Abstract
Abstract. Preferential flow paths have been found to be important for runoff generation, solute transport, and slope stability in many areas around the world. Although many studies have identified the particular characteristics of individual features and measured the runoff generation and solute transport within hillslopes, very few studies have determined how individual features are hydraulically connected at a hillslope scale. In this study, we used dye staining and excavation to determine the morphology and spatial pattern of a preferential flow network over a large scale (30 m). We explore the feasibility of extending small-scale dye staining techniques to the hillslope scale. We determine the lateral preferential flow paths that are active during the steady-state flow conditions and their interaction with the surrounding soil matrix. We also calculate the velocities of the flow through each cross-section of the hillslope and compare them to hillslope scale applied tracer measurements. Finally, we investigate the relationship between the contributing area and the characteristics of the preferential flow paths. The experiment revealed that larger contributing areas coincided with highly developed and hydraulically connected preferential flow paths that had flow with little interaction with the surrounding soil matrix. We found evidence of subsurface erosion and deposition of soil and organic material laterally and vertically within the soil. These results are important because they add to the understanding of the runoff generation, solute transport, and slope stability of preferential flow-dominated hillslopes.
Highlights
Subsurface flow in hillslopes dominates the hydrological regime, the transport of solutes and nutrients, and can affect slope stability, especially in steep forested watersheds in humid climates
We aim to describe lateral preferential flow paths that are active during subsurface flow, their interaction with the surrounding soil matrix, and the velocities of the flow through each cross-section of the hillslope (Sidle et al, 2001)
Most of the material on the bottom of the soil pipes was fine gravel. The soil surrounding this portion of the network was shallow with a clay-rich mineral horizon (Bg) and a deep Ah horizon of well decomposed organic material
Summary
Subsurface flow in hillslopes dominates the hydrological regime, the transport of solutes and nutrients, and can affect slope stability, especially in steep forested watersheds in humid climates. Researchers have used dyes and excavation to determine how water exploits vertical and lateral preferential flow paths Weiler and Fluhler, 2004) These experiments have been used at the smallest scales (2 m or less) and often focus on the vertical movement of water during infiltration. This method is labour intensive and destroys the soil structure, but it has been proven effective. Less destructive methods such as ground penetrating radar, fibre optics, and electrical conductivity have been tested, but they require expensive equipment and have seen limited successes (e.g. Holden et al, 2002; Sherlock and McDonnell, 2003)
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