Effects of Roughness Coefficients and Complex Hillslope Morphology on Runoff Variables under Laboratory Conditions

Abstract

The geometry of hillslopes (plan and profile) affects soil erosion under rainfall-runoff processes. This issue comprises of several factors, which must be identified and assessed if efficient control measures are to be designed. The main aim of the current research was to investigate the impact of surface Roughness Coefficients (RCs) and Complex Hillslopes (CHs) on runoff variables viz. time of generation, time of concentration, and peak discharge value. A total of 81 experiments were conducted with a rainfall intensity of 7 L min−1 on three types of soils with different RCs (i.e., low = 0.015, medium = 0.016, and high = 0.018) and CHs (i.e., profile curvature and plan shape). An inclination of 20% was used for three replications. The results indicate a significant difference (p-value ≤ 0.001) in the above-mentioned runoff variables under different RCs and CHs. Our investigation of the combined effects of RCs and CHs on the runoff variables shows that the plan and profile impacts are consistent with a variation in RC. This can implicate that at low RC, the effect of the plan shape (i.e., convergent) on runoff variables increases but at high RC, the impact of the profile curvature overcomes the plan shapes and the profile curvature’s changes become the criteria for changing the behavior of the runoff variables. The lowest mean values of runoff generation and time of concentration were obtained in the convex-convergent and the convex-divergent at 1.15 min and 2.68 min, respectively, for the soil with an RC of 0.015. The highest mean of peak discharge was obtained in the concave-divergent CH in the soil with an RC of 0.018. We conclude that these results can be useful in order to design planned soil erosion control measures where the soil roughness and slope morphology play a key role in activating runoff generation.

Analysis of sheet erosion component variability on four complex hillslopes and consecutive storms under laboratory conditions

“…SCs in the fourth and fifth events on these hillslopes were less compared to the third event whereas on concave-convergent and convex-convergent hillslopes the increasing trend in variations continued. Based on results reported by Geranian et al (2013) and Meshkat et al (2019), parallel hillslopes exhibited almost constant variations in the components of sheet erosion considering their constant upstream and downstream width; whereas, on convergent hillslopes, variations in SC still increased with the passage of time because of the greater upstream area compared to the downstream area. In the study of the profiles of the hillslopes also, concave profiles, because of their lower slope at the end of the plot, could be a site for storage and accumulation of surface runoff and sediment deposition compared to the other profiles.…”

“…Hillslopes with straight-convergent, concave-convergent, and convex-convergent geometries in the 2 m by 1 m plot were designed using plexiglass sheets for the convergent plan and mineral aggregate for the concave and convex plan (Figure 1). According to Figure 2 and Table 2, the length and width of the plot were calculated using Equations ( 1)-( 3) and utilizing plexiglass sheets and the profile elevation employing mineral aggregate for the various types of CHs including straight-parallel, straight-convergent, concave-convergent, and convex-convergent and implemented on the 2 m by 1 m plot (Talebi et al 2008;Meshkat et al 2019). where z, x, and y are the elevation, the horizontal distance in the direction of the length of hillslope towards the end of the basin, and the horizontal distance from the center of the gradient in the vertical direction towards the length of the hillslope, respectively.…”

“…Various studies have been carried out worldwide on the components of sheet erosion, such as surface runoff and soil loss on complex hillslopes (CHs) (Agnese et al 2007). In this regard, we can mention research by Talebi et al (2008Talebi et al ( , 2016; Sabzevari et al (2010), Geranian et al (2013), Amanian et al (2018), andMeshkat et al (2019), who studied the effects of CHs including hillslope plan shapes (convergent, divergent, parallel) and their longitudinal profiles (straight, convex, and concave) on the behavior and volume of produced surface and sub-surface runoff and soil loss during the rainfall-runoff process under various laboratory conditions. The results of these studies suggest that dynamic changes happen in surface runoff and soil loss on CHs in various laboratory conditions.…”

The Effect of Hydrology on Soil Erosion

“…They evaluated the hydrological response under different intensities of simulated rainfall of different devices under the same conditions. On the other hand, Meshkat et al [11] assessed the geometry of hillslopes (plan and profile), which can affect soil erosion under rainfall-runoff processes. They studied the impact of surface roughness coefficients and complex hillslopes on runoff variables viz.…”

Validation of the USPED Erosion and Deposition Model at Schofield Barracks, O‘ahu, Hawai‘i

“…Alternatively, complex landscapes have been computationally divided into semi-homogeneous planes, and erosion has been calculated for each plane, thus giving some consideration to hillslope convexity and concavity (Foster and Wischmeier 1974). However, in both approaches, erosion is calculated only along straight flow lines without full consideration of the influence of flow convergence and divergence which can affect soil erosion greatly (Hallema et al 2016, Meshkat et al 2019. Neither approach provides adequate spatially distributed information on erosion necessary to effectively optimize erosion and sediment control efforts.…”