Generation of storm runoff and the role of animals in a small upland headwater stream

Abstract

This paper illustrates the hillslope storm runoff mechanisms and the effects of livestock in upland areas. The research site was a small upland catchment area on Dartmoor (Southwest England). It was shown that overland flow on the tracks and paths created by animals in the area responded very rapidly to rainfall, in the same order of magnitude as stream runoff. Livestock stocking densities were significantly different in different vegetation compositions. The topsoil bulk density values, moisture content and spatial track densities were significantly higher in areas associated with higher stocking rates. These areas reach a wetness threshold at an earlier state than surrounding, drier areas. When isolated, the wetter areas start discharging water only locally into downslope drier areas, but are not contributing to storm runoff in the stream. In areas with a high density of animal tracks, water is being discharged onto the track directly. The tracks comprised an ephemeral hydrological network contributing storm runoff to the stream quickly after rainfall. They transmit water rapidly downhill, short‐circuiting local areas, reducing runoff lag time and increasing storm stream runoff. The runoff producing mechanism, in which soil conditions, vegetation types and path networks are a complex interplay of contributing factors, may be relevant to other uplands, especially when they act as water reservoir or source area for possible flooding events. Therefore, upland management policies need to take into account that the heterogeneity of hillslopes at local scales has implications for storm runoff at the catchment scale. Copyright © 2014 John Wiley & Sons, Ltd.

A statistical comparison of spatio‐temporal surface moisture patterns beneath a semi‐natural grassland and permanent pasture: From drought to saturation

“…Land‐use alone does not significantly improve prediction because its importance is already captured within the interaction terms. Modelling results compare well with Meijles et al (2006) and Meijles et al (2015), who concluded that vegetation was the dominant control on soil wetness during “dry” conditions at Dartmoor (semi‐natural grassland).…”

“…This may be because of weak vegetation differentiation within the SNG plot, with many sampling grids containing both rush and grass species. Other studies have more successfully differentiated semi‐natural grassland vegetation species, with Meijles et al (2015) outlining that moorland grasses saturate faster than heather or bracken ( Pteridium aquilinum ). Conversely to the SNG plot, soil beneath common rushes in PP was wetter than ryegrass during August and October sampling dates, although similar in May and November (Table 7).…”

“…A 1 m resolution topographic survey of the site was undertaken four months after the θ V sampling, as topography may influence soil θ V patterns (following Meijles et al, 2015; Meijles, Williams, Ternan, Anderson, & Dowd, 2006; Minet et al, 2011). The terrain survey combined a differential GPS (Trimble R8‐Integrated GNSS) with a total station (Trimble, Robotic‐S6), giving both the coordinates and elevation of each point.…”

“…Antecedent θ V preceding storm events can dictate rainfall–runoff responses by changing the likelihood of Saturation‐excess Overland Flow (SOF) generation, even from highly permeable soils, so elevating both flood risk and water‐quality degradation (Dunne & Black, 1970; Entekhabi, Rodriguez‐Iturbe, & Castelli, 1996; Marshall et al, 2009; Minet, Laloy, Lambot, & Vanclooster, 2011). The precise spatial arrangement of θ V is fundamental in determining a rainfall–runoff response, as purely using θ V probability distributions does not capture spatial structures and therefore contributory area connectivity (Bonell & Williams, 1986; Grayson & Blöschl, 2000; Meijles, Dowd, Williams, & Heppell, 2015; Minet et al, 2011; Zehe & Blöschl, 2004). Soil θ V is equally important during drought, determining water stress for agricultural crops, wildfire frequency etc.…”

Native woodland establishment improves soil hydrological functioning in UK upland pastoral catchments

“…This connectivity results in the rapid conversion of water to stream T A B L E 3 The influence of newly established woodland on surface soil physical properties along the four study river catchments located in Dartmoor, SW England Note: M (±SE and SD) values of surface soil compaction (Kpa), bulk density with stones (g cm −3 ) (BD), macro-porosity (%) (M porosity), percentage of small stones (%) and organic matter (%) (SOM) of soils in establishing 'woodland' sites are compared with control grazed 'pasture' areas using two-way ANOVA with significant (p ≤ .05) differences denoted in bold font. The tion (Meijles, Dowd, Williams, & Heppell, 2015;Meyles et al, 2006). It is likely, therefore, that establishing woodland offers effective NFM by reducing the number of wet source areas, the connectivity of hillslope moisture and the conversion of rainfall to stream discharge.…”