Stream power

About: Stream power is a research topic. Over the lifetime, 1135 publications have been published within this topic receiving 51324 citations.

Scale-dependent controls upon the fluvial export of large wood from river catchments

Abstract: The annual fluvial export of large wood (LW) was monitored by local reservoir management offices in Japan. LW export per unit watershed area was relatively high in small watersheds, peaked in intermediate watersheds, and decreased in large watersheds. To explain these variations, we surveyed the amount of LW with respect to channel morphology in 78 segments (26 segments in each size class) in the Nukabira River, northern Japan. We examined the differences in LW dynamics, including its recruitment, transport, storage, and fragmentation and decay along the spectrum of watershed sizes. We found that a large proportion of LW produced by forest dynamics and hillslope processes was retained because of the narrower valley floors and lower stream power in small watersheds. The retained LW pieces may eventually be exported during debris flows. In intermediate watersheds, the volume of LW derived from hillslopes decreased substantially with reductions in the proportion of channel length bordered by hillslope margins, which potentially deliver large quantities of LW. Because these channels have lower wood piece length to channel width ratios and higher stream power, LW pieces can be transported downstream. During transport, LW pieces are further fragmented and can be more easily transported. Therefore, the fluvial export of LW is maximized in intermediate watersheds. Rivers in large watersheds, where the recruitment of LW is limited by the decreasing hillslope margins, cannot transport LW pieces because of their low stream power, and thus LW pieces accumulate at various storage sites. Although these stored LW pieces can be refloated and transported by subsequent flood events, they may also become trapped by obstacles such as logjams and standing trees on floodplains and in secondary channels, remaining there for decades and eventually decaying into fine organic particles. Thus, the fluvial export of LW pieces is low in large watersheds. Copyright © 2009 John Wiley & Sons, Ltd.

Using airborne multispectral imagery to evaluate geomorphic work across floodplains of gravel-bed rivers

Abstract: Fluvial processes of cut and fill alluviation and channel abandonment or avulsion are essential for maintaining the ecological health of floodplain ecosystems char- acteristic of gravel-bed rivers. These dynamic processes shape the floodplain landscape, resulting in a shifting mosaic of habitats, both above and below ground. We present a new and innovative methodology to quantitatively assess the geomorphic work potential nec- essary to maintain a shifting habitat mosaic for gravel-bed river floodplains. This approach can be used to delineate critical habitats for preservation through land acquisition and conservation easements, often critical elements of river restoration plans worldwide. Spa- tially explicit modeling of water depth, flow velocity, shear stress, and stream power derived from surface hydraulic measurements was combined with airborne multispectral remote sensing for detailed modeling of floodplain water surfaces over tens to hundreds of square kilometers. The model results were then combined within a GIS framework to determine potential nodes of channel avulsion that delineate spatially explicit zones across the flood- plain where the potential for geomorphic work is the greatest. Results of this study dem- onstrate the utility of integrating existing multispectral remote sensing data coupled with time-lagged ground-based measures of flow hydraulics to model fluvial processes at rela- tively fine spatial resolutions but over broad regional extents.

Rill erosion in natural and disturbed forests: 2. Modeling Approaches

Abstract: [1] As forest management scenarios become more complex, the ability to more accurately predict erosion from those scenarios becomes more important. In this second part of a two-part study we report model parameters based on 66 simulated runoff experiments in two disturbed forests in the northwestern U.S. The 5 disturbance classes were natural, 10-month old and 2-week old low soil burn severity, high soil burn severity, and logging skid trails. In these environments the erosion rates were clearly detachment limited, and the rill erodibility parameters calculated from four hydraulic variables increased by orders of magnitude. The soil shear stress based erodibility parameter, Kr, was 1.5 × 10−6 s m−1in the natural plots, 2.0 × 10−4 s m−1 in the high soil burn severity plots, and 1.7 × 10−3 s m−1 in the skid trail plots; Kr values for the low soil burn severity plots had negative sign. The erodibility value for the skid trail plots fell within ranges reported for tilled agricultural fields and also for forest roads. The Kr values decreased as erosion occurred in the plots and therefore should not be a constant parameter. The stream power produced the largest R2 value (0.41) when hydraulic predictors and the sediment flux were log-transformed, but none of the four hydraulic variables (soil shear stress, stream power, unit stream power, and unit length shear force) explained much of the variability in sediment flux rates across the five levels of disturbance when evaluated in the linear form of the erosion models under consideration.

Scaling relationships between bed load volumes, transport distances, and stream power in steep mountain channels

Abstract: Bed load transport during storm events is both an agent of geomorphic change and a significant natural hazard in mountain regions. Thus, predicting bed load transport is a central challenge in fluvial geomorphology and natural hazard risk assessment. Bed load transport during storm events depends on the width and depth of bed scour, as well as the transport distances of individual sediment grains. We traced individual gravels in two steep mountain streams, the Erlenbach (Switzerland) and Rio Cordon (Italy), using magnetic and radio frequency identification tags, and measured their bed load transport rates using calibrated geophone bed load sensors in the Erlenbach and a bed load trap in the Rio Cordon. Tracer transport distances and bed load volumes exhibited approximate power law scaling with both the peak stream power and the cumulative stream energy of individual hydrologic events. Bed load volumes scaled much more steeply with peak stream power and cumulative stream energy than tracer transport distances did, and bed load volumes scaled as roughly the third power of transport distances. These observations imply that large bed load transport events become large primarily by scouring the bed deeper and wider, and only secondarily by transporting the mobilized sediment farther. Using the sediment continuity equation, we can estimate the mean effective thickness of the actively transported layer, averaged over the entire channel width and the duration of individual flow events. This active layer thickness also followed approximate power law scaling with peak streampower and cumulative stream energy and ranged up to 0.57min the Erlenbach, broadly consistent with independent measurements.