The Story of a Steep River: Causes and Effects of the Flash Flood on 24 July 2017 in Western Norway

Flash floods can cause great geomorphological changes in ephemeral fluvial systems and result in particularly severe damages for the unprepared population exposed to it. The flash flood in the Storelva river in Utvik (western Norway) on 24 July 2017 was witnessed and documented. This study assessed the causes and effects of the 2017 flood and provides valuable information for the calibration and validation of future modelling studies. The flooded area at peak discharge, maximum wetted and dry areas during the entire event, critical points and main flow paths were reconstructed using on-site and post-event (i) visual documentation, such as photographs and videos, and (ii) aerial surveying, such as orthophotographs and laser scanning, of the lowermost reach. The steep longitudinal slope together with the loose material forming the valley and riverbed contributed to a large amount of sediment transport during this extreme event. Steep rivers such as the Storelva river have very short response times to extreme hydrologic conditions, which calls for exhaustive monitoring and data collection in case of future events, as well as modelling tools that can emulate the hydro-morphodynamics observed during events such as the 2017 flash flood.

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Hydro-meteorological reconstruction and geomorphological impact assessment of the October 2018 catastrophic flash flood at Sant Llorenç, Mallorca (Spain)

Natural Hazards and Earth System Science ◽

10.5194/nhess-19-2597-2019 ◽

2019 ◽

Vol 19 (11) ◽

pp. 2597-2617 ◽

Cited By ~ 4

Author(s):

Jorge Lorenzo-Lacruz ◽

Arnau Amengual ◽

Celso Garcia ◽

Enrique Morán-Tejeda ◽

Víctor Homar ◽

...

Keyword(s):

Prediction Models ◽

Extreme Event ◽

Response Times ◽

Flash Flood ◽

Weather Prediction ◽

Early Warning Systems ◽

Rain Gauge ◽

Management Service ◽

Convective Rainfall ◽

Hydraulic Simulation

Abstract. An extraordinary convective rainfall event, unforeseen by most numerical weather prediction models, generated a devastating flash flood (305 m3 s−1) in the town of Sant Llorenç des Cardassar, Mallorca, on 9 October 2018. Four people died inside this village, while casualties were up to 13 over the entire affected area. This extreme event has been reconstructed by implementing an integrated flash flood modelling approach in the Ses Planes catchment up to Sant Llorenç (23.4 km2), based on three components: (i) generation of radar-derived precipitation estimates, (ii) modelling of accurate discharge hydrographs yielded by the catchment (using FEST and KLEM models), and (iii) hydraulic simulation of the event and mapping of affected areas (using HEC-RAS). Radar-derived rainfall estimates show very high agreement with rain gauge data (R2=0.98). Modelled flooding extent is in close agreement with the observed extension by the Copernicus Emergency Management Service, based on Sentinel-1 imagery, and both far exceed the extension for a 500-year return period flood. Hydraulic simulation revealed that water reached a depth of 3 m at some points, and modelled water depths highly correlate (R2=0.91) with in situ after-event measurements. The 9 October flash flood eroded and transported woody and abundant sediment debris, changing channel geomorphology. Water velocity greatly increased at bridge locations crossing the river channel, especially at those closer to the Sant Llorenç town centre. This study highlights how the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments continue to challenge the implementation of early warning systems, which effectively reduce people's exposure to flash flood risk in the region.

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Hydrometeorological extremes derived from taxation records for south-eastern Moravia, Czech Republic, 1751–1900 AD

Climate of the Past ◽

10.5194/cp-8-467-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 467-481 ◽

Cited By ~ 23

Author(s):

R. Brázdil ◽

K. Chromá ◽

H. Valášek ◽

L. Dolák

Keyword(s):

Czech Republic ◽

Crop Yields ◽

Extreme Event ◽

Flash Flood ◽

Secondary Importance ◽

Agricultural Work ◽

South Eastern ◽

Tax Relief ◽

Taxation System ◽

The Impact

Abstract. Historical written records associated with tax relief at ten estates located in south-eastern Moravia (Czech Republic) are used for the study of hydrometeorological extremes and their impacts during the period 1751–1900 AD. At the time, the taxation system in Moravia allowed farmers to request tax relief if their crop yields had been negatively affected by hydrological and meteorological extremes. The documentation involved contains information about the type of extreme event and the date of its occurrence, while the impact on crops may often be derived. A total of 175 extreme events resulting in some kind of damage are documented for 1751–1900, with the highest concentration between 1811 and 1860 (74.9% of all events analysed). The nature of events leading to damage (of a possible 272 types) include hailstorm (25.7%), torrential rain (21.7%), flood (21.0%), followed by thunderstorm, flash flood, late frost and windstorm. The four most outstanding events, affecting the highest number of settlements, were thunderstorms with hailstorms (25 June 1825, 20 May 1847 and 29 June 1890) and flooding of the River Morava (mid-June 1847). Hydrometeorological extremes in the 1816–1855 period are compared with those occurring during the recent 1961–2000 period. The results obtained are inevitably influenced by uncertainties related to taxation records, such as their temporal and spatial incompleteness, the limits of the period of outside agricultural work (i.e. mainly May–August) and the purpose for which they were originally collected (primarily tax alleviation, i.e. information about hydrometeorological extremes was of secondary importance). Taxation records constitute an important source of data for historical climatology and historical hydrology and have a great potential for use in many European countries.

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Ensemble cloud-resolving modelling of a historic back-building mesoscale convective system over Liguria: the San Fruttuoso case of 1915

Climate of the Past ◽

10.5194/cp-13-455-2017 ◽

2017 ◽

Vol 13 (5) ◽

pp. 455-472 ◽

Cited By ~ 10

Author(s):

Antonio Parodi ◽

Luca Ferraris ◽

William Gallus ◽

Maurizio Maugeri ◽

Luca Molini ◽

...

Keyword(s):

Extreme Event ◽

Flash Flood ◽

Western Mediterranean ◽

Mesoscale Convective Systems ◽

Convective System ◽

Water Vapour Content ◽

Ligurian Sea ◽

Convective Systems ◽

Position Errors ◽

Mesoscale Convective

Abstract. Highly localized and persistent back-building mesoscale convective systems represent one of the most dangerous flash-flood-producing storms in the north-western Mediterranean area. Substantial warming of the Mediterranean Sea in recent decades raises concerns over possible increases in frequency or intensity of these types of events as increased atmospheric temperatures generally support increases in water vapour content. However, analyses of the historical record do not provide a univocal answer, but these are likely affected by a lack of detailed observations for older events. In the present study, 20th Century Reanalysis Project initial and boundary condition data in ensemble mode are used to address the feasibility of performing cloud-resolving simulations with 1 km horizontal grid spacing of a historic extreme event that occurred over Liguria: the San Fruttuoso case of 1915. The proposed approach focuses on the ensemble Weather Research and Forecasting (WRF) model runs that show strong convergence over the Ligurian Sea (17 out of 56 members) as these runs are the ones most likely to best simulate the event. It is found that these WRF runs generally do show wind and precipitation fields that are consistent with the occurrence of highly localized and persistent back-building mesoscale convective systems, although precipitation peak amounts are underestimated. Systematic small north-westward position errors with regard to the heaviest rain and strongest convergence areas imply that the reanalysis members may not be adequately representing the amount of cool air over the Po Plain outflowing into the Ligurian Sea through the Apennines gap. Regarding the role of historical data sources, this study shows that in addition to reanalysis products, unconventional data, such as historical meteorological bulletins, newspapers, and even photographs, can be very valuable sources of knowledge in the reconstruction of past extreme events.

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Synergistic Approach of Remote Sensing and GIS Techniques for Flash-Flood Monitoring and Damage Assessment in Thessaly Plain Area, Greece

Water ◽

10.3390/w11030448 ◽

2019 ◽

Vol 11 (3) ◽

pp. 448 ◽

Cited By ~ 10

Author(s):

Emmanouil Psomiadis ◽

Konstantinos Soulis ◽

Melpomeni Zoka ◽

Nicholas Dercas

Keyword(s):

Flash Flood ◽

Radar Data ◽

Threshold Method ◽

Plain Area ◽

Elevation Data ◽

Landsat 7 ◽

Synergistic Approach ◽

Flooded Area ◽

Earth Observation Satellites ◽

Elevation Model

This paper describes the synergetic use of earth observation satellites optical and radar data with a high-resolution digital elevation model (DEM) to detect flooded areas and explore the impacts of a flood event. A flash flood episode took place in May 2016, in the central-eastern part of West Thessaly (Central Greece). Landsat-7 ETM+ and a Sentinel-1 SAR images were acquired. For Landsat-7, several water indices were applied and for the Sentinel-1 a threshold method was implemented. Elevation data were also used to improve the delineation of the inundated areas, and to estimate flood water depth. Furthermore, Sentinel-2 images were utilized so as to record the land use/cover of the flooded area. The inundated areas and the affected cultivations were delineated with high precision, and the financial effects were evaluated.

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UNMANNED AERIAL VEHICLE LASER SCANNING FOR EROSION MONITORING IN ALPINE GRASSLAND

ISPRS Annals of Photogrammetry Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-annals-iv-2-w5-405-2019 ◽

2019 ◽

Vol IV-2/W5 ◽

pp. 405-412 ◽

Cited By ~ 2

Author(s):

A. Mayr ◽

M. Bremer ◽

M. Rutzinger ◽

C. Geitner

Keyword(s):

Unmanned Aerial Vehicle ◽

Point Cloud ◽

Laser Scanning ◽

Test Site ◽

Satellite System ◽

Alpine Grassland ◽

Proof Of Concept ◽

Aerial Vehicle ◽

Geomorphological Changes ◽

Global Navigation Satellite

Abstract. With this contribution we assess the potential of unmanned aerial vehicle (UAV) based laser scanning for monitoring shallow erosion in Alpine grassland. A 3D point cloud has been acquired by unmanned aerial vehicle laser scanning (ULS) at a test site in the subalpine/alpine elevation zone of the Dolomites (South Tyrol, Italy). To assess its accuracy, this point cloud is compared with (i) differential global navigation satellite system (GNSS) reference measurements and (ii) a terrestrial laser scanning (TLS) point cloud. The ULS point cloud and an airborne laser scanning (ALS) point cloud are rasterized into digital surface models (DSMs) and, as a proof-of-concept for erosion quantification, we calculate the elevation difference between the ULS DSM from 2018 and the ALS DSM from 2010. For contiguous spatial objects of elevation change, the volumetric difference is calculated and a land cover class (bare earth, grassland, trees), derived from the ULS reflectance and RGB colour, is assigned to each change object. In this test, the accuracy and density of the ALS point cloud is mainly limiting the detection of geomorphological changes. Nevertheless, the plausibility of the results is confirmed by geomorphological interpretation and documentation in the field. A total eroded volume of 672&thinsp;m3 is estimated for the test site (48&thinsp;ha). Such volumetric estimates of erosion over multiple years are a key information for improving sustainable soil management. Based on this proof-of-concept and the accuracy analysis, we conclude that repeated ULS campaigns are a well-suited tool for erosion monitoring in Alpine grassland.

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A framework for estimating the determinants of spatial and temporal variation in vital rates and inferring the occurrence of unobserved extreme events

10.1101/033720 ◽

2015 ◽

Author(s):

Simone Vincenzi ◽

Dušan Jesenšek ◽

Alain J Crivelli

Keyword(s):

Brown Trout ◽

Extreme Events ◽

Extreme Event ◽

Flash Flood ◽

Spatial And Temporal Variation ◽

Source Population ◽

Vital Rates ◽

Population Densities ◽

Poor Recruitment

AbstractWe develop an overarching framework that combines long-term tag-recapture data and powerful statistical and modeling techniques to investigate how population, environmental, and climate factors determine variation in vital rates and population dynamics in an animal species, using as a model system the population of brown trout living in Upper Volaja (Western Slovenia). This population has been monitored since 2004; Upper Volaja is also a sink, receiving individuals from a source population living above a waterfall. We estimate the numerical contribution of the source population on the sink population and test the effects of temperature, population density, and extreme events on variation in vital rates among more than 2,500 individually tagged brown trout. We found that fish dispersing downstream from the source population help maintain high population densities in the sink population despite poor recruitment. The best model of survival for individuals older than juveniles includes additive effects of year-of-birth and time. Fast growth of older cohorts and higher population densities in 2004-2005 suggest very low population densities in late1990s, which we hypothesize were caused by a flash flood that strongly reduced population size and created the habitat conditions for faster growth and transient higher population densities after the extreme event.

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Effects of the Karkheh Dam construction on haze generation due to geomorphological changes (in the Khuzestan Province, Southwest of Iran)

Water Science & Technology Water Supply ◽

10.2166/ws.2021.376 ◽

2021 ◽

Author(s):

Arash Adib

Keyword(s):

Cross Sections ◽

Dust Storms ◽

Dam Construction ◽

Khuzestan Province ◽

Longitudinal Slope ◽

Geomorphological Changes ◽

The Stability ◽

Southwest Of Iran ◽

Hydrometric Station ◽

The Karkheh River

Abstract An important factor for occurrence of dust storms is the construction of the Karkheh Dam in the Khuzestan province of Iran. It has reduced the annual mean of flow discharge in the Karkheh River from 120 to 50 m3/s and dried lands around river. The area of dried lands is 90.17 km2 around river and 333.45 km2 in the Hawr-al-Azim wetland. The Rosgen method, Fluvial-12 software, Shulits equation showed instability of the plan, cross sections of river and longitudinal slope of river, respectively, around Pay-e-pol hydrometric station (the upstream of river). After dam construction, extreme erosion occurred in this part of river. The type of sediment is clay and silt with D50 = 8 μm. The eroded sediment settles in downstream of river (around Hamidiyeh hydrometric station) and the Hawr-al-Azim wetland. The wind can easily lift these particles especially from May to July. Because of size of these particles, the haze concentration increased from 25% to 45% in dust storms. After construction dam, the dust storm days increased to 90 days in 2008. By increasing the stability of the river, the dust storms reduced from 2011. The annual volume of generated haze by geomorphological characteristic changes is almost 3107 m3.

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A forensic hydrometeorological and geomorphological reconstruction of the catastrophic flash flood occurred in Mallorca (Spain) on October 9th, 2018

10.5194/egusphere-egu2020-3881 ◽

2020 ◽

Author(s):

Arnau Amengual ◽

Jorge Lorenzo-Lacruz ◽

Celso Garcia ◽

Enrique Morán Tejeda ◽

Víctor Homar ◽

...

Keyword(s):

Prediction Models ◽

Extreme Event ◽

Flash Flood ◽

Weather Prediction ◽

Early Warning Systems ◽

Management Service ◽

Convective Rainfall ◽

Hydraulic Simulation ◽

Flood Peak ◽

The Town

An extraordinary convective rainfall event &#8211;unforeseen by most numerical weather prediction models&#8211; led to a devastating flash flood in the town of Sant Lloren&#231; des Cardassar, eastern Mallorca, on 9th October 2018. Four people died inside the village, while the total death toll was of 13 and economic damages amounted to 91 M&#8364;. The observed flooded extension inside the town by the Copernicus Emergency Management Service &#8211;based on Sentinel-1 imagery&#8211; far exceeded the extension for a 500-year return period flood. This extreme event has been reconstructed by implementing an integrated flood modelling approach over the semi-arid and small-sized Ses Planes basin up to Sant Lloren&#231; (23.4 km&#178;). This procedure is based on three components: (i) generation of high spatial and temporal resolution radar-derived precipitation estimates; (ii) modelling of the hydrologic response based on post-flood peak discharge estimates; and (iii) hydraulic simulation and mapping of the affected areas based on high water marks. Radar-derived rainfall estimates and the simulated flooding extent and water depths highly correlate with observations. The hydraulic simulation has revealed that water reached a depth of 3 m at some points inside Sant Lloren&#231; and that water velocity greatly increased at bridges&#8217; locations close to the town centre. Even if the catastrophic flash flood was not a debris flow, the flood bore eroded enough material to change channel geomorphology. This study also highlights how the concurrence of the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments still challenges the implementation of early warning systems, which effectively reduce people&#8217;s exposure to flash flood risk in the region.

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Anatomy of extraordinary rainfall and flash flood in a Dutch lowland catchment

Hydrology and Earth System Sciences ◽

10.5194/hess-15-1991-2011 ◽

2011 ◽

Vol 15 (6) ◽

pp. 1991-2005 ◽

Cited By ~ 34

Author(s):

C. C. Brauer ◽

A. J. Teuling ◽

A. Overeem ◽

Y. van der Velde ◽

P. Hazenberg ◽

...

Keyword(s):

Soil Moisture ◽

Extreme Event ◽

Initial Conditions ◽

Flash Flood ◽

Heavy Rainfall Event ◽

Financial Loss ◽

Groundwater Response ◽

The 1960S ◽

Microwave Link ◽

Reservoir Filling

Abstract. On 26 August 2010 the eastern part of The Netherlands and the bordering part of Germany were struck by a series of rainfall events lasting for more than a day. Over an area of 740 km2 more than 120 mm of rainfall were observed in 24 h. This extreme event resulted in local flooding of city centres, highways and agricultural fields, and considerable financial loss. In this paper we report on the unprecedented flash flood triggered by this exceptionally heavy rainfall event in the 6.5 km2 Hupsel Brook catchment, which has been the experimental watershed employed by Wageningen University since the 1960s. This study aims to improve our understanding of the dynamics of such lowland flash floods. We present a detailed hydrometeorological analysis of this extreme event, focusing on its synoptic meteorological characteristics, its space-time rainfall dynamics as observed with rain gauges, weather radar and a microwave link, as well as the measured soil moisture, groundwater and discharge response of the catchment. At the Hupsel Brook catchment 160 mm of rainfall was observed in 24 h, corresponding to an estimated return period of well over 1000 years. As a result, discharge at the catchment outlet increased from 4.4 × 10−3 to nearly 5 m3 s−1. Within 7 h discharge rose from 5 × 10−2 to 4.5 m3 s−1. The catchment response can be divided into four phases: (1) soil moisture reservoir filling, (2) groundwater response, (3) surface depression filling and surface runoff and (4) backwater feedback. The first 35 mm of rainfall were stored in the soil without a significant increase in discharge. Relatively dry initial conditions (in comparison to those for past discharge extremes) prevented an even faster and more extreme hydrological response.

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Hydro-meteorological reconstruction and geomorphological impact assessment of the October, 2018 catastrophic flash flood at Sant Llorenç, Mallorca (Spain)

10.5194/nhess-2019-226 ◽

2019 ◽

Author(s):

Jorge Lorenzo-Lacruz ◽

Celso Garcia ◽

Enrique Morán-Tejeda ◽

Arnau Amengual ◽

Víctor Homar ◽

...

Keyword(s):

Prediction Models ◽

Response Times ◽

Flash Flood ◽

Early Warning Systems ◽

Rain Gauge ◽

Management Service ◽

Hydrological Response ◽

Convective Rainfall ◽

Hydraulic Simulation ◽

Highly Nonlinear

Abstract. An extraordinary convective rainfall event, unforeseen by most prediction models, generated a devastating flash flood in Sant Llorenç des Cardassar, Mallorca on October 9, 2018. Four people died in the town (13 people died in the entire affected area). The event was reconstructed, implementing an integrated flash flood modelling approach in this small (23.4 km2) and semi-arid ungauged Mediterranean catchment, with a highly nonlinear hydrological response to heavy precipitation, based on three components: (i) generation of radar-derived precipitation estimates during the event; (ii) modelling of an accurate discharge hydrograph yielded by the basin; and (iii) hydraulic simulation of the event and mapping of affected areas. Radar-derived rainfall estimates showed very high agreement with rain gauge data (R2 = 0.98). Modelled flooding extent is in close agreement with the observed extension by Copernicus Emergency Management Service, based on Sentinel-1 imagery, and both far exceed the extension for a 500-year return period flood. Hydraulic simulation showed that water reached a depth of 3 m at some points, and modelled water depths highly correlate (R2 = 0.91) with in-situ after-event measurements. The flash flood eroded and transported woody and abundant sediment debris, changing channel geomorphology. Water velocity greatly increased at bridge locations crossing the river channel, especially at those closer to Sant Llorenç town centre. This study shows how the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments continue to challenge the implementation of early warning systems, which effectively reduce people's exposure to flash flood risk in the region.

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