Predicting sediment delivery from debris flows after wildfire

doi:10.1016/j.geomorph.2015.08.023

Geomorphology

Volume 250, 1 December 2015, Pages 173-186

https://doi.org/10.1016/j.geomorph.2015.08.023 Get rights and content

Highlights

•
Debris flows occur regularly after wildfire in some parts of southeast Australia.
•
Sediment yields from post-fire debris flows range from 113 to 294 t ha^− 1.
•
These rates are 2–3 orders of magnitude higher than annual background erosion rates.
•
A susceptibility model was developed from an inventory of 315 debris flows.
•
Debris flow susceptibility varies with slope, burn severity and aridity.

Abstract

Debris flows are an important erosion process in wildfire-prone landscapes. Predicting their frequency and magnitude can therefore be critical for quantifying risk to infrastructure, people and water resources. However, the factors contributing to the frequency and magnitude of events remain poorly understood, particularly in regions outside western USA. Against this background, the objectives of this study were to i) quantify sediment yields from post-fire debris flows in southeast Australian highlands and ii) model the effects of landscape attributes on debris flow susceptibility. Sediment yields from post-fire debris flows (113–294 t ha^− 1) are 2–3 orders of magnitude higher than annual background erosion rates from undisturbed forests. Debris flow volumes ranged from 539 to 33,040 m³ with hillslope contributions of 18–62%. The distribution of erosion and deposition above the fan were related to a stream power index, which could be used to model changes in yield along the drainage network. Debris flow susceptibility was quantified with a logistic regression and an inventory of 315 debris flow fans deposited in the first year after two large wildfires (total burned area = 2919 km²). The differenced normalised burn ratio (dNBR or burn severity), local slope, radiative index of dryness (AI) and rainfall intensity (from rainfall radar) were significant predictors in a susceptibility model, which produced excellent results in terms identifying channels that were eroded by debris flows (Area Under Curve, AUC = 0.91). Burn severity was the strongest predictor in the model (AUC = 0.87 when dNBR is used as single predictor) suggesting that fire regimes are an important control on sediment delivery from these forests. The analysis showed a positive effect of AI on debris flow probability in landscapes where differences in moisture regimes due to climate are associated with large variation in soil hydraulic properties. Overall, the results from this study based in the southeast Australian highlands provide a novel basis upon which to model sediment delivery from post-fire debris flows. The modelling approach has wider relevance to post-fire debris flow prediction both from risk management and landscape evolution perspectives.

Introduction

Debris flows after fire can be a major process by which sediment erodes from hillslopes and headwaters (Wohl and Pearthree, 1991, Meyer et al., 2001, Cannon et al., 2003, Gabet and Bookter, 2008, Kean et al., 2011, Nyman et al., 2011, García-Ruiz et al., 2013, Jordan, 2015). Their frequency and magnitude are therefore important for landscape evolution and sediment availability in upland rivers and streams (Rutherfurd et al., 1994, Gomi et al., 2002, Benda et al., 2003, Miller et al., 2003). Debris flows can also pose a considerable threat to water supply systems (White et al., 2006, Smith et al., 2011a) and other assets (Cannon and Gartner, 2005, Lyon and O'Connor, 2008). Models for predicting sediment delivery and hazards from post-fire debris flows are therefore needed. Currently the major limitation in the development of such models is the lack of fundamental data on event magnitude and the susceptibility of different landscapes to erosion by debris flows. Lack of data also means that the longer-term implications of these high magnitude events remain poorly understood.

Wildfire-related debris flows can be triggered by slope failure due to reduced root cohesion (Benda and Dunne, 1997, Wondzell and King, 2003) or they can be runoff-generated and triggered by overland flow and sediment bulking (Meyer and Wells, 1997, Cannon et al., 2003). Wildfire contributes to runoff-generated (or progressively bulked) debris flows by reducing infiltration and increasing sediment availability on hillslopes (Wells, 1987, Cannon et al., 2001a, Gabet and Sternberg, 2008, Nyman et al., 2013, Nyman et al., 2014a). The processes causing runoff-generated debris flows include a combination of i) runoff production (Cannon et al., 2001a, Kean et al., 2011), ii) rill erosion (Cannon et al., 2001a), iii) thin hillslope failures (Gabet, 2003) and iv) channel incision in converging zero-order headwaters (Cannon et al., 2001b, Gabet and Bookter, 2008). The persistence of debris flow processes in downstream channels depends on local slope and channel configuration as well as changes in flow rheology due to runoff accumulation, sediment entrainment and deposition within channels (Iverson, 1997, Cannon et al., 2003, Pelletier and Orem, 2014, Kean et al., 2013, Staley et al., 2014, Gartner et al., 2015).

Attributes related to infiltration are an important source of variation in debris flow susceptibility in burned areas (Wells, 1987, Cannon et al., 2001b, Jordan et al., 2004, Nyman et al., 2011). Infiltration is affected by burn severity (Moody et al., 2015) but can also vary with intrinsic catchment attributes related to climate, vegetation and soils in the burned area (Jenny, 1994, Wondzell and King, 2003, Nyman et al., 2014a). Aridity (or the balance between net radiation and precipitation) in particular is emerging as an important source of variation in hillslope processes at the local and regional scales (Wondzell and King, 2003, Ebel, 2013, Sheridan et al., 2015). After a fire the runoff response will also depend on the intensity and duration of rainfall (Cannon et al., 2011, Kean et al., 2012, Staley et al., 2012), which can be spatially variable during the vulnerable post-fire period. The role of burn severity, intrinsic landscape attributes, and rainfall patterns in controlling runoff production and debris flow response from burned areas is further complicated by variation in the scale (or drainage area) within which the debris flow processes operate. In low relief terrain for instance, the debris flows are confined to relatively small drainage areas with terminal deposits located in 1st or 2nd order drainage lines (e.g. 0.01–0.1 km²). In high relief terrain the debris flows persist into 3rd and 4th order drainages and thus operating within a much larger spatial domain (e.g. 0.1–10 km²).

The physical processes contributing to the initiation and propagation of runoff generated debris flows are complex and difficult to model. Using a mechanistic modelling approach Kean et al. (2013) showed that the initiation, frequency and magnitude of debris flow surges are regulated by channel slope with low gradient sections acting as ‘sediment capacitors’ temporarily storing eroded sediment before its released as mass failure due to the downstream forces exceeding the resisting forces. This process is sensitive to runoff production, sediment availability, grain-size and topographic attributes. The parameters needed to model these processes are rarely available for large areas, and for practical purposes the debris flow magnitude and susceptibility are often modelled though empirical analysis of inventories (Van Den Eeckhaut et al., 2006, Blahut et al., 2010, Cannon et al., 2010). Statistical models of debris flow initiation and magnitude have been developed specifically for burned areas to help mitigate post-wildfire risks (Gartner et al., 2008, Gartner et al., 2014, Pak and Lee, 2008, Cannon et al., 2010). These models use information on catchment attributes and rainfall to produce estimates of debris flow probability and magnitude at the catchment outlet where infrastructure, homes and people may be at risk of direct impact from the debris flow.

In southeast Australia, debris flows in burned areas were only recently recognised as an important erosion process (Nyman et al., 2011, Smith et al., 2012). The lack of data on post-fire debris flows in this region mean that their magnitude, sediment sources and the factors contributing to variability in susceptibility remain poorly understood. In this study the overall goal is therefore to collect the data needed for developing models of sediment delivery from debris flows. The study takes a landscape-scale approach towards predicting debris flow probability while seeking to explicitly represent the distribution of erosion and deposition within debris flow producing catchments. The study was designed with three main objectives:

1.
Use field surveys of post-fire debris flows to quantify magnitude of erosion, the sediment sources and the triggering storm conditions
2.
Analyse erosion and deposition rates with respect to slope and drainage area
3.
Develop a model of debris flow susceptibility for large burned areas using data on burn severity, landscape attributes (e.g. slope and aridity) and rainfall intensity that are available at regional scales

Section snippets

Study area

The study is carried out in the eastern uplands of Victoria, southeast Australia (Fig. 1). The region forms part of the Great Dividing Range, and is described by Jenkins (1991) as a belt of “ridges, plateaus and corridors”. Elevation ranges from 200 m above sea level (a.s.l.) in foothills to 2000 m a.s.l. in the alpine regions along ridges and on upland plateaus. A large majority of the bedrock is of Palaeozoic origin and consists of marine sedimentary rocks (mudstone, shales and sandstone). The

Post-fire debris flows: rainfall intensity and sediment yield

Erosion surveys of debris flows were carried out in 10 catchments at seven sites (Fig. 1, Table 1). These sites were selected because i) information on the date of the debris flow response was available from catchment management authorities and/or local landowners, ii) the debris flows could be readily accessed, and iii) rainfall data (usually rainfall totals) were available from nearby rain gauges. Hillslope and channel erosion measurements at Rose River 1, Yarrarabula 2 and Germantown 1 (data

Post-fire debris flows: rainfall intensity and sediment yield

Rainfall totals for debris flow triggering storms ranged from 16 to 34 mm (Fig 4). The average 30-min (I₃₀) and 15-min (I₁₅) rainfall intensity of debris flow triggering rainfall events ranged from 17 to 60 mm h^− 1 and 35–85 mm h^− 1, respectively, corresponding to average return intervals (ARI) between 2 and 10 years. The range of 15-min peak intensities were higher than the minimum intensities reported by Kean et al. (2011) and Staley et al. (2012) for post-fire debris flows in the San Gabriel

Conclusions

The study set out to quantify sediment yields from post-fire debris flows in southeast Australian highlands and model the effects of landscape attributes on debris flow susceptibility. We found that post-fire debris flows produce sediment yields of 113–294 t ha^− 1 which are 2–3 orders of magnitude higher than background erosion rates in undisturbed forests. Sediment yields could be modelled along the drainage network by expressing erosion as a function of local slope and contributing area and

Acknowledgments

The research was funded by the Bushfire Cooperative Research Centre for the Victorian Department of Environment, Land, Water and Planning and the Melbourne Water Corporation. We are also thankful to Philip Noske, Matt Richardson and Rene van der Sant for support in the field. Comments from two anonymous reviewers and the editor helped improve the manuscript.

References (94)

M.A. Adams
Mega-fires, tipping points and ecosystem services: managing forests and woodlands in an uncertain future
For. Ecol. Manag.
(2013)
L. Benda et al.
Effects of post-wildfire erosion on channel environments, Boise river, Idaho
For. Ecol. Manag.
(2003)
J. Blahut et al.
Analysis of landslide inventories for accurate prediction of debris-flow source areas
Geomorphology
(2010)
J.A.H. Brown
Hydrologic effects of a bushfire in a catchment in south-eastern New South Wales
J. Hydrol.
(1972)
S.H. Cannon et al.
Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California
Geomorphology
(2008)
S.H. Cannon et al.
Wildfire-related debris-flow initiation processes, storm king mountain, Colorado
Geomorphology
(2001)
M.G. Cruz et al.
Anatomy of a catastrophic wildfire: the black Saturday Kilmore east fire in Victoria, Australia
For. Ecol. Manag.
(2012)
E.J. Gabet et al.
A morphometric analysis of gullies scoured by post-fire progressively bulked debris flows in southwest Montana, USA
Geomorphology
(2008)
E.J. Gabet et al.
The effects of vegetative ash on infiltration capacity, sediment transport, and the generation of progressively bulked debris flows
Geomorphology
(2008)
J.M. García-Ruiz et al.
Fire-related debris flows in the Iberian range, Spain
Geomorphology
(2013)

J.E. Gartner et al.

Empirical models for predicting volumes of sediment deposited by debris flows and sediment-laden floods in the transverse ranges of southern California

Eng. Geol.

(2014)

J.E. Gartner et al.

Empirical models to predict the volumes of debris flows generated by recently burned basins in the western U.S.

Geomorphology

(2008)

R. Guthrie et al.

An examination of controls on debris flow mobility: evidence from coastal British Columbia

Geomorphology

(2010)

K. Hyde et al.

Predicting gully rejuvenation after wildfire using remotely sensed burn severity data

Geomorphology

(2007)

P.N.J. Lane et al.

Changes in sediment loads and discharge from small mountain catchments following wildfire in South eastern Australia

J. Hydrol.

(2006)

D. Miller et al.

Time, space, and episodicity of physical disturbance in streams

For. Ecol. Manag.

(2003)

P. Nyman et al.

Modeling the effects of surface storage, macropore flow and water repellency on infiltration after wildfire

J. Hydrol.

(2014)

P. Nyman et al.

Evidence of debris flow occurrence after wildfire in upland catchments of south-east Australia

Geomorphology

(2011)

W.J. Reed et al.

Power-law behaviour and parametric models for the size-distribution of forest fires

Ecol. Model.

(2002)

K.L. Riley et al.

Frequency–magnitude distribution of debris flows compiled from global data, and comparison with post-fire debris flows in the western US

Geomorphology

(2013)

P.M. Santi et al.

Sources of debris flow material in burned areas

Geomorphology

(2008)

H.G. Smith et al.

Wildfire and salvage harvesting effects on runoff generation and sediment exports from radiata pine and eucalypt forest catchments, south-eastern Australia

For. Ecol. Manag.

(2011)

H.G. Smith et al.

Wildfire effects on water quality in forest catchments: a review with implications for water supply

J. Hydrol.

(2011)

H.G. Smith et al.

Quantifying sources of fine sediment supplied to post-fire debris flows using fallout radionuclide tracers

Geomorphology

(2012)

D.M. Staley et al.

Characterizing the primary material sources and dominant erosional processes for post-fire debris-flow initiation in a headwater basin using multi-temporal terrestrial laser scanning da'ta

Geomorphology

(2014)

M. Van Den Eeckhaut et al.

Prediction of landslide susceptibility using rare events logistic regression: a case-study in the Flemish Ardennes (Belgium)

Geomorphology

(2006)

E.E. Wohl et al.

Debris flows as geomorphic agents in the Huachuca mountains of southeastern Arizona

Geomorphology

(1991)

S.M. Wondzell et al.

Postfire erosional processes in the pacific northwest and rocky mountain regions

For. Ecol. Manag.

(2003)

S.W. Anderson et al.

Exhumation by debris flows in the 2013 Colorado front range storm

Geology

(2015)

J.C. Bathurst et al.

Modelling the impact of forest loss on shallow landslide sediment yield, Ijuez river catchment, Spanish Pyrenees

Hydrol. Earth Syst. Sci. Discuss.

(2007)

L. Benda et al.

Stochastic forcing of sediment supply to channel networks from landsliding and debris flow

Water Resour. Res.

(1997)

G. Bowman et al.

Particle size analysis

R.A. Bradstock et al.

Effects of weather, fuel and terrain on fire severity in topographically diverse landscapes of south-eastern Australia

Landsc. Ecol.

(2010)

L. Bren

Forest hydrology and catchment management: an Australian perspective

(2014)

W. Cai et al.

Positive Indian ocean dipole events precondition southeast Australia bushfires

Geophys. Res. Lett.

(2009)

S.H. Cannon

Debris-flow generation from recently burned watersheds

Environmental & Engineering Geoscience

(2001)

S. Cannon et al.

Rainfall intensity–duration thresholds for postfire debris-flow emergency-response planning

Nat. Hazards

(2011)

S. Cannon et al.

Wildfire-related debris-flow generation through episodic progressive sediment-bulking processes, western USA

S.H. Cannon et al.

Wildfire-related debris flow from a hazards perspective

S.H. Cannon et al.

A process for fire-related debris flow initiation, Cerro Grande fire, New Mexico

Hydrol. Process.

(2001)

S.H. Cannon et al.

Predicting the probability and volume of postwildfire debris flows in the intermountain western United States

Geol. Soc. Am. Bull.

(2010)

R.S. Carmichael

B.C. Chessman

Impact of the 1983 wildfires on river water quality in East Gippsland, Victoria

Mar. Freshw. Res.

(1986)

B.A. Ebel

Simulated unsaturated flow processes after wildfire and interactions with slope aspect

Water Resour. Res.

(2013)

E. Gabet

Post-fire thin debris flows: sediment transport and numerical modelling

Earth Surf. Process. Landf.

(2003)

J.E. Gartner et al.

Implemetation of post-fire debris-flow hazard assessments along drainage networks, southern California, U.S.A

J.E. Gartner et al.

Predicting locations of post-fire debris-flow erosion in the San Gabriel Mountains of southern California

Nat. Hazards

(2015)

Cited by (63)

A landscape scale model to predict post-fire debris flow impact zones
2024, Geomorphology
Post-fire debris flows pose a significant hazard in mountainous regions, but accurate assessment of the associated risk at large scales, particularly in the context of mega-fires, is limited. Although numerous models exist, few are functional at the landscape scale, and none integrate assessments of downstream effects with the likelihood of flow initiation to define both the frequency and magnitude of potential flows. The aim of this work, therefore, was to develop a post-fire debris flow model that could characterise both the occurrence frequency and associated runout of debris flow events and which could be rapidly applied to fire events at the landscape scale. We achieve this using a model integration approach that included the development of a reduced-complexity debris flow runout model, which was calibrated and independently tested for its application at large scales with a dataset of 1377 individual post-fire flows across south-eastern Australia. This model was then integrated with previously published methods determining debris flow source areas and likelihood of initiation specific to our study area. The developed model is intentionally designed for rapid response hazard management. Therefore, it predominantly incorporates only the fundamental, lowest parameter form drivers of debris flow initiation and runout termination, thus minimising computational complexity while ensuring prediction accuracy sufficient for hazard assessment even at application scales as large as mega-fires. Accounting for debris flows initiated from single headwaters and cases where flows simultaneously converge from multiple initiation points, our integrated model effectively characterises debris flow hazard across a geomorphologically diverse landscape encompassing >200,000km² (capturing ~640,000 potential debris flow initiation locations across Victoria, Australia). Model testing using an independent validation dataset resulted in debris flow runout predictions with root mean square error (RMSE) of 176 and 308 m for non-convergent and convergent flows respectively. Crucially, these predictions can be computed rapidly for large (up to landscape scale) fire events with minimal input requirements and the use of a remotely-sensed observation dataset for domain calibration. As such, the model provides a critical means of addressing the capacity gap in assessments of post-fire debris flow hazard by efficiently integrating measures of occurrence frequency and runout for functional application at large scales. This new work empowers land managers to rapidly predict the hazard arising from post-fire erosion processes and represents an important applied step towards better understanding and mitigating the impacts of wildfire-induced debris flows.
Soil erosion after fire in volcanic terrain: Assessment and implications for post-fire soil losses
2023, Journal of Hydrology
Wildfires can dramatically modify the hydrologic and erosion response of ecosystems, increasing risks to population and assets downslope of fire affected hillslopes. This applies especially to volcanic areas in fire-prone regions which often exhibit steep terrain and high population densities. However, the effects of fire on key hydrologic and erosion parameters, which are critical for modelling runoff-erosion processes, predicting related post-fire risks and for selecting effective mitigation measures, have not been extensively assessed in this terrain type. Here we evaluate water erosion processes of two contrasting volcanic soils in recently burned forest areas of Tenerife (Canary Islands, Spain) at hillslope scale using erosion plots monitoring and rill erosion simulation experiments. The results show that both the lithology and the degree of weathering of the volcanic material govern the post-fire water erosion by concentrated flow (rill erosion experiments) and by the combination of interrill and rill erosion (erosion plots). Mature volcanic soils showed less susceptibility to erosion than weakly weathered volcanic soils and soils with non-volcanic lithologies. The results also show that the availability of easily detachable and transportable soil particles swiftly decreases after the fire, leading to the exhaustion of sediments and a decrease of the erosion rates with cumulative runoff events. These findings have direct implications for the modelling of runoff-erosion processes in volcanic terrain.
Unique challenges posed by fire disturbance to water supply management and transfer agreements in a headwaters region
2023, Journal of Environmental Management
As a headwaters region, Colorado is a critical source of water for surrounding states and Mexico. But fuel densification and shifts in hydrometeorological processes, such as climate aridification and precipitation sharpening, are causing increasingly severe and erratic wildfire behavior and post-disturbance geomorphic hazards in and downstream of its forested source water areas. Human development patterns and inter and intra-state water rights agreements further complicate resource management. This is prompting land managers to consider progressive planning and management tools to mitigate fire-related degradation of water supply and irrigation systems. This narrative review examines aspects of Colorado's geography, demography, and hydrology that make its water supply systems and transfer agreements particularly vulnerable to landscape disturbance and then provides hazard mitigation recommendations. Readers are introduced to Colorado's water supply portfolio including how water is moved, stored, treated, and consumed; why those systems are vulnerable to wildfire disturbance; and how risk can be reduced before and after fires occur. Lessons learned are applicable to other source water areas facing similar challenges. By synthesizing our review findings, we identified numerous research and programmatic gaps including the need for more interdisciplinary studies; a lack of explicit research into how disturbance-driven hydromodification may hinder the ability of headwater regions to exercise their water rights and fulfill water transfer agreements (crucial for reducing potential future water conflict); an unresolved debate regarding the potential effects of forest treatments on water yield; and the need for additional funding to roll out tools and educational programs to communities experiencing severe wildfire activity for the first time.
The effects of large-scale forest disturbances on hydrology – An overview with special emphasis on karst aquifer systems
2022, Earth-Science Reviews
Large-scale forest disturbances (LSFD) are an essential component of forest ecosystem dynamics. The effects of rapid loss of forest cover and other changes in forest ecosystems are inextricably linked to hydrologic processes such as evapotranspiration, soil and recharge processes. Among all hydrogeological systems, karst aquifers are important because of their exceptionally rich and unique biodiversity, biomass, and groundwater resources. At the same time, they are characterized by specific hydrological processes that make them highly vulnerable to environmental changes. Therefore, this study paid special attention to the effects of LSFD on karst hydrology. Using the PRISMA checklist, a thorough literature review of studies published between 2001 and 2020 was compiled into a comprehensive matrix dataset. In addition, an initial assessment of the global and regional distribution of forests on carbonate rocks was made based on publicly available geodatabases of forests and karst aquifers. The compiled information provides the first global overview of hydrological processes affected by LSFD, and identifies important knowledge gaps and future research challenges. The matrix dataset contained 117 full-text articles with a total of 160 case studies. Most publications were from 2011 to 2017, with more than half of the studies at the plot level and more than one-third at the catchment level. Studies on the effects of fires and pest and diseases infestations predominated. However, no articles were found on the effects of ice storms on hydrology in general or on the effects of pest and disease infestations on hydrology in karst areas. Of the 45.6 M km² of forested land worldwide, 6.3 M km² or 13.9% of all forests are underlain by carbonate rocks. Carbonate rocks cover about 15% of the land surface, which means that 31.3% of the world's karst aquifers are covered by forest. 29% of all case studies were conducted in karst areas, which is a high proportion compared to the proportion of forests in karst areas. However, these studies are unevenly distributed geographically. Most studies were conducted at the plot level, and only 21% of studies focused on natural LSFD, so forest management and land use change studies predominated. Although studies on the effects of LSFD on evapotranspiration processes between vegetation, air and soil are fairly well represented, infiltration and recharge processes in karst areas remain poorly understood and knowledge is lacking, particularly on groundwater flow and related hydrological processes. Regional studies and impacts on groundwater resources are also insufficient. The results indicate an urgent need for an integrated holistic interdisciplinary approach and a comprehensive understanding of the individual influencing factors, which would allow more accurate modelling of hydrological processes in forested karst aquifers.
Characteristics and predictive models of hillslope erosion in burned areas in Xichang, China, on March 30, 2020
2022, Catena
Wildfires often greatly aggravate hillslope erosion, which is a complex, highly dynamic and constantly changing water-soil interaction process. In this study, the remote sensing interpretation, field investigation, in-situ soil erosion pins experiments, and laboratory test were used to examine the controlling factors of post-fire hillslope erosion after the Xichang Fires occurred on March 30, 2020, in southwest Sichuan Province, China. We developed an empirical model to predict predicting post-fire hillslope erosion, and evaluated the model performance at watershed scale combined with the Sediment Delivery Ratio model (SDR). The controlling factors of hillslope erosion (fire severity, soil properties, rainfall, and topography) were collected. The correlations between rainfall events-based hillslope erosion depth (HED) and the controlling factors were examined. The results show that the fire severity has the strongest correlation, followed by soil properties, rainfall, and topography. The new predictive models were developed using multiple linear and non-linear (power law relationship) regression based on the normalized differenced Normalized Burn Ratio (ndNBR), soil erodibility (K), accumulated rainfall erosivity (∑R) and topographic factor (LS). Then, the methods were evaluated by comparing the predicted and observed values on the testing subset based on the statistical coefficients including R-squared, root mean squared error (RMSE) and discrepancy ratio (DR). The results suggest that the developed empirical model based on multiple non-linear (power law relationship) has a better performance (R-squared: 0.600, RMSE: 1.948), and the discrepancy ratio of 87.2% data range from 0.5 to 2. The model was used to estimate the spatial distribution of hillslope erosion depth across the entire study area, and the sediment yield at watershed scale (WSY) combined with the SDR model. The comparison between the observed sediment mobilized by debris flow and the predicted WSY shows that the model combined with the SDR showed an acceptable performance at watershed scale.
Shallow landslides and vegetation at the catchment scale: A perspective
2021, Ecological Engineering
Shallow, rainfall-triggered landslides are an important catchment process that affect the rate and calibre of sediment within river networks and create a significant hazard, particularly when shallow landslides transform into rapidly moving debris flows. Forests and trees modify the magnitude and rate of shallow landsliding and have been used by land managers for centuries to mitigate their effects. We understand that at the tree and slope scale root reinforcement provides a significant role in stabilising slopes, but at the catchment scale root reinforcement models only partially explain where shallow landslides are likely to occur due to the complexity of subsurface material properties and hydrology. The challenge of scaling from slopes to catchments (from 1-D to 2-D) reflects the scale gap between geomorphic process understanding and modelling, and temporal evolution of material properties. Hence, our understanding does not, as yet, provide the necessary tools to allow vegetation to be targeted most effectively for landslide reduction. This paper aims to provide a perspective on the science underpinning the challenges land and catchment managers face in trying to reduce shallow landslide hazard, manage catchment sediment budgets, and develop tools for catchment targeting of vegetation. We use our understanding of rainfall-triggered shallow landslides in New Zealand and how vegetation has been used as a tool to reduce their incidence to demonstrate key points.

View all citing articles on Scopus

View full text