On river-floodplain interaction and hydrograph skewness

Abstract

Understanding hydrological processes occurring within a basin by looking at its outlet hydrograph can improve and foster comprehension of ungauged regions. In this context, we present an extensive examination of the roles that floodplains play on driving hydrograph shapes. Observations of many river hydrographs with large floodplain influence are carried out and indicate that a negative skewness of the hydrographs is present among many of them. Through a series of numerical experiments and analytical reasoning, we show how the relationship between flood wave celerity and discharge in such systems is responsible for determining the hydrograph shapes. The more water inundates the floodplains upstream of the observed point, the more negatively skewed is the observed hydrograph. A case study is performed in the Amazon River Basin, where major rivers with large floodplain attenuation (e.g., Purus, Madeira, and Juruá) are identified with higher negative skewness in the respective hydrographs. Finally, different wetland types could be distinguished by using this feature, e.g., wetlands maintained by endogenous processes, from wetlands governed by overbank flow (along river floodplains). A metric of hydrograph skewness was developed to quantify this effect, based on the time derivative of discharge. Together with the skewness concept, it may be used in other studies concerning the relevance of floodplain attenuation in large, ungauged rivers, where remote sensing data (e.g., satellite altimetry) can be very useful.

Quantifying peakflow attenuation/amplification in a karst river using the diffusive wave model with lateral flow

“…The ceiling of outflow intensity with the increase of discharge into the river is most probably explained by the occurrence of overbank flow, knowing that flood plain attenuation can play a key role on the modification of hydrograph shape (Fleischmann et al, ; Rak et al, ; Sholtes & Doyle, ; Valentova, Valenta, & Weyskrabova, ). Indeed in the study case, outflow on the flood plain appears to be an important process of peakflow attenuation for the highest floods, because the increase in infiltration with an increased input peakflow is stopped (Figure ).…”

“…As shown on Figure , several types of lateral flow occur during floods, depending upon catchment descriptors such as climate, relief, geology, and soil. For highest peakflows, lateral outflow (Figure a) is generally considered in the case of overbank flow when waters from the river flow to the flood plain, without been returned to the river during the flood (Jothityangkoon & Sivapalan, ; Moussa & Bocquillon, ), modifying the shape of the hydrograph (Rak, Kozelj, & Steinman, ; Fleischmann, Paiva, Collischonn, Sorribas, & Pontes, ). Another case favouring lateral outflow is specific to permeable basins, where river losses infiltrate and recharge the underlying aquifer (Charlier et al, ; Dvory et al, ; Sorman, Abdulrazzak, & Morel‐Seytoux, ).…”

The equilibrium alluvial river under variable flow and its channel‐forming discharge

“…Variability of the flow rate due to flood waves is essential for, for instance, floodplain-related mechanisms [e.g., Lauer and Parker, 2008;Lauer et al, 2016;Viparelli et al, 2013;Fleischmann et al, 2016] and plant colonization of exposed bars [Tal and Paola, 2010;Vargas-Luna, 2016]. Although extreme events may induce changes to the river system that moderate flows cannot [Buffington, 2012], for instance, the formation of new gullies, the creation of meander cutoffs, floodplain scour, and the movement of huge boulders [Wolman and Miller, 1960;Pickup and Warner, 1976;Lenzi et al, 2006], flow events of moderate magnitude, which recur relatively Our objective is to determine relations linking the equilibrium channel slope, channel width, and bed surface texture under variable flow and to provide a definition of the slope-equivalent or channel-forming discharge.…”

Riverine phytoplankton functional groups response to multiple stressors variously depending on hydrological periods

“…The index H20 provided two opposite trends across different hydrological periods. One river could present two types of hydrograph on skewness depending on the hydrological conditions, such as in the river Piquiri, South Brazil, where small (large) floods present positive (negative) skewness (Fleischmann et al, 2016). The maximum value of skewness of flow in the studied catchment was observed in the tributary Jerrisbek during the wet season.…”