This research has two parts. First we built a model of the water system of the Albufera Natural Park, a wetland located in the Spanish Mediterranean coast whose most characteristic feature is its central lake. We have called this model Cabhal, an acronym for Calidad de aguas y balance hídrico en L'Albufera (Water Quality and Water balance in L’Albufera). This model includes: 1) a quantification of water inputs from the natural cycle 2) a quantification of changes caused by the irrigation system and urban pressure 3) an assessment of inputs, outputs and changes in storage, both in the lake and the surrounding rice crops 4) an analysis of the spatial distribution of water intake 5) a quantification of pollutant loads and 6) a module of the quality processes related to eutrophication.
For its construction we applied the principle of superposition and we have studied separately the natural flow system (based on the model “Simpa” by Cedex) and the modified flow regime. The module related to the water balance includes five reservoirs; four of them simulate the rice fields within the park and the fifth, the lake. We have added a module of spatial distribution and a module to calculate pollutant loads based on standard concentrations for different types of inflows. The module of water quality in the lake has been built with the two-dimensional simulation software “Sobek WQ” by Deltares.
Second, we used the model to generate monthly series of the main indicators of the system, including 1) total water inflow 2) number of annual renewals in its central lake 3) external loads and 4) average concentrations of organic matter, phosphorus and nitrogen in water inflows. We paid particular attention to assessing the indicators in the early seventies when the lake rose sharply to a turbid state dominated by phytoplankton. We also evaluated those indicators after the completion of major infrastructures for nutrient diversion.
We started from a central hypothesis: there are substantive aspects of the development of L'Albufera trophic status that can only be explained through its relation to the water system infrastructure.
The Cabhal model can be used to study the environmental flow requirements of L'Albufera de València. The main value of the model, which overcomes shortcomings of previous works, is a strong anchor in the area through a detailed process of calibration and validation. We obtained results that reasonably reproduced the reality over a long period of time in different sectors of this wetland under very different circumstances.