Comparison of the Flood Response of a Braided and a Meandering River, Conditioned by Anthropogenic and Climatic Changes

Garzón, G.; Alonso, Alejandro Roa

doi:10.1002/9781444304299.ch13

Cited by 9 publications

(10 citation statements)

References 5 publications

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“…This situation could be due to an overall tendency to incision in several Mediterranean rivers as described by Garzón and Alonso (2002), Liebault and Piegay (2002), Uribelarrea et al (2003) and Hooke (2006). These refer to a present tendency towards entrenchment and confinement in the channel domain, accompanied by reduced deposition in floodplain areas, probably due to river adjustment following the excessive sediment build-up derived from the 19th-century (Late Little Ice Age) increase of flooding.…”

Section: Discussionmentioning

confidence: 99%

“…In Spain, "rambla" is a term used in the scientific literature to refer to an ephemeral gravel-bed stream that is hydrologically dependent on rainfall (Camarasa and Segura, 2001). The lithological profile of the mountains (NE Betic Range) includes several sedimentary and low-grade metamorphic materials, where the complex but still active tectonics has induced abrupt slopes on the highly fractured and erodible rocks (Goy and Zazo, 1982;Sanz de Galdeano, 1983;Silva et al, 1992Silva et al, , 1994. Within this mountain range, Tertiary basins and Plio-quaternary valleys have developed, and that is where the Azohía Rambla and alluvial fan is located (Fig.…”

Section: Study Areamentioning

confidence: 99%

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

Ortega

Razola

Garzón

2014

Nat. Hazards Earth Syst. Sci.

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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 postflood 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.

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Section: Discussionmentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

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

Ortega

Razola

Garzón

2014

Nat. Hazards Earth Syst. Sci.

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“…There is a high energy deposition layer at 0.90 m depth where even coarse fragments of pottery and bricks are found. An age of around 150 ± 65 14 C yr BP was obtained at the intermediate level of the floodplain stratigraphical section under the overbank sediments by Garzón and Alonso (2002). 4.…”

Section: Samplingmentioning

confidence: 99%

Application of lead isotopic methods to the study of the anthropogenic lead provenance in Spanish overbank floodplain deposits

Sanjuan

Flem

Borrajo

et al. 2015

Environ Geochem Health

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Changes in the principal sources of Pb in overbank sediment profiles have been documented for two Spanish areas by using Pb isotopes and Pb concentrations. These locations (Madrid and Tinto-Odiel basin) represent two of the most contaminated regions in Spain. The Community of Madrid is characterized by heavy industrial and urban activity, focused mainly in Madrid City. The Tinto-Odiel basin drains the Iberian Pyrite Belt, which hosts many polymetallic massive sulphides and is heavily affected by mining activities in their headwaters. It has been proven that the influence of anthropogenic activity is reflected in these overbank deposits by variations in Pb concentrations that, in general, correlate with shifts in the (206)Pb/(207)Pb ratio. Rivas profile (downstream of Madrid) was found to be the most anthropogenically influenced site. The sediments within this profile which were recently deposited (170 ± 40 years BP) have the least radiogenic signatures. (206)Pb/(207)Pb ratios ranged between 1.1763 and 1.1876 indicating significant contributions of anthropogenic Pb. In contrast, profiles upstream of Madrid possess an average (206)Pb/(207)Pb ratio of 1.2272. It is difficult to clearly identify the most prominent source as the sediments appear to be characterized by an input from several sources. The floodplain profiles in the Tinto-Odiel basin exhibit uniform (206)Pb/(207)Pb ratios ranging from 1.1627 (Odiel river) to 1.1665 (Tinto river). These ratios are similar to the ones possessed by sulphide ores in the area and differ from the ratios of other nonmineralized formations in the basin, indicating that mining activities are the primary, if not sole, source of Pb to the sediments.

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“…The lithological profile of the mountains (NE Betic Range) includes several sedimentary and low-grade metamorphic J. A. Ortega et al: Recent human impacts and change in dynamics and morphology of ephemeral rivers materials, where the complex but still active tectonics has induced abrupt slopes on the highly fractured and erodible rocks (Goy and Zazo, 1982;Sanz de Galdeano, 1983;Silva et al, 1992Silva et al, , 1994. Within this mountain range, Tertiary basins and Plio-quaternary valleys have developed, and that is where the Azohía Rambla and alluvial fan is located (Fig.…”

Section: Study Areamentioning

confidence: 99%

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

Ortega¹,

Razola²,

Garzón³

2013

Preprint

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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.

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Comparison of the Flood Response of a Braided and a Meandering River, Conditioned by Anthropogenic and Climatic Changes

Cited by 9 publications

References 5 publications

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

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

Application of lead isotopic methods to the study of the anthropogenic lead provenance in Spanish overbank floodplain deposits

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

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