River Channel Incision Research Articles

Impact Of Channel Incision On Floods: A Case Study In The South-Eastern Subcarpathians (Romania)

Despite numerous researches on river channel incision, there are fewer studies on the impact of channel adjustments on floods. This paper aims to investigate channel adjustments and to analyse their impact on the frequency of floods by estimating the return period of the bankfull discharge of the Prahova River in the South-Eastern Subcarpathians (Romania). The study is based on the analysis of the maximum annual discharges and cross-section profiles of the Prahova River at Câmpina gauging station (1976–2015). To estimate the return period of the bankfull discharge, the log Pearson III distribution was used. Overall, the maximum depth and the cross-section area at the bankfull stage increased during the analysed period, indicating channel incision and lateral stability. The bankfull discharge of 1976 could be reached every year and the one of 2015 could occur almost every 5 years. Therefore, due to channel incision and increased channel capacity, overflowing the bankfull stage is a less frequent hazard on the Prahova River at Câmpina gauging station. River management appears to maintain this situation as no measure is taken to decrease channel incision.

Variable‐Threshold Behavior in Rivers Arising From Hillslope‐Derived Blocks

Geomorphologists often rely on simple models of river channel incision for predicting rates of landscape evolution and channel response to perturbations, as well as extracting climatic and tectonic signals from river longitudinal profiles. Recent work has shown that large, hillslope‐derived blocks delivered to rivers may noticeably alter the form and evolution of river profiles from the behavior predicted by the most common models. Here we use a 1‐D model of river reach erosion and hillslope block delivery to explore the conditions under which block delivery strongly influences channel evolution. We use global sensitivity analysis to understand which model parameters most strongly affect the channel longitudinal profile. We explore the effects of blocks on the relationship between erosion rate and channel gradient, and on the erosion rate‐channel steepness exponent ϕ, and find that block effects result in highly variable slope and ϕ over the range of erosion rates and climatic conditions (discharge mean and variability) tested. The influence of blocks on erosion rate‐slope scaling may be approximated by a piecewise model: The erosion threshold imposed by blocks scales linearly with erosion rate when blocks are infrequently mobile and remains constant when blocks are frequently mobile. We explore the implications of this variable‐threshold model for the erosion rate‐channel steepness relationship and find that erosion rate‐dependent thresholds imposed by hillslope‐derived blocks cause significant departures from previous models but may be consistent with existing field data sets. Our work has implications for landscape evolution modeling and the inversion of channel profiles for forcing information.

Coastal knickpoints and the competition between fluvial and wave-driven erosion on rocky coastlines

Active margin coastlines are distinguished by rock erosion that acts in two different directions: waves erode the coast horizontally or landwards, a process that creates sea cliffs; and rivers and streams erode the landscape vertically via channel incision. The relative rates of each process exert a dominant control on coastline morphology. Using a model of river channel incision and sea-cliff retreat, we explore how terrestrial and marine erosion compete to shape coastal topography, and specifically what conditions encourage the development of coastal knickpoints (i.e., a river or stream channels that end at a raised sea-cliff edge). We then compare results to actual landscapes. Model results and observations show that coastal knickpoint development is strongly dependent on drainage basin area, where knickpoints typically occur in drainage basins smaller than 5×105–6×106m2, as well as channel geometry and sea-cliff retreat rate. In our study area, coastal knickpoints with persistent flow (waterfalls) are uncommon and form only within a small morphological window when 1) drainage basin area is large enough to sustain steady stream discharge, but not large enough to out-compete sea-cliff formation, 2) sea-cliff retreat is rapid, and 3) channel concavity is low so that channel slopes at the coast are high. This particular geomorphic combination can sustain sea-cliff formation even when streams tap into larger drainage basins with greater discharge and more stream power, and provides an initial explanation of why persistent coastal waterfalls are, along many coastlines, relatively rare features.

Test the topographic steady state in an active mountain belt

Landscape evolution is the window to the link between deep earth and surface processes. One of the key issues in landscape evolution is to characterize the topographic steady state of mountain belts. The Taiwan mountain belt is an extraordinary case due to its extremely high uplift and denudation rates. The uplift of Taiwan Island is caused by the oblique collision between the Luzon Arc and the East Asian continent. In this case, the mountain building process in the north always occurs earlier than that in the south, which causes the spatial distribution of steady-state regions. The East Central Range receives much research attention with the presence of river basins that mainly distribute along the trajectory of the collision propagation. Normally, based on analyses of geomorphic parameters, the whole Central Range, or at least part of it, should be at a topographic steady state. However, the balance between uplift rates and denudation rates that exist in these regions is seldomly tested. In this contribution, we make a comprehensive literature review on the uplift and denudation rates derived from various approaches, including sediment yields, in-situ cosmogenic nuclide 10Be, incision of river channels, thermochronology, and GPS observations. This literature review reveals that the topographic steady state may prevail in the northern and middle parts of the East Central Range. However, an obvious inconsistency in denudation rates calculated by different methods prevents us from better constraining the topographic steady state in some regions of this mountain range.

Geographic Information Systems (GIS) as a tool for interpretation of neotectonics in the Podhale area, Poland

A combination of approaches to the study of neotectonics is discussed. As an example, an analysis is presented for part of the Podhale region, where changes in the hydrogeological regime were observed. Comments are made on the manifestation of geological processes and principles in investigations of neotectonics, due to the results of precise digital terrain modelling (DTM) and geodetic surveys. The results obtained lead the authors to the conclusion that a reliable study on the geological activity of an area evaluated from considerations of river-channel morphology requires attention to changes in spatial development as a factor controlling the intensity of the hydrological regime. In such cases, a database of complex geodata information is required. A geodetic approach is presented, based on GNSS observations that become a new standard in geomorphologic studies. The results of GNSS observations provide quantitative estimates of displacements in the study area and allow assessment of their kinematics. The Liesek1 and Nowy Targ GNSS stations reveal a significant variation in the annual rate of uplift changing from 0.8 to 0.2 mm/yr, respectively. The difference in displacement azimuths (30° at Liesek1 and 300° in Nowy Targ) indicates rotation of the Podhale area. The GNSS-derived dissimilar displacement vectors imply the impact of neotectonic movements on the channel geometry of the Czarny Dunajec River. However, according to the analysis presented, this geometry is strongly influenced by land use and climate, resulting in the incision of river channels in Quaternary sediments. The annual rate of channel indentation reached a mean value of 1.4 cm, and a maximum value 5.5 cm during the studied period from 1965 to 1975. This outcome corresponds to a cumulative effect of neotectonic uplift combined with the results of human activity and climatic changes. Consequently, our study shows that a particular attention must be exercised in drawing conclusions on neotectonic displacements based solely on geomorphological observations.

Fluvial adjustments in response to glacier retreat: Skaftafellsjökull, Iceland

This study describes changes to the proglacial drainage network of Skaftafellsjökull, Iceland from 1998 to 2011. Proglacial landscapes are highly sensitive to glacier retreat, and the retreat of glaciers around the world has accelerated since the mid‐1990s. Skaftafellsjökull has retreated at an average rate of 53 m per year since 1999. From 1999 to 2003, the river incised and formed a sequence of now abandoned channels and fluvial terraces extending ∼1 km downstream from the glacier. Retreat of the glacier from an over‐deepened ice‐contact slope meant that there was a positive correlation between the distance of glacier retreat and the amount of fluvial incision. Incision was episodic, occurring annually in response to drainage reactivation and reorganization. On an annual basis, the rate of retreat is moderately negatively correlated with the rate of incision. This is partly because the ice‐contact slope decreases away from the position of maximum glacier extent, and also because more sediment is released with faster retreat, counteracting the effect of retreat down an ice‐contact slope. From 2003 onwards, proximal terrace formation ceased, as a proglacial lake became established. Downstream of the lake outlet further incision deepened the channel, with most change occurring during a flood in 2006, where incision in the upstream confined reach was accompanied by downstream aggradation and terrace formation. These observations indicate that proglacial changes in response to glacier retreat are a result of the interactions of river channel incision and terrace formation, aggradation, lake development, and flooding, which together control river channel changes, sediment redistribution and sandur stratigraphy.

Human-induced regulations of river channels and implications for hydrological alterations in the Pearl River Delta, China

Sound understanding of hydrological alterations and the underlying causes means too much for the water resource management in the Pearl River Delta. Incision of river channels plays the key role in the hydrological alterations. As for the causes behind the river channel incision, sand dredging within the river network of the Pearl River Delta is usually assumed to play the overwhelming role in changes of geometric shapes of the river channels. Based on thorough analysis of well-collected data of channel geometry, streamflow, sediment load and water level, this study exposes new findings, investigating possible underlying causes behind the changes of the geometric shapes of the river channels at the Sanshui and Makou station. The results of this study indicate: (1) different changing properties of the geometric shapes are identified at the Sanshui and Makou stations. Larger magnitude of changes can be found in the river channel geometry of the cross section at the Sanshui station when compared to that at the Makou station. Lower water level due to fast riverbed downcutting at the Sanshui station than that at the Makou station is the major reason why the reallocation of streamflow occurred and hence the hydrological alterations over the Pearl River Delta; (2) depletion of sediment load as a result of construction of water reservoirs in the middle and upper Pearl River basin, sand dredging mainly in the Pearl River Delta and heavy floods all contribute much to the incision or deposition of the riverbed. Regulations of erosion and siltation process of the river channel often alleviate the incision of the river channels after a relatively long time span, and which makes it even harder to differentiate the factors causing the river channel incision; (3) the intensifying urbanization in the lower Pearl River basin greatly alters the underlying surface properties, which has the potential to shorten the recession of the flood event and may cause serious scouring processes and this role of flash floods in the incision of the river channels can not be ignored. This study is of great scientific and practical merits in improving human understanding of regulations of river channels and associated consequences with respect to hydrological alterations and water resource management, particularly in the economically booming region of China.

Climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont–axial system: Cuyama Valley, California, USA

AbstractChannels on the north‐facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River.To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age–elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ∼1 m kyr−1 of regional uplift affecting the Cuyama River and its tributaries.Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental‐scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by ‘early warming’ of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd.

Holocene land-use change and its impact on river basin dynamics in Great Britain and Ireland

River basins in Great Britain and Ireland have been characterized by periods of hillslope and valley floor instability during the Holocene, reflecting sensitivity to both climate change and anthropogenic disturbance. In contrast to climatic controls, which have been relatively well documented, human impacts on and interactions with river basins remain unclear. There is now, however, a growing impetus to elucidate more fully the impact of anthropogenic activity on sediment supply and runoff, given that land-use change is thought to have exacerbated recent flooding in the UK (eg, the ‘Millennium'floods of 2000). The aim of this paper is to critically review the significance of Holocene land use on hillslope and valley floor stability in Great Britain and Ireland. The most widely reported impacts of land-use change on geomorphic activity include hillslope erosion and gully development, valley floor alluviation, river channel incision and elevated water tables. In the majority of cases, however, causal relationships are difficult to establish, due primarily to inadequate dating control. Even where geomorphic instability can be linked to land-use change, it is apparent that eroded material is often stored as colluvium, which together with evidence of diachronus hillslope and valley floor instability, raises important questions and identifies uncertainties regarding the dynamics and extent of sediment transfer within river basins. Such uncertainty has important implications for understanding how river basins will behave in response to future environmental change.

Sea‐level and tectonic control of middle to late Pleistocene turbidite systems in Santa Monica Basin, offshore California

AbstractSmall turbidite systems offshore from southern California provide an opportunity to track sediment from river source through the turbidity‐current initiation process to ultimate deposition, and to evaluate the impact of changing sea level and tectonics. The Santa Monica Basin is almost a closed system for terrigenous sediment input, and is supplied principally from the Santa Clara River. The Hueneme fan is supplied directly by the river, whereas the smaller Mugu and Dume fans are nourished by southward longshore drift. This study of the Late Quaternary turbidite fill of the Santa Monica Basin uses a dense grid of high‐resolution seismic‐reflection profiles tied to new radiocarbon ages for Ocean Drilling Program (ODP) Site 1015 back to 32 ka. Over the last glacial cycle, sedimentation rates in the distal part of Santa Monica Basin averaged 2–3 mm yr−1, with increases at times of extreme relative sea‐level lowstand. Coarser‐grained mid‐fan lobes prograded into the basin from the Hueneme, Mugu and Dume fans at times of rapid sea‐level fall. These pulses of coarse‐grained sediment resulted from river channel incision and delta cannibalization. During the extreme lowstand of the last glacial maximum, sediment delivery was concentrated on the Hueneme Fan, with mean depositional rates of up to 13 mm yr−1 on the mid‐ and upper fan. During the marine isotope stage (MIS) 2 transgression, enhanced rates of sedimentation of > 4 mm yr−1 occurred on the Mugu and Dume fans, as a result of distributary switching and southward littoral drift providing nourishment to these fan systems. Longer‐term sediment delivery to Santa Monica Basin was controlled by tectonics. Prior to MIS 10, the Anacapa ridge blocked the southward discharge of the Santa Clara River into the Santa Monica Basin. The pattern and distribution of turbidite sedimentation was strongly controlled by sea level through the rate of supply of coarse sediment and the style of initiation of turbidity currents. These two factors appear to have been more important than the absolute position of sea level.