Debris-flow generation from recently burned watersheds

2001 ◽  
Vol 7 (4) ◽  
pp. 321-341 ◽  
Author(s):  
Susan H. Cannon
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Drainage Basin ◽  
Water Repellency ◽  
Initial Response ◽  
Water Repellent ◽  
Rainfall Events ◽  
Storm Rainfall ◽  
Large Material ◽  
Sand And Gravel

Abstract Evaluation of the erosional response of 95 recently burned drainage basins in Colorado, New Mexico and southern California to storm rainfall provides information on the conditions that result in fire-related debris flows. Debris flows were produced from only 37 of 95 ( approximately 40 percent) basins examined; the remaining basins produced either sediment-laden streamflow or no discernable response. Debris flows were thus not the prevalent response of the burned basins. The debris flows that did occur were most frequently the initial response to significant rainfall events. Although some hillslopes continued to erode and supply material to channels in response to subsequent rainfall events, debris flows were produced from only one burned basin following the initial erosive event. Within individual basin, debris flows initiated through both runoff and infiltration-triggered processes. The fact that not all burned basins produced debris flows suggests that specific geologic and geomorphic conditions may control the generation of fire-related debris flows. The factors that best distinguish between debris-flow producing drainages and those that produced sediment-laden streamflow are drainage-basin morphology and lithology, and the presence or absence of water-repellent soils. Basins underlain by sedimentary rocks were most likely to produce debris flows that contain large material, and sand- and gravel-dominated flows were generated primarily from terrain underlain by decomposed granite. Basin-area and relief thresholds define the morphologic conditions under which both types of debris flows occur. Debris flows containing large material are more likely to be produced from basins without water-repellent soils than from basins with water repellency. The occurrence of sand-and gravel-dominated debris flows depends on the presence of water-repellent soils.

scholarly journals STAV VÝZKUMU BLOKOVOBAHENNÍCH PROUDŮ NA ZÁPADNÍCH SVAZÍCH KEPRNICKÉ HORNATINY (HRUBÝ JESENÍK)

2014 ◽  
Vol 21 (1-2) ◽  
Author(s):  
Radek Tichavský ◽  
Karel Šilhán
Keyword(s):  
Debris Flow ◽  
Tree Ring ◽  
Debris Flows ◽  
Drainage Basin ◽  
Climatic Conditions ◽  
Tree Ring Analysis ◽  
Geomorphological Mapping ◽  
Spatial Dimensions ◽  
Ring Analysis ◽  
Channel Bottom

The debris flows are fast dangerous processes initiated also in mid-mountains of the Czech Republic, frequently damaging forest stands. An occurrence of debris flows in the Hrubý Jeseník Mts. is connected with steep slopes and high-gradient channels predisposed by landuse, morphometric, lithological and especially climatic conditions. The first stage of research was implemented in the Klepáčský brook drainage basin. In 2013, a field geomorphological mapping and sampling of disturbed trees for dendrogeomorphic research (tree ring analysis) were carried out. There are preserved several remnants of former debris flows. The oldest accumulations in a form of terraces above the channel bottom, younger but stable and overgrown lateral levees and recent fresh frontal lobes directly in the channel were distinguished. At least 9 debris flow events in the last 60 years were dated in the Klepáčský brook from the tree ring analysis; the year 2010 was the last known and the most represented period in the tree ring series. Spatial dimensions, magnitudes of debris flows and places of their origin has been changed during the last decades so we could analyze their different behaviour patterns (e. g. 1991, 1997 and 2010), recorded in disturbed trees along the brook. The research will be extended to other basins in the Keprnická hornatina Mts., focusing on factors of debris flow predisposition and chronology with an application of dendrogeomorphic methods being actually the most accurate approach for dating of events in far-flung tree-covered basins.

scholarly journals Relations between rainfall and triggering of debris-flow: case study of Cancia (Dolomites, Northeastern Italy)

2003 ◽  
Vol 3 (1/2) ◽  
pp. 71-79 ◽  
Author(s):  
M. Bacchini ◽  
A. Zannoni
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Warning System ◽  
Warning Signal ◽  
Mean Annual Precipitation ◽  
Predictive Tool ◽  
Northeastern Italy ◽  
Storm Rainfall ◽  
Flow Threshold ◽  
Flow Activity

Abstract. Debris-flows occurring in the area of Cancia (Dolomites, Northeastern Italy) in recent years have exposed the population to serious risk. In response to the recurring hazard, an alarm and monitoring system was installed to provide a sufficient level of safeguard for inhabitants and infrastructures. The data recorded at three rain gauges during debris-flow events has been analysed, taking into consideration the different elevation of the gauges to delineate the storm rainfall distributions. Rainfall data is compared with the occurrence of debris-flows to examine relations between debris-flow initiation and rainfall. In addition, the data is compared with that recorded during debris-flows which occurred under similar or different geological settings in the Eastern Italian Alps, in order to define triggering thresholds. A threshold for debris-flow activity in terms of mean intensity, duration and mean annual precipitation (M.A.P.) is defined for the study area The normalised rainfall and the normalised intensity are expressed as a per cent with respect to M.A.P. This threshold is compared with thresholds proposed by other authors, and the comparison shows that a lower value is obtained, indicating the debris-flow susceptibility of the area. The threshold equations are:  R/M.A.P. = - 1.36 · ln(I) + 3.93  where I > 2 mm/h  I /M.A.P. = 0.74 · D-0.56.  The determination of a debris-flow threshold is linked to the necessity of a fast decisional phase in a warning system for debris-flow protection. This threshold cannot be used as a predictive tool, but rather as a warning signal for technicians who manage the monitoring/warning system.

scholarly journals Wildfires Effect on Debris Flow Occurrence in Italian Western Alps: Preliminary Considerations to Refine Debris Flow Early Warnings System Criteria

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 422
Author(s):  
Davide Tiranti ◽  
Roberto Cremonini ◽  
Daniele Sanmartino
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Thick Layer ◽  
Soil Surface ◽  
Close Correlation ◽  
Moderate Intensity ◽  
Rainfall Events ◽  
Rainfall Analysis ◽  
Permeability Characteristics ◽  
Fine Grained

Rarely, a close correlation between wildfires and the occurrence of channelized debris flows has been observed in the Western Italian Alps. Only two cases in history have been reported, after brief and localized rainfall events of moderate intensity in Italy's Piemonte region (NW Italy) caused debris flows, on 18 July 2005, in Verbania province (Pallanzeno municipality), and on June 2018 in Turin province (Bussoleno municipality). These phenomena occurred after a large portion of the catchments were affected by wide wildfires in the preceding months. Debris flow deposits showed an unusually large number of fine-grained particles, forming dark-brown mud-rich deposits associated with burnt wood deposits. Rainfall analysis related to the period between the wildfires' occurrence and the debris flow events, using both raingauge and weather radar data, pointed out that the debris flows triggered in July 2005 and June 2018 were characterized by greater magnitude but associated with less precipitation intensity rates as compared with previous mud flows occurring just after wildfires. These behaviors can be explained by the presence of burned organic material and fine-grained sediment, generated from the soil's thermal reworking, which formed a thick layer, centimeters deep, covering a large percentage of catchments and slopes. Most of this layer, generated by wildfires’ action were winnowed by rainfall events that had occurred in the months before the debris flow events, of significant magnitude, exhuming a discontinuous hydrophobic soil surface that changed the slopes’ permeability characteristics. In such conditions, runoff increased, corrivation time shortened, and, consequently, discharge along the two catchments’ channels-network increased as well. Consequently, the rainfall effects associated with rainfall events in July 2005 and June 2019 were more effective in mobilizing coarse sediments in channel beds than was typical for those catchments.

scholarly journals Recent changes in rainfall characteristics and their influence on thresholds for debris flow triggering in the Dolomitic area of Cortina d'Ampezzo, north-eastern Italian Alps

2010 ◽  
Vol 10 (3) ◽  
pp. 571-580 ◽  
Author(s):  
M. Floris ◽  
A. D'Alpaos ◽  
C. Squarzoni ◽  
R. Genevois ◽  
M. Marani
Keyword(s):  
Debris Flow ◽  
Short Duration ◽  
High Intensity ◽  
Debris Flows ◽  
Meteorological Data ◽  
Rain Gauge ◽  
Annual Rainfall ◽  
Interarrival Time ◽  
Italian Alps ◽  
Rainfall Events

Abstract. In this paper, we examine variations in climate characteristics near the area of Cortina d'Ampezzo (Dolomites, Eastern Italian Alps), with particular reference to the possible implications for debris-flow occurrence. The study area is prone to debris-flow release in response to summer high-intensity short-duration rainfalls and, therefore, it is of the utmost importance to investigate the potential increase in debris-flow triggering rainfall events. The critical rainfall threshold is agreed to be a crucial triggering factor for debris-flows. Data from a monitoring system, placed in a catchment near Cortina (Acquabona), show that debris-flows were triggered by rainfalls with peak rainfall intensities ranging from 4.9 to 17.4 mm/10 min. The analyses of meteorological data, collected from 1921 to 1994 at several stations in the study area, show a negative trend of annual rainfall, a considerable variation in the monthly rainfall distribution, and an increase in the temperature range, possibly related to global climate changes. Moreover, high-intensity and short-duration rainfall events, derived from data collected from 1990 and 2008, show an increase in exceptional rainfall events. The results obtained in a peak-over-threshold framework, applied to the rainfall data measured at the Faloria rain gauge station from 1990 to 2008, clearly show that the interarrival time of over-threshold events computed for different threshold values decreased in the last decade. This suggests that local climatic changes might produce an increase in the frequency of rainfall events, potentially triggering debris flows in the study area.

scholarly journals Multiply factors driving continual post-wildfire debris flows with varied rainfall thresholds in the Reneyong Valley, southwestern China

2017 ◽  
Author(s):  
Mingfeng Deng ◽  
Yong Zhang ◽  
Mei Liu ◽  
Yuanhuan Wang ◽  
Wanyin Xie ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Water Repellency ◽  
Drainage Area ◽  
Southwestern China ◽  
Soil Water Repellency ◽  
Rainfall Thresholds ◽  
Rain Gauges ◽  
Ash Layer ◽  
Fire Debris

Abstract. In early June of 2014, wildfire struck the Reneyong Valley in the central Hengduan Mountains of southwestern China. Three days after the wildfire, the first debris flow was triggered in branch No. 3, followed by 2 other debris flows that same year. In August 2015, another debris flow occurred in branches No. 1, No. 2 and No. 3, respectively. Rainfall data from three nearby rain gauges and rainfall totals speculated from debris flow volume suggest the three debris flows in 2014 were generated by isolated convective rainfall. Later, we found that varied rainfall thresholds existed among the branches and that these thresholds might be related to the geological and geomorphic characteristics. The results show that (1) the thresholds of post-fire debris flows tend to increase as time passes; (2) post-fire debris flows in the Reneyong Valley occur with high frequency not only because of the loss of the natural canopy, the occurrences of an ash layer and dry ravels and an increase in soil water repellency but also because of the geology, drainage area, channel gradient and regional arid climate, which may not be affected by wildfire; and (3) the varied rainfall thresholds among the different branches are dependent on the drainage area, as entrainment is controlled by the magnitude of discharge.

scholarly journals Recent changes in the number of rainfall events related to debris-flow occurrence in the Chenyulan Stream Watershed, Taiwan

2012 ◽  
Vol 12 (5) ◽  
pp. 1539-1549 ◽  
Author(s):  
J. C. Chen ◽  
W. S. Huang ◽  
C. D. Jan ◽  
Y. H. Yang
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Lower Boundary ◽  
Extreme Rainfall ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Average Rainfall ◽  
Average Probability ◽  
Central Taiwan ◽  
Variation Trends

Abstract. This study analyzed the variability in the number of rainfall events related to debris-flow occurrence in the Chenyulan stream watershed located in central Taiwan. Rainfall data between 1970 and 2009 measured at three meteorological stations nearby/in the watershed were collected and used to determine the corresponding regional average rainfall for the watershed. Data on debris-flow events between 1985 and 2009 were collected and used to study their dependence on regional average rainfall. The maximum 24-h regional rainfall Rd was used to analyze the number of rainfall events Nr, the number of rainfall events that triggered debris flows Nd, and the probability of debris-flows occurrences P. The variation trends in Nr, Nd and P over recent decades under three rainfall conditions (Rd > 20, 230, and 580 mm) related to debris-flow occurrence were analyzed. In addition, the influences of the Chi-Chi earthquake on Nd and P were presented. The results showed that the rainfall events with Rd > 20 mm during the earthquake-affected period (2000–2004) strongly responded to the increases in the average number of rainfall events that triggered debris flows and the average probability of debris-flows occurrences. The number of rainfall events with Rd > 230 mm (the lower boundary for the rainfall ever triggering debris flow before the Chi-Chi earthquake), and Rd > 580 mm (the lower boundary for extreme rainfall ever triggering numerous debris flows) in the Chenyulan stream watershed increased after 2000. The increase in the number of extreme rainfall events with Rd > 580 mm augmented the number of rainfall events ever triggering numerous debris flows in the last decade. The increase in both the number of rainfall events that ever triggered debris flows and the probability of debris-flow occurrences was greater in the last decade (2000–2009) than in 1990–1999.

Investigations into and optimisation of the performance of sewage detention tanks during storm rainfall events

1999 ◽  
Vol 39 (2) ◽  
pp. 43-52 ◽  
Author(s):  
R. Kowalski ◽  
J. Reuber ◽  
Jürgen Köngeter
Keyword(s):  
Flow Field ◽  
Pollutant Transport ◽  
Cleaning Efficiency ◽  
Rainfall Events ◽  
Transient Phenomena ◽  
Numerical Studies ◽  
Hydraulic Load ◽  
Storm Rainfall ◽  
Different Levels ◽  
Sewage Systems

Combined Sewage Detention Tanks (CSDT) are components of combined sewage systems commonly used in Germany. A lack of knowledge of the processes occurring within these structures causes the engineer to apply conceptual approaches in the simulation of pollutant transport. The investigations presented were implemented in an integrated systematic way. Extensive analytical, experimental and numerical studies of steady and transient phenomena taking place in CSDTs were carried out simulating different levels of hydraulic load. The study of the flow field and the simulation of sedimentation and erosion under realistic conditions resulted in proposals for modification and optimisation of the function of CSDTs. A simple way of predicting the cleaning efficiency is presented.

Non-adhesive lotus and other hydrophobic materials

2008 ◽  
Vol 366 (1870) ◽  
pp. 1539-1556 ◽  
Author(s):  
David Quéré ◽  
Mathilde Reyssat
Keyword(s):  
Solid Surface ◽  
Room Temperature ◽  
Water Repellency ◽  
Short Review ◽  
Water Repellent ◽  
Practical Applications ◽  
Hydrophobic Materials ◽  
Volatile Liquid ◽  
Air Cushion ◽  
The Stability

Superhydrophobic materials recently attracted a lot of attention, owing to the potential practical applications of such surfaces—they literally repel water, which hardly sticks to them, bounces off after an impact and slips on them. In this short review, we describe how water repellency arises from the presence of hydrophobic microstructures at the solid surface. A drop deposited on such a substrate can float above the textures, mimicking at room temperature what happens on very hot plates; then, a vapour layer comes between the solid and the volatile liquid, as described long ago by Leidenfrost. We present several examples of superhydrophobic materials (either natural or synthetic), and stress more particularly the stability of the air cushion—the liquid could also penetrate the textures, inducing a very different wetting state, much more sticky, due to the possibility of pinning on the numerous defects. This description allows us to discuss (in quite a preliminary way) the optimal design to be given to a solid surface to make it robustly water repellent.

scholarly journals Learning Case Study of a Shallow-Water Model to Assess an Early-Warning System for Fast Alpine Muddy-Debris-Flow

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 750
Author(s):  
Antonio Pasculli ◽  
Jacopo Cinosi ◽  
Laura Turconi ◽  
Nicola Sciarra
Keyword(s):  
Debris Flow ◽  
Shallow Water ◽  
Early Warning ◽  
Debris Flows ◽  
Early Warning System ◽  
Warning System ◽  
Extreme Weather Events ◽  
Water Model ◽  
Computational Time ◽  
Processing Unit

The current climate change could lead to an intensification of extreme weather events, such as sudden floods and fast flowing debris flows. Accordingly, the availability of an early-warning device system, based on hydrological data and on both accurate and very fast running mathematical-numerical models, would be not only desirable, but also necessary in areas of particular hazard. To this purpose, the 2D Riemann–Godunov shallow-water approach, solved in parallel on a Graphical-Processing-Unit (GPU) (able to drastically reduce calculation time) and implemented with the RiverFlow2D code (version 2017), was selected as a possible tool to be applied within the Alpine contexts. Moreover, it was also necessary to identify a prototype of an actual rainfall monitoring network and an actual debris-flow event, beside the acquisition of an accurate numerical description of the topography. The Marderello’s basin (Alps, Turin, Italy), described by a 5 × 5 m Digital Terrain Model (DTM), equipped with five rain-gauges and one hydrometer and the muddy debris flow event that was monitored on 22 July 2016, were identified as a typical test case, well representative of mountain contexts and the phenomena under study. Several parametric analyses, also including selected infiltration modelling, were carried out in order to individuate the best numerical values fitting the measured data. Different rheological options, such as Coulomb-Turbulent-Yield and others, were tested. Moreover, some useful general suggestions, regarding the improvement of the adopted mathematical modelling, were acquired. The rapidity of the computational time due to the application of the GPU and the comparison between experimental data and numerical results, regarding both the arrival time and the height of the debris wave, clearly show that the selected approaches and methodology can be considered suitable and accurate tools to be included in an early-warning system, based at least on simple acoustic and/or light alarms that can allow rapid evacuation, for fast flowing debris flows.

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