Showing papers on "Stream power published in 1999"

Dynamics of the stream‐power river incision model: Implications for height limits of mountain ranges, landscape response timescales, and research needs

Abstract: The longitudinal profiles of bedrock channels are a major component of the relief structure of mountainous drainage basins and therefore limit the elevation of peaks and ridges. Further, bedrock channels communicate tectonic and climatic signals across the landscape, thus dictating, to first order, the dynamic response of mountainous landscapes to external forcings. We review and explore the stream-power erosion model in an effort to (1) elucidate its consequences in terms of large-scale topographic (fluvial) relief and its sensitivity to tectonic and climatic forcing, (2) derive a relationship for system response time to tectonic perturbations, (3) determine the sensitivity of model behavior to various model parameters, and (4) integrate the above to suggest useful guidelines for further study of bedrock channel systems and for future refinement of the streampower erosion law. Dimensional analysis reveals that the dynamic behavior of the stream-power erosion model is governed by a single nondimensional group that we term the uplift-erosion number, greatly reducing the number of variables that need to be considered in the sensitivity analysis. The degree of nonlinearity in the relationship between stream incision rate and channel gradient (slope exponent n) emerges as a fundamental unknown. The physics of the active erosion processes directly influence this nonlinearity, which is shown to dictate the relationship between the uplift-erosion number, the equilibrium stream channel gradient, and the total fluvial relief of mountain ranges. Similarly, the predicted response time to changes in rock uplift rate is shown to depend on climate, rock strength, and the magnitude of tectonic perturbation, with the slope exponent n controlling the degree of dependence on these various factors. For typical drainage basin geometries the response time is relatively insensitive to the size of the system. Work on the physics of bedrock erosion processes, their sensitivity to extreme floods, their transient responses to sudden changes in climate or uplift rate, and the scaling of local rock erosion studies to reach-scale modeling studies are most sorely needed.

Geologic constraints on bedrock river incision using the stream power law

Abstract: Denudation rate in unextended terranes is limited by the rate of bedrock channel incision, often modeled as work rate on the channel bed by water and sediment, or stream power. The latter can be generalized as KA m S n , where K represents the channel bed's resistance to lowenng (whose variation with lithology is unknown), A is drainage area (a surrogate for discharge), S is local slope, and m and n are exponents whose values are debated. We address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method. We vary m, n, and K to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles. We find at least two end-member incision laws, KA 0.3-0.5 S for Australian rivers with stable base levels and K f A 0.1-0.2 S n for rivers in Kauai subject to abrupt base level change. The long-term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion, characterized by K f Incision patterns from Japan and California could follow either expression. If they follow the first expression with m = 0.4, K varies from 10 -7 -10 -6 m 0.2 /yr for granite and metamorphic rocks to 10 -5 -10 -4 m 0.2 /yr for volcaniclastic rocks and 10 -4 -10 -2 m 0.2 /yr for mudstones. This potentially large variation in K with lithology could drive strong variability in the rate of long-term landscape change, including denudation rate and sediment yield.

Soil erosion by surface water flow on a stony, semiarid hillslope

Abstract: Soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows. This study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment. A field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface. The method allowed for measurements in this study of flow erosion at a much wider range of slopes (2·6 to 30·1 per cent) and unit discharge rates (0·0007 to 0·007 m2 s−1) than have been previously feasible. Flow velocities were correlated to discharge and hydraulic radius, but not to slope. The lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity. The detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected. Flow detachment rates were better correlated to a power function of either shear stress (r2 = 0·51) or stream power (r2 = 0·59). Published in 1999 by John Wiley & Sons, Ltd.

Development of mountainous topography in the Basin Ranges, USA

Abstract: We use the landcape evolution model Zscape to explore quantitatively the development of mountainous topography in the Basin and Range province (formerly the Basin Ranges), USA, as a function of faulting, surface processes and microclimate. Many of the classic morphologies of mountains in the Basin and Range were described in the late part of the 19th century. The varied topography coupled with differing experiences led to a similarly diverse set of explanations. We are able to demonstrate through a variety of numerical experiments that a diverse landscape is easily obtained by the simple, steady combination of tectonic and surface processes. Numerical landscapes reveal the same features observed in the field, including facets, spur benches, piedmonts, and relatively linear and regularly spaced drainages. In all cases, a steady-state landscape is generated on the order of 106 years, so that there remains little information in the landscape that can tell us about processes or conditions prior to 1 million years ago. The fundamental form of the steady-state landscape (including the facet and spur bench morphology) is governed by the spacing of rivers and bedrock strength and the resulting relief is for the most part strength-limited. Neither hillslope nor facet relief is dependent on the rate of fault slip or channel incision. Relief is incision-limited, however, nearer the headwaters of rivers where stream power is relatively low. Topographically asymmetric ranges may be generated over tectonically symmetric horsts by allowing precipitation to be driven by orographic processes, but the asymmetry is likely to be dependent on the ability to remove eroded material from the adjacent basins. The value of the experiments presented here is to demonstrate that the astute and impressive observations made by the likes of Gilbert, Davis and Dutton are reproducible using a relatively simple description of the relevant physics and that we can recognize and explain various landscape morphologies that have in the past been the subject of necessarily qualtitative reasoning.

Stream power influence on southern Californian riparian vegetation

Abstract: . Mechanical damage by floodwaters is frequently invoked to explain the distribution of riparian plant species, but data have been lacking to relate vegetation to specific estimates of flood damage potential. This research uses detailed estimates of unit stream power (an appropriate measure of the potential for mechanical damage) in conjunction with vegetation cover data to test this relationship at 37 valley-bottom sites in the Transverse Ranges of Southern California. A computer program, HEC-2, was used to model the slope and the variation in flow depth and velocity of the 20-yr flood across the sites. Regression models tested the influence of stream power (and of height above the water table) on the woody species composition of 393 4-m cross-section segments of the valley-bottom sites. Results indicate that unit stream power does have a significant effect on the riparian vegetation, but that the amount of that influence and its importance relative to the influence of height above the water table varies between watersheds. Some species are found primarily in locations of high stream power, while others are limited to portions of the valley bottom that experience only low stream power.

Levee morphology and sedimentology along the lower Tuross River, south‐eastern Australia

Abstract: Levees on the lower Tuross River in south-eastern Australia reflect a complex interplay between depositional and erosional processes. Stream power, conditioned primarily by valley width, is the key determinant of levee morphology and sedimentology in this confined valley setting. Three styles of levee are described. The Rewlee levee is functionally linked to a flood channel in narrow valley settings (< 250 m). These levees contain a diverse facies assemblage characterized by various scales of erosion surfaces. Vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping. The levee at the Mortfield site is associated with less confined settings (valley width 500–600 m), which present lower flood stage and stream power conditions. This levee hosts a wide range of facies, but erosion surfaces are seldom observed. In the more open valley setting at the Central site (valley width 700–1000 m), levees comprise uniform, fine-grained deposits, which grade to pronounced distal floodplains with backswamps. As levees reflect a combination of within-channel and overbank processes, both depositional and erosional, these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin.

Influence of storm‐related sediment storage on the sediment delivery from tributary catchments in the upper Waipaoa River, New Zealand

Abstract: Although much is known about overall sediment delivery ratios for catchments as components of sediment production and sediment yield, little is known about the component of temporary sediment storage. Sediment delivery ratios focused on the influence of storm-related sediment storage are measured at Matakonekone and Oil Springs tributaries of the Waipaoa River basin, east coast of New Zealand. The terrace deposits of both tributaries show abundant evidence of storm-related sedimentation, especially sediment delivered from Cyclone Bola, a 50 year return rainfall event which occurred in 1988. The sediment delivery ratio is calculated by dividing the volume of sediment transported from a tributary to the main stream by the volume of sediment generated at erosion sites in the tributary catchment. Because the sediment delivery volume is unknown, it can be calculated as the difference between sediment generation volume and sediment storage volume in the channel reach of the tributary. The volume of sediment generated from erosion sites in each tributary catchment was calculated from measurements made on aerial photographs dating from 1960 (1:44 000) and 1988 (1:27 000). The volume of sediment stored in the tributary can be calculated from measurements of cross-sections located along the tributary channel, which are accompanied by terrace deposits dated by counting annual growth rings of trees on terrace surfaces. Sediment delivery ratios are 0·93 for both Matakonekone catchment and Oil Springs catchment. Results indicate that Oil Springs catchment has contributed more than twice the volume of sediment to the Waipaoa River than the Matakonekone catchment (2·75 × 106 m3 vs 1·22 × 106 m3). Although large volumes of sediment are initially deposited during floods, subsequent smaller flows scour away much of these deposits. The sediment scouring rate from storage is 1·25 × 104 m3 a−1 for Matakonekone stream and 0·83 × 104 m3 a−1 for Oil Springs stream. Matakonekone and Oil Springs channels respond to extreme storms by instantaneously aggrading, then gradually excavating the temporarily stored sediment. Results from Matakonekone and Oil Springs streams suggest a mechanism by which event recurrence interval can strongly influence the magnitude of a geomorphic change. Matakonekone stream with its higher stream power is expected to excavate sediment deposits more rapidly and allow more rapid re-establishment of storage capacity. Copyright © 1999 John Wiley & Sons, Ltd.

BRI-STARS Model for Alluvial River Simulation

Abstract: The Bridge StreamTube Model for Alluvial River Simulation (BRI-STARS) is a semi-two-dimensional model capable of computing alluvial scour/deposition through subcritical, supercritical, and a combination of both flow conditions involving hydraulic jumps. The use of streamtubes allow the modeling of scour/deposition of applications involving bridges not only along a study reach but also across alluvial channels. In this paper, the basic formulations used in the BRI-STARS model are presented and various hydraulic, sediment transport, local scour, and stream power minimization computations are described. The BRI-STARS model runs on IBM PC-AT or compatibles.