Discontinuous headwater stream networks with stable flowheads, Salmon River basin, Idaho

Abstract

Headwater streams expand, contract, and disconnect in response to seasonal moisture conditions or those related to individual precipitation events. The fluctuation of the surface flow extent, or active drainage network, reflects catchment storage characteristics and has important impacts on stream ecology; however, the hydrological mechanisms that drive this phenomenon are still uncertain. Here, we present field surveys of the active drainage networks of four headwater streams in Central Idaho's Frank Church‐River of No Return Wilderness (7–21 km2) spanning the spring and summer months of 2014. We report the total length of the active drainage networks, which varied as a power law function with stream discharge with an average exponent of 0.11 ± 0.03 (range of 0.05–0.20). Generally, these active drainage networks were less responsive to changes in discharge than many streams in past studies. We observed that the locations where surface flow originates, or flowheads, were often stable, and an average of 64% of the change in active drainage network length was explained by downstream discontinuities. Analysis of geologic and geomorphic characteristics of individual watersheds and flowheads suggests that most flowheads below approximately 2200 m are supported by stable flowpaths controlled by bedrock structure. At higher elevations, small accumulation areas and saturation of shallow and conductive soil and colluvium after snowmelt result in more mobile flowhead locations. The dynamics of active drainage networks can help illuminate the spatiotemporal structure of flowpaths supporting surface flow. Copyright © 2016 John Wiley & Sons, Ltd.

Topographic Controls on the Extension and Retraction of Flowing Streams

“…This wide range in β indicates that some stream networks extend dramatically as catchments become wetter, while others remain nearly fixed in place ( Figure 1). For example, subsurface transport capacity can be sensitive to valley slope (Jensen et al, 2018;Whiting & Godsey, 2016;Wondzell, 2011), sediment size (Costigan et al, 2016;Wondzell, 2011), tectonic structures (Kennedy et al, 1984;Whiting & Godsey, 2016), and river behavior (e.g., incision versus aggradation; Costigan et al, 2016), but attempts to quantitatively relate these properties to stream network dynamics are rare. For example, subsurface transport capacity can be sensitive to valley slope (Jensen et al, 2018;Whiting & Godsey, 2016;Wondzell, 2011), sediment size (Costigan et al, 2016;Wondzell, 2011), tectonic structures (Kennedy et al, 1984;Whiting & Godsey, 2016), and river behavior (e.g., incision versus aggradation; Costigan et al, 2016), but attempts to quantitatively relate these properties to stream network dynamics are rare.…”

“…We calibrate this predictive model using measured values of β from 17 mountainous stream networks in humid and semiarid climates (Godsey & Kirchner, 2014;Jensen et al, 2017;Lovill et al, 2018;Roberts & Klingeman, 1972;Shaw, 1968;Whiting & Godsey, 2016). We calibrate this predictive model using measured values of β from 17 mountainous stream networks in humid and semiarid climates (Godsey & Kirchner, 2014;Jensen et al, 2017;Lovill et al, 2018;Roberts & Klingeman, 1972;Shaw, 1968;Whiting & Godsey, 2016).…”

“…At Caspar and Sagehen Creeks, which have consistent topographic curvature along the length of the ephemeral channel network, values of transmissivity exhibit only weak downstream trends. This empirical relationship can be substituted into equation (4): (Godsey & Kirchner, 2014;Jensen et al, 2017;Lovill et al, 2018;Roberts & Klingeman, 1972;Shaw, 1968;Whiting & Godsey, 2016) and values of θ and α measured from DEMs (Figures 2g and 2h). While the linear relationship between δ and γ (Figure 3a) does not directly validate the mechanisms we have proposed to relate transmissivity and topographic curvature (Figure 2c), it does provide an empirical basis for estimating the transmissivity scaling exponent γ based on the topographic curvature coefficient δ.…”

“…While these topographic metrics are likely to be useful for predicting stream network dynamics under wetting and drying (Figure 3b), the position and mobility of individual stream heads will often be controlled by bedrock and soil heterogeneities in each headwater valley (Godsey & Kirchner, 2014;Vaux, 1968;Whiting & Godsey, 2016). For example, stream heads are sometimes pinned in place by localized flow that brings water to the surface at permanent springs, and the positions of these fracture zones can be controlled by lithologic contacts or faults, rather than topography (Whiting & Godsey, 2016).…”

“…The partitioning of water above and below the surface is important for a wide range of Earth-surface processes: the extent and connectivity of surface flows determine the mobility and dispersion of freshwater macroinvertebrates (Clarke et al, 2008); fast-moving surface water is required to move sediment and carve valleys into the landscape (Howard et al, 1994); and the total land area covered by surface water is a key control on carbon-dioxide efflux from continents, as well as dissolved organic carbon (DOC) export in rivers Aufdenkampe et al, 2011;Zimmer & McGlynn, 2018). However, even within an individual catchment, the density of actively flowing streams can vary by up to an order of magnitude seasonally or during rainstorms Blyth & Rodda, 1973;Day, 1978;Godsey & Kirchner, 2014;Goulsbra et al, 2014;Gregory & Walling, 1968;Jensen et al, 2017;Lovill et al, 2018;Roberts & Archibold, 1978;Roberts & Klingeman, 1972;Shaw, 2016;Whiting & Godsey, 2016;Wigington et al, 2005;Zimmer & McGlynn, 2017; Figure 1), and it is unclear what controls the temporal variability in wetted stream length. However, even within an individual catchment, the density of actively flowing streams can vary by up to an order of magnitude seasonally or during rainstorms Blyth & Rodda, 1973;Day, 1978;Godsey & Kirchner, 2014;Goulsbra et al, 2014;Gregory & Walling, 1968;Jensen et al, 2017;Lovill et al, 2018;Roberts & Archibold, 1978;Roberts & Klingeman, 1972;Shaw, 2016;Whiting & Godsey, 2016;Wigington et al, 2005;Zimmer & McGlynn, 2017; Fi...…”