Reconstruction and characterization of the surface drainage system functioning during extreme rainfall: the analysis with use of the ALS-LIDAR data—the case study in two small flysch catchments (Outer Carpathian, Poland)

Abstract

A surface drainage system (SDS) controls catchment hydrology and acts as an indicator of geomorphologic processes. In this study, a field-based and GIS-integrated approach enabling reconstruction of a surface drainage system, which operates during heavy rainfall in small flysch catchments, has been proposed. The reconstruction is based on the ALS-LIDAR data. The reconstruction of the SDS gave the opportunity for analysis of the changes between the river system and the SDS operating during heavy rainfalls. Results have revealed that the SDS operating during heavy rainfalls is several times better developed than the river system. The density has increased from c.a. 1.5 to 13.7 km·km − 2 . Moreover, the structure of the SDS has changed, what was confirmed by the parameters of the Hortonian type of the analyses. The most significant changes were related to the first-and second-order streams. These streams were, the most frequently, the man-origin incisions and natural-origin incisions/concavities on the hillslopes conditioned by micro-relief. The man-origin sub-system reached up to 35% of the SDS functioning during heavy rainfalls, whereas the sub-system composed of incisions/concavities conditioned by micro-relief reached up to 24% of this SDS. Smaller lateral valleys included to the SDS during heavy rainfalls constitute up to 37% of the SDS. The permanent streams constitute the remaining part of the SDS. Changes in the SDS have the influence on the drainage pattern, hydrological response of a catchment, and intensity of geomorphological processes; therefore, the changes in the SDS and their consequences have been discussed.

A Quantitative Analysis of Surface Changes on an Abandoned Forest Road in the Lejowa Valley (Tatra Mountains, Poland)

“…Our research indicates that the flow velocity is locally comparable for road segments with rock outcrops where the value comes to 0.91 m s −1 . The values obtained for road segments with rock outcrops are close to flow rates obtained for unpaved roads on the Carpathians' flysch hillslopes, which exceed 1 m s −1 [53,54]. However, the maximum average value, found in our research, is lower than the flow rate in small catchments in the Carpathians during flash floods, which ranges from 1.6 to 2 m s −1 [55].…”

“…Human intervention associated with the construction of forest roads and special logging roads in mountain areas contributes to an increase in the level of activity of selected geomorphologic processes occurring on hillslopes [51][52][53]. Gullies often develop in such areas.…”

Surface Drainage Systems Operating during Heavy Rainfall—A Comparative Analysis between Two Small Flysch Catchments Located in Different Physiographic Regions of the Western Carpathians (Poland)

“…In order to reach the goals of this study, the operation of the SDS during extreme hydrometeorological conditions was reconstructed according to the methodology described by Bryndal and Kroczak [27].…”

“…The changes result from the incorporation of the river system, including (1) natural-origin elements (such as smaller lateral valleys or incisions conditioned by micro-relief) and (2) man-origin incisions (e.g., paved and unpaved roads, ditches and plough furrows). The density of the man-origin elements exceeds the density of the natural-origin valley system at least two times [26][27][28][29][30] and some of them (roads) are preserved in the environment for centuries [29]. During extreme hydro-meteorological events such as heavy rainfalls, when the most preferable conditions for the overland flow formation occur [1], the natural-and man-origin incisions operate as one 'real' SDS.…”

“…So far, knowledge about the parameters of these systems is limited, mainly due to the difficulties in the reconstruction of the 'real' SDS, which had been made in the post-event investigation and covered small areas [17,18,21,22]. The ALS-LIDAR data released in recent years gave a new opportunity in the 'real' SDS reconstruction and characterization [27,28].…”