Tributary-junction alluvial fan response to an ENSO rainfall event in the El Huasco watershed, northern Chile

2020 ◽  
Vol 44 (5) ◽  
pp. 679-699 ◽  
Author(s):  
Albert Cabré ◽  
Germán Aguilar ◽  
Anne E. Mather ◽  
Víctor Fredes ◽  
Rodrigo Riquelme
Keyword(s):  
Debris Flows ◽  
Alluvial Fan ◽  
Storm Event ◽  
Arid Zones ◽  
Alluvial Fans ◽  
Main Trunk ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Main River ◽  
Longitudinal Connectivity

Tributary-junction alluvial fans situated at the intersection of confined valleys with <100 km2 tributary catchments are of special interest to evaluate the heterogeneous consequences of extreme rainfall events in arid zones. These fans record the episodic sedimentological behaviour of the hillslope response to rainstorm events within tributary catchments, together with the influence on the main fluvial systems. In this paper, we benefit from the March 2015 event (23–26 March 2015), which produced 75–46 mm of precipitation over four days in the southern portion of the Atacama Desert. This storm event triggered several debris flows in El Huasco River watershed tributaries and, therefore, tributary-junction alluvial fans received a total of ∼106 m3 of sediments across 49 activated catchments. We find that the characteristic storm signature across the catchments can be synthetised in a conceptual fan formation model based on field mapping of facies (F1 to F6) present in the fans. The characteristic signature is a record of initially high sediment-to-water flows restricted to the fan environments (mainly debris flows) followed by later, more dilute (mainly hyper-concentrated to fluvial) flows that incise the tributary-junction alluvial fan deposits and link tributary catchments with the main river. These later-stage flood event deposits, locally, are capable of ponding and compartmentalising the main river where the longitudinal connectivity of the tributary-junction catchment is effective. This situation improves tributary-junction fan slope and main-trunk-channel linkages. This approach provides a reference framework for understanding the distribution and routing of effective runoff from similar rainfall events that control the aggradation and incision of the fluvial system, which is of great value when studying past stratigraphic arrangements in these arid alleys.

scholarly journals Hydrogeomorphic processes and torrent control works on a large alluvial fan in the eastern Italian Alps

2010 ◽  
Vol 10 (3) ◽  
pp. 547-558 ◽  
Author(s):  
L. Marchi ◽  
M. Cavalli ◽  
V. D'Agostino
Keyword(s):  
Urban Areas ◽  
Debris Flows ◽  
Land Use Changes ◽  
Integrated Approach ◽  
Alluvial Fan ◽  
Aerial Photographs ◽  
European Alps ◽  
Alluvial Fans ◽  
Economic Activities ◽  
Hazard Management

Abstract. Alluvial fans are often present at the outlet of small drainage basins in alpine valleys; their formation is due to sediment transport associated with flash floods and debris flows. Alluvial fans are preferred sites for human settlements and are frequently crossed by transport routes. In order to reduce the risk for economic activities located on or near the fan and prevent loss of lives due to floods and debris flows, torrent control works have been extensively carried out on many alpine alluvial fans. Hazard management on alluvial fans in alpine regions is dependent upon reliable procedures to evaluate variations in the frequency and severity of hydrogeomorphic processes and the long-term performance of the torrent training works. An integrated approach to the analysis of hydrogeomorphic processes and their interactions with torrent control works has been applied to a large alluvial fan in the southern Carnic Alps (northeastern Italy). Study methods encompass field observations, interpretation of aerial photographs, analysis of historical documents, and numerical modelling of debris flows. The overall performance of control works implemented in the early decades of 20th century was satisfactory, and a reduction of hazardous events was recognised from features observed in the field and in aerial photographs, as well as from the analysis of historical records. The 2-D simulation of debris flows confirms these findings, indicating that debris flow deposition would not affect urban areas or main roads, even in the case of a high-magnitude event. Present issues in the management of the studied alluvial fan are representative of situations frequently found in the European Alps and deal with the need for maintenance of the control structures and the pressures for land use changes aimed at the economic exploitation of the fan surface.

Influence of Wildfire on Earth Surface Processes and Geomorphology

2021 ◽  
Author(s):  
Paul Santi ◽  
Francis Rengers
Keyword(s):  
Debris Flows ◽  
Management Practices ◽  
Mass Movement ◽  
Soil Formation ◽  
Alluvial Fan ◽  
Water Repellent ◽  
Alluvial Fans ◽  
Stream Channels ◽  
Sediment Delivery ◽  
Recurrence Intervals

&lt;p&gt;Wildfire is a global phenomenon that is expected to increase in extent and severity due to shifting land management practices and climate change. It removes vegetation, deposits ash, influences water-repellent soil formation, and physically weathers rock. These changes typically lead to increased erosion through sheetwash, rilling, rock spalling, and dry ravel, as well as increased mass movement in the form of floods, debris flows, rockfall, and landslides. Post-wildfire changes in these processes bring about landform changes as hillslopes are lowered and stream channels aggrade or incise at increased rates. Research has documented increases in erosion after wildfire ranging from 2-1000 times the pre-fire rates. Post-wildfire landscape lowering by erosion has been measured in the western U.S. at magnitudes of 2 mm per year, with sediment delivery at the mouths of canyons increased in the range of 160-1000% during the post-wildfire window of disturbance. Furthermore, post-wildfire sediment transport enhances the development of alluvial fans, debris fans, and talus cones. Debris-flow likelihood is increased following wildfire, such that modest rainstorms with &lt;2 year recurrence intervals are typically sufficient to trigger debris flows with volumes much larger (270-540%) than at unburned sites. In the western U.S., as much as 25-50% of alluvial fan accumulation can be attributed to post-wildfire debris flows and other post-wildfire fluvial transport. The window of disturbance to the landscape caused by wildfire is typically on the order of three to four years, with some effects persisting up to 30 years. &amp;#160;Consequently, wildfire is an important agent of geomorphic change.&lt;/p&gt;

scholarly journals A modeling methodology to study the tributary-junction alluvial fan connectivity during a debris flow event

2021 ◽  
Author(s):  
Alex Garcés ◽  
Gerardo Zegers ◽  
Albert Cabré ◽  
Germán Aguilar ◽  
Aldo Tamburrino ◽  
...  
Keyword(s):  
Debris Flow ◽  
Computational Cost ◽  
Alluvial Fan ◽  
Storm Event ◽  
Modeling Methodology ◽  
Complex Interactions ◽  
Main River ◽  
Flow Transport ◽  
High Computational Cost

Abstract. Traditionally, interactions between tributary alluvial fans and the main river have been studied on the field and in the laboratory, giving rise to different conceptual models explaining its role in the sediment cascade. On the other hand, numerical modeling of these complex interactions is still limited because the broad debris flow transport regimes are associated with different sediment transport models. Even though sophisticated models capable of simulating many transport mechanisms simultaneously exist, they are restricted to research purposes due to their high computational cost. In this article, we propose a workflow to model the response of an alluvial fan in the Huasco Valley, located in the Atacama Desert, during an extreme storm event. For the Crucecita Alta alluvial fan, five different deposits were identified and associated with different debris flow surges. Using a commercial software, our workflow concatenates these surges into one model. This study depicts the significance of the mechanical classification of debris flows to reproduce how an alluvial fan controls the tributary-river junction connectivity. Once our model is calibrated, we use our workflow to test if a channel is enough to mitigate the impacts of these flows and the effects on the tributary-river junction connectivity.

scholarly journals Erosion after an extreme storm event in an arid fluvial system of the southern Atacama Desert: an assessment of the magnitude, return time, and conditioning factors of erosion and debris flow generation

2020 ◽  
Vol 20 (5) ◽  
pp. 1247-1265 ◽  
Author(s):  
Germán Aguilar ◽  
Albert Cabré ◽  
Victor Fredes ◽  
Bruno Villela
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Atacama Desert ◽  
Storm Event ◽  
Alluvial Fans ◽  
Sediment Discharge ◽  
Stream Networks ◽  
Erosion Rates ◽  
Extreme Storm ◽  
High Sediment

Abstract. The contribution of an individual extreme storm event to long-term erosion rates has been estimated for the first time in the Atacama Desert. A mean erosion of 1.3 mm has been calculated for the March 2015 event that impacted the southernmost part of the Atacama Desert. The estimated erosion is consistent with millennial erosion rates and the previously reported return times of high-sediment-discharge events in the study area. This is significant because erosion rates, related to events of high sediment discharge in arid fluvial systems, are difficult to measure with sediment loading due to destruction of gauges by devastating flash floods and therefore have not been directly measured yet. During the March 2015 storm, debris flows were reported as the main sediment transport process, while gullies and channels erosion were the main source of sediments that generated debris flows reaching the tributary junctions and the trunk valleys. Sediment yield at tributary outlets is highly dependent on the ability of catchments to store sediments in stream networks between storms. The largest tributary catchments, the high hydrological hierarchy, the low topographic gradient and the gentle slopes are the most determining factors in generating debris flows capable of reaching alluvial fans in any storm event from large sediment volumes stored in the stream networks. Our findings better assess the susceptibility to debris flow of arid catchments, which is significant for the southernmost valleys of the Atacama Desert because human settlements and industries are mostly established in alluvial fans.

scholarly journals Storm pulses of particulate and dissolved organic carbon in a forested headwater stream and their environmental implications – importance of extreme rainfall events

2014 ◽  
Vol 11 (5) ◽  
pp. 6877-6908 ◽  
Author(s):  
B.-J. Jung ◽  
J.-K. Lee ◽  
H. Kim ◽  
J.-H. Park
Keyword(s):  
Organic Carbon ◽  
Extreme Rainfall ◽  
Headwater Stream ◽  
Storm Event ◽  
Extreme Rainfall Event ◽  
Storm Events ◽  
Environmental Implications ◽  
Extreme Rainfall Events ◽  
Organic C ◽  
Rainfall Events

Abstract. Despite recent debates on erosion-enhanced sinks of CO2 and contrasting findings on the biodegradation of recalcitrant organic materials in large rivers, little attention has been paid to the export and transformations of particulate organic carbon (POC) and dissolved organic C (DOC) in mountainous headwater watersheds under monsoon climates. To comparatively evaluate the significance of heavy monsoon rainfalls for the magnitude and environmental implications of storm-enhanced export of POC and DOC, the relationships between storm magnitude and C export were examined in a mountainous, forested headwater stream in the Haean Basin, South Korea, during 50 storm events over the 4 year monitoring period. We also compared biodegradation and disinfection byproduct (DBP) formation potentials of the DOC and POC exported during an extreme rainfall event. Event mean concentrations and export of POC increased nonlinearly above thresholds of precipitation and discharge, significantly exceeding the increases of DOC. The export of POC during a few storm events with a total rainfall above 200 mm per event exceeded the annual organic C export during dry years. During the large storm event (209 mm), concentrations of total trihalomethanes formed by POC-derived dissolved components changed synchronously with POC concentrations, exhibiting lower levels than those formed by DOC. During a 30 day incubation at 25 °C, both DOC and POC exported during peak flow initially exhibited rapid biodegradation of labile components, whereas POC-derived materials increased continuously not only DOC concentrations, but also fulvic- and humic-like fluorescent components. These results highlight the significance of extreme rainfall events as "hot moments" for POC export and also suggest that storm pulses of POC can provide potential sources of labile DOC components that can rapidly biodegrade and form DBPs in headwater streams, contrasting with other studies assuming mountainous rivers as a passive conduit of organic C.

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.

scholarly journals Erosion after an extreme storm event in an arid fluvial system of the southern Atacama Desert: an assessment of magnitude, return time, and conditioning factors of erosion caused by debris flows

2019 ◽  
Author(s):  
Germán Aguilar ◽  
Albert Cabré ◽  
Victor Fredes ◽  
Bruno Villela
Keyword(s):  
Debris Flows ◽  
Atacama Desert ◽  
Return Time ◽  
Storm Event ◽  
Drainage Network ◽  
Alluvial Fans ◽  
Sediment Discharge ◽  
Erosion Rates ◽  
Extreme Storm ◽  
High Sediment

Abstract. We have calculated a mean erosion of 1.3 mm caused by an individual storm event in March 2015 that impacted a large mountainous area of the southernmost Atacama Desert. The calculated erosion agrees with millennial erosion rates and with return time of high sediment discharge events previously reported in the study area. Here, we quantify for the first time the contribution of an individual extreme storm event to long-term erosion rates in the Atacama Desert. This is significant because erosion rates, related to high sediment discharge events in arid fluvial systems, are hard to measure with sediment load due the destruction of gauges by devastating flashfloods and thus have not been directly measured yet. During the March 2015 storm, debris flows were reported as the main sediment transport process. Erosion of gullies and channels are the main source of sediments that finally generate debris flows that reach the tributary junctions and the trunk valleys. The sediment yield to the tributary outlets strongly depends on the hydraulic capacity of catchments to store sediments in the drainage network between storms. Larger tributary catchments, high hydrological hierarchy, low topographic gradient and gentle slopes are the most susceptible catchments to generate debris flows that reach alluvial fans at any storm event from large debris volumes stored in the drainage network. Our findings better assess debris flow susceptibility of arid catchments, which is significant for the southernmost Atacama Desert valleys because human settlements and industries are mostly established in alluvial fans.

The Influence of Geographical Factors on Extreme Rainfalls in Lampung Province

2019 ◽  
Vol 1 (1) ◽  
pp. 33
Author(s):  
M Welly
Keyword(s):  
Geographical Location ◽  
Daily Rainfall ◽  
Extreme Rainfall ◽  
Design Flood ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Ungauged Basin ◽  
Flood Discharge ◽  
Design Rainfall ◽  
Geographical Factors

Many people in Indonesia calculate design rainfall before calculating the design flooddischarge. The design rainfall with a certain return period will eventually be convertedinto a design flood discharge by combining it with the characteristics of the watershed.However, the lack of a network of rainfall recording stations makes many areas that arenot hydrologically measured (ungauged basin), so it is quite difficult to know thecharacteristics of rain in the area concerned. This study aims to analyze thecharacteristics of design rainfall in Lampung Province. The focus of the analysis is toinvestigate whether geographical factors influence the design rainfall that occurs in theparticular area. The data used in this study is daily rainfall data from 15 rainfallrecording stations spread in Lampung Province. The method of frequency analysis usedin this study is the Gumbel method. The research shows that the geographical location ofan area does not have significant effect on extreme rainfall events. The effect of risingearth temperatures due to natural exploitation by humans tends to be stronger as a causeof extreme events such as extreme rainfall.Keywords: Influence, geographical, factors, extreme, rainfall.

CLIMATOLOGY OF EXTREME RAINFALL EVENTS IN EASTERN AND NORTHERN SANTA CATARINA STATE, BRAZIL: PRESENT AND FUTURE CLIMATE

2013 ◽  
Vol 31 (3) ◽  
pp. 413 ◽  
Author(s):  
André Becker Nunes ◽  
Gilson Carlos Da Silva
Keyword(s):  
Climate Model ◽  
Climate Modeling ◽  
Linear Trend ◽  
Extreme Rainfall ◽  
Eastern Region ◽  
Santa Catarina ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
History Of ◽  
Santa Catarina State

ABSTRACT. The eastern region of Santa Catarina State (Brazil) has an important history of natural disasters due to extreme rainfall events. Floods and landslides are enhancedby local features such as orography and urbanization: the replacement of natural surface coverage causing more surface runoff and, hence, flooding. Thus, studies of this type of events – which directly influence life in the towns – take on increasing importance. This work makes a quantitative analysis of occurrences of extreme rainfall events in the eastern and northern regions of Santa Catarina State in the last 60 years, through individual analysis, considering the history of floods ineach selected town, as well as an estimate through to the end of century following regional climate modeling. A positive linear trend, in most of the towns studied, was observed in the results, indicating greater frequency of these events in recent decades, and the HadRM3P climate model shows a heterogeneous increase of events for all towns in the period from 2071 to 2100.Keywords: floods, climate modeling, linear trend. RESUMO. A região leste do Estado de Santa Catarina tem um importante histórico de desastres naturais ocasionados por eventos extremos de precipitação. Inundações e deslizamentos de terra são potencializados pelo relevo acidentado e pela urbanização das cidades da região: a vegetação nativa vem sendo removida acarretando um maior escoamento superficial e, consequentemente, em inundações. Desta forma, torna-se de suma importância os estudos acerca deste tipo de evento que influencia diretamente a sociedade em geral. Neste trabalho é realizada uma análise quantitativa do número de eventos severos de precipitação ocorridos nas regiões leste e norte de Santa Catarina dos últimos 60 anos, por meio de uma análise pontual, considerandoo histórico de inundações de cada cidade selecionada, além de uma projeção para o fim do século de acordo com modelagem climática regional. Na análise dos resultados observou-se uma tendência linear positiva na maioria das cidades, indicando uma maior frequência deste tipo de evento nas últimas décadas, e o modelo climático HadRM3P mostra um aumento heterogêneo no número de eventos para todas as cidades no período de 2071 a 2100.Palavras-chave: inundações, modelagem climática, tendência linear.

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