scholarly journals Recent human impacts and change in dynamics and morphology of ephemeral rivers

2014 ◽  
Vol 14 (3) ◽  
pp. 713-730 ◽  
Author(s):  
J. A. Ortega ◽  
L. Razola ◽  
G. Garzón
Keyword(s):  
Single Channel ◽  
Flash Flood ◽  
Human Impacts ◽  
Morphological Changes ◽  
Flood Damage ◽  
Alluvial Fan ◽  
Valley Floor ◽  
Ephemeral Streams ◽  
Flood Events ◽  
Channel Conditions

Abstract. Ephemeral streams induce flash-flood events, which cause dramatic morphological changes and impacts on population, mainly because they are intermittent and less predictable. Human pressures on the basin modify load and discharge relationships, inducing dormant instability on the fluvial system that will manifest abruptly during flood events. The flash-flood response of two ephemeral streams affected by load supply modification due to land use changes is discussed in a combination of geomorphic and hydraulic approaches. During the Rivillas flash flood, intensive clearing on the basin led to high rates of sediment flowing into an artificially straightened and inefficient channel. The stream evolved from a sinuous single channel into a shallow braiding occupying the entire width of the valley floor. Misfits and unsteady channel conditions increased velocity, stream power and sediment entrainment capacity and considerably magnified flood damage. Resulting morphosedimentary features revealed a close relationship with the valley floor post-flood hydraulic model, and pre-event awareness would have made it possible to predict risk-sensitive areas. In the second case, the Azohía stream, modelling of current pre-flood channel conditions make it possible to determine channel narrowing and entrenchment in the lower alluvial fan stretch. Abandonment of intensive agriculture, basin reforestation and urbanization diminish load contribution and trigger channel incision. This induces an increase in slope and velocity in the bankfull channel, producing renewed erosive energy and thus activating upstream propagation of incision and bank undermining. The absence of water-spreading dynamics on the alluvial fan in favour of confinement in a single channel produces an unstable dynamic in the system, also offering a false sense of stability, as long as no large magnitude floods occur. When modelling flood-prone areas and analysing hydraulic variables, it is important to detect possible anthropic disturbances that may affect basin load budgets in order to anticipate catastrophic consequences resulting from inappropriate fluvial management before the occurrence of an extraordinary event.

scholarly journals Hydrodynamic characterization of past flash-flood events and their associated hazards from dendrogeomorphological evidence in Caldera de Taburiente National Park (Canary Islands, Spain)

2016 ◽  
Author(s):  
Julio Garrote ◽  
Andrés Diez-Herrero ◽  
José M. Bodoque ◽  
María A. Perucha ◽  
Pablo Mayer ◽  
...  
Keyword(s):  
Canary Islands ◽  
National Park ◽  
Single Channel ◽  
Flash Flood ◽  
Flood Hazard ◽  
Hazard Analysis ◽  
Flood Damage ◽  
Data Sources ◽  
Flood Events ◽  
River Bank

Abstract. Las Angustias river is an ungauged stream located in the Caldera de Taburiente National Park (La Palma, Canary Islands, Spain), where frequent intense flash-flood events occur, sometimes with fatal consequences (4 deaths, November 2001) and considerable financial implications (over 700 000 euros in recent years). The aim of this research is to analyse the flood hazard at the Playa de Taburiente, one of the most popular sites in this protected area, with more than 60 000 visitors per year. The use of classic data sources and hydrological or hydraulic modelling methods for flood hazard analysis has important limitations in this area because of incomplete precipitation and flow data information and low representative values of the statistical time series, which may lead to under- or over-estimated results. Alternative or complementary data sources and methods including palaeohydrological techniques can therefore be used here for flood hazard analysis. A detailed dendrogeomorphological study of the river system was carried out using Canarian pine trees located on the stream bed and river bank with external evidence of flash-flood damage, including scars and exposed roots. The preliminary results identify and date at least eight winter flood events between 1962–1963 and 2011–12. In spite of the uncertainties deriving from the incomplete precipitation data and the mobile alluvial riverbed, the models provide an estimate of past flood discharge magnitudes. E.g. for the 1997 flood event a 1235 m3 s-1 flood minimizes the RMSE over the disturbed tree sample; furthermore, this flow value clearly exceeds the return period considered and means a distinct behavioral change in this gorge, from a braided channel with emerged bars to a single channel occupying the whole river bed. These numerical results and maps could improve flood hazard and risk analysis and should be useful for the national park land use management and visitors planning.

From Flash Flood Vulnerability and Risk Assessment to Property Damage Prediction: the Value of Machine Learning

2020 ◽  
Author(s):  
Atieh Alipour ◽  
Peyman Abbaszadeh ◽  
Ali Ahmadalipour ◽  
Hamid Moradkhani
Keyword(s):  
Machine Learning ◽  
Flash Flood ◽  
Rapid Onset ◽  
Flash Floods ◽  
Flood Damage ◽  
Flood Events ◽  
Property Damage ◽  
Damage Prediction ◽  
Financial Consequences

<p>Flash floods, as a result of frequent torrential rainfalls caused by tropical storms, thunderstorms,<br>and hurricanes, are a prevalent natural disaster in the southeast U.S. (SEUS), which frequently<br>threaten human lives and properties in the region. According to the U.S. National Weather<br>Service (NWS), flash floods generally initiate within less than six hours of an intense rainfall<br>onset. Therefore, there is a limited chance for effective and timely decision-making. Due to the<br>rapid onset of flash floods, they are costly events, such that only during 1996 to 2017 flash<br>floods imposed 7.5 billion dollars property damage to the SEUS. Therefore, estimating the<br>potential economic damages as a result of flash floods are crucial for flood risk management and<br>financial appraisals for decision makers. A multitude of studies have focused on flood damage<br>modeling, few of which investigated the issue on a large domain. Here, we propose a systematic<br>framework that considers a variety of factors that explain different risk components (i.e., hazard,<br>vulnerability, and exposure) and leverages Machine Learning (ML) for flood damage prediction.<br>Over 14,000 flash flood events during 1996 to 2017 were assessed to analyze their characteristics<br>including frequency, duration, and intensity. Also, different data sources were utilized to derive<br>information related to each event. The most influential features are then selected using a multi<br>criteria variable selection approach. Then, the ML model is implemented for not only binary<br>classification of damage (i.e., whether a flash flood event caused any damage or not), but also for<br>developing a model to predict the financial consequences associated with flash flood events. The<br>results indicate a high accuracy for the classifier, significant correlation and relatively low bias<br>between the predicted and observed property damages showing the effectiveness of proposed<br>methodology for flash flood damage modeling applicable to variety of flood prone regions.</p>

scholarly journals The Flashiest Watersheds in the Contiguous United States

2015 ◽  
Vol 16 (6) ◽  
pp. 2365-2381 ◽  
Author(s):  
Brianne K. Smith ◽  
James A. Smith
Keyword(s):  
United States ◽  
Pacific Northwest ◽  
West Coast ◽  
Urban Areas ◽  
Flash Flood ◽  
The United States ◽  
Flood Damage ◽  
Flood Events ◽  
Discharge Data ◽  
South Central

Abstract The authors identify the flashiest watersheds in the contiguous United States based on frequency of discharge peaks exceeding 1 m3 s−1 km−2. The entire digitized record of USGS instantaneous discharge data is used for all stream gauging stations with over 10 years of data. Using the 1 m3 s−1 km−2 threshold, the flashiest basins in the contiguous United States are located in urban areas along a swath of states from the south-central United States to the mid-Atlantic and in mountainous areas of the West Coast, especially the Pacific Northwest. The authors focus on small watersheds to identify the flashiest cities and states across the country and find Tulsa, Oklahoma; Baltimore, Maryland; and St. Louis, Missouri, to be the flashiest cities in the contiguous United States. Thunderstorms are major agents for peak-over-threshold flood events east of the Rocky Mountains, and tropical cyclones play a secondary role, especially in the Southeast. West Coast flood events are associated with winter storms. Flooding west of and within the Rockies is linked to steeply sloped terrain and compact watersheds. East of the Rockies, urban areas dominate flashy watersheds. The authors find that watersheds northeast (downwind) of city centers are flashier than other urban watersheds, consistent with the downwind maximum in rainfall found in many urban regions. They examine anomalous flood response in the Illinois–Missouri region; St. Louis is among the flashiest cities in the United States, while Chicago is among the least flashy. Their flashiness map is compared with other measures of flooding, including flood damage and National Weather Service flash flood reports.

scholarly journals Recent human impacts and change in dynamics and morphology of ephemeral rivers

2013 ◽  
Vol 1 (2) ◽  
pp. 917-956 ◽  
Author(s):  
J. A. Ortega ◽  
L. Razola ◽  
G. Garzón
Keyword(s):  
Flash Flood ◽  
Human Impacts ◽  
Morphological Changes ◽  
Flood Event ◽  
Stream Power ◽  
Fluvial Systems ◽  
Before And After ◽  
Ephemeral Rivers ◽  
Natural Dynamics ◽  
Channel Patterns

Abstract. Ephemeral streams induce flash-flood events which cause dramatic morphological changes and impacts on population, due the intermittent activity of these fluvial systems. Human pressure changes the fluvial environment and so enhances the effects of natural dynamics. Local human-induced modifications can be latent over long periods of time. These changes can be studied after the flood event, to quantify their effects and detect which are most harmful. In this paper we study flash-flood effects at two sites in Spain and compare the results before and after a~flood event. Erosion is associated with areas where there have been more anthropogenic changes in floodplains and channels. Deposition is related to erosional processes in the watershed and to the tributaries. Disruption of river channel patterns changes connectivity and scouring appears due to energy excess. This excess tends to concentrate at weak points downstream produced by anthropic disturbances. Riparian vegetation is an energy sink and reaches with more cover show less erosion than those with deforestation. Infrastructures perpendicular to the direction of flow increase stream power, but peaks of erosion on the floodplain appear displaced downstream. It is important to detect human changes by analysis of hydraulic variables before the occurrence of an extraordinary event in order to anticipate catastrophic consequences resulting from inappropriate fluvial management.

Effects of 2017 Early Flash Flooding on Agriculture in Haor Areas of Sunamganj

2021 ◽  
Vol 12 (1-2) ◽  
pp. 117-125
Author(s):  
S Mondal ◽  
L Akter ◽  
HJ Hiya ◽  
MA Farukh
Keyword(s):  
Agricultural Production ◽  
Flash Flood ◽  
Eastern Region ◽  
Fish Production ◽  
Flood Events ◽  
Flash Flooding ◽  
The North ◽  
North Eastern ◽  
Boro Rice

The Sunamganj district is covered by major Haor systems in the north-eastern region of Bangladesh. Flash flood is the most commonly occurring water related disaster in the Haor areas. During the flash flood it is very common that people lost their primary agricultural productions which are the only source of their livelihood. The present study focuses on the effects of 2017 early flash flooding on rice and fish production of Sunamganj Haor areas. The flood caused enormous damage to agriculture such as rice especially Boro rice and fish production on which the Haor dwellers rely upon for their livelihood. The total affected land of Boro rice cultivation in Haors of Sunamganj was 149,224 hectare and the total amount of damaged rice was 393,855 metric ton (MT). The total number of affected farmers was 315,084. The early flash flood also affects the quality of Haor water which caused the death of fishes. The total amount of damaged fish was 49.75 MT and the loss was 158.70 lakh taka. The total number of affected fishermen was 44,445. This findings could be very useful for the environmental scientists to predict the probable future effects on agricultural production due to early flash flood events in Sunamganj Haors areas. Environ. Sci. & Natural Resources, 12(1&2): 117-125, 2019

Representative flash flood events in Romania Case studies

2008 ◽  
pp. 1587-1596
Author(s):  
G Stancalie ◽  
B Antonescu ◽  
C Oprea ◽  
A Irimescu ◽  
S Catana ◽  
...  
Keyword(s):  
Case Studies ◽  
Flash Flood ◽  
Flood Events

Methodology for risk assessment of flash flood events due to climate and land use changes

2012 ◽  
Author(s):  
M Velasco ◽  
A Cabello ◽  
I Escaler ◽  
J Barredo ◽  
A Barrera-Escoda
Keyword(s):  
Risk Assessment ◽  
Land Use ◽  
Flash Flood ◽  
Land Use Changes ◽  
Flood Events

scholarly journals MobRISK: a model for assessing the exposure of road users to flash flood events

2017 ◽  
Vol 17 (9) ◽  
pp. 1631-1651 ◽  
Author(s):  
Saif Shabou ◽  
Isabelle Ruin ◽  
Céline Lutoff ◽  
Samuel Debionne ◽  
Sandrine Anquetin ◽  
...  
Keyword(s):  
Exposure Assessment ◽  
Flash Flood ◽  
Activity Patterns ◽  
Traffic Load ◽  
Road User ◽  
Population Exposure ◽  
Flood Events ◽  
Population Mobility ◽  
Road Users ◽  
Adverse Weather

Abstract. Recent flash flood impact studies highlight that road networks are often disrupted due to adverse weather and flash flood events. Road users are thus particularly exposed to road flooding during their daily mobility. Previous exposure studies, however, do not take into consideration population mobility. Recent advances in transportation research provide an appropriate framework for simulating individual travel-activity patterns using an activity-based approach. These activity-based mobility models enable the prediction of the sequence of activities performed by individuals and locating them with a high spatial–temporal resolution. This paper describes the development of the MobRISK microsimulation system: a model for assessing the exposure of road users to extreme hydrometeorological events. MobRISK aims at providing an accurate spatiotemporal exposure assessment by integrating travel-activity behaviors and mobility adaptation with respect to weather disruptions. The model is applied in a flash-flood-prone area in southern France to assess motorists' exposure to the September 2002 flash flood event. The results show that risk of flooding mainly occurs in principal road links with considerable traffic load. However, a lag time between the timing of the road submersion and persons crossing these roads contributes to reducing the potential vehicle-related fatal accidents. It is also found that sociodemographic variables have a significant effect on individual exposure. Thus, the proposed model demonstrates the benefits of considering spatiotemporal dynamics of population exposure to flash floods and presents an important improvement in exposure assessment methods. Such improved characterization of road user exposures can present valuable information for flood risk management services.

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