Channel Longitudinal Profiles Research Articles

Reducing the dynamic impact of a landslide on buildings and transport structures in the village of Toktogul, Uzgen district of the Kyrgyz Republic

In the Kyrgyz Republic, there is a significant increase in landslide activity against the backdrop of ongoing climate change, especially in the southern mountainous regions of the country. The volume of soil during a landslide in this region can reach tens and hundreds of thousands of cubic meters, and in some cases more. The rate of landslide displacement ranges from several meters per year to several meters per second. The purpose of this study is to unload the landslide area to protect the population, roads and other structures of the village of Toktogul, Uzgen district of the Kyrgyz Republic. This landslide area was studied on the basis of field research on the ground and the results of desk work. The sliding of soil masses in the area can cause destruction and debris of residential and administrative buildings, roads and power lines, as well as injury and death. Considering the equilibrium of the system of forces acting on the subsidence soil mass of the slope section and analyzing them, measures for unloading the landslide body in this section are proposed. The proposed longitudinal profiles of drainage channels to reduce the moisture content of subsidence soil and transverse profiles of developed soil to reduce the weight of subsidence soil are presented. Based on the results of processing research data and analysis, it is recommended to reduce the weight of unstable (subsidence) soil by stepwise development along the slope of the site and transporting it up to 5 km for subsequent brick production. It is also recommended to protect subsidence soil from waterlogging by installing drainage channels. Based on the results of the research, a real project was developed to protect the site from landslides near the village of Toktogul. The proposed measures make it possible to reduce the risk of a landslide in the area under consideration using methods and technical means that are inexpensive and accessible to government agencies and local administrations.

Technology for reducing the risk of landslides by unloading the landslide mass

The work has developed measures to reduce the risk of a landslide in the area near the village of Toktogul, Uzgen district of the Kyrgyz Republic. This landslide area was studied on the basis of field research on the ground and the results of desk work. The sliding of soil masses in the area can cause destruction and debris of residential and administrative buildings, roads and power lines, as well as injury and death. Considering the equilibrium of the system of forces acting on the mass of filler soil of the slope section and analyzing them, measures for unloading the landslide body in this section are proposed. The proposed longitudinal profiles of drainage channels to reduce the moisture content of subsidence soil and transverse profiles of developed soil to reduce the weight of subsidence soil are presented. Based on the results of processing research data and analysis, it is recommended to reduce the weight of unstable (subsidence) soil by stepwise development along the slope of the site and transporting it up to 5 km for subsequent brick production. It is also recommended to protect subsidence soil from waterlogging by installing drainage channels. Based on the results of the research, a real project was developed to protect the site from landslides near the village of Toktogul. The proposed measures make it possible to reduce the risk of a landslide in the area under consideration using methods and technical means that are inexpensive and accessible to government agencies and local administrations.

Steady-state forms of channel profiles shaped by debris flow and fluvial processes

Abstract. Debris flows regularly traverse bedrock channels that dissect steep landscapes, but our understanding of bedrock erosion by debris flows and their impact on steepland morphology is still rudimentary. Quantitative models of steep bedrock channel networks are based on geomorphic transport laws designed to represent erosion by water-dominated flows. To quantify the impact of debris flow erosion on steep channel network form, it is first necessary to develop methods to estimate spatial variations in bulk debris flow properties (e.g., flow depth, velocity) throughout the channel network that can be integrated into landscape evolution models. Here, we propose and evaluate two methods to estimate spatial variations in bulk debris flow properties along the length of a channel profile. We incorporate both methods into a model designed to simulate the evolution of longitudinal channel profiles that evolve in response to debris flow and fluvial processes. To explore this model framework, we propose a general family of debris flow erosion laws where erosion rate is a function of debris flow depth and channel slope. Model results indicate that erosion by debris flows can explain the occurrence of a scaling break in the slope–area curve at low-drainage areas and that upper-network channel morphology may be useful for inferring catchment-averaged erosion rates in quasi-steady landscapes. Validating specific forms of a debris flow incision law, however, would require more detailed model–data comparisons in specific landscapes where input parameters and channel morphometry can be better constrained. Results improve our ability to interpret topographic signals within steep channel networks and identify observational targets critical for constraining a debris flow incision law.

Inversion of Late Miocene uplift history from the transient Daxia River landscape, NE Tibetan Plateau

The mechanisms of the upward and outward growth of the Tibetan Plateau are crucial for understanding the geodynamic significance of Cenozoic continental collisions. Northeastern Tibet has been suggested as one of the youngest deforming and uplifting margins surrounding the plateau. The existence of fluvial knickpoints and low-relief topographic surfaces along the Yellow River and its tributaries indicate the transience of the landscape in response to active tectonic uplift. Therefore, the uplift history of the North Eastern Tibetan Plateau (NETP) can be potentially inverted from the disequilibrium channel profiles of the Yellow River and its tributaries. The West Qinling Fault (WQF) is part of the geomorphological and topographic boundaries of the NETP. Its uplift history helps to clarify the deformation history of the Tibetan Plateau. In this study, the focus was on the Daxia River (one of the Yellow River tributaries) to identify the distribution of peneplain surfaces and knickpoints, and to present a linear inversion on the fluvial longitudinal profiles for the relative uplift history of the West Qinling. We obtained a relative uplift history with two pulses of change in the uplift rates at ∼5 and ∼2 Ma. Rates of relative uplift maintained low values during the Late Miocene, then slowly increased from 0.1 to 0.2 mm a −1 after ∼5 Ma and suddenly jumped to 0.3 mm a −1 at ∼2 Ma, consistent with recent findings on the deformation records in the NE Tibetan Plateau. We suggest that (1) the Late Miocene–Pliocene landscape evolution was driven by both tectonics and climate change and (2) inversion of the transient longitudinal channel profiles, if applied, may provide broader insights into the upward and outward growth patterns of the NE Tibetan Plateau. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

A new approach to simulate watershed sediment graphs

Soil loss management requires reliable data for assessing the conditions prevailing in a watershed. Suspended sediment concentration (SSC) is one of the indicators of soil loss, and its data and associated properties are essential for integrated watershed management. However, until now, practical methods for estimating the temporal variation of SSC at the watershed scale, i.e., a sediment graph (SG), using measured data have been given less attention. Therefore, the current study was planned to simulate the SG through conceptual modeling of the soil erosion process and sediment yield. The Galazchai Watershed in West Azerbaijan Province, Iran, was selected as a case study. In this regard, the isochrone histograms were initially prepared using two methods of the longitudinal channel profile and spatially distributed travel time. Soil erosion was calculated in each isochrone segment using the Revised Universal Soil Loss Equation (RUSLE), applying the lumped and cellular automata approach. The soil erosion between isochrones was subsequently routed using the Hadley, WaTEM/SEDEM, and newly modified U.S. Forest Service methods. The last method was developed based on seven standardized variables for the current research. Synthetic SGs were ultimately derived from 12 different combinations of the study methods. The modeling performance was assessed using 38 storm events collected over several years. The base time, time to peak, peak value, and total sediment load of the simulated and observed SGs were evaluated using relative error. Comparison based on the evaluation indicators indicated better performance of the combination of the spatially distributed travel time method, cellular automata, and modified U.S. Forest Service method with the coefficient of efficiency and the normalized coefficient of efficiency varying from −1.16 to 0.99 and from 0.32 to 0.99 for the calibration and validation stages, respectively. However, none of the models were simulating satisfactorily the entire sediment graphs.

Debris‐Flow Process Controls on Steepland Morphology in the San Gabriel Mountains, California

AbstractSteep landscapes evolve largely by debris flows, in addition to fluvial and hillslope processes. Abundant field observations document that debris flows incise valley bottoms and transport substantial sediment volumes, yet their contributions to steepland morphology remain uncertain. This has, in turn, limited the development of debris‐flow incision rate formulations that produce morphology consistent with natural landscapes. In many landscapes, including the San Gabriel Mountains (SGM), California, steady‐state fluvial channel longitudinal profiles are concave‐up and exhibit a power‐law relationship between channel slope and drainage area. At low drainage areas, however, valley slopes become nearly constant. These topographic forms result in a characteristically curved slope‐area signature in log‐log space. Here, we use a one‐dimensional landform evolution model that incorporates debris‐flow erosion to reproduce the relationship between this curved slope‐area signature and erosion rate in the SGM. Topographic analysis indicates that the drainage area at which steepland valleys transition to fluvial channels correlates with measured erosion rates in the SGM, and our model results reproduce these relationships. Further, the model only produces realistic valley profiles when parameters that dictate the relationship between debris‐flow erosion, valley‐bottom slope, and debris‐flow depth are within a narrow range. This result helps place constraints on the mathematical form of a debris‐flow incision law. Finally, modeled fluvial incision outpaces debris‐flow erosion at drainage areas less than those at which valleys morphologically transition from near‐invariant slopes to concave profiles. This result emphasizes the critical role of debris‐flow incision for setting steepland form, even as fluvial incision becomes the dominant incisional process.

Recent basement fault reactivation and fluvial drainage modification in an intraplate setting, eastern Bundelkhand Craton, Madhya Pradesh, India

North-central India is underlain by three northeast-trending paleo-topographic ridges of Precambrian Indian basement, bounded by lithospheric-scale basement faults. The Pokhara Fault defines the eastern edge of the Faizabad paleo-topographic ridge, which exposes the Archean Bundelkhand Craton. Near Panna, Madhya Pradesh, the Pokhara Fault coincides with a monocline developed in the Proterozoic Vindhyan Supergroup rocks along the Bundelkhand cratonic margin. Fluvial morphology of basins along the monocline, as well as a deeply incised abandoned meander preserved where the Ken River flows through the monocline, are investigated using longitudinal stream profiles and other geomorphic data along the length of the monocline to assess potential linkages with active basement fault reactivation.Normalized steepness indices in analyzed channel profiles along the monocline increase significantly downstream, with some channels exhibiting convex, over-steepened segments. Normalized steepness indices, knickpoint elevations, and incision depths are on average much higher in streams along the southwest segment of the monocline compared to streams along the northeast segment. Most channel profiles exhibit a knickpoint with slope-break morphology. The obtained longitudinal channel profiles exhibit characteristics of a fluvial system in a transient state subjected to an increase in rock uplift that intensifies to the southwest over a reactivated basement fault. Using previously published relationships between erosion rates and channel steepness, we conservatively estimate the onset age of monocline growth to be Plio-Quaternary. Fluvial geomorphic features preserved near Panna also suggest that the Ken River is an antecedent river. The incised meander feature near the crest of the monocline appears to be the abandoned river valley of a former Ken River course that was orphaned during the evolution of the landscape by what is now the present-day Ken River.Our study supports growing evidence that Indian basement faults such as the Pokhara Fault are long-lived and have recorded multiple periods of reactivation. Recent fluvial modification in the Panna region demonstrates that Indian basement faults are also active on the south side of the Ganga Basin, far south of the Himalayan deformation front, and may be linked to intraplate seismicity and active tectonic modification of the landscape.

Geomorphometric characterization and sediment connectivity of the middle Brahmaputra River basin

Knowledge of geomorphic characteristics and sediment connectivity is critical in understanding basin-scale surface processes that include steep mountainous and flat lowlands, particularly if the mid-basin and downstream areas are densely populated and disaster-prone. However, the lack of fluvial and sediment connectivity studies in downstream portions of large rivers of South Asia (particularly Bangladesh), where upper basin morphodynamics, hydrology, and sediment flux highly influence the repeated sediment disasters, limits our understanding of the large-scale fluvial geomorphic processes and basin-scale sustainable river management. Therefore, this article attempts to characterize the morphometric and topographic features along with the spatial sediment connectivity pattern of the middle Brahmaputra River basin (Teesta, Torsa, and Manas basins) covering ~75,000 km2 that influences the hydro-geomorphic response of the deltaic landscape of lowland Bangladesh. This work considers a set of morphometric and topographic parameters including the stream network, longitudinal profiles, stream power index (SPI), and topographic wetness index (TWI) for geomorphometric characterization. The linkage between the sediment sources to downstream areas also has been evaluated with the sediment connectivity (IC) index to understand better the sediment dynamics of the middle Brahmaputra River basin, draining towards lowland Bangladesh from the basin's upstream countries of India and Bhutan. The result of this study demonstrates a highly potential hydro-geomorphic response of the downstream areas attributed to steep topography, steep channel longitudinal profiles, high rainfall, and high sediment connectivity in upstream regions. However, the low topography, presence of anthropogenic stressors, almost flat longitudinal channel profiles with limited change in elevation, and lowered sediment connectivity potential in the mid-to-downstream areas depicts sensitivity to the depositional processes therein, impacting the basin-scale geomorphic connectivity from the upstream to the downstream region. These results will be the basic information for exploring the large-scale hydro-geomorphic response and structural sediment dynamics to understand the complex geomorphological processes in the South Asia region, where the fluvial sedimentation process is not fully understood with limited accessibility for field-based investigations.

Efficacy of Synthetic Sediment Graph Developed using Various Modified Time-Area Methods

Suspended sediment (SS) is an essential indicator for assessing watershed health. However, the temporal variation of SS, called sediment graph (SG) using readily available data, is not always considered, particularly in un-gauged watersheds, which are many in developing countries. Since field measurements of SS are time-consuming and costly, the synthetic SG seems to be a promising alternative. Therefore, it is essential to have reliable SS data for watershed management. This study aimed at simulating SGs through conceptual analysis of soil erosion and sediment yield at the watershed scale. To that end, soil erosion, sediment yield, and sediment routing were modeled using 38 storm events collected during 2011 and 2019 at the Galazchai Watershed in West Azerbaijan Province, Iran. Initially, the Time-Area Method (TAM) was applied, and then two strategies were considered to improve the TAM performance, including RUSLE and sediment delivery ratio (SDR) using gradient ratio and WaTEM/SEDEM methods. Comparing simulated SGs with recorded ones showed that the SDR-based method had the lowest relative error in time to peak and base time, but the peak value had the highest relative error. Results also showed that TAM developed using the spatially distributed travel time method had a better performance than the channel longitudinal profile method. Overall, TAM could not simulate the temporal variation of sediment and needs further research.

Multi‐Stage Growth in the North Margin of the Qinling Orogen, Central China, Revealed by Both Low‐Temperature Thermochronology and River Profile Inversion

AbstractThe Qinling orogen formed as a result of the convergence between North and South China Blocks and was reactivated by India‐Asia collision and/or Pacific subduction in the Cenozoic. We presented new apatite U‐Th/He age‐elevation profiles in the northern margin of the Qinling Mountains and observed Oligocene pulse of rapid exhumation. Thermal modeling on our data (by the HeFTy program) revealed another two early cooling episodes, that is, in the early Cretaceous and the early Cenozoic. Besides, increases in the mountain uplift rates since the late Miocene were retrieved from a linear inversion on modern channel longitudinal profiles. Combining previous studies, we proposed possible geodynamic regimes underlying the multi‐stage cooling and exhumation pattern in the north Qinling. We interpreted the early Cretaceous cooling as a result of the southward intracontinental subduction of North China Block beneath South China Block. The early Cenozoic exhumation was under the Pacific back‐arc extension background and might be influenced by a far‐filed response to Eurasian and Indian plate's collision. The Oligocene phase could be mostly driven by West Pacific plate subduction beneath East Asia. And, the mountain uplift since the late Miocene could be triggered by the growth and expansion of the North East Tibetan Plateau.

Landscape change in response to multiperiod glacial debris flows in Peilong catchment, southeastern Tibet

High-magnitude glacial debris flows in small basins in Himalayas have a significant impact on landscape. The Peilong catchment, a tributary of the Parlung Zangbo River in southeastern Tibet, was chosen as a case study of topographic response to multi-period glacial debris flows. There were no recorded debris flows in the catchment before 1983, but four large-scale glacial debris flow events with peak discharge up to 8195 m3/s blocked the river during 1983–1985 and in 2015. A combination of field survey, examination of historical records and interpretation of multi-period remote sensing images was used to assess triggering factors and geomorphic impact of the events. The results show that the debris flows during 1983 and 1985 may be attributed to seismic events in 1981 and 1982, while the event in 2015 resulted from large amount of landslide deposits caused by glacier retreat during 1993–2013 and high precipitation in 2015. In the upper-midstream broad valley, erosion and accumulation of the flows changed the channel morphology, resulting in course diversion. In the lower-midstream narrow valley, lateral erosion of debris flows induced a large number of landslides but had little impact on the channel longitudinal profile. The ability of massive glacial debris flows to change valley topography is more than ten times that of regular water flows. The landscape of the accumulation fan at the outlet of the valley is controlled by the interaction between the sediment transportation capacity of debris flows and erosional capacity of the main river. The flow transport capacity of the Peilong is greater than the delivery capacity of the Parlung Zangbo, resulting in continuous aggradation of the confluence zone.

A Geospatial Morphometric Analysis of Kulbera and Daurighara River Basins in Western Part of Purulia District of West Bengal, India

Morphometric analysis is used to understand the hydrological process and assessment of hydrological characteristics of surface water basin. In the present paper, an attempt has been made to study the detail morphometric characteristics of Kulbera and Daurighara river basin, which are tributaries of Subarnarekha River in Purulia district, West Bengal. For detailed study, SRTM data has been used for preparing digital elevation model (DEM), and Geographic Information System (GIS) has been used for the analysis of linear, areal, and relief aspects of the basins. Watershed boundary, flow accumulation, flow length, stream ordering have been prepared by using ILWIS 3.0. Different thematic maps i.e. elevation, geology, drainage density, slope and longitudinal profiles of river channels have been prepared by using QGIS 3.0 and MapInfo 10.0 GIS software. More than 58 morphometric parameters of all aspects of the basins have been computed. On the basis of morphometric analysis it has been argued that the erosional development has progressed well beyond maturity and that the drainage development is controlled by lithology. Besides,it can be concluded that this study will also be very useful for rain water harvesting planning and watershed management.

Adjustment of self‐formed bankfull channel geometry of meandering rivers: modelling study

ABSTRACTWe consider the evolution of the hydraulic geometry of sand‐bed meandering rivers. We study the difference between the timescale of longitudinal river profile adjustment and that of channel width and depth adjustment. We also study the effect of hydrological regime alteration on the evolution of bankfull channel geometry. To achieve this, a previously developed model for the spatiotemporal co‐evolution of bankfull channel characteristics, including bankfull discharge, bankfull width, bankfull depth and down‐channel bed slope, is used. In our modelling framework, flow variability is considered in terms of a specified flow duration curve. Taking advantage of this unique feature, we identify the flow range responsible for long‐term bankfull channel change within the specified flow duration curve. That is, the relative importance of extremely high short‐duration flows compared to moderately high longer duration flows is examined. The Minnesota River, MN, USA, an actively meandering sand‐bed stream, is selected for a case study. The longitudinal profile of the study reach has been in adjustment toward equilibrium since the end of the last glaciation, while its bankfull cross‐section is rapidly widening due to hydrological regime change in the last several decades. We use the model to demonstrate that the timescale for longitudinal channel profile adjustment is much greater than the timescale for cross‐sectional profile adjustment due to a lateral channel shift. We also show that hydrological regime shift is responsible for the recent rapid widening of the Minnesota River. Our analysis suggests that increases in the 5–25% exceedance flows play a more significant role in recent bankfull channel enlargement of the Minnesota River than increase in either the 0.1% exceedance flow or the 90% exceedance flow. © 2020 John Wiley & Sons, Ltd.

Study on channel-forming process and a mathematical model for conservation storage for long-term utilized reservoirs

ABSTRACT It was conventionally believed that a large multi-purpose reservoir would eventually be abandoned because of the sediment deposition caused by the long-term elevation of water level. The concept of the reservoir life was introduced based on this convention. The concept of long-term utilization of reservoirs was first proposed by some Chinese researchers, who also investigated the sedimentation process during the long-term operation of reservoirs and applied the long-term operation strategy in the planning and operation practices for large reservoirs. Based on the general law of reservoir sedimentation, the mechanism of the long-term utilization of reservoirs was discussed in this paper. The channel-forming process for long-term utilized reservoirs was investigated, the first and the second channel-forming discharges were introduced, and the formation of the relative equilibrium longitudinal channel profile and cross-section was analysed. A quantitative relation was derived for the conservation cross section and storage with respect to the sediment discharge period and the control water level. A mathematical model was developed for the long-term utilization of reservoirs. As a case study, this model was applied to the planning of the long-term utilization of the Three Gorges Reservoir.

Morphometric diversity of supply-limited and transport-limited river systems in the Himalayan foreland

The Indo-Gangetic basin exhibits highly diverse hydro-geomorphic settings that influence the hydrology, sediment production, and transport rates of the rivers draining this region, and this, in turn, is manifested in morphometric diversity of river systems. The rivers draining the western Gangetic plains (WGP) show incised channels attributable to high stream power and low sediment yield. In contrast, the rivers draining the Eastern Gangetic Plains (EGP) have formed aggradational landforms such as megafans due to low stream power and high sediment yield. For a better process understanding of the causal factors of such spatial inhomogeneities in a river basin, a morphometric characterization of its hinterland is necessary. In this work, a set of morphometric parameters such as stream network, longitudinal profile, and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form-process relationships in two contrasting basins, the upper Ganga basin (UGB) and the upper Kosi basin (UKB). The results of this study suggest that high sediment flux in the UKB is attributed to high rainfall, steep topography, unstable channel longitudinal profiles, and high sediment connectivity. A large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events. However, the UGB produces fewer sediments due to low rainfall, mild topography, stable channel longitudinal profile, and low sediment connectivity. Also, the presence of a major dam at Tehri further reduces the functional sediment connectivity in the Upper Ganga Basin.

Tectonic uplift of the northern Qinling Mountains (Central China) during the late Cenozoic: Evidence from DEM-based geomorphological analysis

The Qinling Mountains, which stretch from east to west in Central China, represent an important geological and geographical boundary between North China and South China. Because of the northeastward growth of the Tibetan Plateau since the late Cenozoic, the northern Qinling Mountains have been strongly reactivated and uplifted. To investigate the landscape response to the tectonic uplift, the geomorphic indices of the northern Qinling Mountains, including the hypsometry, mathematical function of the longitudinal profile, channel longitudinal profile, and steepness index were analyzed. The topographic analysis reveals that the landscape evolution of the Heihe River Basin is in a transient state. The upstream of the Heihe River Basin has undergone a long period of erosion and represents relict landscape. In contrast, the downstream represents adjusting landscape, which formed by river incision in response to the rapid uplift of the northern Qinling Mountains. This is a result of the extension of the Weihe Graben, which has formed due to the northeastward growth of the Tibetan Plateau during the late Cenozoic. The spatial distribution of the geomorphic indices reveals that the NE striking Taibai Fault has experienced strong tectonic activity since the late Cenozoic and is a secondary fault that accelerated the uplift rate of the northern Qinling Mountains. The tectonic stress due to the northeastward growth of the Tibetan Plateau has been transmitted to the northern Qinling Mountains along the Taibai Fault. Therefore, we proposed that the uplift of the northern Qinling Mountains is due to the combined effects of the Weihe Graben extension and Taibai Fault activity, forming the highest peak (Taibai Mountain) of the northern Qinling Mountains near the intersection of the Qinling Piedmont Fault and Taibai Fault.

Detection of channel-hillslope coupling along a tectonic gradient

Landscape morphology reflects the spatial and temporal history of erosion. Erosion in turn embodies the competition between tectonic and climatic processes. Quantitative analysis of topography can therefore reveal the driving tectonic conditions that have influenced landscape development, when combined with theoretical understanding of erosion processes. Recent developments in the automated analysis of high-resolution (<10 m) topographic data mean that integrated analysis of hillslope and channel topographic metrics can provide understanding of the transient response of landscapes to changing boundary conditions. We perform high-resolution topographic analysis of hillslopes and channels in small (<3 km2) catchments spanning an inferred uplift gradient along the Bolinas Ridge, California, USA, revealing tight coupling between channel steepness and hillslope metrics thought to be proxies for erosion rates. We find that the concavity of channel longitudinal profiles varies inversely with uplift rates, although drainage density increases with uplift rates. Both of these results can be explained by the contribution of mass wasting processes to valley formation in steeper (high uplift rate) landscapes. At the catchment scale, hillslope and channel metrics for erosion are correlated, hillslopes and channels steepen in concert, and hilltops (ridges) get sharper with increased uplift rate. This broad agreement suggests that hillslopes are responding to erosion rates in the channel network, which implies that landscape uplift is relatively stable and prolonged. Hillslope morphology deviates systematically from the steady-state predictions of established geomorphic transport laws, suggesting that hillslope adjustment is ongoing and that relief is growing.

Spatial distribution pattern of channel steepness index as evidence for differential rock uplift along the eastern Altun Shan on the northern Tibetan Plateau

Abstract The eastern Altun Shan is a crucial part of the Altun orogenic belt within the Tibetan Plateau. Study of the uplift rate and the related features in this area provides important clues for understanding the uplift mechanism of the Tibetan Plateau as a whole. As an important geomorphic element in landscape development, the fluvial system can record the relationship between tectonic activity and climatic change. In recent years, studies of the Channel Steepness Index Ksn, have been conducted by many researchers, using the geomorphological model of equilibrium channel longitudinal profiles, combining bedrock uplift and river incision and thus making it possible to extract rock uplift history from river profiles. This research show that regional rock uplift rate is a major factor in affecting the Ksn index. Regional tectonic activity and intensity, therefore, can be evaluated from variation in the Ksn index, which can provide a sensitive measure of uplift rate. In this paper, the Digital Elevation Map ‘ASTER GDEM’, with a spatial resolution of 30 m, was utilized as basic data, and combined with ArcGIS and MATLAB software to extract the Ksn index from the equilibrium channel longitudinal profiles model. Meanwhile, we employed statistical methods to analyze the Ksn index. Our results suggest that averaged Ksn indices, obtained from the subrange A，B，C，D, and E of the eastern Altun Shan (from west to east), are 70.93, 139.03, 108.85, 134.44 and 165.39, respectively. Further analysis implies that the variation in this index can be correlated with the distribution pattern of uplift rates within different regions. Its value increases gradually from west to east, reflecting regional uplift rate. Along the western section of the eastern Altun Shan, the uplift rate is slower and characterized by strike-slip movements, while its eastern part has uplifted faster and is controlled by thrust fault systems. Moreover, in contrast with the southern Altun Shan, the uplift rate of the northern part is high. These variations in uplift rate seem to be linked with “the imbricated thrusting transformation-limited extrusion model” of the Tibetan Plateau. Our results can be correlated with previous work on the active characteristics along the eastern Altyn Tagh Fault (ATF).

Self‐Affine Fractal Spatial and Temporal Variability of the San Pedro River, Southern Arizona

AbstractPrevailing mathematical models of alluvial channel evolution generate smooth, idealized longitudinal profiles. Alluvial channel longitudinal profiles in nature, however, have substantial multiscale spatial and temporal variability. In this paper we quantify the spatial and temporal hydrologic and geomorphic variability of a 90‐km‐long reach of the San Pedro River (San Pedro River) in southeastern Arizona and compare that variability to numerical models designed specifically to honor the spatial and temporal variability of alluvial channel systems in nature. A key motivation of this work is the power law frequency size distribution of wet and dry reaches observed in the San Pedro River. We demonstrate that such a distribution is consistent with self‐affine fractal variations of the depth to bedrock and the channel longitudinal profile. At large spatial scales, spatial variations in depth to bedrock control the accommodation space for groundwater, which, in turn, controls spatial variations in surface water discharge. At small spatial scales, the longitudinal profile controls spatial variations in surface water discharge by changing the distance between the channel bed and the water table. These results underscore the complex spatiotemporal behavior of dryland alluvial rivers and the tight coupling that is possible between hydrologic and geomorphic processes in such systems.

A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream

A study approach is developed to assess the longitudinal channel slope under the equilibrium condition as well as the transient evolution of a mixed alluvial-soft-bedrock stream. Both the historical field data and 2D mobile-bed numerical modeling are adopted. The proposed approach is applied to a 14 km reach downstream of the Ji-Ji Weir, Chuo-Shui River, Taiwan, where continuous maintenance works have been carried out to stabilize this reach. In this study, the temporal evolution of the longitudinal channel profile is assessed numerically with three spatial scales: The large (the entire study reach), the medium (four sub-reaches), and the local (cross-sections) scale. The large scale analysis is the approach for purely alluvial streams and is shown to be difficult to use to characterize mixed alluvial-bedrock streams. The local scale analysis shows that the soft-bedrock incision has a widely fluctuating slope, reflecting the compound environmental forcing and complex riverbed setting. With the medium scale analysis, the longitudinal channel profile is found to follow a predictive trend if the reach is partitioned into four distinctive sub-reaches. Characteristics of the dynamic channel slope evolution in different spatial scales are computed and presented. The study results can be used to select the proper locations and types of the engineering stabilizing structures in a mixed alluvial and soft bedrock stream