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

Abstract

The determination of the return period of frequent discharges requires the definition of flood peak thresholds. Unlike daily data, the volume of data to be processed with the generalization of hourly data loggers or even with an even finer temporal resolution quickly becomes too large to be managed by hand. We therefore propose an algorithm that automatically extracts flood characteristics to compute partial series return periods based on hourly series of flow rates. Thresholds are defined through robust analysis of field observation-independent data to obtain five independent flood peaks per year in order to bypass the 1-year limit of annual series. Peak over thresholds were analyzed using both Gumbel’s graphical method and his ordinary moments method. Hydrological analyses exhibit the value in the convergence point revealed by this dual method for floods with a recurrence interval around 5 years. Pebble-bedded rivers on impervious substratum (Ardenne rivers) presented an average bankfull discharge return period of around 0.6 years. In the absence of field observation, the authors have defined the bankfull discharge as the Q0.625 computed with partial series. Annual series computations allow Q100 discharge determination and extreme floods recurrence interval estimation. A comparison of data from the literature allowed for the confirmation of the value of Myer’s rating at 18, and this value was used to predict extreme floods based on the area of the watershed.

The active layer in gravel‐bed rivers: An empirical appraisal

“…Due to the difficulty of defining the bankfull discharge in the two braided/wandering study cases (Drac and Vénéon rivers), we took the ~1‐year return‐period flood as reference discharge in these two cases. There are three advantages of using the dimensionless flow intensity as flow parameter: (i) Q is the flow descriptor most widely reported in the compiled papers, so this ratio is easy to compute; (ii) the bankfull Q is commonly considered as the dominant channel‐forming discharge and it has been traditionally associated with a 1.5 to 2‐year return period flood (Leopold et al ., 1964), although the exact recurrence of the bankfull flow differs with the hydroclimatic setting and the use of partial vs full duration series (Van Campenhout et al ., 2020); and (iii) the bankfull Q has been consistently related to a near‐threshold discharge for bed sediment movement in gravel‐bed rivers (e.g. Phillips and Jerolmack, 2019).…”

Estimation of the area-specific suspended sediment yield from discrete samples in different regions of Belgium

“…The regional classification of stations depends on their location and on the sedimentary setting and the hydrological dynamics of the upstream area. The regional affiliation of each station (Van Campenhout et al 2020) is shown in Table 2 as well as their geological substratum and loess availability. The land cover proportion in each watershed is derived from Copernicus Land Service and the Corine Land Cover maps (Panagos et al 2015;CORINE Land Cover 2018).…”

“…Discharge data from the dataset do not cover the same period at each location because their installation date varies. Figure 2 gives information about the mean number of days per year where discharge is above bankfull discharge (Q b ), which has been observed in the field or computed from partial series with the methodology of Van Campenhout et al (2020). Figure 2 also shows the number of stations with at least 90% of hourly discharge data available for a given year.…”

Caractéristiques hydro-géomorphologiques des microhabitats d’Unio crassus (Ardenne, Belgique)

“…Les données hydrologiques utilisées dans cette étude proviennent de la station limnigraphique de Martelange (L5610, SPW-DGO3). Le débit à pleins bords (Q b ) de la Sûre au niveau de cette station est de 32 m³/s et sa période de retour, calculée sur base des séries partielles, est de 0,8 an (Van Campenhout et al, 2020). Le module est de 3,8 m³/s.…”