The effect of technical characteristics of road-waterway intersection and protective measures on the amount of sediment in forest waterways (A case study of Minodasht flat design in Golestan province)

Document Type : Complete scientific research article

Authors

1 Gorgan Uni.

2 Miniidasht nat. dept.

3 Department of Forestry, Faculty of Forest Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

4 Department of Arid Zones Management, Gorgan University of Agricultural Sciences and Natural Resources, Iran

Abstract

Background and purpose: The crossing of a forest road through a river or natural waterways can lead to structural changes, such as the narrowing of the river's path and, as a result, the increase in flow speed and sediment production. When the runoff exceeds the hydrological capacity of the bridge or bridge, or the inlet pond is blocked with sediments or foliage, the flow overflows onto the road, which leads to the production of sediment. The purpose of this research is to investigate the effect of the road surface condition on the amount of sediment in forest waterways, to investigate the effect of the percentage of coverage of the slopes overlooking the road-waterway intersection and the amount of traffic on the amount of sediment in forest waterways, as well as the effect of soil protection treatments, including geotextiles and dead hedges on the amount of sediment produced at the road-waterway intersection.
Material and Methods: The studied area is a part of a forestry plan in watershed number 91. In this study, firstly, the forest roads were classified into two classes of routes with high traffic (at least 80 traffic per day - mine access road) and low traffic (maximum 5 traffic per day). In each traffic class, two road-waterway intersections with the same conditions were identified. The characteristics of the surface participating in the production of sediment (length and width of the gables at the intersection), the type and percentage of the gables cover and the condition of the roads were evaluated. In the next stage, protection treatments of geotextiles and dead hedges were applied on the slopes overlooking the road-waterway intersection. Before and after the treatments, runoff samples were collected 5 meters before entering the river and 5 meters after leaving the river. In total, 10 repetitions of runoff sampling were done for each treatment. The collected data were then entered into the statistical software for analysis.
Findings: The results showed that the amount of suspended sediment load of forest waterways when crossing the road-waterway intersection increased by 64% and reached from 0.12 g/l to 0.33 g/l. The results of variance analysis showed that traffic, the percentage of hilltops overlooking the road-waterway intersection, and the condition of the roads at the 95% confidence level had a significant effect on the amount of suspended sediment load of forest waterways. While no significant effect was observed from the length of the earth slopes and interaction effects between other independent variables on the amount of suspended sediment load of waterways. As the amount of traffic increased as well as the amount of UPCI, the amount of suspended sediment load decreased. With the increase in the coverage percentage of the gables, the amount of suspended sediment load of the forest waterways at the road-waterway intersection decreased by 48%. Geotextile and dead hedge treatments were able to reduce the amount of suspended sediment load in waterways by 57 and 54%, respectively.
Conclusion: It is necessary to have enough funds for restoration and reconstruction in order to continue the traffic flow on the road. This leads to the production of less suspended sediment load at the road-waterway intersection. In addition, the use of protective treatments such as geotextile and dead hedge are essential for soil protection. The findings showed that the efficiency of these two treatments is the same, but in terms of the economic function, the dead hedge treatment is more cost-effective.

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Journal of Water and Soil Conservation
Volume 31, Issue 4
January 2025
Pages 179-194

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