Effect of bioengineering treatments on reduction of soil erosion from road cut slope and fill slope

Abstract

The efficiency of different conservation practices on soil loss from road side slopes is scarcely identified in the Hyrcanian forests of Iran, which could retard the implementation of these management practices. Sediment of 48 plots on the cut slopes and fill slopes of forest roads were collected to explore their responses to soil conservation practices, including straw bale (SB), living hedge (LH), dead hedge (DH), geo-cell (GC), geotextile (GT), and bare soil (BS). Moreover, the efficiency of conservation practices was evaluated to find a cost-effective approach. Sediment traps were installed at the toe of side slopes in the ditch and end of each treated plot. Sediment volume was measured monthly for six months. The results demonstrated that the lowest soil loss occurred in autumn and fill slopes treated with GC (5.05 g·m–2) and the highest in winter and cut slopes treated with SB (41.81 g·m–2). In all cases, soil loss from BS (126.74 g·m–2) was significantly higher than in plots treated with conservation practices. GC performed well under certain circumstances due to two-dimensional protections of contiguous wooden lumbers. Moreover, it was found that in a short time there were not any significant differences between LH (28.78 g·m–2), DH (36.01 g·m–2), and GT (30.61 g·m–2) in soil loss control ability. Regarding implementation and installation costs, GC (USD 16.67 per plot) was the most expensive, while LH (USD 3.33 per plot) was the cheapest. Regarding GC, it is necessary to conduct long-term research to determine economic efficiency, durability, maintenance, and repair costs. Until then, it is possible to use affordable treatments such as LH, which have yielded favourable results in efficiency.