Dye staining and excavation of a lateral preferential flow network

Abstract

Abstract. Preferential flow features 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, no 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 features 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 features. The experiment revealed that larger contributing areas coincided with highly developed and hydraulically connected preferential features 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 these types of hillslopes.

Intercomparing hillslope hydrological dynamics: Spatio‐temporal variability and vegetation cover effects

“…The question arises as to which factors govern the onset of lateral preferential flow paths under dry summer conditions. Many studies have provided field evidence of lateral subsurface preferential flow paths including flow through soil pipes and along roots [e.g., Anderson et al , 2008; Holden and Burt , 2002; Kienzler and Naef , 2008a; Newman et al , 2004; Retter et al , 2006; Terajima et al , 2000; Tsukamoto et al , 1988; Uchida et al , 2002]. However, the exact mechanisms of self‐organizing networks [ Sidle et al , 2000, 2001] are not known.…”

Macropores and water flow in soils revisited

“…Such heterogeneities are not necessarily obvious from the soil surface and may be the result of the history of soil development and land use, ranging from deep tertiary weathering and Holocene periglacial structures to recent land management and drainage histories. Some larger scale staining experiments have been carried out [e.g., Kung , ; Noguchi et al ., ; Wienhöfer et al ., ; Anderson et al ., ] but the evidence for the importance of preferential flows at this and larger scales tends to be indirect, inferred from the bulk responses of natural or artificial tracer concentrations at some measurement point [e.g., Hornberger et al ., ; Nyberg et al ., ; Rodhe et al ., , Kienzler and Naef , ; McGuire and McDonnell , ]. Kung et al .…”

“…There are now a wide variety of papers suggesting that preferential flows might often be important in controlling hillslope hydrology, and by implication patterns of solute transport, but that these subsurface pathways might, in some environments, only be revealed by digging into the soil. The networks revealed by such destructive sampling can, however, be extensive, even if not all obvious macropores are connected to a flow network [e.g., Noguchi et al ., ; Terajima et al ., ; Weiler and Flühler , ; Anderson et al ., ; Graham and McDonnell , ]. The networks of obvious macropores are often disconnected, such that continuous downslope flows require some mechanism for transmitting flow from one part of the network to another.…”

Soil hydrology: Recent methodological advances, challenges, and perspectives

“…In a push to increase understanding of lateral preferential flow, Anderson et al . [] have recently dye‐stained and excavated a subsurface flow network. Clearly, such excavations involve a tremendous amount of work, and noninvasive characterization of such networks would be highly preferable.…”