Test of three methods to detect the overbank flow from water level time‐series analysis

Abstract

International audienceIn this study, we propose to identify morphological and hydraulic characteristics related to overbank flows in the water level time-series available at many gauged stations. The results obtained at 13 river stations (the catchment sizes vary from 10 to 1700 km2 with contrasted geology, land use and rainfalls regime) show that overflow mechanisms at the river-reach scale can be systematically identified in the water level frequency distribution estimated with the peaks-over-threshold (POT) method. A first level (Lts1) was in the range of the incipient flooding onto the floodplain. Even if the definition of this level is variable in terms of flooded area at the reach scale, this method can be useful in providing a first estimation of the bankfull level for many gauged stations, without complex and costly field surveys. A second level (Lts2) was systematically detected on average 38 cm above the topographic flat floodplain elevation. The Lts2 inflection in the water-level frequency distribution is assumed to reflect a composite effect of catchment hydrology and local hydraulics and channel geometry, without possibility to make a clear distinction between both processes at the moment. The local or reach scale effect would probably play an essential role in the frequency distribution as flood attenuation at catchment scale may explain the inflection Lts2 at only three sites. In light of the knowledge acquired in laboratory flumes with compound channels, most of the time Lts2 level would correspond to the level of resumption of flow both in the main channel and the floodplain. Once this method is validated in various physiographic contexts, it should apply to many hydrometric stations for both synchronic (e.g. regional analysis) and diachronic analysis (e.g. evolution over time of the bankfull discharge) to evaluate anthropic impacts on river morphology. Copyright © 2010 John Wiley & Sons, Ltd

Are periurban areas key places to mitigate urban inundations?

“…From the proposed calculation method we can see the vulnerability amount has doubled between the 70s and the 90s. If we consider that the 2-year flood is representative of the full bank flow (Navratil et al, 2010), we can notice from Figure 6 that its ratio is not far from 1. This means the flooding hazard has not increase in regard to the urban development.…”

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

“…The catchment conditions are dynamically variable, and therefore, such a comparison can be not representative of torrent hydrology and morphology at a given time [36]. An approach based on comparisons of catchments with or without check dams under the same hydrological input and environmental conditions could be more suitable to provide useful indications on the effects of torrent control works and to inform attempts of catchment managers to optimize their design and functioning [37,38]. However, this approach has been rarely adopted, also because of the difficulty to collect historical observations of peak flows and erosion in unregulated and regulated catchments with the same climatic and geomorphological characteristics in the semi-arid environment.…”

Return Period of Characteristic Discharges from the Comparison between Partial Duration and Annual Series, Application to the Walloon Rivers (Belgium)

“…The most common of them are: field observation at a hydrometric station equipped with a stable rating curve, hydraulic geometry of the section [29,30], flood frequency analysis, or a determination through Manning equation. Other authors analyze water level time-series in order to detect the overbank flow [31].…”