Volume XIV |

Snow avalanche tracks mapping within Bâlea glacial valley (the Făgăraș Mountains) using semi-automated detection methods

Abstract: Mapping of snow avalanche tracks based on topographic maps, aerophotos and field data to achieve inventories for the whole mountaineous areas in Romania is an important step in snow avalanche risk assessment and other related geomorphic processes. This requires experience and it is a time consuming process. In the absence of field data, the process of snow avalanche tracks mapping is influenced by the subjectivity of those who digitize.
Thus, we propose a semi-automated method for detection of snow avalanche tracks based mainly on geomorphometric parameters that can be extracted from the Digital Elevation Model (DEM) like slope gradient, plan and profile curvature, mean curvature, runoff.
In this study we used an object based analysis to detect snow avalanche tracks in central part of the Făgăraș Mts. This approach has two steps, segmentation and classification. First, we segmented the area based on plan curvature (which is the most important parameter that describes these snow avalanche tracks) in order to obtain objects. In the process of classification we added other conditions such as fuzzy function for slope gradient, thresholds for altitude and runoff and a shape index of objects. The results obtained were very close to the mapped tracks using digitizing techniques. The maps resulted from the classification were compared to the those resulted from digitizing in both number of objects and spatial agreement of the class of objects. There was a very good fit in case of the number of objects and total area of objects. The method could be improved if we apply on high resolution DEMs and also on more case studies with different topography and existing vector database.

Volume XIV |

The temporal variation of suspended sediment transport according to the dominance of suspended sediment sources. Case study: the Trotuş river between 2000 and 2014

Abstract: Based on the data series of average daily streamflow and suspended sediment load recorded between 2000 and 2014 at four gauging stations (Lunca de Sus, Goioasa, Târgu Ocna and Vrânceni), the temporal variation of the suspended sediment transport was investigated according to the prevalence of source areas. Thus, a significant temporal variability (monthly, seasonal, annual) was determined, in close relation with the amount of precipitation and the streamflow. The following equation was determined between the mean monthly suspended sediment load (Ṝ) and the mean discharge (Ǭ) at Vrânceni section: R= 0,0035Q2,2895, r=0,899. We believe this relation has a high degree of confidence for the indirect determination of solid load and it is comparable with other equations of this type. Along the entire length of the river, July was the month during which the highest suspended sediment load was recorded, with an average percentage of 37% of the total amount. At the opposite end, December is the month with the lowest documented suspended sediment load, with just 0.5% of the total amount transported annually by the Trotuş. As regards the seasonal variability of the suspended sediment load, the following values were determined along the entire length of river Trotuş: during the winter season the volume of sediment carried by the river amounts to approx. 2.1% of the total annual transported suspended sediment, the spring season accounts for 33.7% of the annual volume, the summer season accounts for ca. 55.5%, and the fall for 8.7%. In order to plot the R-Q correlation, the wettest, as well as driest years were selected for every gauging station. On the resulting plots, there were identified the thresholds based on which the two sources were separated depending on the area of origin: dominant from the catchment or dominant from the river bed. Overall, during the investigated period on the Trotuş river, the river beds contributed with about 21% of the total volume of transported suspended sediment. Depending on the type of the year (wet, dry or normal), the average input of the beds to the annual volume of suspended alluvium was as follows: 4% in wet years; 43% in dry years; 15% in normal years. The total volume of suspended sediment transported through the four sections on the Trotuş river between 2000 and 2014 amounted to approx. 39×106 t, thus the average annual volume was 2,598,000 t. A large share of this suspended sediment yield was produced during major floods. For example, at Vrânceni ca. 61% of the total sediment yield for the 15 year-period under investigation resulted from just 3 flood events (2005, 2010 and 2012).

Volume XIV |

Geotechnical Properties of Some Soils in a Tar Sand Area of Southwestern Nigeria

Abstract: Engineering properties of some soil samples in Idiobilayo and Idiopopo areas of Southwestern Nigeria were studied with the aim of determining their geotechnical properties which can aid in the exploitation plan of the tar sands deposits in the area.
A total of six sampling locations with three samples each were established in the study area. Samples of soil both disturbed and undisturbed were obtained from the trial pits to a depth of about 1.5m at 0.5m vertical interval. The disturbed samples were subsequently subjected to classification tests such as grain size distribution and consistency limits using British standards 1377 procedure. However, the undisturbed samples were subjected to permeability test.
Results obtained in this study showed that the area of study is underlain essentially by sandy soils, with substantial silty content. Clay and gravel content are quite minimal. The particle size distribution curves confirmed a general dominance of silt to coarse-grained sand size particles in the soil matrix with minor but complimentary clayey and gravelly materials. Amounts of fines in the soils are less than 50% except in trial pts 4 and 5 where they are slightly above 50%.
The soils consist of sand (60.0 %) and silt (35.0 %). The percentage of fines (silt and clay sized fraction) in the soils was about 38.0 %, and makes the soils good base for landfill, since recommended percentage of fines, should not be less than 20.0 %. However the obtained values of permeability coefficient of 5.5 X 10-6 mm/s to 1.2 X 10-4 mm/s call for the lining of the base to avoid groundwater pollution by leachates.

Volume XIV |

Landscape metrics as a tool for landform pattern delineation. A case study on dune fields

Abstract: During the recent years, landform detection and mapping has been one of the most active fields of geomorphometry. However, there is still a need for quantitative work addressing the issue of classifying repeating landform types (MacMillan et al., 2004). The main issue in developing an accurate automatic classification algorithm of repetitive landform types is given by the difficulty to integrate contextual information within the analysis (Evans, 2012). Therefore, the motivation of the current approach is strongly related to the importance of context analysis in the field of specific geomorphometry. Introduced in landscape ecology to evaluate the spatial structure of a landscape, the concept of landscape metrics embraces a series of specific indicators for quantifying topological and contextual information. Thus, considering the fact that the assessment of topological and contextual attributes is not possible based on local, statistical and regional land-surface variables, the main objective of this study is to assess the applicability of landscape metrics for the delineation of landform patterns.
The quantification of landscape metrics involved the segmentation and classification of the following morphometric variables: elevation, profile curvature and local relief. Using an unsupervised method, the Iso Cluster Unsupervised Classification tool from ArcGIS10® software, a total of 24 classes have been used in order to fulfill the minimum requirement imposed by the concept of landscape metrics and further statistical analysis. In order to test the transferability degree of landscape metrics among different dune fields, a set of statistical analyses was carried out. The proposed methodology has been applied on freely available ASTER GDEM’s. This paper provides new prospects regarding the applicability of landscape metrics for the delineation of landform patterns.

Volume XIV |

Near surface thermal characteristics of alpine steep rockwalls in the Retezat Mountains

Abstract: The characteristics of the near surface thermal regime of two rockwalls with different aspect in the Retezat Mountains were investigated using two miniature thermistors. Three one-year (2012-2013; 2013-2014 and 2014-2015) rock surface temperature time series were available for the north facing rockwall, whereas only two seasons were analyzed for the south facing rockwall. The mean annual rock surface temperature (MARST) values were with 1.5-2°C colder on the northern rockwall compared with the southern steep bedrock face. Due to long daily exposure to sunshine, the south facing rockwall experienced more diurnal freeze-thaw cycles during the cold season compared to the north facing rockwall. Overall, the thermistor with a southern aspect recorded 40 and 55 more freeze-thaw cycles than the northern one. A greater number of effective freeze-thaw cycles were measured on the south facing rockwall. The maximum daily amplitude on the southern rockwall is three times higher than on the north-facing location (39.1°C compared to 13.6°C). Based on our findings it seems that the MARST values recorded on the shaded face of the steep bedrock suggest a quite likely absence of permafrost, whereas the MARST values at TPR indicate a quite certain absence of permafrost.