Lichenometric application to historical and subrecent dynamics and sediment transport of a Corsican stream (Figarella River—France)

Abstract

Lichenometry has been applied to blocks, canyon walls and terrace deposits. A growth curve, specific to Corsica, was made based on information obtained from tombstones, old monuments from the Genoese occupation of Corsica and Roman megaliths. This allowed us to create a curve going as far back as 2000 years. The curve is similar to those developed in Mediterranean environments (C! evennes and Eastern Pyrenees), but is very different from those developed in Alpine and Arctic regions.Lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined. The lichenometric study of the Figarella shows firstly that there is high stream competence. Blocks approximately 100 cm wide are moved during the 5-year flood. Recent important flood events were identified in 1973 and 1869. These correspond well with historical sources. Other older and much more important floods were also identified. This analysis has allowed us to extend the specific streampower curves proposed by Costa (Geol. Soc. Am. Bull. 94 (1983) 986) and Williams (Geogr. Ann. 65A (1983) 227) to blocks of more than 2 m wide.Lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the Little Ice Age. Aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active.

The influence of sediment size, relative grain size and channel slope on initiation of sediment motion in boulder bed rivers. A lichenometric study

“…Indeed, despite very high stream powers, 3 to 4 m wide particles are not mobilized. By comparing the relationships derived from this study to those in the literature (Costa, 1983;Williams, 1983;Gob et al, 2003, Jacob et al, 2006Lenzi et al, 2006;Mao et al, 2008) (Figure 4 and Table IV) one can see that the criteria for particle motion may be quite different from one river to the next, even for the same types of rivers (boulder and block rivers). In Figure 4, the curves are distributed over a wide range of specifi c stream powers.…”

Critical specific stream power in gravel-bed rivers

“…The discharge regime is relatively variable because these rivers are Gob et al (2003) developed on an impermeable substratum (lower Devonian quartzite and quartzo-phillite). However, some are developed partly on limestone with a dominant baseflow regime.…”

“…Furthermore, two lichenometric studies in the Mediterranean region have allowed relations for streams carrying clasts larger than 2 m (relations 8 and 9 in Table 1) to be established. Jacob (2003) highlighted a relation for rivers with mobilised material ranging from 700 mm to 2300 mm and Gob et al (2003) worked in a river transporting clasts between 900 and 2000 mm. In these last two relations the largest mobilised boulder size was considered rather than the D 50 of the bedload, as is generally the case.…”

Bedload Transport and Morphological Effects of High-Magnitude Floods in Small Headwater Streams - Moravskoslezské Beskydy Mts. (Czech Republic)

“…In order to provide correct measurement within these approaches, it is advisable to use bedload traps or geophone sensors installed in gauging stations (Rickenmann, 1997;Demir and Walsh, 2005;Mao et al, 2008). Gob et al (2003) have applied a method of lichenometric dating to reconstruct flow magnitudes which were able to transport large boulders in Corsican streams. Finally, the method of marked particle displacement is based on regular observations of the motion of marked and mapped particles located in a stream bed or channel bars (Mao et al, 2008).…”