Study of the Residence Time of the Albufera of Valencia, a Mediterranean Coastal Lagoon

The Albufera of Valencia is a coastal lagoon located in the western area of the Mediterranean Sea, in the Iberian Peninsula. It has an area of 23.1 km2 and an average depth of only 1 m, with a maximum depth of 1.6 m. This lagoon is the rest of an original and more extensive wetland of about 220 km2, mostly dedicated to rice cultivation nowadays. Surface water is supplied through several main and many secondary canals for a total of 64 water entry points and three exit points to the sea. It is difficult to evaluate the renewal rate due to the lack of reliable measurements of the inflow or outflow, as well as continuous measurements. Between 1988 and 2018 several procedures have been used, synthesizing in this work the result, in which it is observed a decrease of the inflow in these thirty years, and therefore the residence time is increasing. There is a temporal variation during the year of renewal influenced by rainfall and cultivation periods. Likewise, it is observed that the natural hydrological zoning of the lagoon causes a spatial heterogeneity with small areas with more renewal, practically weekly, and large extensions with little renewal during months. It is impossible to know this information if flow measurements are not taken in each of the main watercourses.