Soil moisture variation on the outlet area of devices dewatering forest roads in Beskid Sądecki

Abstract

Water run-off - a natural part of water circulation in the natural environment - is a harmful and undesired phenomenon for humans. The most spectacular and most serious one is its erosive activity. In adverse conditions, such a runoff has high energy, it causes serious reshaping of a terrain and it destroys the natural environment and infrastructure. In the forest environment, a run-off process occurs basically on roads, skidding trails and in log storage sites, which are areas with soil cover properties changed by humans. The devices used for dehydrating a transport system direct water collected in the form of concentrated streams to a slope, which frequently causes serious linear damage or landslides. The objective of the tests carried out was to determine the spatial distribution of soil moisture on the area behind the outlet of devices dehydrating forest roads within the context of changes in selected soil properties affecting a risk of landslide formation. The tests included four water drains dehydrating a forest slope road with a soil surface. In the area located behind the outlet, according to the model accepted, soil samples were collected for testing a current moisture value, determining grain composition and a hydraulic conductivity coefficient, calculated based on the simplified Hazen formula. There were significant differences in the soil moisture means in the three-measurement series conducted; nevertheless, the highest moisture means were obtained after the lowest precipitation, and the lowest moisture means were obtained after the highest precipitation. It applies to all water drains observed, separately and collectively. Average moisture measures in all dehydrating facilities differed among one another, although in different sessions, this dependence was observed in various facility pairs. The statistical analysis did not demonstrate any significant differences in moisture in terms of the distance of moisture testing location from the road edge, or in locations with different distances from the water run-off line behind the outlet of dehydrating devices. Significant differences could be observed in the analysis of average moisture values in the soil layers. Such an analysis result could be explained by a relatively low soil permeability and low slope gradient on the area examined. Usually, a few percent fluctuation in soil moisture, despite precipitation diversity, in combination with a high amount of granular soil structure, does not create conditions facilitating the formation of landslides.