Fluvial Landform Evolution Research Articles

Basin-scale reconstruction of late Pleistocene-Holocene fluvial landform evolution and its mechanisms in transitional areas between Taihang Mountain and North China Plain

The processes and mechanisms of fluvial landform evolution, especially in the transitional zones between mountains and plains, are of great significance for predicting future regional sustainability and ecosystem stability in the basin. As a region of significant cultural and ecological importance, the transitional area between Taihang Mountain and North China Plain still has a limited understanding of the fluvial landform evolution. With detailed field surveys and 39 optically stimulated luminescence (OSL) ages of 14 sections, we reconstruct fluvial landform evolution in the southern piedmont of the Taihang Mountain since the late Pleistocene. The results show that two major fluvial processes occurred during 18–10 ka BP and 9–3 ka BP. Meanwhile, the late Pleistocene-Holocene can be divided into 5 intervals in the alluvial fan and floodplain areas, with corresponding ages of 3 ka BP, 9–3 ka BP, 10–9 ka BP, 18–10 ka BP, and before 20 ka BP, respectively. The results also indicate that the regional fluvial processes primarily result from climate change and tectonic activities, and secondarily result from sea level fluctuation. Additionally, the prehistoric settlement pattern was also shaped by the evolution of regional rivers. Our research is significant for understanding the evolution and mechanisms of fluvial landforms in transitional zones.

Self-organization of channels and hillslopes in models of fluvial landform evolution and its potential for solving scaling issues

Abstract. Including hillslope processes in models of fluvial landform evolution is still challenging. Since applying the respective models for fluvial and hillslope processes to the entire domain causes scaling problems and makes the results dependent on the spatial resolution, the domain is explicitly subdivided into channels and hillslopes in some models. The transition from hillslopes to channels is typically attributed to a given threshold catchment size as a proxy for a minimum required discharge. Here we propose a complementary approach for delineating channels based on the discrete representation of the topography. We assume that sites with only one lower neighbor are channelized. In combination with a suitable model for hillslope processes, this concept initiates the self-organization of channels and hillslopes. A numerical analysis with a simple model for hillslope dynamics reveals no scaling issues, so the results appear to be independent of the spatial resolution. The approach predicts a break in slope in the sense that all channels are distinctly less steep than hillslopes. On a regular lattice, the simple D8 flow-routing scheme (steepest descent among the eight nearest and diagonal neighbors) harmonizes well with the concept proposed here. The D8 scheme works well even when applied to the hillslopes. This property simplifies the numerical implementation and increases its efficiency.

Controls on the regional distribution of landslide dams and implications for fluvial landform evolution in Bhutan and its surrounding area

Controls on the regional distribution of landslide dams and implications for fluvial landform evolution in Bhutan and its surrounding area

Tectonic Significances of the Geomorphic Evolution in the Southern Alashan Block to the Outward Expansion of the Northeastern Tibetan Plateau

Fluvial landscapes are a result of lithospheric tectonic movement, climate evolution and surface processes. Existing evidence proves that regional tectonic deformation can be reflected by the evolution of fluvial landforms. The southern Alashan Block lies the closest to the northeastern Tibetan Plateau and has become the latest plateau outward expansion boundary. Yabrai Shan is located at the intersection of the Tibetan Plateau, Alashan and Ordos Blocks, thereby recording the evolution of the surface processes and tectonic activities in the northeastern Tibetan Plateau and its surrounding regions. Herein, we conducted the quantitative landform analysis and field investigations of Yabrai Shan, and the spatiotemporal distribution of geomorphological parameters indicated that Yabrai Shan is in the mature stage of geomorphological evolution controlled by tectonic activities of the Yabrai range-front fault. Based on the paleochannel reconstruction model and previous research on fault activity, two tectonic acceleration events were identified, with estimated geomorphic response times of 0.15–1.10 Ma and 1.42–2.92 Ma. Different distribution characteristics of two-phase knickpoints are caused by the change of tectonic stress in this region, revealing that the late knickpoints are the result of tectonic acceleration under the influence of the northeast expansion of the Tibetan Plateau. The transformation of Yabrai Shan from the original extensional environment affected by the Ordos Block to the compressional environment affected by the northeast expansion of the Tibetan Plateau occurred after 1.10 Ma.

Theoretical and numerical considerations of rivers in a tectonically inactive foreland

Abstract. Modeling the dynamics of alluvial rivers is theoretically and numerically more challenging than modeling erosion of bedrock channels in active mountain ranges. As a consequence, the majority of the approaches developed in the context of alluvial rivers are one-dimensional. However, recent advances in the numerics of fluvial landform evolution models allow for two-dimensional simulations of erosion and sediment transport over time spans of several million years. This study aims at finding out fundamental properties of rivers in a tectonically inactive foreland of a mountain range by investigating a simple reference scenario theoretically and numerically. This scenario consists of a mountain range and a foreland in a quasi-steady state wherein the material eroded in the mountain range is routed through the foreland. In order to understand the properties of foreland rivers, a subdivision into two classes – carriers and redistributors – is introduced. Carriers originate in the mountain range and are thus responsible for the large-scale sediment transport to the ocean. In turn, redistributors are rivers whose entire catchment is located in the foreland. Using the concept of carriers and redistributors, it is shown that the drainage network in the foreland permanently reorganizes so that a steady state in the strict sense is impossible. However, the longitudinal profiles of carriers are described well by a steady-state approximation. Their concavity index is considerably greater than that of rivers in the mountain range. Carriers predominantly deposit sediment at high rates, while redistributors erode at much lower rates. Despite the low erosion rates, the sediment flux from redistributors into carriers is a major component of the overall sediment budget and finally the main driver of the highly dynamic behavior of the carriers.

Contribution of soil erosion to the evolution of the plateau-plain-delta system in the Yellow River basin over the past 10,000 years

Soil erosion, sediment transport, and delta deposition are of great importance to the evolution of fluvial landforms. In this study, we carry out a quantitative and comprehensive analysis to identify dynamic processes and mechanisms of soil erosion, fluvial plain deposition, and river delta formation in response to Holocene environmental changes over the past 10,000 years. In this investigation, the following results are achieved. First, spatial variations of the monsoon border (400 mm isohyet) resulted in dynamic changes in soil erosion on the Loess Plateau, sediment transportation downstream, and fluvial deposition on the plains and delta during the Holocene. Climate change and human activities played essential roles in variations of the plateau-plain-delta system during different periods. In the early Holocene, the number and scale of Neolithic cultural sites in the Yellow River basin increased. In the past 3000 years, human activities have strongly influenced and dominated environmental evolution in this region. Second, soil erosion was the critical contributor to the construction of the North China Plain. The Yellow River Delta provided the preliminary living environment where historical civilization in the Yellow River basin formed and developed, giving birth to the Yellow River civilization. Sediment discharge in the Loess Plateau was the primary source for river channel development and shaping of the river delta.

Significance of fluvial landform evolution and river reorganization in settlement development over the past 50 ka: A case study of Baodun site on Chengdu Plain, SW China

The Baodun archaeological site, which is representative of Baodun Culture (4.5–3.6 cal. ka BP), is a well-known walled site covering large areas of the Chengdu Plain (CDP), which is located in the upper reaches of the Yangtze River. The CDP is a low-lying sedimentary basin that is one of the cradles of Chinese civilization and was formed by many rivers originating from the northeastern part of the Qinghai–Tibetan Plateau. Geological and hydrological characteristics have strongly influenced the development of ancient cultures on the CDP. However, their relationship has not been validated. Based on field investigations, ground surveys, microgeomorphological discrimination, grain-size measurements, tree species identification, and the analysis of fluvial deposits, including age dating, height measurement, and observations of gravel layers, we investigated the effects of geomorphology and river channel migration on the evolution of the Baodun site. The results showed that three grades of terraces developed at the Baodun site region during the past ~50 ka BP, which had important impacts on the regional evolution of geomorphology and river systems. The chronology constrains the ages of terraces T1, T2, and T3 to ~7, ~22, and ~48 ka, respectively; T2 and T3 were closely related to tectonic activity, whereas T1 was related to climate variation. Similar to the modern river system, ancient waterflow primarily originated from the northwest; however, it mixed with water from other directions in the past. We attribute the construction of the Baodun site to the persistently outcropped terraces and the attraction of more stable rivers, which provided space and resources for the Baodun people. The evolution of the river system influenced the safety of the Baodun site, and flooding was the main factor leading to its decline and abandonment. The stability of the terrace and sedimentary environments and the decreased precipitation were important factors influencing the large-scale habitation of archaeological sites on the CDP during the middle and late Holocene.

Causes of pulsating evolution of fluvial landforms since the marine isotopic stage-2 in the belt of Schuppen, Nagaland, NE India

ABSTRACT The Belt of Schuppen (BoS) of Nagaland is a NE-SW trending linear zone lying adjacent to the Brahmaputra Valley of Assam in Northeast India. Geomorphic, stratigraphic and chronologic data from the Dzüdza and Chathe river valleys that cut across the BoS have been studied to understand the influence of climate on landform evolution in parts of the BoS. Fluvial landforms in the Dzüdza and Chathe river valleys evolved in four major phases bracketed between 22–17 ka (Phase IV), 13–9.0 ka (Phase III), 7–5 ka (Phase II) and 3.5–1.5 ka (Phase I), indicating multi-centennial to millennial changes in monsoon intensity. Climatically, Phase-III was dominated by valley aggradation initiated by onset of the Indian Summer Monsoon (ISM) and persisted intermittently till the early Holocene-strengthened ISM. The other phases of aggradation are attributed to transient or weak ISM. The present study suggests that fluvial aggradation was associated with enhanced precipitation and sediment supply in the BoS valley, whereas the transient and weak ISM is manifested in episodic pulses of alluvial ingression from the tributaries to the trunk valleys; along with post depositional tectonic modifications of the landforms.

Climate-tectonic imprints on the Late Quaternary Ravi River Valley Terraces of the Chamba region in the NW Himalaya

• The present manuscript provides pristine OSL ages of the Ravi River Valley terraces, a tributary of the Indus River. • Aggradation events were mainly induced by climate, whereas the incisions phases were governed by both tectonic and climate. • Synchronous incision phases in Hinterland (Ravi River) and Indus plain suggest akin Late Quaternary climatic conditions. • Unlike Ganga River system, Ravi River system does not show any time lag for incision between the hinterland and the plain. • The first report on reactivation age (46 ka) of the MBT and the Chamba Thrust in NW Himalaya. An attempt has been made to reconstruct the landform evolution in monsoon-dominated the Ravi River Valley (a major tributary of the Indus River), Chamba Nappe, Lesser Himalaya based on detailed field mapping, supported by the Optically Stimulated Luminescence (OSL) dates. In the upper Ravi River Valley sediments are generated by glaciation-paraglaciation processes and accumulated in terraces and alluvial fan deposits in lower reaches north of the Main Central Thrust during deglaciation and periods of intensified monsoonal phases. Field study and OSL dating demonstrate aggradation of river terraces and debris-flow terraces occurred in two major phases: 73–46 ka and 39–23 ka and at least six minor phases between <23 ka and 7 ka. The incision was initiated shortly after 7 ka and ascribed to the decrease in overall monsoon intensity and simultaneous reduction in sediment flux. The first phase (73–46 ka) of aggradation was regional and occurred in a pre-existing river valley, whereas the later phases (39 ka onward) occurred as cut-and-fill and degraded terraces. The incision of the first major phase (220 m thick) accelerated between ∼46 ka and 39 ka due to reactivation of the Chamba Thrust and the Main Boundary Thrust (MBT). The study suggests that the fluvial dynamics and aggradation phases in the Ravi River Valley were regulated by monsoon variability, whereas both tectonic activity and climatic variables governed the incision of these deposits. The contemporaneous aggradation and incision in the hinterland and the Indo-Gangetic plains suggest that the Late Quaternary climate variability was the main factor in the evolution of fluvial landforms.

Modeling glacial and fluvial landform evolution at large scales using a stream-power approach

Abstract. Modeling glacial landform evolution is more challenging than modeling fluvial landform evolution. While several numerical models of large-scale fluvial erosion are available, there are only a few models of glacial erosion, and their application over long time spans requires a high numerical effort. In this paper, a simple formulation of glacial erosion which is similar to the fluvial stream-power model is presented. The model reproduces the occurrence of overdeepenings, hanging valleys, and steps at confluences at least qualitatively. Beyond this, it allows for a seamless coupling to fluvial erosion and sediment transport. The recently published direct numerical scheme for fluvial erosion and sediment transport can be applied to the entire domain, where the numerical effort is only moderately higher than for a purely fluvial system. Simulations over several million years on lattices of several million nodes can be performed on standard PCs. An open-source implementation is freely available as a part of the landform evolution model OpenLEM.

Late Quaternary fluvial landform evolution and controlling factors along the Yulin River on the Northern Tibetan Plateau

The Yulin River in the northern Tibetan Plateau, consists of multiple geomorphological features, including alluvial fans, fluvial terraces, and river profile knickpoints. Collectively, these provide a natural laboratory for exploring the late Quaternary fluvial landform evolution in response to both climatic change and tectonic activities in the region of the Altyn Tagh Fault. In this study, we investigated the distribution, sequences and sediment characteristics of the fluvial landforms along the Yulin River based on high-precision (0.5 m-resolution) Worldview satellite images and field observations. Mid-Pleistocene alluvial fans formed the highest fluvial landform surface into which ten major inset fluvial terraces were developed, distributed along three stream segments. Real-time kinematic global positioning system (RTK-GPS) measurement of terrace surfaces and the modern river longitudinal profiles was conducted across the Dongbatu Shan to show fluvial landform geometry and tectonic deformation. Fluvial terrace surfaces were deformed due to fault uplift as illustrated by spatially variable surface geometries. The chronological sequences of terraces along the Yulin River since 160 ka were reconstructed based on 10Be terrestrial cosmogenic nuclides (TCNs) dating. Results indicated that river incision occurred mainly during periods of climate transition, suggesting that terrace evolution was partly controlled by climate changes. Moreover, terrace exposure ages showed an upstream younging trend along the river, demonstrating a probable response to knickpoint retreat. Combined with terrace deformation and ages, fault uplift rates were constrained, which were lower than the river incision rates during the Late Quaternary, indicating that crustal shortening was mainly absorbed by the growth of the regional anticline. Collectively, our results suggest that the evolution of fluvial landforms along the Yulin River is a function of interplay between regional tectonic activities and climatic changes, which is significant to understand the NW-outward splay of the Altyn Tagh Fault.

The role of pre-existing topography in the evolution of post-glacial fluvial landforms in the middle Satluj valley, north-western Himalaya, India

Abstract In tectonically active orogen like the Himalaya while computing the bedrock incision rate it is assumed that the underlying incised bedrock is genetically related to the overlying alluvium. This assumption may not be applicable universally, considering that the trans-Himalayan rivers were in existence before Miocene or earlier. Therefore, the sediments preserved at various locations represent the youngest phase of aggradation on the pre-existing valley topography – a cumulative expression of multiple cycles of erosion and aggradation. Considering that the fluvial terraces are extensively used to estimate the incision/uplift rates, it is therefore pertinent to ensure that the underlying bedrock topography is indeed genetically related to the overlying fluvial sediments and is not a relic of the pre-existing topography. The present study is aimed at understanding the relationship between the valley and channel-fill sediments and the underlying bedrock topography in the evolution of fluvial landforms. Based on the detailed field mapping of the relict channel/fossil valley-fill sequences, geomorphometry and limited optical ages the study suggests that the bedrock topography is cumulative expression of multiple cycles of erosion while the post glacial valley-fill sediments (dated to 14 ka and 8 ka) represent the most recent aggradation phase. The discreet linear strath terraces and epigenetic gorges represent a combination of climate and tectonically induced mid-Holocene river adjustment particularly in the areas proximal to local thrusts. Further, the study suggests that the securely dated strath terraces may provide the average tectonically induced incision/uplift rates whereas the epigenetic gorges largely represent climatically controlled focused and local uplift/incision in the study area. A preliminary estimate based on the strath terraces indicate that the terrain is being incised/uplifted at ∼0.6–1.3 mm/yr whereas as expected the epigenetic gorges provide a relatively higher incision rate (3.8 mm/yr to 12.5 mm/yr). Finally, the study cautions against using the conventional age-depth relationship of valley-fills and the underlying incised bedrock to ascertain the incision/uplift rates. Instead it suggests that the morphology of the underlying bedrock must be taken in to account in order to avoid erroneous estimate of incision/uplift rates (crustal deformation) in a tectonically active orogen.

Fluvial landforms and their implication towards understanding the past climate and seismicity in the northern Katrol Hill Range, western India

The tectonically active Kachchh peninsula in western India lies in the southwest monsoon trajectory and hence provides a rare opportunity to decipher the temporal changes in climate–tectonics interaction in the evolution of the fluvial landforms. Reconstructions based on geomorphology, sedimentology, and geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the Indian Summer Monsoon (ISM) after the Last Glacial Maximum (LGM). The sedimentary characteristics and major elemental concentrations suggest that the sediments are dominated by fluvially reworked miliolites with subordinate contribution from the Mesozoic sandstones and shales and were deposited with the initiation of the ISM after the LGM. Temporal changes in facies architecture and major element concentrations suggest a progressive strengthening of the monsoon between 17 and 12 ka. This was succeeded by an overall strengthened ISM phase with fluctuations after 12 ka and <8 ka. Following this, a gradual decline in the ISM is inferred until around 3 ka. However, presence of the younger valley-fill sediments which are dated to ∼1 ka are ascribed to a short-lived phase of renewed strengthened ISM in the region before the onset of present day aridity.Based on the morphology of the fluvial landforms, two major events of enhanced uplift can be suggested. The geomorphic expression of the older uplift event dated to >17 ka is represented by the beveled Mesozoic bedrock surfaces which accommodated the post LGM valley-fill aggradation. The younger event of enhanced uplift which is assigned to <3 ka was responsible for the incision of the fill sediments and the Mesozoic bedrock, and the evolution of the present day fluvial landforms. The time averaged incision/uplift rate indicates that the Katrol Hill Range is uplifting at the rate of ∼4 mm per year, implying seismically active terrain.

Late Quaternary climate and seismicity in the Katrol hill range, Kachchh, western India

A channel fill sequence in the upper catchment of the Khari river in the south of the Katrol Hill Fault (KHF) has been investigated to understand the role of climate and tectonics in the evolution of fluvial landforms. Detailed sedimentology and limited optical chronology suggest that the channel incision occurred during weak summer monsoon (prior to 19.9ka) and is attributed to the activity along the KHF and its subsidiary faults. The post-glacial to early Holocene was a phase of landscape stability (subdued tectonics) which persisted until around 7.1ka. Particularly, between 9.4ka and 7.1ka, an enhanced monsoon activity is inferred. A renewed phase of uplift is suggested after 7.1ka that probably continues till present.

Interactions between river flows and colonizing vegetation on a braided river: exploring spatial and temporal dynamics in riparian vegetation cover using satellite data

ABSTRACTField, laboratory, and numerical modelling research are increasingly demonstrating the potential of riparian tree colonization and growth to influence fluvial dynamics and the evolution of fluvial landforms. This paper jointly analyses multi‐temporal, multispectral ASTER data, continuous river stage and discharge data, and field observations of the growth rates of the dominant riparian tree species (Populus nigra) along a 21 km reach of the Tagliamento River, Italy. Research focuses on the period 2004–2009, during which there was a bankfull flood on 24 October 2004, followed by 2 years with low water levels, nearly 2 years with only modest flow pulses, and then a final period from 15 August 2008 that included several intermediate to bankfull flow events. This study period of increasing flow disturbance allows the exploration of vegetation dynamics within the river's active corridor under changing flow conditions. The analysis demonstrates the utility of ASTER data for investigating vegetation dynamics along large fluvial corridors and reveals both spatial and temporal variations in the expansion, coalescence, and erosion of vegetated patches within the study reach. Changes in the extent of the vegetated area and its dynamics vary along the study reach. In sub‐reaches where riparian tree growth is vigorous, the vegetated area expands rapidly during time periods without channel‐shaping flows, and is subsequently able to resist erosion by bankfull floods. In contrast, in sub‐reaches where tree growth is less vigorous, the vegetated area expands at a slower rate and is more readily re‐set by bankfull flood events. This illustrates that the rate of growth of riparian trees is crucial to their ability to contribute actively to river corridor dynamics. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Impacts of fluvial land form evolution and global change in urban environments

Understanding of the character of urban environments, which have been increasingly embraced by geomorphological research in the last four decades, has progressed to the way in which they are currently perceived. For fluvial geomorphology it is necessary to understand the palimpsest inherited from long-term evolution under pre-urban conditions. This includes understanding the way urban hazards arise, appreciating the diverse consequences of short-term land form changes influenced by human activity, and contemplating the nature and implications of management methods in relation to future global changes including those instigated by changed urban hazards.

Late Quaternary deposition and incision sequences of the Golmud River and their environmental implications

Golmud River is a large river that originates from the Kunlun Mountains and drains into the Qaidam Basin on northern Tibetan Plateau. Well-developed fluvial terraces in the river valley record complex history of tectonic movements and climate changes in this area. The current study investigated fluvial terraces in three cross sections along the river (Xiaogangou, Nachitai and Sanchahe). The ages of the terraces were constrained using optically stimulated luminescence (OSL) and radiocarbon dating methods. The results characterize two stages of fluvial landform evolution since the Late Quaternary: the Sanchahe deposition stage (82–16 ka) and the Golmud incision stage (16 ka until now). During the deposition stage, tectonic movements were relatively stable, which drove the deposition. Meanwhile the enhanced glaciations and precipitation during the Last Glacial promoted the aggradations in the river valley as well. During the incision stage, four substages at 16–13 ka, 13–11 ka, 11–5 ka and 5 ka till now are identified. These substages correspond to the incision of the four terraces. The incision was mainly driven by the tectonic uplift after the Last Glacial Maximum.

Fractal behavior in space and time in a simplified model of fluvial landform evolution

Two general approaches have been applied to understanding the fractal structure of fluvial topography: (1) deterministic, process-based models, and (2) stochastic partial differential equations (PDE). Deterministic models reproduce the fractal behavior of fluvial topography but have two limitations: they often underestimate the amount of lateral valley and ridge migration that occurs in nature, and the complexity has made it difficult to identify the precise origin of fractal behavior in fluvial landscapes. The simplicity of stochastic PDE models has made them useful for investigating fractal behavior, but they incorrectly suggest that fractal behavior is only possible with stochastic forcing. In this paper I investigate whether simplified, deterministic PDE models of landform evolution also exhibit fractal behavior and other features of complexity (i.e. deterministic chaos). These models are based on the KPZ equation, well known in the physics literature. This equation combines diffusion (i.e. hillslope processes) and nonlinear advection (i.e. bedrock or alluvial channel incision). Two models are considered: (1) a deterministic model with uniform erodibility and random initial topography, and (2) a deterministic model with random erodibility and uniform initial topography. Results illustrate that both of these deterministic models exhibit fractal behavior and deterministic chaos. In this context, chaotic behavior means that valley and ridge migration and nonlinear amplification of small perturbations in these models prevent an ideal steady state landscape from ever developing in the large-system limit. These results suggest that fractal structure and deterministic chaos are intrinsic features of the evolution of fluvial landforms, and that these features result from an inverse cascade of energy from small to large wavelengths in drainage basins. This inverse cascade differs from the direct cascade of three-dimensional turbulence in which energy flows from large to small wavelengths.

River Types, Site Evolution and Successional Vegetation Patterns in Peruvian Amazonia

Lateral migration of Amazonian lowland rivers causes a vegetation succession on recently deposited fluvial sediments. The forest ground is formed gradually in se- quence, giving rise to age-zonation of the successional stages. Using Landsat MSS maps and field observations, we studied variations in fluvial landform evolution and river character. The widely used characterizations of the rivers ac- cording to their suspension-load character and channel pattern were evaluated in relation to the vegetation succes- sion. Sequential successional forests appear extensively along meandering white-water rivers, which are rich in sus- pended sediments and are characterized by mobile channels. Conversely, vegetation zonation is less pronounced at the margins of slowly eroding suspension-poor rivers. Line transects were established to document meander develop- ment along eight different rivers. The chemical composition of the recently deposited alluvium differs markedly both among rivers and along the transects. Concentrations of organic carbon and nitrogen increase toward the meander neck along with the acid reaction of the soil. The rate of riv- erine forest regeneration in Peruvian lowland Amazonia was extrapolated on the basis of erosion data from four different rivers, and suggests that approximately 130 km2 of forest is annually eroded and replaced by successional vegetation, the equivalent of 0.2% of the present floodplain area of this region.