Graphical methods of river profile analysis to unravel drainage area change,uplift and erodibility contrasts in the Central Range of Taiwan

To reveal river channel steepness patterns and variance in settings with significant variation in rock uplift rate, rock erodibility and moving water divides, we present a series of graphical methods to interpret channel profiles. To complement Cartesian χ plots, longitudinal profiles and mapping methods, we introduce a new method based on a radial coordinate system. We map each basin onto polar coordinates in which the radial dimension is χ and the azimuthal coordinate, ?, is calculated with an increment (Δ?) scaled to the distance to neighboring channel heads. The elevation is contoured on this mapping. Average channel steepness is estimated by fitting a conical surface to the elevation. The graph simplifies the comparison of χ and elevation between channels that share a divide, and helps identify spatial changes in drainage area and patterns of erodibility. We apply this approach to derive the uplift pattern in the eastern and southern Central Range of Taiwan, where the high tectonic convergence and uplift rates combined with sub‐tropical climate and frequent typhoons results in high exhumation rate, and well‐developed, detachment‐limited river networks. Additionally, the tectonic activity leads to drainage basin reorganization. We identify examples of divide migration, discrete river capture as well as anomalous steepness that we attribute to local variability in rock erodibility. Estimated basin‐average steepness values show the highest and a near constant value from Hsinwulu basin to Liwu basin in the center of the Island. To the north and south of this region, the values gradually decrease. These estimates show good correlation with the topography of the Central Range and erosion rates derived from in situ ¹⁰Be concentrations in river‐borne quartz. We conclude that the basin steepness reflects systematic differences in rock uplift rate and erosion rate. Copyright © 2016 John Wiley & Sons, Ltd.     

ACTIVITY CHARACTERISTICS OF THE HUASHAN PIEDMONT NORMAL FAULT: INSIGHTS FROM FLUVIAL GEOMORPHIC PARAMETERS

The Huashan piedmont fault, forming a part of the southern margin of the Weihe graben, is one of the important normal faults that control the subsidence of the intracontinental rift. Developing on the footwall of the fault, the Huashan block has experienced rapid cooling during the Cenozoic, especially since the early-middle Miocene. Mountain exhumation causes and transports a great amount of sediments to the adjacent hanging wall, setting a typical case of mountain-basin coupling system. Studies on active tectonics, historical and paleo earthquakes and field investigations reveal that the middle section(Huaxian-Huayin)of the fault is much more active than the west(Lantian-Huaxian)and east(Huayin-Lingbao)sections.
We extracted channel profiles of rivers that originate from the main water divide of the northern flank of the Huashan Mountain. Based on the method of slope-area analysis and the integral approach, we identified knickpoints, calculated channel concavity and steepness indices, and constructed paleo river profiles. Of most rivers, the concavities are within a relatively narrow range of 0.3~0.6, with no obvious correlation with tectonics. However, channel steepness and knickpoint distribution vary spatially. In the east section, rivers are under steady-state with smooth, concave-up channels and lower steepness((104±30)m^0.9). In the other two sections, rivers are mainly under transient state with slope-break knickpoints. For the channel segments below knickpoints, steepness indices are much higher in the middle section((230±92)m^0.9)than in the west((152±53)m^0.9). Thus, the variance of fault activity can be reflected by channel steepness pattern. Above the knickpoints, channel steepness indices are much lower(middle(103±23)m^0.9, west(60±14)m^0.9). What's more, we found a statistically significant power-law scaling between knickpoint retreat distance and catchment drainage area. Thus, we attributed these knickpoints to be the results of recent rapid uplift of the Huashan block. The relief of paleo channels(middle(1000±153)m, west(751±170)m)accounts for~60%~80% of the relief of modern rivers(middle(1323±249)m, west(1057±231)m), which means that ~20%~40% of modern channel relief was caused by the episode of the rapid uplift. Assuming a balance between the rates of rock uplift and downstream river incision, a power-law function between uplift rates and channel steepness can be derived. According to the fault throw rates of the middle section 1.5~3mm/a(since late Pleistocene), we constrained slope exponent n~0.5 and channel erodibility K~1.5×10^-4m^0.55/a. Combining the knickpoint age formula, we estimated that the rapid mountain uplift/fault throw began at ~(0.55±0.25)Ma BP. Therefore, the middle of the Huashan piedmont fault is more active than the west and east sections. The fast fault throw of the west and middle sections since the middle Pleistocene has caused rapid mountain uplift and high topographic relief.     

GEOMORPHIC FEATURES OF THE SHULE RIVER DRAINAGE BASIN IN QILIANSHAN AND ITS INSIGHT INTO TECTONIC IMPLICATIONS

Because of the strong uplift of the Qilian Shan since late Cenozoic,the drainage basins that are derived from the mountains have undergone strong tectonic deformation.So the typical geomorphology characteristics of these drainage basins may indicate the strong tectonic movement in the region.For example,the Shule River drainage basin,which originates from the western part of the Qilian Shan owns unique geomorphology characteristics which may indicate the neotectonic movement. Stream networks of the Shule drainage basin extracted from the DEM data based on GIS spatial analysis technology are graded into five levels using Strahler classification method.Four sub-catchments,numbered 1,2,3 and 4 are chosen for detailed analysis.Furthermore,the four sub-catchments,the hypsometric integral curves,Hack profiles,SL index and average slope of the Shule drainage basin are determined by GIS tools.In addition,we analyzed the slope spectrum of the Shule drainage basin. The average elevation of the Shule drainage basin is very high,however,the slope of the drainage basin is very low,the gentle slope occupies so large area proportion that the slope spectrum shows a unimodal pattern and a peak value is in low slope region (0°~5°),so tectonic movement has a strong influence on the drainage basin.Under the intensive impact of the tectonic movement of the active fault and regional uplift,the hypsometric integral curve is sigmoid,revealing that the Shule drainage basin is in the mature stage.The Hack profile is on a convex,the longitudinal profile is best fitted by linear fitting and the abnormal data of the SL index of the Shule River has a good fit with the section through which the active fault traverses,that means the tectonic movement of the active fault has strong influence on the river's SL index.It is worth noting that lithologic factors also have great impact on the river geomorphology in some sections. According to the above analysis,we recognize that in the interior of active orogen,the evolution of river geomorphology usually is influenced by tectonic movement and reveals the regional neotectonics in turn.     

GEOMORPHOLOGICAL CHARACTERISTICS OF DAQINGSHAN DRAINAGE AREA IN THE NORTHERN MARGIN OF HETAO BASIN

The Daqingshan Fault located in the northern margin of the Hetao Basin has experienced intensive activity since late Quaternary, which is of great significance to the molding of the present geomorphology. Since basin geomorphological factors can be used to reflect regional geomorphological type and development characteristics, the use of typical geomorphology characteristics indexes may reveal the main factors that control the formation of topography. In recent years, more successful research experience has been accumulated by using hypsometric integral(HI) values and channel steepness index(k_sn)to quantitatively obtain geomorphic parameters to reveal regional tectonic uplift information. The rate of bedrock uplifting can be reflected by channel steepness index, the region with steep gradient has high rate of bedrock uplifting, while the region with slower slope has low rate of bedrock uplifting. The tectonic uplift can shape the geomorphic characteristics by changing the elevation fluctuation of mountains in study area, and then affect the hypsometric integral values distribution trend, thus, the HI value can be used to reflect the intensity of regional tectonic activity, with obvious indicating effect. Knick point can be formed by fault activity, and the information of knick point and its continuous migration to upstream can be recorded along the longitudinal profile of stream. Therefore, it is possible and feasible to obtain the information of tectonic activity from the geomorphic characteristics of Daqinshan area. The research on the quantitative analysis of regional large-scale tectonic activities in the Daqingshan area of the Yellow River in the Hetao Basin is still deficient so far. Taking this area as an example, based on the method of hypsometric integral(HI) and channel steepness index(k_sn), we use the DEM data with 30m resolution and GIS spatial analysis technology to extract the networks of drainage system and seven sub-basins. Then, we calculate the hypsometric integral(HI) values of each sub-basin and fit its spatial distribution characteristics. Finally, we obtain the values of channel steepness index and its fitting spatial distribution characteristics based on the improved Chi-plot bedrock analysis method. Combining the extraction results of geomorphic parameters with the characteristics of fault activity, we attempt to explore the characteristics of drainage system development and the response of stream profile and geomorphology to tectonic activities in the Daqingshan section of the Yellow River Basin. The results show that the values of the hypsometric integral in the Daqingshan drainage area are medium, between 0.5~0.6, and the Strahler curve of each tributary is S-shaped, suggesting that the geomorphological development of the Daqingshan area is in its prime, and the tectonic activity and erosion is strong. Continuous low HI value is found in the tectonic subsidence area on the hanging wall of the Daqingshan Fault. The distribution characteristics of the HI value reveal that the Daqingshan Fault controls the geomorphic difference between basin and mountain. Longitudinal profiles of the river reveal the existence of many knick points. The steepness index of river distributes in high value along the trend of mountain which lies in the tectonic uplift area on the footwall of the Daqingshan Fault. It reflects that the bedrock uplift rate of Daqingshan area is faster. The distribution characteristics of the channel steepness index show that the uplift amplitude of Daqingshan area is strong and the bedrock is rapidly uplifted, which is significantly different from the subsidence amplitude in the depression basin at the south margin of the fault, indicating that the main power source controlling the basin mountain differential movement comes from Daqingshan Fault. Based on the comparison and analysis on tectonic, lithology and climate, there is no obvious corresponding relationship between the difference of rock erosion resistance and the change of geomorphic parameters, and the precipitation has little effect on the geomorphic transformation of Daqingshan area, and its contribution to the geomorphic development is limited. Thus, we think the lithology and rainfall conditions have limited impact on the hypsometric integral, longitudinal profiles of the river and channel steepness index. Lithology maybe has some influences on the channel knick points, while tectonic activity of piedmont faults is the main controlling factor that causes the unbalanced characteristics of the longitudinal profile of the channel and plays a crucial role in the development of the channel knick points. So, tectonic activity of the Daqingshan Fault is the main factor controlling the uplift and geomorphic evolution of the Daqingshan area.     

Modeling of wind gap formation and development of sedimentary basins during fold growth: application to the Zagros Fold Belt,Iran

Mountain building and landscape evolution are controlled by interactions between river dynamics and tectonic forces. Such interactions have been extensively studied, however a quantitative evaluation of tectonic/geomorphic feedbacks, which is imperative for understanding sediments routing within orogens and fold‐and‐thrust belts, remains to be undertaken. Here, we employ numerical simulations to assess the conditions of uplift and river incision necessary to deflect an antecedent drainage network during the growth of one, or several, folds. We propose that a partitioning of the river network into internal (endorheic) and longitudinal drainage arises as a result of lithological differences within the deforming crustal sedimentary cover. Using examples from the Zagros Fold Belt (ZFB), we show that drainage patterns can be linked to the non‐dimensional incision ratio R between successive lithological layers, corresponding to the ratio between their relative erodibilities or incision coefficients. Transverse drainage networks develop for uplift rates smaller than 0.8 mm yr^?1 and low incision ratios (?10 < R < 10). Intermediate drainage networks are obtained for uplift rates up to 2 mm yr^?1 and large incision ratios (R > 20). Parallel drainage networks and the formation of sedimentary basins occur for large values of incision ratio (R > 20) and uplift rates between 1 and 2 mm yr^?1. These results have implications for predicting the distribution of sediment depocenters in fold‐and‐thrust belts, which can be of direct economic interest for hydrocarbon exploration. They also put better constraints on the fluvial and geomorphic responses to fold growth induced by crustal‐scale tectonics. Copyright © 2016 John Wiley & Sons, Ltd.     

RESPONSES OF THE S-A DOUBLE-LOG GRAPH,CONCAVITY INDEX AND STEEPNESS INDEX OF CHANNELS TO THE TECTO-NIC MOVEMENT OF THE HUOSHAN PIEDMONT FAULT

The Huoshan piedmont fault is a small watershed region in Shanxi Province. We utilized the high-resolution DEM data and the stream-power incision model which describes the relationship between the tectonic uplift and fluvial incision to analyze the S-A double-log graph, concavity index (θ)and steepness index (logk_s) of the 64 channels across this fault and discuss their responses to the tectonic movement of the fault. The results show that (1)the S-A double-log graphs all exhibit an obvious convex form, which is the direct expression of the response to the situation that the bedrock uplift rate is higher than the fluvial incision rate. (2)All of the concavity index (θ)values of 64 channels are lower than 0.35 with an average value of 0.223, much lower than the empirical value (0.49)of the rivers in steady state. These low values are the quantitative reflections of the channels' slightly concave profiles. Meanwhile they imply that these channels across the fault are very young. There is no enough time for them to adjust the profiles through the fluvial incision to the steady state because of the fault's frequent and strong tectonic movements. (3)The steepness index values of the channels located in the Laoyeding Mt. are highest, while they are lower in the northern and southern mountains. Moreover, the steepness index values of the channels in the northern mountains, on average, are higher than those of the channels in the southern mountains. To a certain extent, this distribution of the steepness index corresponds to the difference in the uplift rates of the Huoshan piedmont fault. It means that the uplift rate of the middle fault segment in the Laoyeding Mt. is highest, and the uplift rate of the northern segment is higher than that of the southern segment.     

DEVELOPMENT OF TRANSVERSE DRANAGES AND FORMATION OF WIND GAPS ON ACTIVELY GROWING FOLD: REVIEW AND CASE STUDY

The most compelling phenomena for transverse drainage in active fold belt are lateral diversion of channels and development of water/wind gaps. This phenomenon is the result of competition between uplift and erosion, which is controlled by fault vertical/lateral propagation and segment linkage, fault geometry, climate condition and lithology. Previous studies found that the higher the uplift rate is, the greater number of wind gaps form, and the variation of the uplift rate is also critical to the sustainability of transverse rivers. Lateral propagation and linkage of several separate folds in fold-and-thrust belts will lead to defeat of streams and diversion into a trunk drainage; if the trunk is still unable to keep pace with uplift, water gap will be abandoned and left as a wind gap. For lateral propagation of an anticline associated with development of tear faults, the locations of wind/water gaps are likely to coincide with the trace of tear fault and it's not quite clear about the relation between tear faulting and stream deflection. Nonzero dip of the underlying detachment induces a lateral surface slope in the direction of fault propagation, which in turn makes rivers deflection more efficient. Climate and rock erodibility control the water/sediment discharge, and further influence river transport/incision capacity. The changing climate and rock erodibility conditions enable river to abandon the current waterway to create a wind gap unless they could down-cut through a growing fold. However, the role of climate cycle in the formation of wind gap is still controversial. In addition, wind gaps are commonly developed along the divides where parts of longitudinal river have been captured by transverse catchments. Generally, the development of transverse drainages and the formation of wind gaps in nature are result from a combination of tectonic and fluvial process. The wind gap pattern and transverse drainage evolution in fold-and-thrust belts contain plenty of information on fault growth, interaction between tectonic uplift and fluvial erosion, and development of sedimentary basin. Such researches have significant implications in geomorphology, seismic hazard assessment and hydrocarbon exploration. However, there are still many knowledge gaps on the study of transverse river evolution in active fold areas. First, adequate chronology and geomorphic/strata mark to quantify fold growth and erosion is commonly not available, which leads to a poorly constrained rate in both river incision and lateral propagation of growing folds. In addition, more geological and geomorphological processes could influence the evolution of transverse drainages. For examples, (1)during the formation of a young range or anticline, the mechanism of fault-related folding may change over time, e.g. from fault-propagation folding to surface breaking; (2)Besides the knickpoint retreat in downstream, efficient lateral planation and downstream sweep erosion are also important in understanding the erosion of folds by rivers flowing through it. These processes make the development of transverse drainage across folds more complex and should be considered in more comprehensive models. There are lots of rivers originating from the Tibetan plateau and cutting through young surrounding mountains. These surrounding mountains, such as Qilian Mountains, Tianshan Mountains and Longmen Mountains, are ideal areas for the study of transverse river evolution and wind gap formation. In the end, combining with the geological and geomorphological features of the Heli Shan-Jintanan Shan, north of Hexi Corridor, we propose that the Heihe River has experienced deflection, beveling and incision since Mid Pleistocene. These processes have led to 1)the formation of a wind gap on the western Heli Shan, 2)a layer of fluvial gravels from the Qilian Shan preserved on the top surface of the Jintanan Shan, and overlying angular unconformity upon older strata, and 3)the incision of the Heihe River to form the Zhengyi Gorge through the linked structure between Heli Shan and Jintanan Shan. Thus, we propose a general model for the development of transverse drainages in the central Hexi Corridor: deflection-beveling-incision.     

Implications of the saltation–abrasion bedrock incision model for steady‐state river longitudinal profile relief and concavity

The saltation–abrasion model predicts rates of river incision into bedrock as an explicit function of sediment supply, grain size, boundary shear stress and rock strength. Here we use this experimentally calibrated model to explore the controls on river longitudinal profile concavity and relief for the simple but illustrative case of steady‐state topography. Over a wide range of rock uplift rates we find a characteristic downstream trend, in which upstream reaches are close to the threshold of sediment motion with large extents of bedrock exposure in the channel bed, while downstream reaches have higher excess shear stresses and lesser extents of bedrock exposure. Profile concavity is most sensitive to spatial gradients in runoff and the rate of downstream sediment fining. Concavity is also sensitive to the supply rate of coarse sediment, which varies with rock uplift rate and with the fraction of the total sediment load in the bedload size class. Variations in rock strength have little influence on profile concavity. Profile relief is most sensitive to grain size and amount of runoff. Rock uplift rate and rock strength influence relief most strongly for high rates of rock uplift. Analysis of potential covariation of grain size with rock uplift rate and rock strength suggests that the influence of these variables on profile form could occur in large part through their influence on grain size. Similarly, covariation between grain size and the fraction of sediment load in the bedload size class provides another indirect avenue for rock uplift and strength to influence profile form. Copyright © 2008 John Wiley & Sons, Ltd.     

Regional analysis of bedrock stream long profiles: evaluation of Hack's SL form,and formulation and assessment of an alternative (the DS form)

The equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones, and in continental margin and other intraplate settings, as well as other base‐level changes such as due to sealevel fluctuations. The Hack SL form of the long profile, which describes a straight line on a log–normal plot of elevation (normal) versus distance (logarithmic), is the equilibrium long profile form that has been most widely used in such studies; slope–area analysis has also been used in recent years. We show that the SL form is a special case of a more general form of the equilibrium long profile (here called the DS form) that can be derived from the power relationship between stream discharge and downstream distance, and the dependence of stream incision on stream power. The DS form provides a better fit than the SL form to river long profiles in an intraplate setting in southeastern Australia experiencing low rates of denudation and mild surface uplift. We conclude that, if an a priori form of the long profile is to be used for investigations of regional landscape history, the DS form is preferable. In particular, the DS form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance (parallel shift in the DS plot) to be distinguished from disequilibrium steepening due to long profile rejuvenation (disordered outliers on the DS plot). Slope–area analysis and the slope–distance (DS) approach outlined here are complementary approaches, reflecting the close relationship between downstream distance and downstream catchment area. Copyright © 2006 John Wiley & Sons, Ltd.     

The effects of deforestation on slope and channel evolution in the tectonically active Darjeeling Himalaya

The main indicators of Quaternary tectonic uplift are the young mountain slopes of the Darjeeling Himalaya, rising straight above the Ganga–Brahmaputra foredeep, fragments of uplifted river terraces and fresh fault scarps. Evidence for the continuation of the uplift includes downcutting of the Tista and other straight rivers in the bedrock, continuing aggradation in the plains and overriding of the metamorphic rocks on the alluvia. Owing to deforestation and extensive land use, the earlier natural tendency of a dominance of channel incision over slope degradation has changed to prevailing aggradation, even in steep valley reaches, caused by intensive slope mass movements and the overloading of the mountain creeks. Aggradation progresses upstream along the rivers dissecting the mountain front.     

Network‐scale dynamics of grain‐size sorting: implications for downstream fining,stream‐profile concavity,and drainage basin morphology

We explore the link between channel‐bed texture and river basin concavity in equilibrium catchments using a numerical landscape evolution model. Theory from homogeneous sediment transport predicts that river basin concavity directly increases with bed sediment size. If the effective grain size on a river bed governs its concavity, then natural phenomena such as grain‐size sorting and channel armouring should be linked to concavity. We examine this hypothesis by allowing the bed sediment texture to evolve in a transport‐limited regime using a two grain‐size mixture of sand and gravel. Downstream ?ning through selective particle erosion is produced in equilibrium. As the channel‐bed texture adjusts downstream so does the local slope. Our model predicts that it is not the texture of the original sediment mixture that governs basin concavity. Rather, concavity is linked to the texture of the sorted surface layer. Two different textural regimes are produced in the experiments: a transitional regime where the mobility of sand and gravel changes with channel‐bed texture, and a sand‐dominated region where the mobility of sand and gravel is constant. The concavity of these regions varies depending on the median gravel‐ or sand‐grain size, erosion rate, and precipitation rate. The results highlight the importance of adjustments in both surface texture and slope in natural rivers in response to changes in ?uvial and sediment inputs throughout a drainage network. This adjustment can only be captured numerically using multiple grain sizes or empirical downstream ?ning rules. Copyright © 2004 John Wiley & Sons, Ltd.     

Adjustment processes of mountainous rivers affected by tilting uplift: Laboratory experiments and a case study of Yakushima Island,Japan

Mountainous river basins are one of the main sources of sediment. Over long time scales, sediment production is sustained by the persistent dissection of river basins, which is promoted by tectonic activity. The response or adjustment of rivers to forcing factors such as uplift is based on the concept of the graded river and a feedback mechanism between the incision and uplift. Although the development of graded rivers under natural circumstances has been discussed for a long time, knowledge about the transition of river basins under heterogeneous uplift is not enough. To understand the development of a river basin with a non‐uniform uplift rate, two simple cases are examined: landward and seaward tilting uplift, where the uplift rate varies linearly in space. For our study, laboratory experiments were conducted and the results were compared with those of natural river basins; two river basins in Yakushima Island were selected for this purpose. In both the laboratory and Yakushima, the longitudinal profile of the river basin under landward‐tilting uplift has a convex‐up zone and a specific knickpoint is formed at the upstream end of this zone. This knickpoint is inactive with respect to migration and incision owing to the insufficient cumulative uplift to the equilibrium state. It was also observed in both the experimental and natural cases that the profile of the river basin under seaward tilting is unlikely to have such a convex‐up zone in the long term, and will instead have a smooth concave profile. Therefore, the spatiotemporal pattern of dissection differs depending on the type of tilting uplift, which suggests that sediment production also varies in time and space according to the type of uplift.     

Hillslope response to knickpoint migration in the Southern Appalachians: implications for the evolution of post‐orogenic landscapes

The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post‐orogenic landscape remain enigmatic. The non‐glaciated Cullasaja River basin of south‐western North Carolina, with uniform lithology, frequent debris flows, and the availability of high‐resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post‐orogenic landscape through the lens of hillslope–channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km², a conservative estimate of the transition from fluvial to debris‐flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint‐driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area–elevation and slope distributions is presented that may be representative of post‐orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel–hillslope coupling is an important factor in tectonically‐inactive (i.e. post‐orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering‐limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial and temporal controls on historical channel responses – study of an atypical case: Someşu Mic River,Romania

In this paper the spatial and temporal responses of the Some?u Mic River (Romania) to natural and anthropogenic controls over the past 150 years are analysed, based on a series of morphometric parameters extracted from five successive sets of topographic maps and one set of orthophotos. Prior to the intensive hydrotechnical interventions of the last four decades, the river was characterized by a complex alternation of different channel types, resulting in a mixture of alluvial and mixed sinuous – meandering – sinuous anabranched – meandering anabranched reaches, each a few hundred metres to a few kilometres long. The main cause for this spatial behaviour was the local geology. Its effects were intensified by a larger scale slope, slightly higher than along a longitudinal profile with normal concavity, as a consequence of the presence of a 400 m elevation knick‐point located in the catchment area. A generalized maintenance of river in the floodplain perimeter during the entire interval of study (centennial scale), with local planform adjustments and lack of median scale avulsion in lateral tilting areas and along the anabranched reaches, channel lengthening and meander development during hydrological stable periods and channel shortening and increasing of natural cutoffs during periods with higher incidence of floods (decadal scale), and the incapacity of local morphologic changes resulted from human interventions to completely counterbalance general trends (decadal scale), supports the idea of decreasing the amplitude and frequency of important floods, after the end of the Little Ice Age. Channel metamorphosis by canalization, diminishing/elimination of overflows and medium‐scale avulsions by changes in flow regimes (dams) and the presence of dykes in the floodplain perimeter, channel narrowing (43%) and incision (at least after 1945) downstream from dams, and probably because of in‐channel gravel mining are the main anthropically induced changes along the Some?u Mic River. Even if human impact is important, both at the drainage basin scale and along the Some?u Mic River, it has only local impacts, subordinated to climate. The low level of human impact on this river could be the consequence of the higher general slope downstream from 400 m elevation knick‐point, which probably forces the positioning of its effects under an important internal threshold of the fluvial system. This boundary condition defines Some?u Mic River as an atypical river. This study supports the idea that climate has a more important role in the post‐Little Ice Age (LIA) rivers' behaviour than currently accepted. Copyright © 2011 John Wiley & Sons, Ltd.     

GEOMORPHIC FEATURES OF THE HEIHE RIVER DRAINAGE BASIN IN WESTERN QILIAN SHAN-HEXI CORRIDOR AND ITS TECTONIC IMPLICATIONS

Using quantitative geomorphic factors for regional active tectonic evolution is becoming more and more popular. Qilian Mountains-Hexi Corridor which locates in the northern edge of Qinghai-Tibet plateau is the most leading edge of the plateau's northward extension. The uplift rate of all segments and the intensity of influence from tectonic activity are the important evidences to understand the uplift and extension of the plateau. Heihe River Basin is located at the northern piedmont of the western segment of Qilian Mountains, the development of the rivers is influenced by the tectonic activity of the Qilian Mountains, and the unique river morphology is important carriers of the regional tectonic uplift. Geomorphologic indexes such as hypsometric integral, geomorphologic comentropy and river longitudinal profiles were extracted by GIS tools with free access to the Shuttle Radar Topography Mission(SRTM)DEMs, and according to the different expression of the geomorphological indexes in the Heihe River Basin, we divided the drainage basin into two parts and further compared them to each other. Recent studies reveal that obvious differences exist in the landscape factors(hypsometric integral, geomorphology entropy and river profiles)in the east and west part of the Heihe Basin. The structural intensity of the west part is stronger than that of the east, for example, in areas above the main planation surface on the western part, the average HI value is 0.337 8, and on the eastern part the HI value is 0.355. Accordingly, areas under the main planation surface are just on the contrary, indicating different structural strength on both sides. Similar phenomenon exists in the whole drainage basins. Furthermore, by comparing the fitting river profiles with the real river profiles, differential uplift is derived, which indicates a difference between west and east(with 754m on the western part and 219m on the east). Comprehensive comparison and analysis show that the lithologic factors and precipitation conditions are less influencing on the geomorphic factors of the study area, and the tectonic activities, indicated by field investigation and GPS inversion, are the most important element for geomorphic evolution and development. The variation of the geomorphologic indexes indicates different tectonic strength derived from regional structures of the Qilian Shan.     

An integral approach to bedrock river profile analysis

Bedrock river profiles are often interpreted with the aid of slope–area analysis, but noisy topographic data make such interpretations challenging. We present an alternative approach based on an integration of the steady‐state form of the stream power equation. The main component of this approach is a transformation of the horizontal coordinate that converts a steady‐state river profile into a straight line with a slope that is simply related to the ratio of the uplift rate to the erodibility. The transformed profiles, called chi plots, have other useful properties, including co‐linearity of steady‐state tributaries with their main stem and the ease of identifying transient erosional signals. We illustrate these applications with analyses of river profiles extracted from digital topographic datasets. Copyright © 2012 John Wiley & Sons, Ltd.     

Quaternary drainage network reorganization in the Colombian Eastern Cordillera plateau

Dramatic drainage reorganization from initial longitudinal to transversal domains has occurred in the Eastern Cordillera of Colombia. We perform a regional analysis of drainage basin geometry and transformed river profiles based on the integral form of the slope-area scaling, to investigate the dynamic state of drainage networks and to predict the degree of drainage reorganization in this region. We propose a new model of drainage rearrangement for the Eastern Cordillera, based on the analyses of knickpoint distribution, normalized river profiles, landforms characteristic of river capture, erosion rates and palaeodrainage data. We establish that the oldest longitudinal basin captured by the Magdalena River network was the Suárez Basin at ≈409 ka, inferring the timing of abandonment of a river terrace using in situ produced cosmogenic beryllium-10 (¹⁰Be) depth profiles and providing a first estimation of incision rate of 0.07 mm/yr. We integrate published geochronologic data and interpret the last capture of the Sabana de Bogotá, providing a minimum age of the basin opening to the Magdalena drainage at ≈38 ka. Our results suggest that the Magdalena basin Increased its drainage area by integrating the closed basins from the western flank of the Eastern Cordillera. Our study also suggests that the Magdalena basin is an aggressor compared to the basins located in the eastern flank of the orogen and provides a framework for examining drainage reorganization within the Eastern Cordillera and in similar orogenic settings. The results improve our understanding of headward integration of closed basins across orogenic plateaux. © 2020 John Wiley & Sons, Ltd.     

Interaction between the controls on fluvial system development: tectonics,climate, base level and river capture – Rio Alias,Southeast Spain

Fluvial systems in uplifting terrain respond to tectonic, climatic, eustatic and local base‐level controls modified by specific local factors, such as river capture. The Rio Alias in southeast Spain is an ephemeral, transverse‐to‐structure fluvial system. The river drains two interconnected Neogene sedimentary basins, the Sorbas and Almeria basins, and crosses two major geological structures, the Sierras de Alhamilla/Cabrera and the Carboneras Fault Zone. Regional epeirogenic uplift resulted in sustained fluvial incision during the Quaternary, punctuated by major climatically driven periods of aggradation and dissection, which created a suite of five river terraces. The river terrace sequence was radically modified in the late Pleistocene by a major river capture (itself a response to regional tectonics), localized tectonic activity and eustatic base‐level change. The Rio Alias is defined by four reaches; within each the climatically‐generated, region‐wide, fluvial response was modified by tectonics, base‐level change or river capture to varying degrees. In the upper part of the basin (Lucainena reach), climate was the dominant control on river development, with limited modification of the sequence by uplift of the Sierra Alhamilla and local drainage reorganization by a local river capture. Downstream of the Sierra Alhamilla in the Polopus reach, the climatic signal is dominant, but its expression is radically modified by the response to a major river capture whereby the Alias system lost up to 70% of its pre‐capture drainage area. In the reach adjacent to the Carboneras Fault Zone (Argamason reach), modification of the terrace sequence by local tectonic activity and a resultant local base‐level fall led to a major local incisional event (propagating c. 3–4 km upstream from the area of tectonic disturbance). At the seaward end of the system (El Saltador reach) Quaternary sea‐level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles. The signals generated by regional tectonics and the Quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics, river capture and sea‐level change are spatially restricted and define the four reaches. The connectivity of the system from the headwaters to the coast decreased through time as incision progressed, resulting in changes in local coupling characteristics. Copyright © 2012 John Wiley & Sons, Ltd.     

Controls on knickpoint migration in a drainage network of the moderately uplifted Ardennes Plateau,Western Europe

Much research has been devoted to the development of numerical models of river incision. In settings where bedrock channel erosion prevails, numerous studies have used field data to calibrate the widely acknowledged stream power model of incision and to discuss the impact of variables that do not appear explicitly in the model's simplest form. However, most studies have been conducted in areas of active tectonics, displaying a clear geomorphic response to the tectonic signal. Here, we analyze the traces left in the drainage network 0.7 My after the Ardennes region (western Europe) underwent a moderate 100–150 m uplift. We identify a set of knickpoints that have traveled far upstream in the Ourthe catchment, following this tectonic perturbation. Using a misfit function based on time residuals, our best fit of the stream power model parameters yields m = 0.75 and K = 4.63 × 10^‐8 m^‐0.5y^‐1. Linear regression of the model time residuals against quantitative expressions of bedrock resistance to erosion shows that this variable does not correlate significantly with the residuals. By contrast, proxies for position in the drainage system prove to be able to explain 76% of the residual variance. High time residuals correlate with knickpoint position in small tributaries located in the downstream part of the Ourthe catchment, where some threshold was reached very early in the catchment's incision history. Removing the knickpoints stopped at such thresholds from the data set, we calculate an improved m = 0.68 and derive a scaling exponent of channel width against drainage area of 0.32, consistent with the average value compiled by Lague for steady state incising bedrock rivers. Copyright © 2014 John Wiley & Sons, Ltd.