose in the upper portion of the watershed. We hypothesized that this diminution in the freshwater flow led to a higher amplitude of the tidal signal in the lower river that outweighs the associated decrease in the subtidal water level. The river influences the wetland hydrology by lateral seepage and bank overflow during high tide events. Hence, an increase in the tidal amplitude would lead to a higher occurrence of flooding events of the wetland, redefining the hydrology of this fragile ecosystem. We measured water level, temperature and conductivity at a 15-minute resolution in three locations along the low Tempisque river, as well as the surface and subsurface water in the wetland nearby to the river edge during 5 months to 2.5 years. We also measured currents, salinity and temperature profiles during a complete tidal cycles (12.5-hour periods) in three lower-river transects with an acoustic Doppler current profiler and a conductivity-temperature-depth profiler. We combined statistical signal processing tools in the temporal and frequency domains, harmonic analysis and existing analytical expressions to demonstrate and quantify the variation in tidal amplitude and of the subtidal component under different values of discharge. We used it to assess the change of occurrence and intensity of flooding events under different estimations of long-term river discharge diminution. Significant evidence has been drawn showing that the wetland hydrology has been significantly altered due to those changes. This could be a factor that caused the observed degradations in this unique system. In a more general way, the developed methodology can be used for other systems where tidal variations as a response to altered discharge needs to be assessed.