The impact of late Holocene climatic variability and land use change on the flood hydrology of the Guadalentín River, southeast Spain

Abstract

a b s t r a c t a r t i c l e i n f oThe Guadalentín River, located in southeast Spain, is considered one of the most torrential rivers in Spain, as indicated by catastrophic events such as the 1879 flood that caused 777 fatalities in the Murcia region. In this paper, flood frequency and magnitude of the upper Guadalentín River were reconstructed using geomorphological evidence, combined with one-dimensional hydraulic modelling and supported by records from documentary sources at Lorca in the lower Guadalentín catchment. Palaeoflood studies were conducted along a 2.5-km reach located at the confluence of the Rambla Mayor (162 km 2 ) and Caramel River (210 km 2 ). These tributaries join at the entrance of a narrow bedrock canyon, carved in Cretaceous limestone, which is 15-30 m wide and 40 m deep. Six stratigraphic profiles were described, the thickest and most complete corresponding to flood benches deposited upstream of the canyon constriction. The stratigraphic and documentary records identify five main phases of increased flood frequency. Phase 1, based on sedimentary palaeoflood evidence alone, occurred at c. AD 950-1200 with at least ten floods with minimum discharge estimates of 15-580 m 3 s − 1 . Phases 2-5, identified through combined sedimentary and documentary evidence occurred at: (a) AD 1648-1672, with eight documentary floods and two palaeofloods exceeding 580-680 m 3 s − 1 (most probably the AD 1651 and 1653 events); (b) AD 1769-1802, comprising seven documentary floods, of which at least two events (N 250 m 3 s − 1 ) are preserved in the sedimentary record; (c) AD 1830-1840, with four documentary floods, and at least two events recorded in the stratigraphy (760-1035 m 3 s − 1 ); and finally (d) the AD 1877-1900 period that witnessed seven documentary floods, with three palaeofloods exceeding 880 m 3 s − 1 .The palaeoflood and historical flood information indicate an anomalous increase in the frequency of large magnitude floods between AD 1830 and 1900, which can be attributed to climatic variability accentuated by intensive deforestation and land use practices during the first decades of the nineteenth century.

Reliability of equivalent-dose determination and age-models in the OSL dating of historical and modern palaeoflood sediments

“…Municipal Archive, of which 15 were classified as ordinary, 7 extraordinary and 9 167 catastrophic (Benito et al, 2010). During the second half of the 19th century, an 168 increase in frequency of extraordinary and catastrophic floods is reflected both in the 169 documentary record (with high economic losses and casualties) and in the 170 palaeoflood record (with high energy sedimentary structures).…”

“…We consider our age control -historical records and radiocarbon for 586 the oldest sample T-17 (~1000 years) -sufficiently reliable to allow us to assign 587 calendar ages to individual flood events (Benito et al, 2010) and so derive expected 588 equivalent doses. 589…”

Quantitative historical hydrology in Europe

“…scars on trees and tilting; Herget, 2012;Benito and Díez-Herrero, 2015). A number of studies have combined both historical and geological indicators to ascertain the magnitude and frequency of past flood, increasing the robustness of the frequency analysis of rare floods (Benito et al, 2010). This paper aims to describe the different techniques and approaches used in order to obtain quantitative information from historical flood data, as well as to draw attention to its different scientific and engineering applications.…”

“…Viglione et al (2013) demonstrated that the number of floods exceeding the perception threshold is more important than the uncertainty on discharge value A reduction on the error is obtained for a return period of the largest historical flood about twice length of the pre-instrumental record . Many documentary-based flood studies shown that flood frequency has been influenced by the internal variability of atmospheric circulation, with flood clusters at some time periods (Glaser et al, 2010), or by impacts on the environmental patterns such as land use (Benito et al, 2010) and engineering works (Machado et al, 2015). A simple test of stationarity for censored samples (systematic and/or non-systematic) was proposed by Lang et al (1999) assuming that the flood series can be described by a homogenous Poisson process (Naulet et al, 2005).…”

“…Moreover, the age uncertainty of numerical dating (radiocarbon respectively optically stimulated luminescence methods) used in palaeoflood studies may be refined based on known documentary floods (Medialdea et al, 2014). The SPHERE project has revealed the complementary of palaeoflood and historical flood information with major gain on the quality of past flood records in terms of time and discharge, as is demonstrated in the studies performed for the rivers Gardon (Naulet et al, 2005;Sheffer et al, 2008), Ardèche (Sheffer et al, 2003;Naulet et al, 2005), Llobregat (Thorndycraft et al, 2005), and Guadalentin (Benito et al, 2010;Medialdea et al, 2014). Recent palaeoflood reconstructions from floodplain sediments have analysed geochemical proxies from continuous alluvial records and investigate local documentary flood data to calibrate the palaeohydrological records (e.g.…”