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The outer bank slump blocks play a fundamental role in modulating the rate of bank erosion, and consequently, have a profound influence on many geomorphic and ecologic processes in meandering streams, e.g., channel evolution and habitat creation. To date, no adequate research has been developed regarding how these blocks, partially strengthened by roots of herbaceous plants, impact the near-bank flow velocity, bank erosion, and migration of streambanks. This paper analyzes 246 slump blocks in a meandering stream on the Marqu Meadow, China. Aerial surveys were conducted once a year from 2018 to 2021 and the lateral migration rates (M) of streambanks are estimated by superimposing the current-year drone imagery onto its previous-year counterpart. When compared to the outer bank segments lacking slumps, our research findings indicate that the bank segments exhibiting slumps demonstrate a reduction of 57 % and 43 % in the maximum and average bank erosion rates, respectively. Overall, the wider blocks provide stronger bank protection; nevertheless, they may also introduce or enhance local scouring in their vicinity, thereby increasing the heterogeneity of bank erosion rates. To elucidate this complex influence mechanism, we simulate the three-dimensional flow velocity field of a ~100 m meandering bend containing three slump blocks using the MIKE-3 model. Furthermore, we compare one-year bank migration distance with and without the blocks by correlating the lateral migration distance of outer banks to the longitudinal gradient of near-bank velocity. The paper provides valuable insights into the complex interplay between flow dynamics and streambank behavior in real-world settings, thereby enhancing the effectiveness of future management and restoration practices. • 246 slump blocks were analyzed in a meander on Marqu Meadow, China. • Slump blocks can persist for years but may be washed away in high flows. • The outer bank slump blocks play a vital role in modulating bank erosion rates. • Slump blocks protect outer banks by redistributing the high flow and secondary flow. • Slump blocks help protect bank overall but it may introduce scour in their vicinity. [ABSTRACT FROM AUTHOR]

The occurrence of earthquakes has the potential to significantly modify river morphology and cause notable effects on the aquatic ecosystem. Prior to the 2008 Wenchuan earthquake with a magnitude of 8.0, the Shiting River located in the upper basin of the Yangtze River was stable. Rapid bed incision or degradation has continued since the earthquake, and weirs and bank revetments were constructed to mitigate degradation. The impacts of channel morphology adjustment and human activities on biodiversity are not clear, which prohibits efficient river restoration. This paper evaluated the morphological quality of the Shiting River by employing the Morphological Quality Index (MQI), an approach recommended in the European Water Framework Directive. Macroinvertebrate diversity was analyzed in relation to the impacts of morphological adjustment and human activities based on field data collected in 2021. The results showed that the channel degraded and deepened after the earthquake, the planform changed from multi-threaded to single-threaded, and swamps on the floodplains disappeared. The quality of channel morphology in 2021 was evaluated using the MQI and was found to be ranging from poor to moderate. The diversity metrics of macroinvertebrates, specifically the Shannon, Simpson, and Evenness indices, exhibited a positive and significant correlation with four MQI sub-indices, which represented channel geomorphological functionality, artificiality, morphological pattern, and substrate, respectively. However, there was no significant correlation observed between the diversity metrics and the overall MQI score. The results imply that channels with superior morphological functionality, slower channel adjustment, and lower levels of anthropogenic disturbances tend to exhibit greater macroinvertebrate diversity. The study found a significant decrease in macroinvertebrate richness downstream of weirs and bridges. The community structures upstream and downstream of weirs and bridges were also significantly different. This study may help inform the ecological response of rivers to dynamic morphological changes and intense anthropogenic disturbances following disastrous earthquakes. • Post-earthquake channel morphological quality was poor to moderate. • Channels with higher morphological quality had higher macroinvertebrate diversity. • Morphology changes and human activities impacted macroinvertebrates. • Higher macroinvertebrate richness upstream of weirs and bridges than downstream. [ABSTRACT FROM AUTHOR]

The coastal mountain system (CMS) of southeastern China has been a natural place to study paleotopographic changes primarily due to its marked topographical contrast since the Late Cretaceous. For a quantitative reconstruction of the paleotopographic evolution of the CMS, this paper provides key information from along the Ningde–Jianyang and Huilai–Longchuan cross-sections using apatite (U-Th)/He (AHe) and zircon (U-Th)/He (ZHe) data combined with thermal history and paleotopographic modeling. For the Ningde–Jianyang section, the AHe dates are in the range of 44.3–70.8 Ma, and the ZHe dates are between 58.5 and 102.9 Ma. For the Huilai–Longchuan section, the resulting AHe dates are in the range of 37.9–73.8 Ma, and ZHe dates are between 65.5 and 119.7 Ma. The modeling results suggest that: 1) the CMS had an asymmetric topography during the Late Cretaceous with the SE segment being significantly higher (peak elevation = 3.8 km) than the NW segment (peak elevation = ~2 km). The marked decreases in elevation and relief of the CMS occurred during 80–40 Ma, followed by relatively minor topographic changes since ~40–30 Ma; 2) The SE segment of the southern CMS experienced significantly faster exhumation (~0.44 km/Myr) than northern CMS (0.16 km/Myr) during 70–60 Ma, which was probably related to thinning of the crust and orogenic collapse linked to the initial-rifting of the South China Sea; 3) The SE segment of southern CMS experienced slower exhumation than northern CMS during 60–40 Ma, likely resulting from the lower elevations in the southern CMS than in the northern CMS during 60–40 Ma. • The coastal mountain system forms a climatic boundary in southeastern China. • Thermochronological data collected along two horizontal transects. • Transect thermochronology results used for topography modeling. • Rapid exhumation from 70-60 Ma along the south 2-D transect linked to rifting. • Rapid exhumation from 60–40 Ma along the north 2-D transect linked to climate change. [ABSTRACT FROM AUTHOR]

Cirques are typical erosional landforms of glaciers and have been used as bases for paleoclimate and paleoenvironment reconstruction and for understanding the interactions between glacial erosion, climate, and topography. The availability of high-resolution digital elevation models (DEMs) provides the opportunity to map large populations of cirques for regional and global scale analysis. However, cirque outlines are still mainly determined based on manual digitization, which is time consuming and labor intensive. This paper introduces an automated method to recognize and delineate cirques using DEMs based on a series of hydrological and morphological analyses, including delineating stream network, filtering streams, determining potential cirque threshold points, and delineating cirque outlines. A semi-automated tool is also developed based on user-specified threshold points or cross sections. The related tools are coded in python and imported into ArcGIS as a toolbox, AutoCirque, with user friendly interfaces. Comparison in a test area of the eastern Tian Shan, China, indicated that the population statistics are relatively consistent between manually digitized and auto-delineated cirques. Detailed comparisons for 11 selected cirques indicated that the AutoCirque-delineated and manually digitized cirque outlines are similar in shape with an average boundary offset of approximately one DEM cell size (30 m) and a 70–90% overlap-fit percentage. The derived cirque metrics are also similar, especially for elevation, slope, and aspect related metrics. This toolbox can significantly speed up the analytical processes, remove the subjectivity in delineating cirque outlines, and allow for the comparison of cirque morphology and metrics at regional and global scales. • This paper presents an automated method to delineate cirque outlines from DEMs. • The developed ArcGIS toolbox incudes both fully automated and semi-automated tools. • Delineated cirques have consistent population statistics with manual-digitized ones. • Manual- and auto-derived cirques are similar in shape with high overlap percentage. • This toolbox allows for large population analyses of cirques at different scales. [ABSTRACT FROM AUTHOR]

Numerical modeling of landform evolution is the key to understanding the formation of land surfaces. However, landform evolution occurs under certain initial topographic conditions, while existing landform evolution models often use a plane or a randomly produced surface to establish the initial topographic conditions. This misunderstanding of the initial topographic conditions causes the landform evolution results to deviate greatly from the real terrain. Therefore, the initial topographic conditions must be reconstructed and integrated into the current numerical landform evolution model. In this paper, the Loess Plateau of China was selected as a typical sample area. The paleotopography was reconstructed and integrated into the numerical landform evolution model. Based on the evolutionary mechanism of loess landforms, modules of surface erosion, matter diffusion and precipitation were selected to construct a numerical model of loess landform evolution. Moreover, randomly produced terrain was used as the initial conditions during the landform evolution process and compared with the paleotopography-constrained evolution results. In addition, the results of the landform evolution process were evaluated with different terrain factors, and the uncertainty of the model was assessed by comparing different model conditions. The results show that, due to the control of paleotopography, the evolution results can maintain the main morphological structure of valleys in the loess landscape. Without considering the paleotopography, a large difference exists between the evolution results and the true ground terrain. These results show that paleotopography is an important feature of loess landform evolution modeling and is indispensable for reasonably expressing the process of landform evolution. Finally, the numerical modeling of loess landform evolution with the consideration of paleotopography can not only help to achieve a better understanding of the loess landform evolution process but also provide a reference for feature dependent landform evolution modeling in different landform applications. • Paleotopography affects the evolution of loess landform in the Loess Plateau. • We integrate the paleotopography into the numerical loess landform evolution model. • Our results can maintain the main morphological structure of loess landform. • Our research provides a reference for feature-concerned landform evolution modeling. [ABSTRACT FROM AUTHOR]

Reconstructing three-dimensional palaeoglacier surface, thickness, and volume provides useful information for quantifying palaeo-climate conditions during glacial stages and assessing the impact of glacier change on water resources. A glacial flowline model has been implemented in Excel and ArcGIS to reconstruct palaeoglaciers based on digital elevation models and geomorphic constraints, such as moraines and trimlines that represent the margins and local heights of palaeoglaciers, respectively. However, significant efforts are still needed in using these tools for palaeoglacier reconstruction, such as digitizing flowlines, adjusting shear stress, and deriving shape factors. This paper presents an automated method, PalaeoIce, to reconstruct palaeoglaciers using geomorphic constraints. Coded in python, PalaeoIce is an ArcGIS toolbox with a set of tools to generate glacial flowlines, optimize shear stress, derive shape factors, calculate ice thickness values along flowlines, and interpolate palaeo ice surfaces based on geomorphic constraints. The use of PalaeoIce is demonstrated using extant glaciers with measured thickness values and moraines/trimlines of the Little Ice Age (LIA) and Marine Isotope Stage (MIS) 2 in the eastern Tian Shan, China. The reconstructed ice thickness values of Glacier No. 1 in this area show a reasonable agreement with field measurements with 1.4 % and 5.4 % differences between measured and reconstructed mean ice thickness values using the two methods included in PalaeoIce: a revised ice thickness model for extant glaciers and a palaeoglacier reconstruction method based on glacier outlines, respectively. Two approaches are then illustrated for palaeoglacier reconstructions using two sets of geomorphic constraints: one with the fully reconstructed glacier outlines during the LIA, and the other with just the terminal moraine and limited trimlines during MIS 2. PalaeoIce can significantly improve the efficiency of palaeoglacier reconstructions and the understanding of the impact of glacier change on water resources. • An automated method, PalaeoIce, is presented for palaeoglacier reconstruction. • Tools are developed to create flowlines, modify DEM, and reconstruct palaeoglaciers. • Reconstructed ice thickness data are validated by field measurements in Tian Shan. • Target geomorphic features are of importance for palaeoglacier reconstruction. [ABSTRACT FROM AUTHOR]

River confluences are key nodes in fluvial systems. Past studies on large river confluences were focused on the Paranà, Amazon, and Yangtze rivers, while the Yarlung Zangbo River (YZR), the longest plateau river in China, has not been investigated yet. This paper investigates a large multi-channel confluence between the YZR and one of its major tributaries, the anabranching Niyang River (NR). A remote-sensing study of this area demonstrated that the confluence planform is very stable compared with its upstream and downstream reaches that suffered from sandbar migration, meandering, and the development of a head-cut. A field survey using Acoustic Current Doppler Profiling (ADCP) was conducted at the confluence in June 2019, when the YZR and NR had discharges of about 1393 m3/s and 1299 m3/s in total, respectively. Although the discharge ratio of this confluence attained a value of 0.93, the existence of an estuary delta with a large area of floodplain largely weakened the impact of the NR on the dynamics of the YZR. The inflows of the multiple channels of the NR separated by the delta created an evident and long mixing interface and produced the left-side secondary cells in the YZR. In contrast, the curved riverbank played a more important role in the formation of deep scour holes, generating heterogeneity of the velocity distribution and the fast-mixing of flows. This study leads to an advancement in our current knowledge about multi-channel confluences. • Remote sensing images show that the plateau river confluence planform is very stable. • A field survey on flow and morphological features of the confluence was conducted. • The estuary delta with large floodplain largely weakened the confluence dynamics. • The curved river bank played an important role in river bed scours and flow mixing. [ABSTRACT FROM AUTHOR]

The Yellow River (YR) flows from Northwest China to North China, crossing three topographic steps: the Tibetan Plateau, the Chinese Loess Plateau (CLP), and the North China Plain (NCP). Determining the river's geomorphological evolution is significant for understanding the formation of macro-geomorphic patterns in China. However, the formation age of YR channelization into the Bohai Sea is highly controversial and uncertain, with estimates ranging from the Late Miocene to the Late Pleistocene. This study conducted grain size analysis, whole-rock geochemistry, and detrital zircon U-Pb dating on ~5.2 Ma sediments from borehole G4 drilled in the Bohai Bay. The geochemical results from borehole G4 indicate that chemical weathering was weak during 5.2–1.6 Ma, but showed diverse characteristics since ~1.6 Ma. Moreover, concordant detrital zircons from borehole G4 (~1.6 Ma) yield a major age population of 350–550 Ma, which, however, is scarcely produced by detrital zircons from the nearby Yanshan and Taihang Mountains. Geochemical signals and detrital zircon U-Pb geochronology suggest that the YR reached the NCP after cutting through the Sanmen Gorge and entered the Bohai Bay since ~1.6 Ma. The massive presence of sediments with an age population of 650–1350 Ma in the top of borehole G4 demonstrates that the present topography of the middle and upper reaches of the YR initially formed at ~0.6 Ma. Subsequently, changes in provenance since ~1.6 Ma influenced the records of paleoclimatic signals indicated by elemental geochemistry in the Bohai Bay. Because of detrital inputs from the YR, the (La/Sm) N and (La/Yb) N ratios of borehole G4 abruptly increased after ~1.6 Ma. Other geochemical indicators exhibited no noticeable variation trend, which differs from the decreasing trend of deep-sea δ18O records, the Chemical Index of Alteration (CIA), and the 87Sr/86Sr ratio of the loess from the Chinese Loess Plateau after the YR entered the NCP at ~1.6 Ma. This paper proposes that the YR gradually triggered fluvial erosion up to its upper reaches after entering the NCP, which is primarily in response to climate change. • Detrital zircon U-Pb geochronology and elemental geochemistry of borehole sediments in Bohai Bay indicate the geomorphological evolution of Yellow River • Yellow River cut through the Sanmen Gorge and reached the North China Plain at ~1.6 Ma • The current geomorphic of the middle and upper reaches of Yellow River was initially formed ~0.6 Ma • Changes in provenance since ~1.6 Ma have influenced the records of paleoclimatic signals in Bohai Bay [ABSTRACT FROM AUTHOR]

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis , Quercus -evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic "cultural fault" in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP. • Grain size, pollen, spores, freshwater algae and dinoflagellate cysts from the Pearl River Estuary were investigated. • Three major phases shown by palynological results were corresponding to the changes in vegetation and climate. • We hypothesized that the Neolithic "cultural fault" is probably related to the storm surges induced by extreme typhoon events. • Natural vegetation cover has suffered large-scale destruction by ancient humans during the Late Holocene. [ABSTRACT FROM AUTHOR]

Seasonal or interannual precipitation differences lead to changes in the water level of a tufa lake, while the underwater topography affects its local depth. Therefore, topo-bathymetry is important to study and protect the aquatic environment of tufa lakes. However, traditional field-based topo-bathymetric surveying methods (e.g., sounding rod or sonar) inevitably disturb the fragile lake ecosystem. In recent years, the emerging remote sensing technology of unmanned aerial vehicles (UAV) has provided a cost-effective solution for measuring topo-bathymetry without disturbance. In this paper, taking Spark Lake in Jiuzhaigou, China, as an example, we captured red-green-blue (RGB) images using a fixed-wing UAV and produced a digital elevation model (DEM) prior to the Jiuzhaigou Earthquake using Structure-from-Motion (SfM) photogrammetry. The underwater topography of Spark Lake was obtained by refraction correction and water color inversion based on the DEM and orthophoto, respectively. For refraction correction, a water depth correction model based on Snell's Law was used. For water color inversion, general band ratio models were replaced by a band difference model (blue band - green band). The qualities of the resulting DEMs produced by the two methods were evaluated against the topography of the drained Spark Lake after the earthquake, and the corresponding DEMs of difference (DoD) were also analyzed. The coefficient of determination (R2) and root mean square error (RMSE) are 0.88 and 1.32 m for refraction correction, and 0.86 and 1.37 m for water color inversion, respectively. The results demonstrated the feasibility and effectiveness of applying UAV-acquired RGB imagery and the two optical remote sensing methods to topo-bathymetric mapping of transparent tufa lakes. • UAV-acquired RGB images were applicable for testifying topo-bathymetry of tufa lake. • Refraction correction demonstrated a good performance for water depths up to 12 m. • The difference between blue and green bands was the optimal spectral combination. • Water color inversion exhibited a fine performance across the entire lake depth range. [ABSTRACT FROM AUTHOR]