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Desir, G., Marín, C.Effects of slope processes and management in gullying .................................................................................................... 38

Dóniz, J., Romero, C.Gully erosion on cinder cones of Tenerife (Canary Islands, Spain) .................................................................................. 40

Dotterweich M., Jared David, M.Prehistoric and modern impacts on gully formation on the loess hills of northern Mississippi, USA ............................. 42

Echeverría, M.T., Ibarra, P., Pérez-Cabello, F.Agricultural land use, piping and gullies activity in the Huelva lower valley (Saragossa, Spain) ................................... 44

Eustace, A.H., Witte, C., Carey, B.W.Evaluating airborne laser scanning for gully erosion detection and baseline mapping in the Fitzroy catchment, QLD,Australia ............................................................................................................................................................................ 46

Giménez, R., Casalí, J., Campo, M.A.Hydrological effects of the sediments deposited off a hillslope affected by rill erosion: project outlines and preliminaryresults ................................................................................................................................................................................ 48

Gómez, Á., Schnabel, S., Felicísimo, A.Modelling the occurrence of gullies in semi-arid areas of south-west Spain ................................................................... 50

Gordon, L., Bennett, S.J., Wells, R., Alonso, C.Ephemeral gully headcut development and migration in stratified soils .......................................................................... 52

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Lucía, A., Sanz, M.A., Vicente, F., Martín, C., Martín, J.F., Bodoque, J.M., Pedraza, J., López, N.A proposal to study gully erosion on silica sand and arkose slopes in central Spain ....................................................... 72

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IV International Symposium on Gully Erosion. J. Casalí and R. Giménez (Eds.)© 2007 Universidad Pública de Navarra, Spain. ISBN 978-84–9769-198-7

A PROPOSAL TO STUDY GULLY EROSION ON SILICA SAND AND ARKOSE SLOPES IN CENTRAL SPAIN

Lucía, A.1, Sanz, M.A.1, Vicente, F.2, Martín, C.1, Martín, J.F.1*, Bodoque, J.M.1, Pedraza, J.1, López, N.3

1Dpto. de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, C/José Antonio Novais s/n,28040, Madrid, Spain. *josefco@geo.ucm.es2 Universidad SEK, Campus de Santa Cruz la Real: C/ Cardenal Zúñiga, 12, 40003 Segovia, Spain.3Dpto. de Biología Vegetal, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid, C/José Antonio Novaiss/n, 28040, Madrid, Spain.

1. Introduction

A research project to be developed, granted by theSpanish Minister of Education and Science (projectCGL2006-07207), aims to investigate gully erosion onsilica sand and arkose slopes in Central Spain. The period ofthe study is from January 2007 to December 2009. In thisabstract, we present the objectives and beginning of the thisresearch project.

2. Geology and landforms

Two areas have been chosen to study gully erosion andsediment movement at the North Slope of the GuadarramaMountains, in the Central System of the Iberian Peninsula(Segovia Province, Castille and Leon Region, Spain).

The first area is underlain by silica sand, shale and gravelsediments of Upper Cretaceous age. They form adepositional sequence, approximately 70 m thick, boundedby two erosional surfaces. The silica sands consist, mainly,of quartz, with a less proportion of feldspar and mica, theselatter transformed to kaolin and smectite. These sedimentsare described as braided fluvial deposits and coastal fandeltas deposits (ITGE, 1991). The landforms under studyare gullies and badlands underlain by the sediments abovedescribed. They occur on slopes of mesas and cuestas,capped by more resistant rocks, limestones and dolostones.Platforms and slopes of these mesas and cuestas are coveredby a mixed holm oak and juniper forest, which is nowrecovering from centuries of overgrazing (Fig. 1).

The second area is underlain by arkosic sand sediments,with pebbles, cobbles and boulders of granite, gneiss andquartz, of Miocene age (ITGE, 1990). These sediments wereformed in alluvial fan systems, emerging from the upliftingof the Guadarrama Mountain range to the south (ITGE,1991). The landscape is characterized by dry cereal crops onrolling uplands, only dissected by the actual fluvial system.At the slopes of the valleys, gullies are developed (Fig. 2).

3. Research proposal

With this project, we mainly intend to characterize andquantify, in terms of type of activity, velocity and frequency,the active geomorphologic processes operation in thereferred gullies. Specifically, we aim to:

Fig 1. Aerial view of the gullies developed on silica sand slopes(in: Díez and Martín Duque, 2006).

Fig 2. Aerial view of the gullies developed on arkosic slopes (in:Díez and Martín Duque, 2006).

1) Understand the origin and development of thesegullies, and their evolution in historical times, since ithas no been explained yet if they have a natural orhuman-induced origin.

2) Study their evolution in recent times (1946 to thepresent, through series of aerial photographs), inorder to determine if the gullies are growing,shrinking, or have stabilized.

3) Characterize and quantify their current functioning,by establishing which geomorphologic processes areeroding and mobilizing the sediments within thegullies. What is the degree of activity, and the speed atwhich the processes of water erosion, piping, massmovements, and sediment transportation operate? To

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do so we intend to follow these approaches: (1)various dendrogeomorphic techniques to measure theamount and rate of both erosion of the interfluves andsedimentation in the collector drainages. In thisrespect, our team has already the experience andexpertise of quantifying sheet erosion rates from theanalysis of exposed Scots pine roots (Bodoque et al.,2005). (2) Installation of rods, erosion pins, pedestalsand micro-profile devices to measure small changesin the topography of the gullies by both water erosionand mass movement. (3) Installation of sediment trapsin the dry washes, to measure the amount of sedimentyield. (4) Instrumentation to measure knickpointmigration within collector washes. (5) Detailedtopographical surveys to quantify the modification ofthe area of the gullies’ watersheds and massmovement processes within the gullies.

4) Identify the effects that the various distinctmeteorological regimes have on the movementof sediment. By installing weather stations, andmodelling the watersheds, to investigate the causes andfrequencies of geomorphic activity. What season of theyear produces the most erosion and transportation ofsediment? What is the relation between meteorologicalconditions and distinct geomorphic processes and rates?

5) Determine how these processes affect vegetationdynamics. The presence of unstable substratum andthe variation that occurs on the nature of the soil, oncethe gullies are formed, have striking effects on thevegetation.

6) As the main conclusion of the project, we intend topropose a model for the origin and development of thegullies, to explain in detail their geomorphic activity,and to determine the implications for the environmentalmanagement of the area.

7) Last but not least, we are interested on obtainingapplicable conclusions for the land reclamation ofmines and quarries on these terrains. Moreover onsilica sand mines, common in the region. In the firstarea, there is a reclaimed silica sand mine, benefitedfrom existing gullies, which reclamation project wasdeveloped by us, based on a geomorphic approach(Martín-Duque et al., 1998). Being able to integratethe knowledge of the gully dynamics with thereclaimed mine system would result in a highlypotential for ecological restoration applications of thistype of mining.

4. The beginning of the research project

It is our intention to start monitoring the geomorphicactivity in the first place (objective 3), so that we can startgathering data, systematically, at the beginning of the 2007-2008 hydrological year (October 1st, 2007). In parallel withthe gathering of the data, objectives 1 and 2 will be tackled.In order to assess the most suitable locations for starting the

systematic monitoring of the geomorphic activity andsediment movement within the gullies, a detailed inventoryof landforms and processes is being carried out during thefirst months of 2007. The inventory is being conducted by:(1) using a specific form, which includes information onphysiography, morphometry, signs of active geomorphicprocesses, signs of stability (description of soils andvegetation) and the potential for installing devices tomeasure geomorphic activity (all that for each gully); (2)depicting detailed geomorphological sketches of the gullies.Simultaneously, a relational database connected to ageographical information system (GIS) is beingconstructed. The database provides the form information,along with graphical images (photos and sketches).

5. First assessment of scale of sediment movement

During the time that this proposal was elaborated, andduring the beginning of the project, a first assessment ofgeomorphic activity within the gullies has been studied. Theaim was to see what scale of sediment movement we will beworking with. Therefore, a series of rods were driven into theground of different dry washes of both areas, each one withwashers levelling the bottom of the dry wash. Measurementswere carried out after each storm or precipitation event. Atwo-year observation period now shows the following patternof sediment movement: (a) winter, snowmelt processes areable to move high amounts of sediment trough the drywashes, with the deepening of the bottom of the gulliesreaching depths up to 20 cm; (b) spring, hardly sedimentmovement through the beginning of the season, but thestorms of May and June trigger the most intense geomorphicactivity and sediment movement processes; intense storms onMay 2007 produced the deepening of some drywashes up to50 cm, and the formation of alluvial cones in almost eachsilica sand gully, some of them filling local roads with sand;(c) summer, general geomorphic inactivity; (d) autumm, lowintensity of erosion and sediment movement.

Acknowledgements: The research project CGL-2006-07207 is financiallysupported by the Spanish Minister of Education and Science.

References

Bodoque, J.M., Díez, A., Martín Duque, J.F. et al. 2005. Sheet erosion ratesdetermined by using dendrogeomorphological analysis of exposed treeroots: two examples from Central Spain. Catena, 64:81-102.

Díez, A. and Martín Duque, J.F. 2006. Las raíces del paisaje. Junta deCastilla y León, Valladolid.

ITGE, 1990. Mapa Geológico de España 1:50.000 (El Espinar, 507).Instituto Tecnológico Geominero de España, Madrid.

ITGE, 1991. Mapa Geológico de España 1:50.000 (Pradena, 458).Instituto Tecnológico Geominero de España, Madrid.

Martín-Duque, J.F., Pedraza, J., Díez, A., Sanz, M.A. and Carrasco, R.M.1998. A geomorphological design for the rehabilitation of an abandoned

sand quarry in central Spain. Landscape and Urban Planning, 42:1-14.

Progress in Gully Erosion Research

IV International Symposium on Gully ErosionSeptember 17-19, 2007. Pamplona, Spain

Título: Progress in Gully Erosion Research

Editores: Javier Casalí / Rafael Giménez

Edita: Universidad Pública de Navarra : Nafarroako Unibertsitate Publikoa

Fotocomposición: Pretexto pretexto@cin.es

Imprime: Ona Industria Gráfica

Depósito Legal: NA-2.519/2007

ISBN: 978-84–9769-198-7

© Autores

© Universidad Pública de Navarra

Impreso en papel ecológico

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