Automatic generation of topologically connected gully networks for integrated erosion control in sloping olive orchards

The severe erosion problems affecting large areas of olive groves on slopes in Andalusia (Spain), whose soil losses exceed 40 kg m-2an  in extreme rainfall events, require an integrated watershed management run by landowners and state or regional agencies.

The most common, and most severe erosion form is gully erosion. Gullies act as preferential ways through which soli particles with adsorbed nutrients and agrochemical substances spread downslope moved by surface runoff, what implies a great water loss.

During the last four years a cooperative innovation project between the University of Cordoba and two joint venture groups to (i) evaluate the extent of the soil loss in selected slopes, (ii) estimate the density and location of check-dams to intercept the water and sediment flows; (iii) design a novel type of modular dams; and (iv) complement th conservation works with new cover crops mixtures.

A by-product of this project is the development of an automatic model for the spatiotemporal evolution of gully networks based on the D8 flow direction algorithm, and a network branches detection scheme to accumulate flow identifying the final outlet.

This model has been successfully applied to two olive cropped slopes of Southern Spain.

The innovative proposal has allowed for: (a) Generation of the DEM (Digital Elevation Model) for hydrological modeling of watersheds and determination of gullies and areas vulnerable to erosion; (b) Development of algorithms for a topologically connected network of gullies to establish the areas of origin of soil loss and sediment deposition (c) Protection and correction of ephemeral and deep gullies in pilot plots by means of dikes of modular pieces, vegetation covers in crop roads, protection of roads and vulnerable areas through native plantations, and burying of pruning remains; (d) Monitoring and follow-up of measures from LiDAR sensors on board UAVs and soil analysis before and after extreme events.

These initiatives have already been successfully tested in several projects in which the University of Cordoba participates, such as the CPI INNOLIVAR project and the HIDROLIVAR Operational Group and will be implemented in new study basins where excellent results are expected due to the fragility of steep slope olive groves in very degraded soils.