A Somolinos quarry land stewardship history: From ancient and recent land degradation to sensitive geomorphic-ecological restoration and its monitoring

This research documents the successful application of a novel holistic approach to return land degraded over thousands of years of use to full ecological function. The surroundings of the Somolinos hamlet in Central Spain illustrate a millennial history of land transformation and degradation by agrarian and extractive activities exacerbated at the second half of the 20th century by mechanized mining. This land stewardship history was culminated by a recent intervention of geomorphic-based ecological restoration and its monitoring. Historic anthropogenic processes which triggered gully erosion were intense deforestation for agriculture and grazing, and construction materials quarrying. From 1963 to 2006 mechanized quarrying operated over ancient extractive landforms. In 2007, a conventional rehabilitation mitigated risks but failed at controlling erosion and promoting soil and vegetation reestablishment. A geomorphic-based ecological restoration was accomplished since 2011. The GeoFluv-Natural Regrade CAD software was used for geomorphic landform design, and construction was completed with a carbonatic colluvium topdressing supplemented with a manure-amended soil, that was seeded with grasses. The whole process was a truly complete application of ecological engineering. One of the main purposes of this research was to carefully scrutinize the completed project, to evaluate its effectiveness and, if any deficiencies were found, to analyze their causes, so that they could be avoided in the future. Therefore, the landscape evolution and erosional behaviour of the restored area has been monitored from 2011 to 2020 through a time-lapse sequence of several oblique aerial photos, and by comparing topographies through Digital Elevation Models (DEMs) of Difference (DoDs). Those topographies were surveyed with differential GPS (DGPS) and with Structure from Motion (SfM) combined with Unmanned Aerial Vehicles (UAVs). This monitoring revealed: (a) landscape healing and diversification of the vegetation community composition and structure, as a result of the environmental heterogeneity of the geomorphic design; and (b) absence of hillslope and channel erosion for 99.8% of the area with limited surface erosion zones in 0.2% of the restored area. Our analysis attributed those limited erosion zones to a combination of: (a) minor design oversights; (b) slight construction deviation from the design grade; and (c) excessive runoff entering the repaired area that exceeded the design discharge. These erosion zones started to stabilize five years after initial restoration and achieved steady-state stability at nine years. The main lesson learnt from these minor deficiencies is that such erosion zones can be avoided at the design phase within GeoFluv-Natural Regrade by checking proper convex-concave slopes and concave channel profiles and by carefully considering any adjacent runoff entering the designed areas, which influence the channel's tractive forces. The use of Landscape Evolution Models, such as SIBERIA, can also identify design anomalies subject to erosion. Then, after rigorously inspecting the design, it is imperative that the construction is completed true to the design by defining and following construction tolerances. • Two millennial of land transformation, degradation and healing in Somolinos (Spain) • A holistic ecological restoration design and monitoring in Somolinos (Spain) • A geomorphic-based ecological restoration, 9-yr monitored, performed successfully. • GeoFluv key findings are reported to address those issues in future work.