Water level control on coastal landform distribution and associated processes in a highly fluctuating shallow lake (Gallocanta Lake, NE Spain)

Abstract

Shallow lakes in semi-arid environments are very sensitive to hydrological alterations associated with climate change. Their shorelines and geometry can change according to water level fluctuations. Gallocanta Lake (NE Spain) is a typical example of such lacustrine conditions because it is exposed to strong winds parallel to its elongation axis and is located in a semi-arid Mediterranean environment. In this work, a high-resolution digital elevation model (DEM) of the area is used to compare the distribution of coastal forms (beaches, barrier islands, deltas, lagoons, etc.) with the frequency at which different water levels are attained. As a result, a clear relationship is obtained between presently active forms and the water levels most frequently reached in the lake. It is deduced that, once formed, the surrounding coastal plains related to these coastal forms control the permanence of water around a given height interval, favouring the development of these morphologies, in a positive feedback mechanism only broken by subsequent climate warming and lake water lowering. The hydrodynamic conditions responsible for activating the coastal forms have been analysed by applying a mathematical model of wind-driven currents in the lake that predicts the present erosional/progradational trends associated with them. The combination of the different results obtained was used to generate a synthetic map of active coastal processes and trends along the lake shore during high water episodes, with two versions according to the two dominant wind scenarios in the region. The distribution of erosion/sedimentation trends along the lake shores has helped to propose the existence of longitudinal littoral cells, each one recording different shoreline trend (retreat, progradation, and stability), depending on the prevailing wind scenario. This synthetic scheme can be useful for predicting the eco-morphological trends of the lake shore and adapting the present management practices in this protected area accordingly.