Global Change and sediment yield from the study of headwater reservoir sedimentation in the Cantabrian Mountains (Northwest Spain).

Over the last few decades, environmental changes have occurred in the Cantabrian Mountains (Northwest Spain) as a result of economic, social and climatic transformations. The depopulation in the rural environment with the transformation of traditional land uses, the closure of coal mining operations, and the increase in temperatures have modified the geometry of channels, water flow, and sediment connectivity of mountain rivers.

The runoff and the sediment load are modified, and the reservoirs located downstream collect all these changes thanks to the gauging stations for water flow, up and down the reservoir and the sediment sequences inside the reservoir. Studies have been carried out in natural cuts of several reservoirs during their dry season with the aim of knowing in detail the effects of each environmental change. The studied variables are accumulation rhythms, exceptional events, granulometry, and some chemical patterns. Data have already been published in the Pisuerga River basin (Palencia) from the analysis of the sediments retained in the La Requejada Reservoir (Pisabarro et al., 2019) but are not still published in Tuerto River basin in the Villameca Reservoir (León) and in Ibias River in the Grandas de Salime Reservoir (Lugo-Asturias).

In the first one, it was found a clear tendency to reduce the grain size since 80’s, when the land use change from crops and grasslands towards rewilding were increased. This process was aid with a decrease of runoff close to 20% between 60’s to 2010’s. In the other two reservoirs, the Villameca and the Grandas de Salime, there are interesting sediment outcrops too, in the last one affected by mining activity. Samples of sediment have been taken which also show the tendency to a smaller grain-size particle in the sediments’ upper levels. In the Villameca Reservoir at consequence of a clear reduction of the extreme events in the last decades.

Significant differences in sediment thickness have been observed between northern and southern slopes of the Cantabrian Mountains partly due to the marked asymmetry slopes, proper of this mountain range. In the first (the Grandas de Salime) up to 5.5 m has been found form since 1953 (2021), but in the La Requejada and Villameca reservoirs (in the Southern slope) only 1-2 m since 1940 (2016) and 1947 (2021). During the next dry season of the reservoirs, the research will be extended to other reservoirs with the main goal of extending this analysis and understanding the Global Change implications in the connectivity and the fluvial dynamics.

 

Pisabarro, A., Pellitero, R., Serrano, E., Lopez-Moreno, J.I. (2019) Impacts of land abandonment and climate variability on runoff generation and sediment transport in the Pisuerga headwaters (Cantabrian Mountains, Spain), Geografiska Annaler: Series A, Physical Geography, 101:3, 211-224, DOI: 10.1080/04353676.2019.1591042