Cristian-Dan LESENCIUC¹, DoruToader JURAVLE¹, Cristian Vasilică SECU¹, Ionuț Cristi NICU² & Iuliana Gabriela BREABĂN^1
1"Al.I.Cuza" University of Iaşi, Faculty of Geography and Geology, Carol I Bd, no 20A,Iaşi, 700505-RO, Romania ²"Al.I.Cuza" University of Iaşi, Interdisciplinary Research Department – Field Science, St. Lascăr Catargi 54 Iași, 700107-RO, Romania, E-mail address: Cristian-Dan Lesenciuc: dlesenci@yahoo.com

USING OLD LANDSLIDE-DAMMED LAKES TO ASSESS SEDIMENT DELIVERY RATES IN SMALL CATCHMENTS – CASE STUDY: IEZER LAKE FROM THE ROMANIAN CARPATHIANS

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The easternmost sector of the Eastern Romanian Carpathians (i.e. the flysch area) has a typical morphology, shaped mainly by gravitation-induced landsliding. The heterogeneity of lithological associations, in conjunction with structure, acts as the main cause of massive landsliding processes that affected the hill slopes across broad areas of up to 2-3 km², during certain stages of evolution of the relief. Whereas the majority of landslides are old and stabilized, the possibility for majors landslides still exists at present, like the case of the Cuejdel landslide in Stânișoara Mountains, which occurred in 1991. Despite the large number of landslides documented in the Eastern Carpathians, landslide-dammed lakes were formed solely in a fraction of these instances, and even fewer survived to the present; among these, Iezer Lake (dammed by the landslide which occurred in Iezer stream valley) has been thoroughly studied in recent years. Landslide-dammed lakes are regarded as local basins for sediment accumulation. Their significance for geomorphology and water engineering is considerably larger compared to man-made reservoirs due to their age (i.e. most are much older compared to reservoirs, therefore the assessment of sediment rates can be carried out for a longer timespan). In this study the sediment accumulation rate in the lake basin is inferred based on the modeling of the present-day and preexisting (i.e. prior to lake formation) topography. In terms of geographical location, the landslide, the lake and the entire catchment upstream are part of the Obcina Feredeu Mountains which overlie a highly folded substrate composed of glauconitic sandstones, compacted clays, variegated clays and sphaerosiderite clays, all of which favor landsliding. The lake is located at 931 m a.s.l. and stretches across 1.63 ha, of which ca. 0.88 ha were covered by paludal vegetation which grew from under a layer of 10 to 20 cm of water (in 2009, when the measurements were performed). Our research was initiated in 2009 when the Iezer landslide and lake basin were surveyed using a GPS and a total station. Based on this survey, the digital elevation model was generated. Furthermore, after scanning the site using a GPR and analysing the cross-sections of the initial valley, a model of Iezer valley prior to the lake formation was obtained. The actual volume of sediments accumulated in the lake basin was determined by overlapping the two topographical models, and the result was further related to the period of sedimentation and the area of the catchment. Consequently, the annual sediment delivery rate was determined, together with the observation that the annual sediment delivery rates in small catchments are lower compared to other areas pertaining to flysch.