Rainfall-runoff modelling and palaeoflood hydrology applied to reconstruct centennial scale records of flooding and aquifer recharge in ungauged ephemeral rivers

Abstract

Abstract. In this study we propose a multi-source data approach for quantifying long-term flooding and aquifer recharge in ungauged ephemeral rivers. The methodology is applied to the Buffels River, at 9000 km 2 the largest ephemeral river in Namaqualand (NW South Africa), a region with scarce stream flow records limiting research investigating hydrological response to global change. Daily discharge and annual flood series were estimated from a distributed rainfall-runoff hydrological model (TETIS) using rainfall gauge records located within the catchment. The model was calibrated and validated with data collected during a two year monitoring programme (2005)(2006) at two stream flow stations, one each in the upper and lower reaches of the catchment. In addition to the modelled flow records, non-systematic flood data were reconstructed using both sedimentary and documentary evidence. The palaeoflood record identified at least 25 large floods during the last 700 yr; with the largest floods reaching a minimum discharge of 255 m 3 s −1 (450 yr return period) in the upper basin, and 510 m 3 s −1 (100 yr return period) in the lower catchment. Since AD 1925, the flood hydrology of the Buffels River has been characterised by a decrease in the magnitude and frequency of extreme floods, with palaeoflood discharges (period 1500-1921) five times greater than the largest modelled floods during the period 1965 -2006 Correspondence to: G. Benito (benito@ccma.csic.es) floods generated the highest hydrograph volumes, however their contribution to aquifer recharge is limited as this depends on other factors such as flood duration and storage capacity of the unsaturated zone prior to the flood. Floods having average return intervals of 5-10 yr (120-140 m 3 s −1 ) and flowing for 12 days are able to fully saturate the Spektakel aquifer in the lower Buffels River basin. Alluvial aquifer storage capacity limiting potential recharge by the largest floods is a common problem in arid environments, with the largest infiltration volumes favoured by increasing depth to groundwater levels.

Quantitative historical hydrology in Europe

“…Flood hydrographs are essential for different engineering applications including dam operation and safety (Swain et al, 2006). The few essays to obtain hydrographs from palaeoflood studies have used probabilistic hydrographs (England et al, 2003;Benito et al, 2011). Recently, Elleder (2010) reconstructed the February 1784 flood of the River Vltava in Prague based on peak flood marks, daily newspapers and explanatory notes accompanying early instrumental measurements on the Klementinum observatory.…”

Enhanced flood hazard assessment beyond decadal climate cycles based on centennial historical data

“…Therefore, these mechanisms were related to main triggering mechanisms of torrential floods in mountain streams in Duero Basin (Ballesteros-Cánovas et al, 2015;Morán-Tejeda et al, 2019). Moreover, during wet winters, characteristic of negative NAO-like phases (López-Moreno et al, 2007), a high moisture soil content prevalence in large portion of the basin, could have enabled a recharge of the groundwater system and therefore favoured the direct rainfall-runoff transformation (Berghuijs et al, 2019;Benito et al, 2010;Benito et al, 2011).…”

Interpreting historical, botanical, and geological evidence to aid preparations for future floods

“…However, adequate flood hazard assessments are limited by the absence of hydrological observations. Using natural flood archives offers a unique opportunity to provide such missing flood information, as performed for example in South Africa (Benito et al, ), Namibia (Greenbaum et al, ; Grodek et al, ), China (Liu et al, ) or Western Indian Himalayas (Ballesteros‐Cánovas et al, ). The use of natural archives may be extended to any ungauged basins, thereby, helping to solve the problematic issue of establishing predictions (Sivapalan et al, ).…”

“…However, adequate flood hazard assessments are limited by the absence of hydrological observations. Using natural flood archives offers a unique opportunity to provide such missing flood information, as performed for example in South Africa (Benito et al, 2011), Namibia (Greenbaum et al, 2014;Grodek et al, 2013), China (Liu et al, 2014) or Western Indian Himalayas (Ballesteros-Cánovas et al, 2017).…”

“…11,161,169 Data used in conventional FFA should comply with the iid assumption, specifically related to stationarity. To this end, a stationarity test for censored series has been developed (Lang, Ouarda, & Bobée, 1999), which has been used on historical (Figure 8(a); Barriendos et al, 2003;Naulet et al, 2005), fluvial (Figure 8(b); Benito et al, 2011) and lake records (Corella et al, 2016). For statistical modeling, FFA uses a combination of a cumulative distribution function (e.g., Gumbel, LP3, GEV, etc.)…”