Erosion Response Research Articles

Structural and functional connectivity as a driver of hillslope erosion following disturbance

Hydrologic response to rainfall on fragmented or burnt hillslopes is strongly influenced by the ensuing connectivity of runoff and erosion processes. Yet cross-scale process connectivity is seldom evaluated in field studies owing to scale limitations in experimental design. This study quantified surface susceptibility and hydrologic response across point to hillslope scales at two degraded unburnt and burnt woodland sites using rainfall simulation and hydrologic modelling. High runoff (31–47 mm) and erosion (154–1893 g m–2) measured at the patch scale (13 m2) were associated with accumulation of fine-scale (0.5-m2) splash-sheet runoff and sediment and concentrated flow formation through contiguous bare zones (64–85% bare ground). Burning increased the continuity of runoff and sediment availability and yield. Cumulative runoff was consistent across plot scales whereas erosion increased with increasing plot area due to enhanced sediment detachment and transport. Modelled hillslope-scale runoff and erosion reflected measured patch-scale trends and the connectivity of processes and sediment availability. The cross-scale experiments and model predictions indicate the magnitude of hillslope response is governed by rainfall input and connectivity of surface susceptibility, sediment availability, and runoff and erosion processes. The results demonstrate the importance in considering cross-scale structural and functional connectivity when forecasting hydrologic and erosion responses to disturbances.

Abrasive slurry jet micro-machining of edges, planar areas and transitional slopes in a talc-filled co-polymer

The abrasive slurry-jet erosion of a talc-filled thermoplastic olefin (TPO) (60% PP, 25% EP rubber and 15% talc) was measured as a function of the impact angle and the talc filler content. A ductile erosion response was observed, showing a maximum erosion rate at 45°. A superposition model was then developed to predict the cross-sectional shapes of small-scale flat-bottomed pockets and curved edges machined in TPO using abrasive slurry-jet micro-machining (ASJM). The model was based on the spatial distribution of the erosion across the jet footprint measured during a shallow “first pass” channel at a specific angle. The model predictions of planar depth and waviness were in close agreement with experimental measurements. The measured dependence of the erosion rate on the impact angle was used to develop novel machining configurations to increase the slope of bounding sidewalls.

The effect of land use on slope failure and sediment generation in the Coromandel region of New Zealand following a major storm in 1995

Part of the Coromandel region (North Island, New Zealand) was subjected to a severe storm in March 1995. Analysis of relevant data provides a valuable opportunity to assess the type, extent, distribution and sediment generation rates by slope failures associated with steep-land forests and harvest practice. Slope failures were mapped at 1:10 000 scale for stands of planted exotic forest, areas of exotic forest cutover, indigenous forest, indigenous secondary regrowth, and pasture. Slope failure dimensions and bulk density were used to calculate catchment-based sediment mass and generation rates by: (i) failure type, (ii) vegetation type, (iii) slope group, (iv) Land Use Capability unit (LUC), and by (v) catchment. The proportion of the total storm sediment load discharged as yield was estimated from records of flow and depth-integrated sediment samples. Storm-initiated slope failures generated ~0.5 Mt of sediment, predominantly by debris avalanche. Most were located within indigenous forest and secondary regrowth and generated ~78% of the total sediment mass. Few slope failures occurred within standing exotic forest and inclusive of areas disturbed by harvesting operations (cutover) generated ~21% of the mass and, 1% was derived from pastoral hill country. Sediment generation rates were greater from areas of exotic forest clearfelled three years before the storm and these were 2.5 times greater than from cutover clearfelled just before the storm. This result is explained by the progressive loss of strength from decaying tree roots that had not yet been countered by an effective root system under a new tree crop. Furthermore, rates were highest for slopes between 26 and 35° and, of the 11 LUC units, were highest for units VIe11 and VIIe2. For the combined Opitonui and Awaroa catchments, ~24% of the storm sediment load was discharged as yield with ~76% remaining as in-channel storage. The erosion response was primarily controlled by rainfall variation and slope, which overrode the influence of vegetation cover. Time since clear-felling had a secondary influence. A re-evaluation of erosion susceptibility in steep-land terrain and a return to the identification, mapping and geomorphic interpretation of site-specific hazards, particularly from an operational perspective—in advance of harvesting—is recommended.

The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate

Continental arcs, such as the modern Andes or the Cretaceous Sierra Nevada batholith, are some of the highest topographic features on Earth. Continental arc volcanoes may produce more CO2 than most other types of volcanoes due to the interaction of magmas with sedimentary carbonates stored in the continental upper plate. As such, global flare-ups in continental arc magmatism may amplify atmospheric CO2 concentrations, leading to climatic warming. However, the high elevations of continental arcs may also enhance orographic precipitation and change global atmospheric circulation patterns, possibly increasing the efficiency of chemical weathering and drawdown of atmospheric CO2, which may subdue the climatic warming response to volcanic activity. To better evaluate the climatic response, we develop models that integrate magmatic crustal thickening, topographic uplift, isostasy and erosion. The topographic response is used to predict how soil formation rates, soil residence times, and chemical weathering rates vary during and after a magmatic episode. Although magmatism leads to crustal thickening, which requires topographic uplift, highest elevations peak ∼10 My after magmatism ends. Relatively high elevations, which enhance erosion and chemical weathering of the continental arc, persist for tens of million years after magmatism ends, depending on erosion kinetics. It has recently been suggested that the Cretaceous–Paleogene greenhouse (high atmospheric CO2 and warm climate) coincided with a global chain of continental arcs, whereas mid- to late Cenozoic icehouse conditions (low atmospheric CO2 and cold climate) coincided with a lull in continental arc activity after 50 Ma. Application of our models to the Sierra Nevada (California, USA) continental arc, which represents a segment of this global Cretaceous–Paleogene continental arc, reproduces the observed topographic and erosional response. Our models require that the newly formed continental arc crust remained high and continued to erode and weather well after (>50 My) the end of magmatism. Thus, in the aftermath of a global continental arc flare-up, both the total volcanic inputs of CO2 decline and the average weatherability of continents increases, the latter due to the increased proportion of widespread remnant topography available for weathering and erosion. This combination leads to a decrease in the long-term baseline of carbon in the ocean/atmosphere system, leading to cooling. Mid-Cenozoic cooling is often attributed solely to increased weathering rates associated with India–Eurasian collision and the Himalayan orogeny. However, the total area of now-extinct Cretaceous–Paleogene continental arcs is 1.3–2 times larger than that of the Himalayan range front and the Tibetan plateau combined, suggesting that weathering of these remnant volcanic arcs may also play a role in drawing down CO2 through silicate weathering and subsequent carbonate burial. In summary, if global continental arc flare-ups lead to greenhouse conditions, long-lived icehouse conditions should follow in the aftermath due to decreased CO2 inputs and an increase in regional weathering efficiency of remnant arc topography.

Effect of vegetation cover on millennial-scale landscape denudation rates in East Africa

The mechanisms by which climate and vegetation affect erosion rates over various time scales lie at the heart of understanding landscape response to climate change. Plot-scale field experiments show that increased vegetation cover slows erosion, implying that faster erosion should occur under low to moderate vegetation cover. However, demonstrating this concept over long time scales and across landscapes has proven to be difficult, especially in settings complicated by tectonic forcing and variable slopes. We investigate this problem by measuring cosmogenic 10 Be-derived catchment-mean denudation rates across a range of climate zones and hillslope gradients in the Kenya Rift, and by comparing our results with those published from the Rwenzori Mountains of Uganda. We find that denudation rates from sparsely vegetated parts of the Kenya Rift are up to 0.13 mm/yr, while those from humid and more densely vegetated parts of the Kenya Rift flanks and the Rwenzori Mountains reach a maximum of 0.08 mm/yr, despite higher median hillslope gradients. While differences in lithology and recent land-use changes likely affect the denudation rates and vegetation cover values in some of our studied catchments, hillslope gradient and vegetation cover appear to explain most of the variation in denudation rates across the study area. Our results support the idea that changing vegetation cover can contribute to complex erosional responses to climate or land-use change and that vegetation cover can play an important role in determining the steady-state slopes of mountain belts through its stabilizing effects on the land surface.

Effects of Rain Intensity and Initial Soil Moisture on Hydrological Responses in Laboratory Conditions

Abstract Although the possibility of measuring and analysing all parts of the rainfall, infiltration, runoff, and erosion process as a natural hydrologic cycle in field conditions is still one of the more unattainable goals in the hydrological sciences, it can be accomplished in laboratory conditions as a way to understand the whole process. The initial moisture content is one of the most effective factors on soil infiltration, runoff, and erosion responses. The present research was conducted on a 2 m2 laboratory plot at a slope of 9% on a typical sandy-loam soil. The effects of the initial soil moisture content on the infiltration, runoff, and erosion processes were studied at four levels of initial soil moisture content (12, 25, 33, and 40 volumetric percentage) and two rainfall intensities (60 and 120 mm h-1). The results showed a significant (p ≤ 0.05) correlation between rainfall intensity and downstream splash, with r = 0.87. The results reflected the theory of hydrological responses, showing significant (p ≤ 0.05) correlations with r =-0.93, 0.98, -0.83, 0.88, and 0.73 between the initial soil moisture content and the time-to-runoff, runoff coefficient, drainage as a part of the infiltrated water, downstream splash, and total outflow sediment, respectively.

Special Issue on Soil Erosion and Sediment Yield Modeling

Soil erosion is one of the most serious environmental problems because it removes fertile soil that is rich in nutrients and, in turn, increases the natural level of sedimentation in rivers and reservoirs, reducing their storage capacity and life span. Land degradation stems from a combination of factors related to land use, agricultural intensification, and intense rainstorms. For maintaining and improving soil productivity, soil resources need to be conserved for optimal land use. In other words, to restore the productivity of soil and prevent further damage, planning for conservation and management of watersheds become vital. For assessing soil erosion and sediment yield from watersheds, several empirical models on the basis of geomorphological parameters have been developed and are available in the literature. Among several methods, the sediment yield index (SYI) method and universal soil loss equation (USLE) are extensively used for the estimation of soil erosion and prioritization of watersheds for their treatment. Research in hydrological modeling and related watershed planning issues form a significant component of the prevailing environmental activities. During the last three decades, a number of empirical and conceptual hydrological models have been developed for the prediction of soil erosion and sediment yield modeling. Thus, there is a need to have another look at different aspects of soil erosion and sediment yield modeling and enhance their understanding for improved practical applications. The present special issue of the Journal of Hydrologic Engineering focuses on soil erosion and sediment yield modeling, including the effects of land use/cover changes, extended applications using empirical and physically based soil erosion and sediment yield models, and watershed management coupling remote sensing and the geographic information system (GIS). Within this framework, the papers of this special issue have been grouped into the following: studies on the basis of physically based, conceptual, and empirical models; advancement and review; watershed management; and experimental work. Papers titled “Identification of Critical Erosion Watersheds for Control Management in Data Scarce Condition Using the SWAT Model,” “Use of Caesium-137 Measurements and Long-Term Records of Sediment Load to Calibrate the Sediment Delivery Component of the SEDD Model and Explore Scale Effect: Examples from Southern Italy,” “Application of SWAT Model and Geospatial Techniques for Sediment-Yield Modeling in Ungauged Watersheds,” “Soil Erosion and Sediment-Yield Prediction at Basin Scale in Upstream Watershed of Miyun Reservoir,” “Improved Hillslope Erosion Module for the Digital Yellow-River Model,” and “Evaluation of GIS-Based Watershed Model for Streamflow and Sediment-Yield Simulation in the Upper Baitarani River Basin of Eastern India” fall in the category of physically based soil erosion and sediment yield modeling. Papers titled “Inductive Group Method of Data Handling Neural Network Approach to Model Basin Sediment Yield,” “Modeling Suspended Sediment Using Artificial Neural Networks and TRMM-3B42 Version 7 Rainfall Dataset,” and “Accounting for Conceptual Soil Erosion and Sediment Yield Modeling Uncertainty in the APEX Model Using Bayesian Model Averaging” deal with conceptual modeling for soil erosion and sediment yield. Papers titled “Application of GISCoupled Modified MMF Model to Estimate Sediment Yield on a Watershed Scale,” “Impact of Climate Change on Future Soil Erosion in Different Slope, Land Use, and Soil-Type Conditions in a Part of the Narmada River Basin, India,” and “Spatially Distributed Sheet, Rill, and Ephemeral Gully Erosion” employ empirical models for the estimation of sediment yield. The paper “Sediment Graphs Based on Entropy Theory,” which derives an instantaneous unit sediment graph (IUSG or USG) to determine sediment discharge and establishes a relation between sediment yield and runoff volume, exhibits an advancement in the field of sediment yield modeling. Conversely, the paper “Geographic Variation of USLE/RUSLE Erosivity and Erodibility Factors” provides a comprehensive review on the subject. The papers “Integrated Modeling Approach to the Response of Soil Erosion and Sediment Export to Land-Use Change at the Basin Scale,” “Evaluating the Impact of the Spatial Distribution of Land Management Practices on Water Erosion: Case Study of a Mediterranean Catchment,” and “Sediment Fingerprinting for Calibrating a Soil Erosion and Sediment-Yield Model in Mixed Land-Use Watersheds” deal with watershed management. The papers “Establishing a Soil Loss Threshold for Limiting Rilling,” “Transport Capacity of Overland Flow with High Sediment Concentration,” “Modeling Rainfall Erosivity by Measured Drop-Size Distributions,” “Modeling Rill Erosion at the Sparacia Experimental Area,” “Rapid Weathering and Erosion of Mudstone Induced by Saltwater Migration near a Slope Surface,” and “Rain Microstructure and Erosivity Relationships under Pressurized Rainfall Simulator” are on the basis of experimental work. The aim of this issue is to present high-quality technical articles representing the most recent developments in the field of soil erosion and sediment yield modeling, including practical applications. This special issue is expected to become the first in a sequence of future issues on this topic.

A Study on Processing, Characterization and Erosion Wear Response of Linz–Donawitz Slag Filled Epoxy Composites

ABSTRACTThis paper reports a study on erosion response of epoxy composites filled with micro‐sized Linz–Donawitz (LD) slag particles. LD slag is a major solid waste generated in huge quantities during steel making. It comes from slag formers such as burned lime/dolomite and from oxidizing of silica, iron etc. while refining the iron into steel in the LD furnace. Although a number of ways for its utilization have been suggested in the past, its potential as a filler material in polymeric matrices has not yet been explored. In this work, composites of five different compositions (0, 7.5, 15, 22.5 and 30 wt% of LD slag reinforced in epoxy resin) are prepared by a simple hand layup technique. The composites are characterized in regard to their density, porosity, micro‐hardness and strength properties. Erosion trials (ASTM G 76) are conducted on the composite samples following a well‐planned experimental schedule based on Taguchi's design of experiments. The study reveals that the impact velocity and LD slag content in the composites are the most significant among various factors that influence the wear rate. This work shows that LD slag, in spite of being a waste, possesses fairly good filler characteristics as it modifies the properties and improves the erosion resistance of the polymeric resin.

Quantifying the environmental controls on erosion of a hard rock cliff

Linking hard rock coastal cliff erosion to environmental drivers is challenging, with weak relationships commonly observed in comparisons of marine and subaerial conditions to the timing and character of erosion. The aim of this paper is to bring together datasets to explore how best to represent conditions at the coast and to test relationships with erosion, which on this coast is primarily achieved via rockfalls. On the N. Yorkshire coast in the UK we compare a continuously monitored microseismic dataset, regionally monitored coastal environmental conditions, modelled at-cliff conditions and periodic high-resolution 3D monitoring of changes to the cliff face over a 2-year period. Cliff-top microseismic ground motions are generated by a range of offshore, nearshore and at-cliff sources. We consider such ground motions as proxies for those conditions that promote the occurrence of rockfalls and erosion. Both these data and modelled at-cliff water levels provide improved insight into conditions at, and wave energy transfer to, the cliff. The variability in microseismic, modelled and regionally-monitored environmental data derives statistically significant relationships with increases in the occurrence of rockfalls. The results demonstrate a marine control on the total volume and size characteristics of rockfalls. The strongest relationships found are with rockfalls sourced from across the entire cliff, rather than just at the toe, indicating that the marine influence, albeit indirectly, extends above and beyond the area inundated. These results identify failure mechanisms driving erosion, where a range of processes unique to the coast trigger failure, but in a manner beyond purely wave action at the cliff toe. Greater erosion occurs at the cliff toe. However, comparing water level inundation frequency, microseismic energy transfer and erosion, we observe that heights up the cliff that correspond with water levels associated with low frequency, high energy storms, or more frequent inundation, do not experience increased erosion. Our results describe the relationship between inundation duration, energy transfer and erosion of hard rock cliffs, and illustrate the relative intensity of erosion response to variations in these conditions. Implicitly our data suggests that in future, cliffed rocky coasts may be relatively quick to respond to changes in environmental forcing.

Synchronous fluvial response to surface uplift in the eastern Tibetan Plateau: Implications for crustal dynamics

Synchronous response of river erosion to surface uplift is often assumed by studies using thermochronometer-constrained erosion histories to estimate changes in landscape and tectonics. We have tested this assumption by studying river incision histories at two sites (Heishui and Lianghekou) located in the westernmost inland part of the deeply incised eastern Tibetan Plateau. Apatite fission track age-elevation plots for the two sites show clear late Miocene inflection points, marking the time when apparent erosion rates increased fourfold to eightfold to 300–800 m/Myr. This timing is further refined as ~10–12 Ma by thermal history modeling and overlaps within analytical uncertainties with that recorded from the eastern Tibetan Plateau margin ~150–200 km to the east, demonstrating that river incision propagated rapidly from the margin to the interior in less than ~2 Ma. Such synchronous regional river incision is consistent with regional surface uplift generated by crustal extrusion along a detachment at depth.

Monitoring the effect of conservation practices on the erosion rates in some small watersheds in Eastern Romania

It is known that the successful implementation of control measures to preserve soil quality on slope agricultural lands depends largely on the designer’s ability to select a control strategy for a specific site, considerable simpler and less costly. The paper refers to several small watersheds with agricultural use, representative for Eastern hilly area ofRomania, where different types of soil conservation measures have been applied. The study included monitoring of some factors to highlight the role of soil conservation practices in reducing water erosion process. In this respect, it was studied the dynamics of the climatic, pedological, relief, vegetation, hydrology and erosion parameters. Runoff and erosion rates for individual storms were studied both at the plot and microbazin level by performing measurements on standard runoff plots, respectively in the network flow sections. Also, RUSLE model and Geographic Information System were used to simulate spatial distribution of erosion and sedimentation processes. Significant interactions and feedbacks were found to occur between soil characteristics and vegetation, which influenced both runoff and erosion responses. Monitoring allowed more direct linkages to be made between management practices and their impacts on runoff and soil erosion.

Role of Process Variables on Solid Particle Erosion of Polymer Composites: A Critical Review

This paper presents a review of the reported research investigations that are related to the solid particle erosion behavior of polymers and polymeric composites. Attention is paid to the effects of test parameters such as erodent type, size of the erodent, impingement angle, impact velocity and stand of distance. On the erosion wear rate of polymer composites. Various predictions and models proposed by different authors to describe and quantify the erosion rate are discussed and their suitability is checked. Recent findings on the erosion response of multi-component hybrid composites are also presented. Lastly the implementation of the design of experiments and statistical techniques in making a parametric appraisal of the erosion processes of composites is discussed.

Erosional response of an actively uplifting mountain belt to cyclic rainfall variations

Abstract. We present an approximate analytical solution to the stream power equation describing the erosion of bedrock in an actively uplifting mountain range subject to periodic variations in precipitation rate. It predicts a time lag between the climate forcing and the erosional response of the system that increases with the forcing period. The predicted variations in the sedimentary flux coming out of the mountain are also scaled with respect to the imposed rainfall variations in a direct proportion to the discharge exponent, m, in the stream power law expression. These findings are confirmed by 1-D and 2-D numerical solutions. We also show that the response of a river channel is independent of its length and thus the size of its catchment area, implying that all actively eroding streams in a mountain belt will constructively contribute to the integrated signal in the sedimentary record. We show that rainfall variability at Milankovitch periods should affect the erosional response of fast uplifting mountain belts such as the Himalayas, Taiwan or the South Island, New Zealand, and predict 1000 to 10 000-year offsets between forcing and response. We suggest that this theoretical prediction could be used to independently constrain the value of the poorly defined stream power law exponents, and provide an example of how this could be done, using geochemical proxy signals from an ODP borehole in the Bengal Fan.

Swelling of biocrusts upon wetting induces changes in surface micro-topography

In most of non-vegetated areas from drylands, soils are colonized by biocrusts, and although they represent a small fraction of the soil profile, they strongly affect several soil surface properties, such as porosity, available nitrogen and carbon content, hydrophobicity or micro-topography. The influence of BSCs on these soil properties has effects on numerous ecosystem processes, including water retention and runoff generation. Previous studies on the hydrological and erosive response of soils covered by biocrusts have highlighted the role of soil surface roughness as a key variable for understanding the influence of biocrusts on runoff and erosion, but biocrusts' effects on surface micro-topography varies depending on crust water content. Biocrusts can absorb large amounts of water in a short period of time, increasing their volume and modifying surface micro-topography, this change depending on biocruts type and development. A correct characterization of these surface variations may increase the knowledge about hydrological response of biocrusts, and for this reason, accurate ground level measurements of biologically crusted surfaces are essential. The objective of this study is to analyze the effect of wetting on surface micro-topography of biologically crusted soils. To achieve this objective, different crust types were scanned in the laboratory with high resolution laser scanner. Five samples were collected for each of the 4 different crust types (bare soil, cyanobacteria biocrust, and two different lichen biocruts). Two different scans were made in each sample, in dry and wet conditions. Random roughness (RR) was calculated for data from every scan, and the RR indexes obtained before and after wetting were compared. According with our initial hypothesis, an increase in surface height and surface roughness up to 0.24 and 0.20 mm respectively was observed in more developed lichen biocruts, under wet conditions respect to dry ones. These differences, despite being very subtle, could exert strong implications on runoff generation, and water evaporation, and show the complex interactions between biocruts, surface micro-topography and water fluxes.

Constraints on the role of tectonic and climate on erosion revealed by two time series analysis of marine cores around New Zealand

Physical and chemical weathering govern rocks and chemical elements cycles at the Earth surface. The importance of climate and tectonic forcings has been identified but their relative influence still needs to be investigated. We address this question by studying neodymium (Nd) isotopic composition time series in two ocean sediment cores located on the eastern and western sides of New Zealand. We measured both detrital and authigenic phases of the sediment to decouple the oceanic from the continental contributions. The current and past climatic and oceanographic settings of this region have already been well studied, providing the underlying framework.The results show glacial–interglacial variations of the authigenic signal, with larger amplitudes for the eastern core. We argue that oceanic influences can be discarded and propose that continental erosion on the South Island controls the Nd isotopes records in both cores. Mixing calculations show that Nd discharge was 2 to 10 times higher during glacial times than during interglacials on the eastern side, whereas these variations are almost negligible on the western side. We suggest that, on the East, larger ice volumes and fluxes during glacials generate higher physical erosion and thus an increase of easily weathered fine grains. In contrast, we observe steady rates on the western side. This implies that where both rock uplift and precipitation are extreme, topography and thus erosion rates are less sensitive to switches from glacial to fluvial erosion. Furthermore, the temporal relationship between climatic indicators like oxygen isotopes and the Nd isotopic composition reveals a nonlinear response of erosion to climate forcing. Those results contrast with previous studies using the same tracer that indicated stronger erosion over the Himalaya during interglacial periods and point out the complexity of erosion and weathering responses to climatic and tectonic forcings.

MODELLING BEACH MORPHODYNAMICS FOR SOUTHERN GOLD COAST BEACH NOURISHMENT PROJECT AT BILINGA BEACH

A new cross shore process model NSBEACH (New SBEACH) has been applied to the Southern Gold Coast Nourishment Project at Bilinga beach (Australia) where nearshore nourishment and bar movement with beach berm and dune building have been simulated. Following the extension of the Tweed River training walls in the late 1960s, the downdrift Southern Gold Coast beaches to the north suffered extensive and prolonged erosion. Between 1988 and 1996, 6.6 million m3 of sand was deposited in both onshore and nearshore locations along the beaches of the Southern Gold Coast. Extensive post-nourishment beach monitoring data shows the recovery of Bilinga beach with the nearshore nourished material transported onshore. There have been many unsuccessful attempts to numerically model the beach recovery processes following the nearshore nourishment on the Southern Gold Coast. Most coastal models have been developed for prediction of storm erosion and as such have limited abilities in simulating bar movement and onshore accretion with beach recovery over extended periods of time. NSBEACH (New SBEACH) has been developed with the ability to simulate short term storm erosion and the longer duration recovery processes under natural or nourished conditions. NSBEACH has been successfully applied at Bilinga beach over an extended simulation period of 8 months with both erosion and accretion responses of the beach successfully simulated.

Biostabilization of cohesive sediments: revisiting the role of abiotic conditions, physiology and diversity of microbes, polymeric secretion, and biofilm architecture.

In aquatic habitats, micro-organisms successfully adhere to and mediate particles, thus changing the erosive response of fine sediments to hydrodynamic forcing by secreting glue-like extracellular polymeric substances (EPS). Because sediment dynamics is vital for many ecological and economic aspects of watersheds and coastal regions, biostabilization of cohesive sediments is one of the important ecosystem services provided by biofilms. Although the research on biostabilization has gained momentum over the last 20 years, we still have limited insights principally due to the complex nature of this topic, the varying spatial, temporal, and community scales examined, oversimplified ecohydraulic experiments with little natural relevance, and the often partial views of the disciplines involved. This review highlights the current state of our knowledge on biostabilization and identifies important areas for future research on: (A) the influence of abiotic conditions on initial colonization and subsequent biofilm growth, focusing on hydrodynamics, substratum, salinity, nutrition, and light climate; (B) the response of microbes in terms of physiological activity and species diversity to environmental settings as well as biotic conditions such as competition and grazing; and (C) the effects of the former on the EPS matrix, its main constituents, their composition, functional groups/substitutes, and structures/linkages. The review focuses specifically on how the numerous mutual feedback mechanisms between abiotic and biotic conditions influence microbial stabilization capacity, and thus cohesive sediment dynamics.

Inversion of fluvial channels for paleorock uplift rates in Taiwan

AbstractThe transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers. However, extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate, as well as other factors such as climate and rock type. We exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of Taiwan. The analytical approach allows us to solve the linear inverse problem, efficiently extracting rock uplift as a function of space and time, from digital elevation data. We assess the potential of fluvial topography to resolve rock uplift rates using three approaches: (1) a synthetic resolution test, (2) analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate, and (3) interpretation of the model resolution matrix. Furthermore, the potential to analyze large data sets reduces the influence of stochastic processes such as landslides, small‐scale river network reorganization, and also local lithological variability. In Taiwan, our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0.5 Ma across the Central Range.

Short-Term Effects of Tree Removal on Infiltration, Runoff, and Erosion in Woodland-Encroached Sagebrush Steppe

Land owners and managers across the western United States are increasingly searching for methods to evaluate and mitigate the effects of woodland encroachment on sagebrush steppe ecosystems. We used small-plot scale (0.5 m2) rainfall simulations and measures of vegetation, ground cover, and soils to investigate woodland response to tree removal (prescribed fire and mastication) at two late-succession woodlands. We also evaluated the effects of burning on soil water repellency and effectiveness of aggregate stability indices to detect changes in erosion potential. Plots were located in interspaces between tree and shrub canopies and on undercanopy tree and shrub microsites. Erosion from untreated interspaces in the two woodlands differed more than 6-fold, and erosion responses to prescribed burning differed by woodland site. High-intensity rainfall (102 mm · h-1) on the less erodible woodland generated amplified runoff and erosion from tree microsites postfire, but erosion (45–75 g · m-2) was minor relative to the 3–13-fold fire-induced increase in erosion on tree microsites at the highly erodible site (240–295 g · m-2). Burning the highly erodible woodland also generated a 7-fold increase in erosion from shrub microsites (220–230 g · m-2) and 280–350 g · m-2 erosion from interspaces. High levels of runoff (40–45 mm) and soil erosion (230–275 g · m-2) on unburned interspaces at the more erodible site were reduced 4–5-fold (10 mm and 50 g · m-2) by masticated tree material. The results demonstrate that similarly degraded conditions at woodland-encroached sites may elicit differing hydrologic and erosion responses to treatment and that treatment decisions should consider inherent site-specific erodibility when evaluating tree-removal alternatives. Strong soil water repellency was detected from 0 cm to 3 cm soil depth underneath unburned tree canopies at both woodlands and its strength was not altered by burning. However, fire removal of litter exacerbated repellency effects on infiltration, runoff generation, and erosion. The aggregate stability index method detected differences in relative soil stability between areas underneath trees and in the intercanopy at both sites, but failed to provide any indication of between-site differences in erodibility or the effects of burning on soil erosion potential.

Runoff, erosion and sediment particle size from smooth and rough soil surfaces under steady rainfall-runoff conditions

The responses of runoff and erosion to soil surface roughness (SSR) have been extensively studied in the past decades; however, most of these studies were conducted at the early stage of rainfall, whereas few studies were specifically conducted during steady runoff conditions. In this study, runoff, soil losses and sediment particle sizes from smooth and rough surfaces were measured after surface runoff stabilisation to improve the understanding of the relationship between SSR and soil erosion. A cascade of two independent soil boxes in which the runoff samples from upslope and downslope boxes can be collected independently or together was used to perform the experiments. The upslope box supplied runoff to the downslope study box. Three rainfall intensities of 50, 75 and 100 mm/h were applied. The results suggest that SSR has a significant effect on soil erosion when runoff reaches a steady state. Although the difference in the runoff rate was small between the rough and smooth surfaces, the sediment rate and concentration of particles were significantly lower for the rough surface than for the smooth surface. Through analysing the particle size distribution (PSD) of sediment, we found that selective sediment delivery is an important reason for the soil erosion reduction by SSR. The rainfall intensity decreased the difference in the sediment rates between the smooth and rough surfaces. The extra inflow increased the runoff rates, sediment rates and concentration rates for both the smooth and rough surfaces; however, the increasing degrees of the runoff rate, sediment rate and concentration rate had significant differences between the rough and smooth surfaces. A stepwise multiple regression showed that significant linear relationships existed between one or more PSDs of 20–50, 50–100, 100–250 and 1000–2000 µm and the sediment rate.