Stream power

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

Particle size variations between bed load and bed material in natural gravel bed channels

Abstract: Particle sizes of bed load and bed material that represent materials transported and stored over a period of years are used to investigate selective transport in 13 previously sampled, natural gravel bed channels. The ratio (D*) of median particle size of bed material to the transport- and frequency-weighted mean of median bed load size decreases to unity with increasing drainage area, bank-full discharge, dimensionless stream power, and bed material sorting. In channels with high values of D*, significant volumes of fine bed load are transported during discharges that are less than bank-full, which is commonly associated with general entrainment of the coarse pavement in many gravel bed channels. This indicates transport of fine bed load over a more stable substrate of coarser bed material. The apparent breakdown in equal mobility of the bed as a whole may be caused by areal segregation of poorly sorted bed material into superiorly sorted patches of varying mean size. Likely sources of selectively transported fine bed load include fine patches that have low entrainment thresholds and high virtual particle velocities. A simple sediment budget applied to measurements from three channels indicates that velocities of material from fine patches in pools relative to velocities of average bed material are high in low-order channels and decrease distally as more bed material that represents the bed as a whole is accessed for bed load by deeper annual scour.

Inland propagation of erosional escarpments and River profile evolution across the Southeast Australian passive continental margin

Abstract: Denudation at passive continental margins occurs over time as erosional escarpments propagate inland, cutting through regions of elevated topography flanking ocean basins. Understanding the actual processes and time variability in propagation rates associated with the advance of escarpments across passive margins remains a largely unsolved problem for tectonic geomorphology. Here we report results from new analyses of detailed river longitudinal profiles and surface exposure age measurements using cosmogenic radionuclides from the New England Tableland portion of the southeast Australian passive margin. In that area, many plateau-draining tributaries of the Macleay River cascade into narrow gorges across large-scale river knickpoints that represent the tips of the leading edge of the inland-advancing escarpment. Previous river profile analyses showed most knickpoints to be the same distance, about 200 km, upstream from the mouth of the river, despite order-of-magnitude variations in the areas drained at the gorge heads. The implication is that all knickpoints have migrated upstream at a speed of about 2 km/Myr averaged over the ∼100 Myr history of the margin. The new profile analyses confirm that, in general, distance upstream from the Macleay River mouth of the knickpoints is not related to area drained at the gorge head. We conclude that if sufficient fluvial transport power is available, the rate of upstream knickpoint migration is governed by slope failure mechanisms and the frequency of resulting mass wasting events on the steep rock slopes in the gorge head vicinity. In terms of the stream power model for channel incision, Z t A m' S n (where A is drainage area and S is channel gradient), the river profile analyses imply that the drainage area exponent m' = 0 (i.e., no dependence on drainage area so long as a threshold is met), and the slope exponent n > 1. Average erosion rates calculated from Be and Al radionuclide concentrations in samples collected across the knickpoint on Baker's Creek indicate that the plateau surface and the channel upstream of the gorge head - knickpoint are eroding slowly, ∼5 m/Myr, whereas the channel at and downstream of the knickpoint is eroding much more rapidly, >100 m/Myr. The pattern of increasing erosion rates across the knickpoint in the downstream direction is consistent with the paradigm of inland escarpment retreat across passive continental margins.

Theoretical model of optimal drainage networks

Abstract: A simulation model of drainage network optimization is presented in which channels shift to minimize total stream power pgQS within the network. The simulation model starts from an arbitrary initial stream network developed on a square matrix, such as produced by random headward growth. Discrete stream capture then is simulated within the network, occurring wherever a new stream linkage would produce a steeper course than the original. Such capture produces a network with minimum power optimization but flow directions constrained to eight directions. Individual segment end points are then allowed to migrate by iterative relaxation with a direction and rapidity of motion governed by the gradient of stream power at the node. This valley migration is subject to the constraint that the sources and outlet remain fixed. The resulting networks are visually and morphometrically more similar to natural stream networks than the original networks produced by the random headward growth model.

Detachment of Undisturbed Soil by Shallow Flow

Abstract: Quantification of soil detachment rates is necessary to establish a basic understanding of soil erosion processes and to develop fundamental-based erosion models. Many studies have been conducted on the detachment rates of disturbed soils, but very little has been done to quantify the rates of detachment for natural soil conditions. This study was conducted to evaluate the influence of flow discharge, slope gradient, flow velocity, shear stress, stream power, and unit stream power on detachment rates of natural, undisturbed, mixed mesic typical Udorthent soil. Flow rates ranged from 0.25 to 2.0 L s -1 and slope gradient ranged from 8.8 to 46.6%. This study was compared with a previous study that used disturbed soil prepared by static compression. The results indicated that the detachment rates of disturbed soil were 1 to 23 times greater than the ones of natural undisturbed soil. It was necessary to use natural undisturbed soil samples to simulate the detachment process and to evaluate the influence of hydraulic parameter on detachment rate. Along with flow rate increasing, detachment rate increased as a linear function. Detachment rate also increased with slope gradient, but the functional relationship between the two variables depended on flow rate. Stepwise regression analysis indicated that detachment rate could be well predicted by a power function of flow rate and slope gradient (R 2 = 0.96). Mean flow velocity was closely correlated to detachment rate (r 2 = 0.91). Flow detachment rate was better correlated to a power function of stream power (r 2 = 0.95) than to functions of either shear stress or unit stream power.