The influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment

This study investigates the role of soil moisture on the threshold runoff response in a small headwater catchment in the Italian Alps that is characterised by steep hillslopes and a distinct riparian zone. This study focuses on: (i) the threshold soil moisture-runoff relationship and the influence of catchment topography on this relation; (ii) the temporal dynamics of soil moisture, streamflow and groundwater that characterize the catchment's response to rainfall during dry and wet periods; and (iii) the combined effect of antecedent wetness conditions and rainfall amount on hillslope and riparian runoff. Our results highlight the strong control exerted by soil moisture on runoff in this catchment: a sharp threshold exists in the relationship between soil water content and runoff coefficient, streamflow, and hillslope-averaged depth to water table. Low runoff ratios were likely related to the response of the riparian zone, which was almost always close to saturation. High runoff ratios occurred during wet antecedent conditions, when the soil moisture threshold was exceeded. In these cases, subsurface flow was activated on hillslopes, which became a major contributor to runoff. Antecedent wetness conditions also controlled the catchment's response time: during dry periods, streamflow reacted and peaked prior to hillslope soil moisture whereas during wet conditions the opposite occurred. This difference resulted in a hysteretic behaviour in the soil moisture-streamflow relationship. Finally, the influence of antecedent moisture conditions on runoff was also evident in the relation between cumulative rainfall and total stormflow. Small storms during dry conditions produced low stormflow amounts, likely mainly from overland flow from the near saturated riparian zone. Conversely, for rainfall events during wet conditions, higher stormflow values were observed and hillslopes must have contributed to streamflow

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A2. Influence of Antecedent Moisture Conditions on Inter-rill Soil Erosion

Once downloaded, these high definition QuickTime videos may be played using a computer video player with H.264 codec, 1280x720 pixels, millions of colors, AAC audio at 44100Hz and 29.97 frames per second. The data rate is 5Mbps. File sizes are on the order of 600-900 MB. (Other formats may be added later.) Free QuickTime players for Macintosh and Window computers may be located using a Google search on QuickTime. The DVD was produced by J. Robert Cooke.Few studies have looked at the effects of antecedent soil moisture conditions on inter-rill soil erosion and in many models soil erodability parameters are considered constant, even though it is well known that the soil’s inherent ability to resist erosion varies temporally due to differences in temperature, soil frost, time since ploughing, consolidation, microbial activity, soil organic matter content, soil moisture, etc. Therefore, 11 high rainfall intensity (>45 mm/hr) experiments were done on the 6-m × 2-m EPFL erosion flume to determine the effects of antecedent moisture conditions on inter-rill soil erosion. Pore pressure at 0.05 m below the soil surface at the start of the experiment had a large effect on peak sediment concentrations; wetter antecedent moisture conditions led to higher peak sediment concentrations, with the largest changes occurring near saturation. Antecedent moisture conditions also influenced the composition of the eroded sediment; wetter conditions led to a disproportionately large flux of clay- and silt- sized particles. The finding that the composition of the eroded sediment not only changes during an event but is also dependent on the antecedent moisture conditions has important implications for modelling the transport of chemical fluxes associated with the sediment flux, such as phosphorous fluxes. Antecedent moisture conditions did not influence the steady-state sediment concentrations. One of the optimized non-dimensional parameters in the analytical solutions of the Hairsine-Rose erosion model (α, the ratio of the re-detachability of the soil and runoff depth to the runoff ratio and the mass per unit area of sediment required for complete shielding) was linearly related to pore pressure at the start of the experiment. Using the linear relation between this non-dimensional parameter and pore pressure, the sediment concentrations and the composition of the eroded sediment could be simulated for a range of antecedent soil moisture conditions and events. This work builds on Dr. Parlange’s contributions to erosion research and finding analytical solutions to describe erosion processes, and is another step towards operational soil erosion models that can be used under a wide range of conditions.1_fr7yko8

Intermittent and perennial streamflow regime characteristics in the Okanagan

Streamflow data from ten Water Survey of Canada gauging stations were analyzed to characterize streamflow regimes in the Okanagan Basin (British Columbia). The differences in the streamflow regime characteristics of the perennial and intermittent streams were subtle, except for the obvious difference in summer low flows. The intermittent streams tended to have faster recessions after spring freshet, steeper flow duration curves, a slightly earlier median day of the year of the start of the freshet, and more variable discharge in fall. In years with high fall precipitation, discharge was also high during fall for the intermittent streams but in other years it was very low. Discharge on August 1

Regional and local patterns in depth to water table, hydrochemistry and peat properties of bogs and their laggs in coastal British Columbia

In restoration planning for damaged raised bogs, the lagg at the bog margin is often not given considerable weight and is sometimes disregarded entirely. However, the lagg is critical for the proper functioning of the bog, as it supports the water mound in the bog. In order to include the lagg in a restoration plan for a raised bog, it is necessary to understand the hydrological characteristics and functions of this rarely studied transition zone. We studied 13 coastal British Columbia (BC) bogs and identified two different gradients in depth to water table, hydrochemistry and peat properties: (1) a local bog expanse-bog margin gradient, and (2) a regional gradient related to climate and proximity to the ocean. Depth to water table generally increased across the transition from bog expanse to bog margin. In the bog expanse, pH was above 4.2 in the Pacific Oceanic wetland region (cooler and wetter climate) and below 4.3 in the Pacific Temperate wetland region (warmer and drier climate). Both pH and pH-corrected electrical conductivity increased significantly across the transition from bog expanse to bog margin, though not in all cases. Na+ and Mg2+ concentrations were generally highest in exposed, oceanic bogs and lower in inland bogs. Ash content in peat samples increased across the bog expanse-bog margin transition, and appears to be a useful abiotic indicator of the location of the bog margin. The observed variation in the hydrological and hydrochemical gradients across the bog expanse-bog margin transition highlights both local and regional diversity of bogs and their associated laggs. © Author(s) 2013

Impacts of rural water diversions on prairie streamflow

Prairie streams have low basin-average runoff, and are significantly impacted by human settlement. Recent studies have suggested that climate change has resulted in a 0.2% per year decrease in southern Alberta's late summer streamflow. However, even in river basins identified by the Water Survey of Canada as having 'natural' flow, more than 5% of the total runoff may be diverted and stored for rural activities. This is often unaccounted for in hydrological models or statistical analyses of streamflow trends. While the cumulative impact of these small water diversions is now recognized in water management decisions for major basins, it has not yet been incorporated into streamflow analyses. This paper highlights the cumulative effects of small water diversions and illustrates that they are at least as large as reported climate change effects, and must be accounted for in any streamflow analysis of Prairie streams. © 2012 Canadian Water Resources Association