The potentials of biological geotextiles in erosion and sediment control during gold mine reclamation in Ghana

摘要

Purpose Soil erosion is a significant environmental impact of surface mining affecting the initial establishment of vegetation, especially on steep slopes, during reclamation. Consequently, we investigated the potentials of biological geotextiles constructed from two local plants, Pennisetum purpureum and Broussonetia papyrifera, in reducing erosion and sedimentation during reclamation at Newmont Ghana Gold Limited.Materials and methods Six experimental plots were constructed on a 33% slope waste rock, covered with a 70-cm layer of stockpiled subsoil. Concrete gutters, lined with silt fence, were installed at the lower end of each plot to collect eroded sediment. The two kinds of biological geotextiles, York mat and elephant grass mat, were used with bare ground as control in a randomized block design with two replicates each. Data on sediment yield was collected after each substantial rainfall. The performance of each geotextile in reducing soil loss was expressed as a percentage from the mean total sediment yield.Results and discussion With total precipitation of 306 mm in the period April 18, to July 4, 2016, both elephant grass mat and York mat significantly (p0.05) reduced soil loss by 56.6% and 97.3%, respectively, compared to the control, indicating both mats were effective in erosion and sediment control. The relatively high performance of York mat was mainly attributed to its more fibers that provided less surface cover (70%) as well as flexibility of the fibers which enabled the mat to absorb more water during rainfall thus increasing its weight. This increase in weight promoted better drapability, with better erosion and sediment control. Gully formations at the site were primarily due to high concentrated runoff flows from the top of reclaiming benches, with time delays between completion of earthworks, geotextile placement, and seeding of plants as predisposing factors.Conclusions The York mat (YM) and the elephant grass mat (EM) individually acted as cover and protected the highly erodible graded mine slope against the erosive forces of tropical rain and runoff until vegetation establishment. Even so, planning and coordinating the reclamation program such that all earthworks are completed at the end of the dry season to enable geotextile installation and plant seeding at the onset of rains, together with installation of temporary slope drains in preventing gully formations from concentrated runoff flows, are considered to contribute significantly to the general reclamation success at Newmont Ghana Gold Limited (NGGL) and similar mine sites.