Extended abstract:

Introduction              

Evaluation of Uvala as one of the typical karstic landforms is important in environmental management. Compared with other karstic holes such as doline and polje that have perennially been studied, uvalas have been less investigated, or have been addressed enigmatically.  The Uvala is a combination of some dolines and in terms of size and dimension is larger than doline and smaller than polje. Distinguishing uvala from other karstic sinkholes should not based on one or two factors, but usage of various parameters such as topography, structural conditions, active tectonics, morphoclimatic heritage, present hydrology and geomorphological features should be considered. In this research, with the help of studying the various factors such as topography, lithology, active tectonics, hydrological processes, environmental activities, and geomorphological parameters affective in kastification (i.e. weathering), it has been tried to study the formation and development of uvala as a surface karstic. The aim of this research is to analyze the morphometry of uvala and to recognize this surface karstic feature. Some field observations were carried out for gathering some quantitative parameters of holes.

Materials and methods

Topographic data of study area were extracted from 1:25,000 topographic maps and geological data derived from 1:100,000 geological maps. In this study, based on field observations, topographic maps, Digital Elevation Model, quantitative and statistical methods, 23 Uvalas were identified in Parav-Biston block. Also aerial photographs, satellite imagery and Google Earth software were used for exact delineation of holes border. In order to extract morphometric characteristics of holes, and to identify and distinguish uvalas, 20 meters Digital Elevation Models were used. Morphometric parameters calculated in this study include perimeter, area, depth, volume, main orientation, elongation ratio, sinuosity, ratio of section area and Pitting index. Statistical correlations between variables were used in order to find the relations between quantitative parameters of Uvala metrics and the affective factors on the formations and development of Uvalas in Parav-Biston block. 

Results and discussion

Result of this study reveals that all studied uvalas are developed in elevations higher than 2000 m asl. and most uvalas are located in elevations between 2600 and 3000 m asl. About 74 percent of uvalas have topographic gradient of 0 to 2 percent, and there is no any uvala in gradients higher than 14%. This demonstrates that the probability of Uvala formation in low gradient slopes is higher than steep slopes. Evaluation of regression analysis between parameters reveals that the pitting index is inversely correlated to uvala area so that pitting index decreases as the uvala area increases. There is also inverse relationship between uvala volume and pitting index as well as between uvala depth and pitting index. The uvala volume is positively correlated to area and depth. The assessment of relation between uvala elongation ratio and maximum diameter of uvala reveals that elongation ratio increases as maximum diameter increases. Results show that 86% of uvala orientation is parallel to overall trend of faults. In contrast to Polje, the bottom of all uvalas is pitted and a little sedimentation takes place in uvalas bed. 95 percent of uvalas are developed in Biston Limeston. Results show that lithology has an important effect on the formation and development of uvalas. In study area, extension and favorable condition of Bisetun Massive Limestone has resulted in the development of 95% of Uvalas in this unit. Analyzing the rose diagram of 200 main faults and fractures in Parav-Biston block reveals that main elongation of most uvalas is parallel to main faults of study area.  

Conclusions

 Various karstic features especially uvala have been developed in calcareous lithology and under the profound effect of tectonic in Parav-Biston block. Result of this study shows that most of uvalas have elongated parallel to main faults of Zagros. This implies that uvala differs in origin from other karstic features such as polje that are often originated from dissolution activity and also from sedimentation in the surface karst. The bad pitting is characteristic of uvala  and this is its main difference with polje. In deeper uvalas, the value of pitting index is lower, implying the smoother bed of uvala. This can be due the development of underground drainages in deep uvalas. Evaluation of uvala shape indicates the tectonic controls on the formation and development of this feature in Parav-Biston block.