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Linking landscape morphological complexity and sediment connectivity   总被引：2，自引：0，他引：2  
Connectivity relates to the coupling of landforms (e.g. hillslopes and channels) and the transfer of water and sediment between them. The degree to which parts of a catchment are connected depends largely on the morphological complexity of the catchment's landscape. Landscapes can have very different and distinct morphologies, such as terraces, V‐shaped valleys or broad floodplains. The objective of this study is to better understand and quantify the relation between landscape complexity and catchment connectivity. We hypothesize that connectivity decreases with increasing landscape morphological complexity. To quantify the connectivity–complexity relationship virtual digital elevation models (DEMs) with distinct morphologies were used as inputs into the landscape evolution model LAPSUS to simulate the sediment connectivity of each landscape. Additionally, the hypothesis was tested on six common real DEMs with widely different morphologies. Finally, the effects of different rainfall time series on catchment response were explored. Simulation results confirm the hypothesis and quantify the non‐linear relation. Results from the exploration of sediment connectivity in response to sequences of rainfall events indicate that feedback between erosion and deposition are more important for certain landscape morphologies than for others: for a given rainfall input, a more effective sediment connectivity and erosion response may be expected from rolling or V‐shaped catchments than from dissected or stepped landscapes. Awareness of the differences in the behaviour and response of different morphologies to catchment processes provides valuable information for the effective management of landscapes and ecosystems through efficiently designed soil and water conservation measures. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
2.
Landscape evolution models (LEMs) simulate the three‐dimensional development of landscapes over time. Different LEMs have different foci, e.g. erosional behaviour, river dynamics, the fluvial domain, hillslopes or a combination. LEM LAPSUS is a relatively simple cellular model operating on timescales of centuries to millennia and using annual timesteps that has had a hillslope focus. Our objective was to incorporate fluvial behaviour in LAPSUS without changing the existing model equations. The model should be able to reproduce alternating aggradation and incision in the floodplains of catchments, depending on simulated conditions. Testing was done using an artificial digital elevation model (DEM) and a demonstration of the ability for fluvial simulation was performed for a real landscape (Torrealvilla catchment, southeast Spain). Model equations to calculate sediment dynamics and water routing were similar for both hillslope and fluvial conditions, but different parameter values were used for these domains, defined based on annual discharge. Parameters changing between the domains are convergence factor p, which is used in the multiple flow algorithm to route water, and discharge and gradient exponents m and n, used in transport capacity calculations. Erodibility and ‘sedimentability’ factors K and P were changed between cold (little vegetation, high erodibility) and warm conditions (more vegetation, lower erodibility). Results show that the adapted parameters reproduced alternating aggradation – due to divergent flow in the floodplain and sediment supply under cold conditions – and incision due to reduced sediment supply and resulting clean water erosion during simulated warm conditions. The simulated results are due to interactions between hillslopes and floodplains, as the former provide the sediments that are deposited in the latter. Similar behaviour was demonstrated when using the real DEM. Sensitivity and resolution analysis showed that the model is sensitive to changes in m, n and p and that model behaviour is influenced by DEM resolution. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
3.
Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250 km2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
4.
Hillslopes in central and western parts of KwaZulu-Natal, South Africa are often mantled by colluvial sediments of the Masotcheni Formation. These sediments have accreted in response to several cycles of deposition, pedogenesis and incomplete erosion. Climatic controls on these cycles are incompletely known. Results from fieldwork, micromorphology, stable carbon isotope analysis and Optically Stimulated Luminescence dating of Masotcheni Formation sediments from Okhombe valley in the Drakensberg foothills are combined. Deposition in the area had at least 11 phases, starting before 42 ka and ending before 0.17 ka. The first six deposits (from before 42 ka to after 29 ka) resulted from the interplay between slope processes and fluvial redistribution under cold conditions. Solifluction was the most important slope process. No deposits have been found from the Last Glacial Maximum, arguably because this period was too dry. The last five deposits (from about 11 ka to before 0.17 ka) resulted from fluvial redistribution of upslope material and older deposits under increasing precipitation. Current extreme gully erosion in the Masotcheni Formation indicates a lack of available upslope material, leaving downslope deposits as the only sediment source for fluvial redistribution. This model for landscape response to climate change may be able to explain how climate controlled landscape processes in other Masotcheni Formation sites in KwaZulu-Natal. In the research area and elsewhere, this proposition may be tested with numerical landscape evolution models.  相似文献   
5.
Semi‐arid ecosystems are often spatially self‐organized in typical patterns of vegetation bands with high plant cover interspersed with bare soil areas, also known as ‘tiger bush’. In modelling studies, most often, straight planar slopes were used to analyse vegetation patterning. The effect of slope steepness has been investigated widely, and some studies investigated the effects of microtopography and hillslope orientation. However, at the larger catchment scale, the overall form of the landscape may affect vegetation patterning and these more complex landscapes are much more prevalent than straight slopes. Hence, our objective was to determine the effect of landform variation on vegetation patterning and sediment dynamics. We linked two well‐established models that simulate (a) plant growth, death and dispersal of vegetation, and (b) erosion and sedimentation dynamics. The model was tested on a straight planar hillslope and then applied to (i) a set of simple synthetic topographies with varying curvature and (ii) three more complex, real‐world landscapes of distinct morphology. Results show banded vegetation patterning on all synthetic topographies, always perpendicular to the slope gradient. Interestingly, we also found that movement of bands – a debated phenomenon – seems to be dependent on curvature. Vegetation banding was simulated on the slopes of the alluvial fan and along the valley slopes of the dissected and rolling landscapes. In all landscapes, local valleys developed a full vegetation cover induced by water concentration, which is consistent with observations worldwide. Finally, banded vegetation patterns were found to reduce erosion significantly as compared to other vegetation configurations. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   
6.
Mulching with forest residues has proved to be highly effective in reducing post-fire soil losses at the plot scale. However, its effectiveness has not been quantified at the application rates that are typically used in operational post-fire land management (2–3 Mg ha-1 using straw), as well as at scales larger than 100 m2. The present study compared post-fire erosion rates for six convergent hillslopes or swales of 500 to 800 m2, three of which were left untreated while the other three were mulched immediately after the fire with shredded eucalypt bark at a rate of 2.4 Mg ha-1. Erosion rates were monitored at irregular intervals during the first three post-fire years, whilst ground cover was assessed yearly. Selected topsoil properties (0–2 cm) such as organic matter content and aggregate stability were determined at a single occasion – two years after the wildfire, for three micro-environments separately: bare soil, and under mulch/litter and vegetation. Soil losses on the untreated swales decreased with post-fire year from 2.2 to 0.4 and 0.11 Mg ha-1 yr-1 (respectively for the first, second and third post-fire years), while the mulched swales produced 84%, 77% and 38% less soil losses than the untreated swales. Soil losses also depended on slope aspect, with the north-facing swales producing less erosion than the west-facing ones. This could be linked to their significant differences in bare soil, vegetation and stone cover, or a combination thereof. The type of micro-environment also played a significant role in topsoil properties (stone content, bulk density, resistance to penetration/shear stress, porosity and organic matter content). The present results add to the increasing evidence that forest residues should be duly considered for operational post-fire land management. Forest residues were highly effective in reducing erosion from swales at application rates as low as the typical 2 Mg ha-1 of post-fire straw mulch. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   
7.
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8.
In semi‐arid areas, high‐intensity rainfall events are often held responsible for the main part of soil erosion. Long‐term landscape evolution models usually use average annual rainfall as input, making the evaluation of single events impossible. Event‐based soil erosion models are better suited for this purpose but cannot be used to simulate longer timescales and are usually applied to plots or small catchments. In this study, the openLISEM event‐based erosion model was applied to the medium‐sized (～50 km2) Prado catchment in SE Spain. Our aim was to (i) test the model's performance for medium‐sized catchments, (ii) test the ability to simulate four selected typical Mediterranean rainfall events of different magnitude and (iii) explore the relative contribution of these different storms to soil erosion using scenarios of future climate variability. Results show that because of large differences in the hydrologic response between storms of different magnitudes, each event needed to be calibrated separately. The relation between rainfall event characteristics and the calibration factors might help in determining optimal calibration values if event characteristics are known. Calibration of the model features some drawbacks for large catchments due to spatial variability in Ksat values. Scenario calculations show that although ～50% of soil erosion occurs as a result of high frequency, low‐intensity rainfall events, large‐magnitude, low‐frequency events potentially contribute significantly to total soil erosion. The results illustrate the need to incorporate temporal variability in rainfall magnitude–frequency distributions in landscape evolution models. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
9.
The improvement of resolution of digital elevation models (DEMs) and the increasing application of the Revised Universal Soil Loss Equation (RUSLE) over large areas have created problems for the efficiency of calculating the LS factor for large data sets. The pretreatment for flat areas, flow accumulation, and slope-length calculation have traditionally been the most time-consuming steps. However, obtaining these features are generally usually considered as separate steps, and calculations still tend to be time-consuming. We developed an integrated method to improve the efficiency of calculating the LS factor. The calculation model contains algorithms for calculating flow direction, flow accumulation, slope length, and the LS factor. We used the Deterministic 8 method to develop flow-direction octrees (FDOTs), flat matrices (FMs) and first-in-first-out queues (FIFOQs) tracing the flow path. These data structures were much more time-efficient for calculating the slope length inside the flats, the flow accumulation, and the slope length linearly by traversing the FDOTs from their leaves to their roots, which can reduce the search scope and data swapping. We evaluated the accuracy and effectiveness of this integrated algorithm by calculating the LS factor for three areas of the Loess Plateau in China and SRTM DEM of China. The results indicated that this tool could substantially improve the efficiency of LS-factor calculations over large areas without reducing accuracy.  相似文献   
10.
Natural damming of upland river systems, such as landslide or lava damming, occurs worldwide. Many dams fail shortly after their creation, while other dams are long‐lived and therefore have a long‐term impact on fluvial and landscape evolution. This long‐term impact is still poorly understood and landscape evolution modelling (LEM) can increase our understanding of different aspects of this response. Our objective was to simulate fluvial response to damming, by monitoring sediment redistribution and river profile evolution for a range of geomorphic settings. We used LEM LAPSUS, which calculates runoff erosion and deposition and can deal with non‐spurious sinks, such as dam‐impounded areas. Because fluvial dynamics under detachment‐limited and transport‐limited conditions are different, we mimicked these conditions using low and high erodibility settings, respectively. To compare the relative impact of different dam types, we evaluated five scenarios for each landscape condition: one scenario without a dam and four scenarios with dams of increasing erodibility. Results showed that dam‐related sediment storage persisted at least until 15 000 years for all dam scenarios. Incision and knickpoint retreat occurred faster in the detachment‐limited landscape than in the transport‐limited landscape. Furthermore, in the transport‐limited landscape, knickpoint persistence decreased with increasing dam erodibility. Stream capture occurred only in the transport‐limited landscape due to a persisting floodplain behind the dam and headward erosion of adjacent channels. Changes in sediment yield variation due to stream captures did occur but cannot be distinguished from other changes in variation of sediment yield. Comparison of the model results with field examples indicates that the model reproduces several key phenomena of damming response in both transport‐limited and detachment‐limited landscapes. We conclude that a damming event which occurred 15 000 years ago can influence present‐day sediment yield, profile evolution and stream patterns. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
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