A spatial information technology approach for the mapping and quantification of gully erosion University of Lleida, Spain José A. Martínez-Casasnovas

Content 1. Introduction. –Spatial information technologies for gully erosion analysis. –The gully erosion problem in the study area. –Objectives. 2. Materials and methods. 3. Results. 4. Conclusions.

1. Introduction A lot of research works on Gully Erosion Mapping have been based on Remote Sensing techniques, and particularly on airphoto interpretation.

Satellite images may also offer interesting possibilities provided that gullies affect areas wide enough to be covered by the resolution of the images. Landsat 5 TM Image Walls Activity Map

At detailed scale, Photogrammetry has also been used to map the volumetric changes in gullies, sediment production and gully erosion rates

The convergence and extension of Photogrammetry, Digital Imaging Technology and GIS have contributed to the use of multi-temporal DEM to compute sedimemt production by gully erosion.

In this context, the present work shows the methods and results of a research to compute Gully Erosion Rates using Spatial Information Technologies: The Channel Incision Rate The Sediment Production Rate The Gully Walls Retreat Rate

España Cataluña Penedès – Suffers serious gully erosion problems – Gully erosion is favoured by the cropping of vineyards The research was carried out in the PENEDÈS Vineyard Region (NE Spain)

Contouring and terracing 1957 Elimination of traditional conservation measures 1993 Particularly important has been the period after the advent of mechanization (1950’s) The area has suffered a substantial transformation.

At present, the problems are so grave that even afect to urban areas, that were built- up in the neighbour of gullies.

Alt Penedès Rierussa Catchment 25 km 2 Martorell Piera Sant Sadurní d’Anoia Sierra Prelitoral Sierra Litoral Study Area Spain Catalonia Lithology MARLS, Sandstones, Conglomerates Rainfall mm/year Autumn & Spring > 100 mm h -1 in short periods L’Anoia

2. Materials and methods

1957 Situation 1993 Situation Aerial Photographs 1957, 1:30000 Aerial Photographs 1986, 1:30000 Orthophoto 1993 DEM Gullied area 1957DEM Gullied area 1993 Changes: Retreat of gully walls Changes: Channel Incision & Sediment Production Gully Walls Retreat / Channel Incision / Sediment Production Photo-interpretationRestitution Photo-interpretation Geo-referenciation

Construction of the 1957 DEM Photogrammetric Restitution of Contours (10 m interval) Filtering Spatial Interpolation

Sediment Production Rate (SPR) 1993 DEM 1957 DEM - GR 2 x ED x Bd A x T SPR = Bulk density (1.735 Mg m -3 ) Time of the studied period (years) Surface of the gullied area (ha) Grid resolution (m) Elevation differences (ED) =

3. Results

1. Gully area extent and Rate of gully walls retreat Overlaying (UNION) of Gully Area Extent Maps Overlay

Contingence matrix: UNION of Gully Areas Year 1993 (ha) Gullied areas Non-gullied areas Year 1957 (ha) Gullied areasNon-gullied areas Areas without changes

Year 1993 (ha) Gullied areas77 Non-gullied areas Year 1957 (ha) Gullied areasNon-gullied areas Contingence matrix: UNION of Gully Areas Gully Retreat

Year 1993 (ha) Gullied areas77 Non-gullied areas Year 1957 (ha) Gullied areasNon-gullied areas New parcel Contingence matrix: UNION of Gully Areas Gully Filling

Year 1993 (ha) Gullied areas77642 Non-gullied areas Total (Year 1957) Year 1957 (ha) Gullied areasNon-gullied areasTotal (Year 1993) Contingence matrix: UNION of Gully Areas

Retreat rate ( Rierusa Catchment ) 2.1 ha year -1 Gully Retreat Rate Linear Retreat Rate 0.2 m year -1 Retreat rate ( m 2 / 1000 m 2 of catchment ) 0.9 ‰ year -1

When did the acceleration of gully erosion processes start ? ha in 36 years Let’s apply back this rate considering that at present there are ~ 640 ha of gullies ~ 1650 From XVI century = Massive plantation of Vineyards under the protection of temporary contracts till the end of vineyards’ life. (Balcells 1980)

Altitude difference (m) ( ) Areas with loss of materials Areas with gain of materials 2. Channel Incision and Sediment Production Rates 0.8 m year m year -1

2. Channel Incision and Sediment Production Rates

Sediment Production Rate Rate in the Gully-eroded Areas /- 142 Mg ha -1 year -1 Rate with respect the total catchment area 331 +/- 35 Mg ha -1 year -1

Comparison with respect other research areas SE France (Bufalo and Nahon 1992) 190 Mg ha -1 year -1 Barasona basin (NE Spain) (Penella 1997) 375 Mg ha -1 year -1 Only account for overland flow erosion processes Mass Movements Penedès, Spain 1322 Mg ha -1 year -1 Channel Incision Overland flow New Zealand (DeRose et al. 1998) Mg ha -1 year -1

4. Conclusions

The present work confirms the conclusions of other researchers who state that sediment production by gully erosion is very far from negligible (around Mg ha -1 year -1 are a lot of tons).

In comparison with other methods of measuring sediment production, the proposed method computes a rate that is one order of magnitude higher. Mass Movements Channel Incision Overland flow The reason is that it integrates the losses due to:

In the Penedès region, the research confirmed the acceleration of erosion since the late Middle Ages because of the massive deforestation and plantation of vineyards, and in the recent past since the advent of mechanization.

At present, we are working on a multi-temporal study centered at the head of the gully system, using 1:5.000 aerial photographs. This will serve to compute gully erosion rates at very detailed scale from high resolution DEMs.