Geographia Napocensis Anul IX, Nr. 1, 2015 QUANTITATIVE EVALUATION OF MULTI-VULNERABILITY TO HYDRO-GEOMORFOLOGICAL HAZARDS IN THE UPPER SECTOR OF NIRAJ CATCHMENT 1 SANDA ROȘCA Abstract. - Quantitative Evaluation Of Multi-Vulnerability To Hydro-Geomorfological Hazards In The High Sector Of Niraj Catchment. A study of the natural hazards indicates that floods, landslides, fluvial erosion and soil erosion have the highest spatial-temporal occurrence and lead to the highest material losses in the study area of the Niraj Basin. The present study focuses on the upper section of1/2015 the Niraj basin, one that still evolving from a hydrological and geomorphological point of view, without any major anthropic interference. Due to its favourability for the establishing of settlements (a consequencenr, of favourable slopes, fertile lands and water resources), the most of the human settlements are situated in the floodplain area, hence in the most flood-prone area during spring and autumn. The rest of the settlements lie on the inferior sectors of the hillslopes, as well as on the valleys of the main tributaryIX, rivers of the Niraj, hence being exposed to the reactivated landslides- a consequence of the abundant rainfall events usually leading to floods. A cumulated approach of a multi-vulnerability type has beenAN chosen, one that allows the classifying of the built-up area and roads into spatial classes exposed to the identified natural hazards. Spatial analysis led to the obtaining of quantitative information concerning the number of constructions and the length of roads that can be exposed once the hydro-geomorphological processes have reactivated. Key-words: vulnerability, flood-prone area, landslide, risk exposure, Niraj basin 1. Introduction of the statistical analysis of data series obtained The quantifying of vulnerability and risk from previous measurements (Roșca et al., 2014). generated by floods and landslidesNAPOCENSIS is necessary Concerning landslides, the identification of to be expressed in qualitative terms, but even cumulated rainfall values considered as thresholds more so in quantitative ones, for the sake of good in the analysed territory is mandatory (Crozier management in the process of establishing the 1997, Schmidt and Dikau 2004, Polemio and priorities for the possible emergencies, as the EU Petrucci 2010). Offices dedicated to the directive (EPA, 2003) recommends, directive in identifying of the risk exposed elements have been which the principles of thegeographianapocensis.acad-cluj.ro multi-risk study are set in Europe, in countries such as Belgium, enumerated (Marzocchi et al., 2009). The authors France, Germany, the Netherlands, Bulgaria, mention that this method allows a comparison Hungary, Romania, Poland and Slovakia and hierarchyGEOGRAPHIA of the natural hazards and their (www.eurosense.com). Urban planning authorities derived effects. Applying a common and risk strategists can obtain valuable methodology implies a probabilistic analysis of information from the hazard analyses individual risk, namely that of terrain accomplished at a local, regional or national scale vulnerability when it comes to the risk generating (Cascini et al., 2005, Fell et al., 2008). processes in the territorial equation. The vulnerability concept reffers to the The spatial identification of the flood and exposure and capacity characterising the risk landslides associated risk, in hydrology, is elements to resist to the hazardous determined by the establishing of floodplain areas conditions/the occured damages. For damage for different probabilities, computed on the basis identification, the authors take into account the 1 Babeş-Bolyai University, Faculty of Geography, 400006, Cluj-Napoca, Romania, e-mail: [email protected] 67 Sanda Roşca spatial-temporal probability of floods and taken place in 12. 07. 2009 when 5 houses and 7 landslides as well as the vulnerability of the households were damaged, 7 small bridges were people in the area and of the exposed elements destroyed and traffic was disrupted on 0,1 km of (Corominas, 2008). From a conceptual and road as well as 1, 2 ha of agricultural terrain were methodological point of view, the identifying of flooded (according to the data of the Inspectorate exposed elements and their vulnerability is for Emergency Situations, Mureș). necessary in the multi-risk studies allowing the The morphometric characteristics of the relief identification and analysis of individual risk and play an important role on the production and of the cumulated risk (Cutter, 2001). evolution of hydrological phenomena; hence it is Hence it is important that a vulnerability and important to take into account the shape of the risk class be assigned to each unit of the hydrographic basin, given by the direction and administrative territory. Risk zoning consists in orientation of the water divide, which determines the division of the analysed territory in the runoff characteristics. Secondly, the river homogenous areas according to their present or length and the water discharge1/2015 of the tributary presumed susceptibility degree, hazard, flood rivers, closely connected with the altitude of a and landslide risk (Corominas, 2008). An open basin (Zăvoianu, 2006)nr, need to be considered as subject stays, nonetheless, the establishment of well. The hydrographic basin was divided in the acceptable risk (tolerated risk) concerning subwatersheds withIX, the help of the ArcHydro9 damages when it comes to the authorities‟ point extension of the ArcG.I.S software. ArcHydro of view, their opinion being different from one offers the possibility of determining watersheds, country to another (Dai et al., 2002). It is a subwatershedsAN and catchments automatically, as known fact that the scales and quality of the well as it allows the intervention of the user via input data in the analysis and risk evaluation its batch watershed delineation function. For the models will determine the amount of details and upper river basin of the Niraj River a number of the practical application of results. 11 hydrographic subwatersheds has been determined, their surfaces ranging between 9 şi 2. Hydro-geomorfological hazards in the 39 km2 (table 1). GIS allowed the computation of study area different morphometric elements such as the The Niraj hydrographic basin is situated in surface of a hydrographic basin and its perimeter the Central-Eastern part of the TransylvanianNAPOCENSIS (necessary for the computing of the circularity Depression. It is a geographically complex coefficient), the length of several sectors of the territory (from a geological, geomorfological and hydrographic network etc. climatic point of view), displaying favourability For the present study area, the values close towards being inhabited (Roșca, 2011) due to its to 1, indicating an almost circular shape, are morphometric and morphographic characteristic only for the Diceal subwatershed characteristics. Hence there exist 14 localities (C=1,01), the rest of the subbasins being (Fig. 1) only in the uppergeographianapocensis.acad-cluj.ro basin, comprising the characterised by values that indicate their mountainous and piedmountainous sector of the prolonged shape (Nirajul Mic, Nirajul Mare, Gurghiului Mountains. Hodoșa, etc.) which determine a delay in the GEOGRAPHIA registering of peak discharges and a decrease of 2.1. Hydrological hazards the flash-floods amplitudes. These subbasins Amongst the types of hydrological hazards regulate river flow as the abundant rainfall existing in the analysed sector, floods are certainly events from the upstream part and the sudden noticeable, being caused by the spring flash-floods snowmelt in the mountainous area have a latter of mixed origin (rainfall and snow) which impact, due to the different situations existing at represent 52% and followed by the pluvial origin a subbasin level, these situations resulting from summer flash-floods representing 32% (Roșca, the geologic diversity and the different levels of 2011, 2014). These events are accompanied by resistance to erosion which are conditioned by negative effects, the last event of such kind having the local topographic level. 68 Quantitative evaluation of multi-vulnerability to hydro-geomorfological hazards in the upper sector of Niraj Catchment 1/2015 nr, IX, Fig. 1. Geographical position of Niraj subwatershed (where: 1 – subwatershed Nirajul Mare, 2 – Nirajul Mic, 3 – Pârâul Cald, 4 – Diceal, 5 – Săcădad, 6 – Aluniș, 7 – Pârâul Litigios, 8 - Ciadon, 9- Hodoșa și 10 – Zambo)AN Tabelul 1. Morphometric characteristics of subwatersheds ORDER Watershed F P C Rc f Dd T N1 N2 N3 N4 23 4 1 - Nirajul Mic 25 36,9 2,08 4,87 1.12 1,31 1,17 18,04 6,33 8,59 - 25 7 1 - Nirajul Mare 39 38,5 1,74 5,28 0.85 1,07 1,26 NAPOCENSIS20,06 13,98 7,88 - 5 2 1 - Mountainous basin Pârâul Cald 10 14 1,25 2,25 0.80 1,29 1,61 9,26 2,76 0,97 - 6 3 2 - Diceal 13 12,9 1,01 1,83 0.92 0,93 1,01 5,8 2,69 3,69 - 5 1 - - Săcădad 10 15,5 1,38 5 0.60 1,1 1,83 7,79 3,4 - - 5 3 1 - Aluniş 8 14,5 geographianapocensis.acad-cluj.ro1,45 2,33 1.13 1,23 1,09 7,71 0,66 1,49 - Pârâul 6 1 - - 13 17,3 1,35 6 0,54 1,36 2,52 Litigios 13,98 3,81 - - 5 1 - - CiadonGEOGRAPHIA 9 16,3 1,53 5 0,67 1,15 1,72 5,69 4,68 - - basinHillside 13 1 - - Hodoşa 38 33,2 1,52 13 0.37 1,23 3,32 34,22 12.51 - - 9 2 1 - Zambo 19 23 1,49 3,25 0,63 1,48 2,35 20,64 4,92 2,59 - 102 25 7 1 Niraj 184 4,88 1,80 1,36 0,75 143,1 55,7 22,6 29 F (km²)-Area of watershed, P – watershed perimeter (km), C – circularity coefficient (km), Alt. max – maximum st altitude (m), N1,2,3,4,5 – river‟s order, Rc = Nx/Nx+1 – confluence report, f – frecvency of 1 order segments (f=N/F), Dd – Drainage density (Dd=ΣL/F, km/km2), T – Torentiality (T = Dd/f) 69 Sanda Roşca As it can be seen in figure 1 the river courses the drainage density and the frequency of display an arborescent hierarchy.