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.

scholarly journals Towards an increase of flash flood geomorphic effects due to gravel mining and ground subsidence in Nogalte stream (Murcia, SE Spain)

2016 ◽  
Vol 16 (10) ◽  
pp. 2273-2286 ◽  
Author(s):  
Jose Antonio Ortega-Becerril ◽  
Guillermina Garzón ◽  
Marta Béjar-Pizarro ◽  
Jose Jesús Martínez-Díaz
Keyword(s):  
Flash Flood ◽  
Time Lag ◽  
Alluvial Fan ◽  
Ground Subsidence ◽  
Flood Event ◽  
Stream Power ◽  
Base Level ◽  
Gravel Mining ◽  
Collateral Effects ◽  
Aquifer Overexploitation

Abstract. Transition from endorheic alluvial fan environments to well-channelized fluvial systems in natural conditions may occur in response to base-level fluctuations. However, human-induced changes in semi-arid regions can also be responsible for similar unforeseen modifications. Our results confirm that in-channel gravel mining and aquifer overexploitation over the last 50 years in the case study area have changed the natural stability of the Nogalte stream and, as a result, its geomorphic parameters including channel depth and longitudinal profile have begun to adapt to the new situation. Using interferometric synthetic aperture radar (InSAR) data we obtain maximum values for ground subsidence in the Upper Guadalentín Basin of  ∼ 10 cm yr−1 for the period 2003–2010. In this context of a lowered base level, the river is changing its natural flood model to a more powerful one. A comparison of the 1973 flood event, the most dramatic flood event ever recorded in the area, with the 2012 event, where there was a similar discharge but a sediment load deficit, reveals greater changes and a new flooding pattern and extension. In-channel gravel mining may be responsible for significant local changes in channel incision and profile. This, together with the collateral effects of aquifer overexploitation, can favour increased river velocity and stream power, which intensify the consequences of the flooding. The results obtained here clearly demonstrate an existing transition from the former alluvial pattern to a confined fluvial trend, which may become more pronounced in the future due to the time lag between the drop in aquifer level and ground subsidence, and introduce a new scenario to be taken into consideration in future natural hazard planning in this area.

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 Towards an increase of flash-flood geomorphic effects due to gravel mining and ground subsidence in Nogalte stream (SE Spain, Murcia)

2016 ◽  
Author(s):  
Jose A. Ortega-Becerril ◽  
Guillermina Garzón ◽  
Marta Béjar-Pizarro ◽  
Jose Jesús Martínez-Díaz
Keyword(s):  
Flash Flood ◽  
Time Lag ◽  
Alluvial Fan ◽  
Ground Subsidence ◽  
Stream Power ◽  
Fluvial Systems ◽  
Base Level ◽  
Gravel Mining ◽  
Collateral Effects ◽  
Aquifer Overexploitation

Abstract. Transition from endorheic alluvial fan environments to well-channelized fluvial systems in natural conditions may occur in response to base-level fluctuations. However, human-induced changes in semi-arid regions can also be responsible for similar unforeseen modifications. Our results confirm that in-channel gravel mining and aquifer overexploitation over the last 50 years in the case study area have changed the natural stability of the Nogalte stream and, as a result, its geomorphic parameters including channel depth and longitudinal profile have begun to adapt to the new situation. Using interferometric synthetic aperture radar (InSAR) data we obtain maximum values for ground subsidence in the Upper Guadalentín basin of ~ 10 cm yr−1 for the period 2003–2010. In this context of a lowered base level, the river is changing its natural flood model to a more energetic one. A comparison of the 1973 flood event, the most dramatic ever recorded in the area, with the 2012 event, where there was a similar discharge but a sediment load deficit, reveals greater changes and a new flooding pattern and extension. In-channel gravel mining may be responsible for significant local changes in channel incision and profile. This, together with the collateral effects of aquifer overexploitation, can favor increased river velocity and stream power, which intensify the consequences of the flooding. The results obtained here clearly demonstrate an existing transition from the former alluvial pattern to a confined fluvial trend, which may become more pronounced in the future due to the time-lag between the drop in aquifer level and ground subsidence, and introduce a new scenario to be taken into consideration in future natural hazard planning in this area.

scholarly journals Characterization of a Mediterranean flash flood event using rain gauges, radar, GIS and lightning data

2008 ◽  
Vol 17 ◽  
pp. 35-41 ◽  
Author(s):  
M. Barnolas ◽  
A. Atencia ◽  
M. C. Llasat ◽  
T. Rigo
Keyword(s):  
Flash Flood ◽  
Radar Data ◽  
Convective Precipitation ◽  
Flood Event ◽  
Flood Events ◽  
Rain Gauges ◽  
Radar Echoes ◽  
Spatial Coverage ◽  
Ephemeral Rivers ◽  
Accumulated Rainfall

Abstract. Flash flood events are very common in Catalonia, generating a high impact on society, including losses in life almost every year. They are produced by the overflowing of ephemeral rivers in narrow and steep basins close to the sea. This kind of floods is associated with convective events producing high rainfall intensities. The aim of the present study is to analyse the 12–14 September 2006 flash flood event within the framework of the characteristics of flood events in the Internal Basins of Catalonia (IBC). To achieve this purpose all flood events occurred between 1996 and 2005 have been analysed. Rainfall and radar data have been introduced into a GIS, and a classification of the events has been done. A distinction of episodes has been made considering the spatial coverage of accumulated rainfall in 24 h, and the degree of the convective precipitation registered. The study case can be considered as a highly convective one, with rainfalls covering all the IBC on the 13th of September. In that day 215.9 mm/24 h were recorded with maximum intensities above 130 mm/h. A complete meteorological study of this event is also presented. In addition, as this is an episode with a high lightning activity it has been chosen to be studied into the framework of the FLASH project. In this way, a comparison between this information and raingauge data has been developed. All with the goal in mind of finding a relation between lightning density, radar echoes and amounts of precipitation. Furthermore, these studies improve our knowledge about thunderstorms systems.

Spatial and temporal distribution of fluvio-morphological processes on a meander point bar during a flood event

2013 ◽  
Vol 44 (6) ◽  
pp. 1022-1039 ◽  
Author(s):  
Kasvi Elina ◽  
Alho Petteri ◽  
Vaaja Matti ◽  
Hyyppä Hannu ◽  
Hyyppä Juha
Keyword(s):  
Flow Velocity ◽  
Morphological Changes ◽  
Flow Characteristics ◽  
Temporal Distribution ◽  
Flood Event ◽  
Stream Power ◽  
Point Bar ◽  
Depositional Processes ◽  
Laser Scanners ◽  
A Minor

Morphological changes and hydraulic parameters are analyzed over a meander point bar along a sand-bedded river. Morphological changes caused by a flood are mapped using terrestrial and mobile laser scanners. The flow characteristics are simulated over the duration of the flood, which inundated the point bar completely. The spatial distribution of depth-averaged flow velocity, direction, and stream power at two different discharges is analyzed. In addition, the temporal variation of flow velocity, depth, and stream power on the point bar is resolved over the whole inundated period. The changes in discharge control the transverse shift of the high velocity core, which, in turn, has a major impact on the changes over the point bar. For example, a minor decrease in discharge may lead to a notable decrease in flow velocity on the point bar margin, enabling filling. Deposition occurs mainly during the recession of the flood, and thus, the duration of moderate discharges greatly influences accretion. The size of the supplied sediment also influences the filling over the bar head. Erosion mainly takes place during high discharges. A rapid decrease in discharge inhibits chute filling. The latest flood event seems to influence more the erosional compared to depositional processes.

scholarly journals Accelerate disaster risk mapping using an automated zonal change detection model for loss estimation and recovery: a flood case study

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Ali Amasha
Keyword(s):  
Change Detection ◽  
Satellite Images ◽  
Flash Flood ◽  
Disaster Risk ◽  
Loss Estimation ◽  
Risk Mapping ◽  
Detection Model ◽  
Applied Model ◽  
High Resolution Satellite Images ◽  
Before And After

Abstract Background The flash flood still constitutes one of the major natural meteorological disasters harmfully threatening local communities, that creates life losses and destroying infrastructures. The severity and magnitude of disasters always reflected from the size of impacts. Most of the conventional research models related to flooding vulnerability are focusing on hydro-meteorological and morphometric measurements. It, however, requires quick estimate of the flood losses and assess the severity using reliable information. An automated zonal change detection model applied, using two high-resolution satellite images dated 2009 and 2011 coupled with LU/LC GIS layer, on western El-Arish City, downstream of Wadi El-Arish basin. The model enabled to estimate the severity of a past flood incident in 2010. Results The model calculated the total changes based on the before and after satellite images based on pixel-by-pixel comparison. The estimated direct-damages nearly 32,951 m2 of the total mapped LU/LC classes; (e.g., 11,407 m2 as 3.17% of the cultivated lands; 6031 m2 as 7.22% of the built-up areas and 4040 m2 as 3.62% of the paved roads network). The estimated cost of losses, in 2010 economic prices for the selected three LU/LC classes, is nearly 25 million USD, for the cultivation fruits and olives trees, ~ 4 million USD for built-up areas and ~ 1 million USD for paved roads network. Conclusion The disasters’ damage and loss estimation process takes many detailed data, longtime, and costed as well. The applied model accelerates the disaster risk mapping that provides an informative support for loss estimation. Therefore, decision-makers and professionals need to apply this model for quick the disaster risks management and recovery.

scholarly journals How effective is river restoration in re-establishing groundwater–surface water interactions? – A case study

2015 ◽  
Vol 19 (6) ◽  
pp. 2663-2672 ◽  
Author(s):  
A.-M. Kurth ◽  
C. Weber ◽  
M. Schirmer
Keyword(s):  
Surface Water ◽  
River Restoration ◽  
Morphological Changes ◽  
Cost Effective ◽  
Urban Stream ◽  
Distributed Temperature Sensing ◽  
River Bed ◽  
Before And After ◽  
Restoration Measures

Abstract. In this study, we investigated whether river restoration was successful in re-establishing groundwater–surface water interactions in a degraded urban stream. Restoration measures included morphological changes to the river bed, such as the installation of gravel islands and spur dykes, as well as the planting of site-specific riparian vegetation. Standard distributed temperature sensing (DTS) and novel active and passive DTS approaches were employed to study groundwater–surface water interactions in two reference streams and an experimental reach of an urban stream before and after its restoration. Radon-222 analyses were utilized to validate the losing stream conditions of the urban stream in the experimental reach. Our results indicated that river restoration at the study site was indeed successful in increasing groundwater–surface water interactions. Increased surface water downwelling occurred locally at the tip of a gravel island created during river restoration. Hence, the installation of in-stream structures increased the vertical connectivity and thus groundwater–surface water interactions. With the methods presented in this publication, it would be possible to routinely investigate the success of river restorations in re-establishing vertical connectivity, thereby gaining insight into the effectiveness of specific restoration measures. This, in turn, would enable the optimization of future river restoration projects, rendering them more cost-effective and successful.

scholarly journals Spectral OCT-Angiography in En Face Mode for Detection of Morphological Changes in the Retinal Pigment Epithelium before and after Selective Micro-Pulse Laser Exposure in Patients with Central Serous Chorioretinopathy

2019 ◽  
Vol 16 (2) ◽  
pp. 192-201
Author(s):  
P. L. Volodin ◽  
E. V. Ivanova ◽  
E. Iu. Polyakova ◽  
A. V. Fomin
Keyword(s):  
Retinal Pigment Epithelium ◽  
Central Serous Chorioretinopathy ◽  
Morphological Changes ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Laser System ◽  
Subretinal Fluid ◽  
Micropulse Laser ◽  
En Face ◽  
Before And After

Purpose — to study the morphological changes of the retinal pigment epithelium (RPE) by optical coherence tomography-angiography (OCT-A) in En Face mode before and after selective micropulse laser irradiation in patients with central serous chorioretinopathy (CSC), determine the correspondence between the topographic location of RPE defects and detachment on the OCT-angiogram in En Face mode and points of leakage on the FAG.Patients and methods. There were 20 patients (21 eyes) with CSC before and after laser treatment under the observation. All patients underwent high-resolution FAG and OCT-A using Angio Retina 2×2 or 3×3 mm protocol and Angio Retina HD 6×6 mm. The treatment was carried out in a selective micropulse mode with individual selection of parameters using the Navilas 577s navigation laser system (OD-OS, Germany) or the IQ 577 laser system (IRIDEX, USA).Results were evaluated at 2 weeks and 1 month after treatment. Results. In all cases, the leaking points of the subretinal fluid on FAG corresponded to the topographic location of defects and detachments of RPE detachment on OKT-A En Face. According to OCT-A En Face, the following morphological changes were revealed: in 5 cases — single defects of RPE, in 7 cases — multiple defects of RPE, in 9 cases of slit-like detachment of RPE, in 3 patients a combination of slit-like detachment and defect RPE. The sizes of RPE defects varied in the range from 21 to 159 microns, while their rounded shape prevailed. 1 month after the selective micropulse laser effect on OCT-A in the En Face mode, the defects were closed and the RPE detachments fit in all patients, which resulted in resorption of the subretinal fluid and the neurosensory retina attachment.Findings. OCT-A in En Face mode is a highly informative diagnostic method that allows noninvasive detection of morphological changes in RPE with a clear topographic localization relative to the retinal vascular network, as well as evaluating the effectiveness of selective micropulse laser treatment in patients with CSC. 

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