Debris flow characteristics and relationships in the Central Spanish Pyrenees

Lorente, Adrián; Beguerı́a, Santiago; Bathurst, James C.; García‐Ruiz, José María

doi:10.5194/nhess-3-683-2003

Cited by 45 publications

(37 citation statements)

References 31 publications

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“…The typical size of the landslides is small (average 16 m wide), and the average runout length of the associated debris flow is about 56 m (Lorente et al, 2003). They affect a thin layer of soil and regolith (less than 1 m in general), and the slip surface coincides with the contact between soil and rock.…”

Section: Study Areamentioning

confidence: 99%

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Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees

2006

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The Pyrenees, like many other mountain areas in Europe, have experienced depopulation and land abandonment during the 20th Century. This has encouraged vegetation recovery in formerly occupied areas, including reforestation to promote woodland. The objective of this study is to analyse the effects of these changes on shallow landsliding, a process responsible for erosion and land degradation in many mountain areas. A sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th Century and a parallel increase in the landslide extinction rate, i.e. the rate at which evidence of landslide activity is removed by vegetation colonisation. A logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides.The result shows that the former arable fields on the valley slopes still facilitate landsliding, even after land abandonment and revegetation by shrubs or trees. A shift in the topographic location of landslides was also detected, pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods.

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Section: Study Areamentioning

confidence: 99%

“…The catchment lies within the Eocene Flysch Sector, consisting of a succession of thin, alternating, heavy folded layers of marls and sandstones. This formation has been identified as very prone to 4 shallow landsliding (García-Ruiz and Puigdefábregas, 1982;García-Ruiz and Valero, 1998;Lorente et al, 2002Lorente et al, , 2003.…”

Section: Study Areamentioning

confidence: 99%

Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees

2006

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“…Materials cleared by landslides become the main sediment source for debris flows (Johnson and Rodine, 1984;Blijenberg, 1998;Lorente et al, 2002Lorente et al, , 2003Beguería, 2006;Bathurst et al, 2007). However, recent reports have attributed the triggering of fire-related debris flows to increased rates of runoff eroding the uppermost areas of hillslopes (Cannon et al, 2001a;Gabet and Bookter, 2008;Cannon et al, 2011;Parise and Cannon, 2011).…”

Section: Introductionmentioning

confidence: 99%

“…Fire-related debris flows are commonly reported in Spanish mountains, particularly the Pyrenees (Lorente et al, , 2003Beguería 2006;García-Ruiz et al, 2010) and the Iberian Range (García-Ruiz et al, 1988). In most cases, the triggering of these debris flows has been attributed to periodical fires ignited by humans to convert shrublands to grasslands.…”

Section: Introductionmentioning

confidence: 99%

Fire-related debris flows in the Iberian Range, Spain

et al. 2013

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Debris flows occurred three weeks following a wildfire in August 1986 in the Najerilla River valley in the Iberian Range, northern Spain. The flows were triggered by a brief, intense rainstorm (approximately 25 mm h-1 over 15 minutes) in a small area with steep slopes covered by a deep colluvium of quartzite clasts. This storm resulted in the development of several unconfined hillslope debris flows and the formation in the Pítare ravine of an alluvial fan, which partially blocked the Najerilla River. We analysed the conditions that led to the development of the debris flows, and estimated the rainfall threshold and the total volume of mobilised sediment. Four factors contributed to the debris flows: (i) the occurrence of a rainstorm three weeks following a wildfire, which had removed the plant cover from the soil; (ii) the steep slopes in the area were most affected by the debris flows (slopes > 30º); (iii) the presence of quartzite scarps on the hillslopes, which favoured the occurrence of a 'firehose effect' involving channelised surface runoff; and (iv) the low plasticity index values of the fine material of the colluvium (indices of 7 to 8), which enabled rapid liquefaction. Estimates of rainfall intensity from the peak flow in the Pítare ravine indicated that 81 mm of rainfall fell in 15 minutes, although this quantity was clearly overestimated given the high proportion of sediment carried out during the peak flow. Various equations applied to relatively similar conditions that occurred elsewhere indicated a rainfall-threshold of approximately 25 mm h-1 for a time of concentration of 15 minutes. The total sediment transported by the debris flows was 10,500 m3 (15,750 Mg, 6,800 Mg km-2), and the Pítare stream alone transported a minimum of 4,000 m3 (6,000 Mg, 2,500 Mg km-2). These results suggest that the rainfall threshold for initiating debris flows is decreased following a wildfire such that a typical rainstorm can trigger a severe erosion and sediment transport event. Given the absence of fresh landslide scars on the hillslopes, the origin of the firerelated debris flows in the Najerilla River valley appears to have been directly linked to increased rates of hillslope runoff, with overland having a greater effect than infiltration for triggered landslides. COVER LETTER EXPLAINING THE CHANGES INTRODUCED IN THE PAPER "FIRE-RELATED DEBRIS FLOWS IN THE IBERIAN RANGE, SPAIN"Authors: José M. García-Ruiz, José Arnáez, Amelia Gómez-Villar, Luis Ortigosa, Noemí Lana-RenaultWe have corrected the paper carefully following the instructions and suggestions from the referees, to whom we acknowledge their detailed work, which helped us to significantly improve the content of the paper. For this reason we include a short reference to the referees in the "Aknowledgements" section.These are the changes we have introduced:Reviewer 1 -"The study is too descriptive". We have estimated both the intensity of precipitation and the volume mobilised by debris flows, and also we have applied some equations in order to co...

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“…In the Pyrenees, debris flows and shallow landslides are not as widely reported as in other mountainous areas, but still represent an important hazard (Lorente et al 2003;Portilla et al 2010). Rainfall triggered landslides that have occurred in the Eastern Pyrenees have usually been analysed on a regional scale (Gallart and Clotet 1988;Santacana et al 2003).…”

Section: Introductionmentioning

confidence: 99%