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Supplements of Geografia Fisica e Dinamica Quaternaria
Volume I - 1988

 

Proceedings of the meeting:
The Morphotectonics in Italy

CICACCI S., D’ALESSANDRO L., FREDI P. & LUPIA PALMIERI E.

Contributo dell’analisi geomorfica quantitativa allo studio dei processi di denudazione nel bacino idrografico del Torrente Paglia (Toscana meridionale – Lazio settentrionale) – Contribution of Quantitative Geomorphology in the study of denudational processes in the drainage basin of Torrente Paglia (Tuscany, Latium)

Pages 171-188

Abstract

The poss ible relati ons exist ing between morphometric parameter s of drainage basins and the type and intens ity of denud ation al processes were investigated. To this end the Torrent e Paglia basin was exami ned; it cons tit ute s the headwater of the Fiume Paglia which joins the Plume Tevere to the SE of Orvieto. The studied basin is emp laced in the gra ben of Radicofani which trends NW·SE and is delimited by the Mo nte Ce rone hor st to the East and by the Monte Civ irella-Mo nte Elmo horst to the West. The basin shape and the pattern of its drainage network are stric tly depending upon the regiona l st ructural condit ions. Denudat ional forms and processes which distinguish the To rren re Paglia drainage basin were ident ified on th e basis of a careful geomorphological survey; grav ity and superficial runnig waters resulted to be the most impor tant morphogenetic agent s. The type and the intensity of these processes arc func t ion not only of local climat ic condi tions but also of the outcroppi ng lithot ype characters. Th e latt er cons ist of four main units : mainl y carbonatic formations of the «Tuscan scric » (Upper Tr ias-Eocene) ; flysch format ions with argillaceous components more or less marked (Cretaceous-Eocene-Oligocene ); argillaceous and sandy argillaceous formations of «Tuscan neogenic cycle» (Lower Pliocene); volcanic format ions tied up to the Q uaternary volcanism of Monte Amiata, of Radicofa ni app arat us and of the Vulsini Complex. To single out the relations existing between denudation al processes and the main morphomet ric characters of drainage basins and net s, some par ticularly inte rest ing parameters were examined. Such parameters, calculated for the whole basin and for i ts main partial basins, are : drainagedensity, reliefenergy and some parameters exp ressing the hierarch ization degree of dr ainage nets (in par t icular, index and demity 0/ hierarchical anomaly). Th e hypsomet ric analysis was also performed; the end was to evaluate the equi libri um stage of the studied basins, from whic h the ent ity and the veloci ty of denudati on al processes are depending. The most interes ting observat ions der ived from the study of hierarchizat ion degree of drai nage nets and from the hypsometric analysis. On the basis of d ata so far obtained it is possible to affirm that when linear erosion processes are preva iling the drainage net s arc better organized while th eir disorganizat ion gradually increases as slope dcnudationa l processes get more and more impor tan t; the less organized nets were observed wherever ecalanchi» occur , The hypsomet ric analysis singled out th at hypsomerric curve trending and the values of th e relevant integrals are strict ly depending on the type of the prevailing dcnudarional processes : the observat ion made allowed the proposal of an interpretative model of the cur ves themselves; this model integrates the t radit ional model proposed by STRAHLER, which referr ed to the «geomorp hic cycle ».

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