Trunk Stream Research Articles

Resistant rock layers amplify cosmogenically‐determined erosion rates

AbstractPrior numerical modeling work has suggested that incision into sub‐horizontal layered stratigraphy with variable erodibility induces non‐uniform erosion rates even if base‐level fall is steady and sustained. Erosion rates of cliff bands formed in the stronger rocks in a stratigraphic sequence can greatly exceed the rate of base‐level fall. Where quartz in downstream sediment is sourced primarily from the stronger, cliff‐forming units, erosion rates estimated from concentrations of cosmogenic beryllium‐10 (10Be) in detrital sediment will reflect the locally high erosion rates in retreating cliff bands. We derive theoretical relationships for threshold hillslopes and channels described by the stream‐power incision model as a quantitative guide to the potential magnitude of this amplification of 10Be‐derived erosion rates above the rate of base‐level fall. Our analyses predict that the degree of erosion rate amplification is a function of bedding dip and either the ratio of rock erodibility in alternating strong and weak layers in the channel network, or the ratio of cliff to intervening‐slope gradient on threshold hillslopes. We test our predictions in the cliff‐and‐bench landscape of the Grand Staircase in southern Utah, USA. We show that detrital cosmogenic erosion rates in this landscape are significantly higher (median 300 m/Ma) than the base‐level fall rate (~75 m/Ma) determined from the incision rate of a trunk stream into a ~0.6 Ma basalt flow emplaced along a 16 km reach of the channel. We infer a 3–6‐fold range in rock strength from near‐surface P‐wave velocity measurements. The approximately four‐fold difference between the median 10Be‐derived erosion rate and the long‐term rate of base‐level fall is consistent with our model and the observation that the stronger, cliff‐forming lithologies in this landscape are the primary source of quartz in detrital sediments. © 2020 John Wiley & Sons, Ltd.

Erosion rates and patterns in a transient landscape, Grand Staircase, southern Utah, USA

AbstractCosmogenic 10Be concentrations in alluvial sediment are widely used to infer long-term, catchment-averaged erosion rates based on the assumption that the landscape is in mass-flux steady state. However, many landscapes are out of equilibrium over millennial time scales due to tectonic and climatic forcing. The Grand Staircase of the Colorado Plateau (North America) is a transient landscape, adjusting to base-level fall from the carving of the Grand Canyon, and is characterized by cliff-bench topography caused by differential erosion of lithologic units. The 10Be concentrations from 52 alluvial and colluvial samples, collected in nested fashion from five catchments, produced inferred erosion rates ranging from 20 to >3500 m/m.y. (or mm/k.y.). We attribute this high variance in part to lithologic-controlled steepness and hotspots of erosion related to cliff retreat along the White Cliffs (escarpment near Mt. Carmel Junction, Utah), as well as headward drainage expansion along the uppermost Pink Cliffs (escarpment within Bryce Canyon National Park). Results from the downslope Vermillion Cliffs (near Kanab) indicate lower erosion rates despite similar slope and rock types, suggesting knick-zone migration has passed that lower region of our study area. The 10Be concentrations measured along trunk streams systematically match local, subcatchment erosion rates, with muted influence from upstream sediment sources. This is consistent with intermittent sediment conveyance between cliff and bench terrain, with sediment storage and localized release associated with ephemeral arroyo systems in the region. Therefore, while detrital cosmogenic nuclide records in transient landscapes may not directly reflect upstream catchment-averaged erosion rates, 10Be inventories can provide insight into unsteady upslope-directed erosion and downslope-directed sediment conveyance in these dynamic landscapes.

Contribution Analysis of the Spatial-Temporal Changes in Streamflow in a Typical Elevation Transitional Watershed of Southwest China over the Past Six Decades

Attribution analyses on streamflow variation to changing climate and land surface characteristics are critical in studies of watershed hydrology. However, attribution results may differ greatly on different spatial and temporal scales, which has not been extensively studied previously. This study aims to investigate the spatial-temporal contributions of climate change and underlying surface variation to streamflow alteration using Budyko framework. Jiangling River Watershed (JRW), a typical landform transitional watershed in Southwest China, was chosen as the study area. The watershed was firstly divided into eight sub-basins by hydrologic stations, and hydrometeorological series (1954–2015) were divided into sub-intervals to discriminate spatial-temporal features. The results showed that long-term tendencies of hydrometeorological variables, i.e., precipitation (P), potential evapotranspiration (E0), and runoff depth (R), exhibited clear spatial patterns, which were highly related to topographic characteristics. Additionally, sensitivity analysis, which interpreted the effect of one driving factor by unit change, showed that climate factors P and E0, and catchment characteristics (land surface parameter n) played positive, negative, and negative roles in R, according to elastic coefficients (ε), respectively. The spatial distribution of ε illustrated a greater sensitivity and heterogeneity in the plateau and semi-humid regions (upstream). Moreover, the results from attribution analysis showed that the contribution of the land surface factor accounted for approximately 80% of the R change for the entire JRW, with an obvious spatial variation. Furthermore, tendencies of the contribution rates demonstrated regulations across different sub-regions: a decreasing trend of land surface impacts in trunk stream regions and increasing tendencies in tributary regions, and vice versa for climate impacts. Overall, both hydrometeorological variables and contributions of influencing factors presented regularities in long-term tendencies across different sub-regions. More particularly, the impact of the primary influencing factor on all sub-basins exhibited a decreasing trend over time. The evidence that climate and land surface change act on streamflow in a synergistic way, would complicate the attribution analysis and bring a new challenge to attribution analysis.

Spatial-temporal Characteristics and Driving Factors of Greenhouse Gas Emissions from Rivers in a Rapidly Urbanizing Area

Rivers play an important role in greenhouse gas emissions. Over the past decade, because of global urbanization trends, rapid land use changes have led to changes in river ecosystems that have had a stimulating effect on the greenhouse gas production and emissions. Presently, there is an urgent need for assessments of the greenhouse gas concentrations and emissions in watersheds. Therefore, this study was designed to evaluate river-based greenhouse gas emissions and their spatial-temporal features as well as possible impact factors in a rapidly urbanizing area. The specific objectives were to investigate how river greenhouse gas concentrations and emission fluxes are responding to urbanization in the Liangtan River, which is not only the largest sub-basin but also the most polluted one in Chongqing City. The thin layer diffusion model method was used to monitor year-round concentrations of pCO2, CH4, and N2O in September and December 2014, and March and June 2015. The pCO2 range was (23.38±34.89)-(1395.33±55.45) Pa, and the concentration ranges of CH4 and N2O were (65.09±28.09)-(6021.36±94.36) nmol·L-1 and (29.47±5.16)-(510.28±18.34) nmol·L-1, respectively. The emission fluxes of CO2, CH4, and N2O, which were calculated based on the method of wind speed model estimations, were -6.1-786.9, 0.31-27.62, and 0.06-1.08 mmol·(m2·d)-1, respectively. Moreover, the CO2 and CH4 emissions displayed significant spatial differences, and these were roughly consistent with the pollution load gradient. The greenhouse gas concentrations and fluxes of trunk streams increased and then decreased from upstream to downstream, and the highest value was detected at the middle reaches where the urbanization rate is higher than in other areas and the river is seriously polluted. As for branches, the greenhouse gas concentrations and fluxes increased significantly from the upstream agricultural areas to the downstream urban areas. The CO2 fluxes followed a seasonal pattern, with the highest CO2 emission values observed in autumn, then successively winter, summer, and spring. The CH4 fluxes were the highest in spring and the lowest in summer, while N2O flux seasonal patterns were not significant. Because of the high carbon and nitrogen loads in the basin, the CO2 products and emissions were not restricted by biogenic elements, but levels were found to be related to important biological metabolic factors such as the water temperature, pH, DO, and chlorophyll a. The carbon, nitrogen, and phosphorus content of the water combined with sewage input influenced the CH4 products and emissions. Meanwhile, N2O production and emissions were mainly found to be driven by urban sewage discharge with high N2O concentrations. Rapid urbanization accelerated greenhouse gas emissions from the urban rivers, so that in the urban reaches, CO2/CH4 fluxes were twice those of the non-urban reaches, and all over the basin N2O fluxes were at a high level. These findings illustrate how river basin urbanization can change aquatic environments and aggravate allochthonous pollution inputs such as carbon, nitrogen, and phosphorus, which in turn can dramatically stimulate river-based greenhouse gas production and emissions; meanwhile, spatial and temporal differences in greenhouse gas emissions in rivers can lead to the formation of emission hotspots.

Environmental efficiency evaluation for Xiangjiang River basin cities based on an improved SBM model and Global Malmquist index

During the past several decades, the economy of China has increased rapidly with a number of energy and environmental problems such as energy shortage, global warming and river pollution. Considering the typical economic development of Xiangjiang River basin at the cost of energy and environment, this paper measures the energy and environmental efficiency of the Xiangjaing River basin cities and takes the further analysis with the total factor productivity. In order to accurately measure the real impact of cities on rivers, we take the water quality of the upstream and downstream of cities as the environmental indicator. An improved slacks-based measure approach is utilized to evaluate the energy and environmental efficiency of 15 trunk streams and tributaries along the Xiangjiang River basin cities during 2008–2014. The empirical results show the efficiencies of trunk streams and tributaries areas were discrepant even in the same city, but their technical change in the same city had significant similarities during the same period.

Impact of confluence on hydrological and morphological characters of the trunk stream: a study on the Manu River of North-east India

Tributaries play a significant role in changing flow structure of the main river through their additional discharge. A study was conducted at the point of convergence of the River Deo with the River Manu using simple geospatial technique and field work to justify the hydrological and morphological changes in downstream of the confluence point. The spatio-temporal change of both the river channels for 10 km length in upstream and downstream of the confluence point was considered. Moreover, field measurements and post-field work were carried out to examine the spatial variation of hydrodynamic characteristics like flow velocity, depth, water discharge, wetted perimeter and hydraulic radius of the selected stretches. Sieving method was applied for grain size analysis of river bed sediment samples. The result revealed that both the aggradation and degradation processes were equally active in the upstream segment of the Manu River but in downstream segment aggradation exceeded the degradation activity, though all the hydrodynamic variables were boosted up in downstream, except flow velocity. The present research highlighted that the steeper gradient of the R. Deo had enhanced its competency to transport medium-sized grains to the R. Manu, where fine grains were commonly found. Moreover, increased wetted perimeter in downstream specified more friction between channel bed and its flow consequent upon reduced flow velocity with extra sediment load accumulation.

Occurrence, distribution and seasonal variation of five neonicotinoid insecticides in surface water and sediment of the Pearl Rivers, South China

Occurrence and distribution of five neonicotinoids (NEOs) in surface water and sediment were studied in the Pearl Rivers, including three trunk streams, Dongjiang, Beijiang, Xijiang River (DR, BR and XR), South China. At least one neonicotinoid was detected in surface water and sediment of the Pearl Rivers, with imidacloprid (IMI) and thiamethoxam (THM) being the frequently detected NEOs. Total amount of NEOs (∑5neonics) in surface water and sediment ranged from 24.0 to 322 ng/L, and from 0.11 to 11.6 ng/g dw, respectively. Moreover, the order of contamination level of NEOs in the Pearl Rivers was as follows: XR > DR > BR for surface water, and BR > DR > XR for sediment. Local agricultural activities and effluents of wastewater treatment plants (WWTPs) could be major sources of NEOs in the Pearl Rivers. Solubilization and dilution of NEOs between surface water and sediment during different seasons (spring and summer) could be attributed to rainfall intensities or climate of the Pearl River Delta. An ecological risk assessment of the exposure to current environmental concentration of imidacloprid and ∑5NEOs suggests a threat to sensitive non-target invertebrates, including aquatic invertebrates. Results would provide a better understanding of NEOs contamination in the Pearl Rivers, as well as being a reliable dataset for decision-making in contamination control and environmental protection.

Regional landscape response to thrust belt dynamics: The Iglesia basin, Argentina

AbstractIntermontane basins are often the result of regionally variable uplift in tectonic settings. Wedge‐top basins, a type of intermontane basin, form along thrust faults within a fold and thrust belt, and provide an ideal environment to study the regional fluvial and surface response to local variations in rock uplift. This study simulates the formation and evolution of an intermontane basin using a landscape evolution model. The modelling results demonstrate that large trunk streams maintain connectivity during basin formation for two reasons: (1) their stream power is enhanced by the capture of smaller streams, enabling them to incise through the uplifting downstream region, and (2) they acquire increased sediment yield to completely infill the upstream accommodation space rather than forming an endorhic basin. During active deformation of the fold‐and‐thrust belt, both channel slope and erosion rates are reduced upstream of the intermontane basin and these changes propagate as a wave of low erosion into the uplands. For a uniform background uplift rate in a landscape previously at steady state, this reduced rate of erosion results in a net surface uplift upstream of the basin. Following the eventual breach of the basin's bounding structural barrier, a wave of high erosion propagates through the basin and increases the channel slope. This onset of increased erosion can be delayed by up to several million years relative to the onset of downstream uplift. Observed paleoerosion rates in paired wedge‐top and foreland basin sequences, and present‐day stream profiles in the Argentine Precordillera support our modelling results. Our results may be extrapolated to other foreland systems, and are potentially identifed using low‐temperature thermochronometers in addition to paleoerosion rates.

白鹤滩库区河段水沙特性初步分析研究

过去在对金沙江进行水沙特性分析时，大多主要针对金沙江下游河段干流进行整体分析，未单独对下游某一段河道进行水沙特性分析。而近年来，受气候、流域下垫面条件变化，以及金沙江梯级水电站蓄水运行等影响，河道水沙特性也发生一系列新的变化，因此有必要在现阶段对拟建白鹤滩水电站库区河段的水沙特性进行分析研究。本文正是从这种需求出发，基于现有资料，以拟建白鹤滩水电站库区河段为对象，除关注干流河段外，还加入库区所含支流河段的分析，通过选择白鹤滩库区所在河段入库控制站、出库控制站以及支流控制站，采用常规的水文数理统计和对比分析等方法，从入库、出库及区间来水来沙变化情况三个方面对白鹤滩库区所在河道历年来的来水来沙特性进行系统分析，找出水沙特性变化的具体时间节点并分析变化原因等。为优化白鹤滩水库运行和管理方式、对比水库建成投入使用后河道水沙特性变化影响，以及为预测白鹤滩水库建成投入使用后出入库水沙变化趋势奠定一些基础。 In the past, the analysis of the water and sediment characteristics in the Jinsha River, mainly aims at the overall analysis of the trunk stream in the downstream of Jinsha River, rather than the single analysis on water and sediment characteristics in a certain period of downstream river. In recent years, affected by changes of climate and watershed underlying surface conditions, and the influence of water storage operation on cascade hydropower stations in Jinsha River, river water and sediment characteristics also had a series of new changes. Therefore, it is necessary to analyze the characteristics of water and sediment in the reservoir section of the proposed Baihetan hydropower station at present. This paper is starting from this demand, based on the existing data, in Baihetan Hydropower Station Reservoir area of the object. In addition to focusing on the main stream reach, the analysis of the tributary of the reservoir is also included, and by choosing the Baihetan reservoir area located in a storage library control station, outbound control station and tributary control station, using the methods of hydrological mathematical statistics and comparative analysis, taking Baihetan reservoir reach as the object to summarize the basic characteristics of the river water and sediment analysis over the years and adopting conventional hydrological mathematical statistics method and comparative analysis method, the coming water and sediment characteristics in Baihetan reservoir reach over the years have been systematically analyzed, finding out the specific time node of water sediment characteristics and analyzing the causes of change. In conclusion, with current commonly used hydrological statistics method and comparative analysis method, this paper used the existing hydrological data to make systematic analysis on river water and sediment characteristics, laying good foundation for optimizing the operation and management methods of Baihetan reservoir, comparing the change influences and predicting the change trend of water and sediment characteristics after the operation of Baihetan reservoir.

Clay mineralogy and source-to-sink transport processes of Changjiang River sediments in the estuarine and inner shelf areas of the East China Sea

We examined the source-to-sink sediment transport processes from the Changjiang River to the estuarine coastal shelf area by analyzing the clay mineral assemblages in suspended sediment samples from the Changjiang River catchment and surface samples from the estuarine coastal shelf area following the impoundment of the Three Gorges Dam (TGD) in 2003. The results indicate that the clay mineral compositions throughout the study area are dominated by illite, with less abundant kaolinite and chlorite and scarce smectite. The clay minerals display distinct differences in the tributaries and exhibit obvious changes in the trunk stream compared with the periods before 2003, and the source of sediment has largely shifted to the mid- to lower reaches of the river after 2003. Spatially, the clay mineral assemblages in the estuarine area define two compositionally distinct provinces. Province I covers the mud area of the Changjiang River estuary and the Zhe-Min coastal region, where sediment is primarily supplied by the Changjiang River. Province II includes part of the Changjiang River estuary and the southeastern portion of the study area, where the sediment is composed of terrestrial material from the Changjiang River and re-suspended material from the Huanghe River carried by the Jiangsu coastal current. Moreover, the other smaller rivers in China (including the Oujiang and Minjiang rivers of mainland China and the rivers of West Taiwan) also contribut sediments to the estuarine and inner shelf areas. In general, the clay mineral assemblages in the Changjiang River estuarine area are have mainly been controlled by sediment supplied from upstream of the Changjiang River tributaries. However, since the completion of the TGD in 2003, the mid- to downstream tributaries have become the main source of sediments from the Changjiang catchment into the East China Sea. These analyses further demonstrate that the coastal currents and the decrease in the sediment load of the river have the greatest impacts on the distribution and transport of clay minerals assemblages in the sediments.

Deep-water plays in the western Black Sea: insights into sediment supply within the Maykop depositional system

Abstract The Oligocene–Early Miocene Maykop depositional system of the Western Black Sea Basin is investigated in terms of sediment supply and provenance. Potential sediment source regions and conduits for sediment supply into the deep-water portion of the basin are evaluated based on the tectonic history and framework of the region, and are supported by observations from published well, reflection seismic and isopach data. The outcrop geology of the present-day land areas adjacent to the basin is used as a guide to the likely provenance and, hence, quality of potential siliciclastic reservoirs. Reservoir presence and reservoir quality are key subsurface risks for exploration in deep-water plays involving Maykop turbidite sandstones and charge from the well-known Maykop organic carbon-rich mudstones that are widespread across the basin. Sediments sourced from the NE Moesian Platform and Dobrogea, channelled into the offshore Black Sea via the Histria Trough, are considered moderate risk in terms of primary reservoir quality, as evidenced by thick packages of fine-grained sediment. In contrast, sediments derived from the southern Strandja Massif fed into the Burgas Basin, and potentially into the deeper-water Turkish Black Sea, are relatively low risk in terms of reservoir quality, given the abundance of acidic intrusions within the massif. Sediment derived from parts of the northern Strandja Massif, especially the volcaniclastics of the Srednogornie region, are likely to have poorer reservoir quality characteristics. Sediments derived from the granitic Bolu Massif within the Pontides might be of good reservoir quality but are likely to be ponded behind the offshore Kozlu Ridge. An important sediment source-to-sink system was derived from the Balkanides and entered the deeper-water western Black Sea via the Kamchia Trough. The present-day Kamchia river is a relatively minor sediment supplier to the Black Sea, but the palaeo-Kamchia river of the Oligocene–Early Miocene would have exploited a much greater drainage area consisting of an axial trunk stream, occupying the newly formed Kamchia Foredeep to the north of the Balkanides, and transverse rivers sourcing sediment from the granitic and gneissic bodies of the Balkan Mountains and from Early Cretaceous and Palaeogene sandstones. These would provide reasonable reservoir quality, and it is estimated from reference source-to-sink relationships that offshore sediment flux via this system was probably at least eight times greater than at present. Known shelf-edge canyons in offshore Bulgaria facilitated this sediment reaching the deep water offshore, where a sedimentary fan with a length in excess of 150 km is likely to have developed. This suggests that the potential is good for encountering good-quality reservoir sands in the Maykop succession deep water of the western Black Sea, and this aspect of regional play risk could be of less concern than was previously considered.

Late Cenozoic landscape evolution along the Ailao Shan Shear Zone, SE Tibetan Plateau: Evidence from fluvial longitudinal profiles and cosmogenic erosion rates

In tectonically active regions, geomorphic features, such as catchment slopes, terraces, and river profiles can be interpreted in the context of tectonic and climatic forcing; however, distinguishing tectonic impacts from other factors such as pre-existing geologic complexities and climate changes is challenging. We use fluvial longitudinal profiles, catchment slopes, and catchment mean erosion rates derived from in-situ cosmogenic 10Be and 26Al to examine the late Cenozoic landscape evolution of the Ailao Shan Shear Zone (ASSZ) in the southeastern Tibetan Plateau. The trunk stream of the Red River, flowing along the eastern side of the shear zone, consists of three sections with distinct channel parameters, separated by knickzones (the Midu, Ejia, and Nansha sections from NW to SE). Tributaries to the Red River within the Ailao Shan Shear Zone in the Ejia and Nansha sections consistently display two channel segments (upper low-gradient and middle steep channel segments); a third set of lower, less steep channel segments are identified only along the tributaries in the Nansha section. Catchment mean erosion rates contrast sharply along strike: ca. 300 m/Myr in the Ejia section and ca. 100 m/Myr in the Nansha section. Collectively, our results provide strong evidence that: 1) two waves of incision induced by pulsed and declining regional uplift are propagating up the Red River shaping the background pattern of river incision; 2) vertical fault displacements, river reorganization and additional factors locally affect river profile morphology. Normalized steepness indices (ksn), catchment slopes, and knickzone distribution vary systematically along the Ailao Shan Shear Zone, indicating long-wavelength regional surface uplift during plateau growth in the middle-late Miocene, which points to a tectonic model involving crustal thickening and diffuse or continuous deformation in the southeastern margin of the Tibetan Plateau.

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley, SEQ, Australia

AbstractThe nature of catchment‐scale sediment (dis)connectivity is the primary influence on sediment delivery to trunk streams and controls the particle size distribution of channel bed sediments. Here, we examine the distribution of major sediment buffers (floodplains, terraces, alluvial fans, trapped tributary fills), barriers (weirs), and effective catchment area (i.e. sediment contributing area) to characterize the potential for coarse sediment (dis)connectivity in 20 tributaries of Lockyer Creek, in the Lockyer Valley, SEQ. We then analyse the distribution of trunk stream sedimentary links to determine how certain tributaries or disconnecting features (buffers and barriers) influence downstream patterns of bed sediment fining along Lockyer Creek. We find that buffering increases downstream in the Lockyer Valley, and that tributary position and shape influence the space available for sediment buffering. Correspondingly, the spatial extent of sediment buffers impacts the distribution of effective catchment area, which influences the sedimentological significance of individual tributaries. Tributary sediment connectivity, the extent of overbank flows (floodwater zones), and weir locations all exert an additional influence on the distribution of sediment links along the trunk stream. These controls are related to the physiographic and climatic setting of the Lockyer Valley, and anthropogenic influences in this system. We conclude that controls on sediment connectivity and bed load sediment characteristics are highly variable between catchments, and that sediment (dis)connectivity merits equal consideration with tributary basin/channel size when determining controls on tributary–trunk stream relationships and channel sediment regime. Copyright © 2017 John Wiley & Sons, Ltd.

Temporal and Spatial Variation Characteristics of the Heavy Metals Content in the Surface Sediment and the Potential Ecological Risk Trends in the Three Gorges Reservoir Area

With the construction progress of the Three Gorges Project, the hydrological situation of Three Gorges Reservoir changes greatly, which causes the changes of suspended solids precipitation conditions and surface sediment traits. This research analyzed the temporal and spatial variation of the heavy metal pollution in the surface sediment and the potential ecological risk trends during the years from 2000 to 2015 in the trunk stream of the Yangtze River from Jiangjin to the Three Gorges Dam area and some major tributaries, such as Jialing River, Yulin River, Wujiang River, Xiaojiang River, Xiangxi River. The results showed that the average content ranges of heavy metals (including Cu, Pb, Mn, As, Hg etc.) in surface sediments at the main stream monitoring sections during the study period were 46.5-85.7 mg·kg-1(Cu), 43.8-65.1 mg·kg-1(Pb), 784.2-910.6 mg·kg-1(Mn), 8.44-11.91 mg·kg-1(As), 0.193-0.236 mg·kg-1(Hg) respectively; The average content ranges of the heavy metals in surface sediments at the main stream monitoring sections during the study period were 16.5-85.6 mg·kg-1(Cu), 25.8-74.8 mg·kg-1(Pb), 573.7-996.3 mg·kg-1 (Mn), 6.96-13.31 mg·kg-1 (As), 0.160-0.232 mg·kg-1 (Hg) respectively. The results also showed that there were obvious differences of the heavy metals content in some areas between the left and right bank of the trunk stream of the Yangtze River in the Three Gorges Reservoir area. The results also showed that the concentration variation trends of the heavy metals were different in the surface sediments, such as Cu, Pb, Mn, As and Hg. The content of Hg was the most influenced element by the water period effect. The concentration variation trends of these elements were different at different monitoring sections during the construction and water harvesting progress of the Three Gorges project. The contents of Cu, Pb, Mn and As in sediment from the Three Gorges Reservoir area showed strong positive correlations between each other. But there was a low correlation between the content of As and those of other elements. There was no significant correlation between the content of Hg and those of other heavy metal elements. According to the geoaccumulation index analytical method, the contents of the heavy metals in surface sediments in the Three Gorges Reservoir area were generally at low enrichment level. But the pollution caused by Hg should be paid attention. The change of potential ecological risk index was small in the main stream and the major tributaries of the Yangtze River (except Wujiang River) in most of the time. It should also be noted that the change of potential ecological risk index fluctuated obviously at a high level before the year of 2008, and then the change fluctuations trends descended with time and tended to be stable.

Eastern margin of Tibet supplies most sediment to the Yangtze River

Zircon provenance studies of modern and ancient fluvial systems help reveal the relative contributions and importance of upstream sediment sources. A 2014 study of detrital zircon U-Pb age distributions from the Yangtze River (China) and its tributaries proposed a strong anthropogenic control on sediment flux. Those data, along with other data from the region, were reanalyzed using multiple detrital zircon U-Pb age distribution comparison techniques and a distribution-mixing model to construct an improved and quantitative view of provenance. The variability in the Yangtze River trunk stream U-Pb age distributions is evaluated with respect to trunk-to-trunk stream comparisons, trunk-to-tributary comparisons, and in mixture models that consider tributary and bedrock contributions, the latter using a comprehensive compilation of bedrock source terranes. Uniformity in the zircon age distribution of the Yangtze River trunk stream is established in the upper reaches, downstream of the first bend, and maintained by the left-bank tributaries to its outlet. Whether considering the bedrock source terranes or only the modern Yangtze River sediments, the major source of sediments contributing to Yangtze River is clearly the eastern edge of the Tibetan Plateau (e.g., Songpan Ganze complex, Longmenshan Range), where rock uplift rates are high. The purported increase in anthropogenic impact on sediment yield in the lowlands, at least as viewed through detrital zircon age distributions, is insignificant.

Catchment response to lava damming: integrating field observation, geochronology and landscape evolution modelling

AbstractCombining field reconstruction and landscape evolution modelling can be useful to investigate the relative role of different drivers on catchment response. The Geren Catchment (~45 km2) in western Turkey is suitable for such a study, as it has been influenced by uplift, climate change and lava damming. Four Middle Pleistocene lava flows (40Ar/39Ar‐ dated from 310 to 175 ka) filled and dammed the Gediz River at the Gediz–Geren confluence, resulting in base‐level fluctuations of the otherwise uplift‐driven incising river. Field reconstruction and luminescence dating suggest fluvial terraces in the Geren Catchment are capped by Middle Pleistocene aggradational fills. This showed that incision of the Geren trunk stream has been delayed until the end of MIS 5. Subsequently, the catchment has responded to base‐level lowering since MIS 4 by 30 m of stepped net incision. Field reconstruction left us with uncertainty on the main drivers of terrace formation. Therefore, we used landscape evolution modelling to investigate catchment response to three scenarios of base‐level change: (i) uplift with climate change (rainfall and vegetation based on arboreal pollen); (ii) uplift, climate change and short‐lived damming events; (iii) uplift, climate and long‐lived damming events. Outputs were evaluated for erosion–aggradation evolution in trunk streams at two different distances from the catchment outlet. Climate influences erosion–aggradation activity in the catchment, although internal feedbacks influence timing and magnitude. Furthermore, lava damming events partly control if and where these climate‐driven aggradations occur. Damming thus leaves a legacy on current landscape evolution. Catchment response to long‐duration damming events corresponds best with field reconstruction and dating. The combination of climate and base level explains a significant part of the landscape evolution history of the Geren Catchment. By combining model results with fieldwork, additional conclusions on landscape evolution could be drawn. Copyright © 2016 John Wiley & Sons, Ltd.

Coexistence of detonation with deflagration in rotating detonation engines

Rotating detonation engines of high thermal efficiency and specific impulse have been studied a lot. However, rotating detonation waves lead to uneven flow field, local high temperature and high pressure, tending to damage the combustor. An experimental way to keep both rotating detonation waves and deflagration in the combustor and to combine the advantages of rotating detonation engines and deflagration engines, is introduced here. Pressure sensors measure the pressure of rotating detonation waves and gas mass flow controllers control the mass flow rates of reactants. A standard speed camera captures the events of rotating detonation and deflagration. It is discovered that the rotating detonation is much more intense than deflagration. Both upstream rotating detonation waves and downstream deflagration respectively dependent on the trunk stream and the tributary can coexist in the combustor. The predetonator is the boundary between the detonation region and deflagration region in the combustor. The coexistence of detonation and deflagration weakens the combustion instability caused by rotating detonation, which may be helpful for rotating detonation to be applied.

Sediment jamming of a trunk stream by hyperconcentrated floods from small tributaries: case of the Upper Yellow River, China

ABSTRACTThe tributary–trunk stream relationship is investigated with respect to hyperconcentrated flows and coupled wind–water processes in the Yellow River, China. Ten small tributaries that drain only 3% of the total drainage area of the trunk stream transport large amounts of relatively coarse sediment from the desert to the trunk stream during hyperconcentrated floods. The resultant strong sedimentation often jams the trunk stream, leading to serious disasters. This study reveals the cause of this interesting phenomenon and proposes countermeasures for disaster reduction. A typical sediment-jamming event (SJE) in July 1989 was thoroughly analysed based on the observational data, including the beginning, development and final stages of the event. An index of the geomorphologic effectiveness of the tributary on the trunk stream and a number of indices describing SJEs and the influencing factors are adopted, based on which a discrimination relationship for the occurrence of SJEs is established and some statistical relationships are also established. The SJE’s hydrological and geomorphologic impacts are discussed at short timescales (from several days to one month) and at long time scales (up to 46 years). The results may help to gain a new insight into the study of the tributary–trunk stream relationship, and provide useful information for sediment management and disaster-reduction planning in the drainage basin. Countermeasures are suggested to reduce the channel sedimentation and the risk of sediment-jamming disaters.Editor M.C. Acreman Associate editor Q. Zhang

Pleistocene fluviatile deposits in the Ourika drainage basin (Marrakech High Atlas, Morocco): indicators of climatic variations associated with base level change

Aggradational packages of alluvial sediment are preserved in the Ourika river basin. Field mapping and DEM analysis allowed us to identify a model sequence of river terraces. We focus on sites where the study of sedimentary sections allow us to decipher the sedimentary evolution of the Ourika watershed. Quaternary evolution of the drainage basin is characterized by major phases of sediment accumulation and erosion, forming alluvial fans and cut-fill terraces. More intense rainfall events during the Middle Pleistocene Ourika drainage basin resulted in increased erosion and transport of sediment from the hillslopes into the trunk river. First, the cut-fill terraces near the sub-basins outlets are formed by a large-scale aggradation, followed by a main vertical incision and lateral erosion. Then, the second sedimentation period was probably a result of increased precipitation that caused landsliding in steep sub-basins. Finally, a last stage of incision in the Ourika Valley is linked to a base level lowering due to climatic fluctuations. We suggest that cyclic climatic fluctuations superimposed on a continuous uplift of the High Atlas are responsible for the generation of stepped terraces along the Ourika River. Sub-basins steep affected by erosion processes dominated by landslides rocky shallow were accompanied by debris flows along convex profiles at their downstream end and associated with steep knickpoints. We interpreted erosion of the Pleistocene deposits as the result of an autocyclic negative feedback such as exhaustion of the hillslope sediment stocks and the resulting increase of the relative capacity of the trunk stream to bring and transfer sediment towards the Ourika Valley.

Morphotectonic analysis of the Madhumati watershed, northeast Kashmir Valley

The present study examined the morphotectonic parameters of the Madhumati basin with the emphasis on its implication for tectonic activity. Data for this study were obtained from toposheets in digital format which were subjected to field confirmation. We performed digital elevation model (DEM) analysis, and we extracted several geomorphic indices: mountain front sinuosity, valley floor width to valley height ratio, hypsometric curve and integral, stream length gradient index, transverse topography symmetry, drainage basin asymmetry and basin elongation ratio. These morphometric parameters may indicate tectonic activity with a tilt to the south of the northern margin of the Kashmir Basin (Madhumati Catchment). The results reveal that the basin area was 453.71 km2 and the basin was found to be tectonically active with average S mf value 1.14, stream gradient index (SL) 1026.7, Vf 0.13 and T 0.56. The results of elongation ratio 0.15 reveal that the basin is strongly elongate and active. Also, the calculated result of AF 68.52 % reveals that the basin has shifted up right to the trunk stream facing downstream. The results of hypsometric integral 0.49 and convex-up hypsometric curve reveal that the basin has high elevation relative to mean, narrow and incised valleys and has rugged topography, is in youthful stage and is tectonically active.