Browsing by Author "Seutloali, Khoboso."

Now showing 1 - 2 of 2

Assessing soil erosion associated with main roads in south-eastern South Africa.
(2014) Seutloali, Khoboso.; Beckedahl, Heinrich Reinhard.
Construction of linear infrastructure such as roads is increasing worldwide for the provision of efficient transportation of both humans and commodities. However, roads have been widely recognised as significant causes of increased soil erosion due to their influence on the hydrologic and geomorphic processes through the modification of natural hill-slope profiles, the construction of cut and fill embankments as well as impervious road surfaces that concentrate runoff. Accelerated soil erosion due to roads is of particular concern since the associated environmental impacts have economic ramifications related to water treatment and soil rehabilitation. In the light of the above, a better understanding of road-related soil erosion is required to guide environmentally sustainable future developments and erosion control efforts. The present study assesses soil erosion associated with main tar roads in the south-eastern region of South Africa. The first part of the study provides an overview of the linkages of roads with soil erosion by water, related structural designs that facilitate soil erosion processes as well as available approaches for assessing road-related soil erosion and the available erosion control techniques. Secondly, the study focuses on exploring the characteristics (i.e. gradient, length, and vegetation cover) of degraded and non-degraded roadcuts with a view to understanding why some roadcuts are degraded while others are not. Moreover, the study investigates the relationship between the characteristics of the roadcuts and the dimensions (i.e. width and depth) of the rills. Results show that degraded roadcuts are steeper, longer and have a lower percentage of vegetation cover when compared to non-degraded roadcuts. The results further show that there is a significant relationship between the width and depth of the rills, and the slope gradient and percentage of vegetation cover of the roadcuts. These results prompted the need to evaluate the volume of soil loss, using rill dimensions on roadcuts as well as an assessment of the relationship between the volume of soil loss and the soil properties. Results show that soil loss correlates significantly with all the rill dimensions, and the rill depth is the foremost variable in calculating rill volume than the rill width and length. In addition, the results show that there is a significant relationship between the volume of soil loss and the soil properties of the roadcuts. The study further used remotely sensed data to assess gully erosion related to road drainage release and examined the relationship between physical and climatic factors (i.e. road contributing surface area, vegetation cover, hillslope gradient and rainfall) and the volume of gullies. The results indicate that the road contributing surface area, vegetation cover and hillslope gradient have a significant contribution and influence on the size of the gullies along major armoured roads. Moreover, the results show that remote sensing technologies have the capability to investigate road-related gully erosion where detailed field work remains a challenge due to economic and time constraints. Finally, in order to evaluate the effectiveness of soil erosion control methods along the roads, the study investigates the performance of different soil erosion control methods utilised on the roadcuts. It was observed that most of the slope stabilisation methods are successful in controlling soil erosion while the majority of drainage control methods performed poorly. The results show that good performance is related to vegetation re-establishment, while poor performance may be attributed to improper application, lack of inspection and maintenance. Overall, the study provides an understanding of erosion related to the post construction phase of roads. In this regard, it is expected that the results of this study will contribute to the management of roads from the soil erosion perspective through appropriate interaction with the South African National Roads Authority (SANRAL). It is hoped that this work will lay the foundation for environmentally sustainable road construction, maintenance and the formulation of effective soil erosion control measures in the future.
The effects of unpaved access roads on runoff and associated water quality within the Seele Estate, New Hanover, South Africa.
(2011) Seutloali, Khoboso.; Beckedahl, Heinrich Reinhard.
Unpaved forestry roads can significantly affect surface runoff and sediment production, with consequential impacts for stream water quality. The potential impact of road runoff on stream water quality is mitigated by the redistribution of runoff into the forest compartments through road drains. The objective of this study was to assess runoff and the associated nutrient loads from unpaved forest access roads, and to evaluate the effectiveness of road runoff redistribution onto the forest compartments. Unpaved road segments in Mondi Forest Plantation in Seele Estate, New Hanover, South Africa were instrumented for runoff measurement in response to natural rainfall. Two road segment classes were investigated for water quality from unbounded runoff plots: steep sloped road segments of road gradients of 9.5° and 7.5°, and gentle sloped road segments of road gradients of 1.6° and 2.0°. Water quality was also assessed by monitoring road runoff, and stream water quality was analysed for water quality parameters including; pH, Nitrates, Nitrites, Phosphates, Total dissolved Oxygen, Oxygen consumption, Ammonium and temperature upstream and downstream of the Estate. The effectiveness of road runoff redistribution into the forest compartments was evaluated through relating water distribution to tree breast height diameter. Two sets of road drains corresponding to the plots of different road gradients were selected as for runoff, and sampled, and corresponding plots or allotments were established to determine tree breast height diameter measurements. The results of the study revealed that, as might have been expected, runoff production increases with the increasing road gradient. The quality of road runoff water was lower than the stream water. There were no significant differences observed in nutrient levels upstream and downstream of the road stream crossings. The nutrient concentrations however, were higher upstream of the estate than downstream. Significant differences in tree breast height diameter were noted between plots of different road gradients. This suggested that the gradient determines the infiltration of redistributed runoff and hence the availability of the water that can be used by the trees within a compartment. The results of the study suggest that unpaved roads are important in the generation of nutrient loads. Much of the nutrient value is redistributed within the compartment itself rather than being transferred to the stream. This suggests that, provided that road runoff can be contained within the compartments, the potentially negative impact of road runoff can be mitigated and may enhance tree growth.