Practical measures fo landslide risk mitigation in the Ukrainian Carpathians

Over 90% of the territory of Ukraine has complex soil conditions. Chernivtsi region located at the piedmont of the Ukrainian Carpathian Mountains is the smallest among 25 regions of Ukraine (its area is 1.3% of the whole territory of the country). Nevertheless, the landslides are significant there. There are approximately 1600 landslide sites. That is more than 9% of the territory (the highest factor in Ukraine). Landslides occupy more than 1500 ha of Chernivtsi city that is 10% of the city area. Local seismological station registers nearly 110-130 seismic events per year. 70-80% of the above events occur within 100 km radius and are of 2-4 earthquake intensity. Chernivtsi region belongs to the area of intensive heavy rains. Some rains last up to 7 hours and amount of precipitations can reach a month and a half norm. These anomalous parameters were connected with the complex influence of natural and technogenic factors: crossing the slopes of dense rivernet; seismological activity connected with 6 local earthquakes zones; active slopes deforestation during last decades of XX century (from 60% up to 25% and lesser); increasing the influence of global climate changes factors (heating, increasing of precipitations, flooding etc.). Principle new and additional factor of landslide activation within Chernivtsi region is increasing of seismic movements after abnormal rainfalls and flooding. In 1985 the “Scheme of anti-landslide structures arrangement on the territory of the city of Chernivtsi” was developed. In the “Scheme …” 31 landslide-prone and slipping slopes of Chernivtsi city are described, the possible sliding surfaces and engineering protection measures are specified, the stability coefficients for natural and “protected” slopes are determined. The engineering protection methods envisaged by the “Scheme …” can be divided into five groups as follows: (1) – shoreline stabilization; (2) - retaining structures; (3) - drainages; (4) -regulation of rivers and streams; (5) – surface-waters diversion. The “Scheme …” developers took the slope stability coefficient equal to one. Based on those data the landslide pressure was determined and the retaining structures were selected. The “Scheme …” analysis concerning the retaining structures types shows that the vertical planning and counter berms were proposed to be applied at all of 19 landslide areas. Moreover, the engineering protection was given a comprehensive approach and was carried out throughout the entire site. It is necessary to draw attention to some mistakes of the “Scheme …” developers, which were practically checked. In the “Scheme …” the landslides were divided into several ones, for example, at the Odeska Street the landslide was divided into two ones. In real life, namely in 1995, there was one continuous landslide. Accordingly, in practice the landslide masses depth was higher. The same occurred with the Dnister-Chernivtsi waterway. Because of the previous mistake of the “Scheme …” developers, the report authors corrected the maximum landslides thicknesses in the table towards the increase. That, accordingly, has led to the increase of landslide pressure value and anti-sliding engineering protection structures prices. The “Scheme …” envisages the counter berms and vertical planning arrangement for almost all areas, which may be connected with significant landslide masses depths and high values of landslide pressure.