Uncertainty Estimate of Surface Irradiances Computed with MODIS-, CALIPSO-, and CloudSat-Derived Cloud and Aerosol Properties

Differences of modeled surface upward and downward longwave and shortwave irradiances are calculated using modeled irradiance computed with active sensor-derived and passive sensor-derived cloud and aerosol properties. The irradiance differences are calculated for various temporal and spatial scales, monthly gridded, monthly zonal, monthly global, and annual global. Using the irradiance differences, the uncertainty of surface irradiances is estimated. The uncertainty (1σ) of the annual global surface downward longwave and shortwave is, respectively, 7?W?m^?2 (out of 345?W?m^?2) and 4?W?m^?2 (out of 192?W?m^?2), after known bias errors are removed. Similarly, the uncertainty of the annual global surface upward longwave and shortwave is, respectively, 3?W?m^?2 (out of 398?W?m^?2) and 3?W?m^?2 (out of 23?W?m^?2). The uncertainty is for modeled irradiances computed using cloud properties derived from imagers on a sun-synchronous orbit that covers the globe every day (e.g., moderate-resolution imaging spectrometer) or modeled irradiances computed for nadir view only active sensors on a sun-synchronous orbit such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation and CloudSat. If we assume that longwave and shortwave uncertainties are independent of each other, but up- and downward components are correlated with each other, the uncertainty in global annual mean net surface irradiance is 12?W?m^?2. One-sigma uncertainty bounds of the satellite-based net surface irradiance are 106?W?m^?2 and 130?W?m^?2.     

Flood hydrology and geomorphic effectiveness in the central Appalachians

This paper compares hydrologic records and geomorphic effects of several historic floods in the central Appalachian region of the eastern United States. The most recent of these, occurring in November 1985, was the largest ever recorded in West Virginia, with peak discharges exceeding the estimated 500-year discharge at eight of eleven stations in the South Branch Potomac River and Cheat River basins. Geomorphic effects on valley floors included some of the most severe and widespread floodplain erosion ever documented and exceeded anything seen in previous floods, even though comparable or greater rainfall and unit discharge have been observed several times in the region over the past 50 years. Comparison of discharge-drainage area plots suggests that the intensity and spatial scale of the November 1985 flood were optimal for erosion of valley floors along the three forks of the South Branch Potomac River. However, when a larger geographic area is considered, rainfall totals and discharge-drainage area relationships are insufficient predictors of geomorphic effectiveness for valley floors at drainage areas of 250 to 2500 km². Unit stream power was calculated for the largest recorded flood discharge at 46 stations in the central Appalachians. Maximum values of unit stream power are developed in bedrock canyons, where the boundaries are resistant to erosion and the flow cross-section cannot adjust its width to accommodate extreme discharges. The largest value was 2570 W m^?2; record discharge at most stations was associated with unit stream power values less than 300 W m^?2, but more stations exceeded this value in the November 1985 flood than in the other floods that were analysed. Unit stream power at indirect discharge measurement sites near areas experiencing severe erosion in this and other central Appalachian floods generally exceeded 300 W m^?2; reach-average values of 200-500 W m^?2 were calculated for valleys where erosion damage was most widespread. Despite these general trends, unit stream power is not a reliable predictor of geomorphic change for individual sites. Improved understanding of flood impacts will require more detailed investigation of interactions between local site characteristics and patterns of flood flow over the valley floor.     

A model of equilibrium bed topography for meander bends with erodible banks

Channel curvature produces secondary currents and a transverse sloping channel bed, along which the depth increases towards the outer bank. As a result deep pools tend to form adjacent to the outer bank, promoting bank collapse. The interaction of sediment grains with the primary and secondary flow and the transverse sloping bed also causes meanders to move different grain sizes in different proportions and directions, resulting in a consistent sorting pattern. Several models have been developed to describe this process, but they all have the potential to over‐predict pool depth because they cannot account for the influence of erodible banks. In reality, bank collapse might lead to the development of a wider, shallower cross‐section and any resulting flow depth discrepancy can bias associated predictions of flow, sediment transport, and grain‐size sorting. While bed topography, sediment transport and grain sorting in bends will partly be controlled by the sedimentary characteristics of the bank materials, the magnitude of this effect has not previously been explored. This paper reports the development of a model of flow, sediment transport, grain‐size sorting, and bed topography for river bends with erodible banks. The model is tested via intercomparison of predicted and observed bed topography in one low‐energy (5·3 W m^?2 specific stream power) and one high‐energy (43·4 W m^?2) study reach, namely the River South Esk in Scotland and Goodwin Creek in Mississippi, respectively. Model predictions of bed topography are found to be satisfactory, at least close to the apices of bends. Finally, the model is used in sensitivity analyses that provide insight into the influence of bank erodibility on equilibrium meander morphology and associated patterns of grain‐size sorting. The sensitivity of meander response to bank cohesion is found to increase as a function of the available stream power within the two study bends. Copyright © 2002 John Wiley & Sons, Ltd.     

An improved hemispherical photography model for stream surface shortwave radiation estimations in a central U.S. hardwood forest

Hemispherical photographs of forest canopies can be used to develop sophisticated models that predict incident below canopy shortwave radiation on the surface of interest (i.e. soil and water). Hemispherical photographs were collected on eight dates over the course of a growing season to estimate leaf area index and to quantify solar radiation incident on the surface of two stream reaches based on output from Gap Light Analyser and Hemisfer software. Stream reaches were shaded by a mixed‐deciduous Ozark border forested riparian canopy. Hemispherical photo model results were compared to observed solar radiation sensed at climate stations adjacent to each stream reach for the entire 2010 water year. Modeled stream‐incident shortwave radiation was validated with above‐stream pyranometers for the month of September. On average, the best hemispherical photo models underestimated daily averages of solar radiation by approximately 14% and 12% for E–W and N–S flowing stream reaches, respectively (44.7 W/m² measured vs 38.4 W/m² modeled E–W, 46.8 W/m² vs. 41.1 W/m²N–S). The best hemispherical photo models overestimated solar radiation relative to in–Stream pyranometers placed in the center of each stream reach by approximately 7% and 17% for E–W and N–S stream reaches respectively (31.3 W/m² measured vs 33.5 W/m² modeled E–W, 31.5 W/m² vs. 37.1 W/m²N–S). The model provides a geographically transferable means for quantifying changes in the solar radiation regime at a stream surface due to changes in canopy density through a growing season, thus providing a relatively simple method for estimating surface and water heating in canopy altered environments (e.g. forest harvest). Copyright © 2012 John Wiley & Sons, Ltd.     

Rate of sediment yield following small‐scale volcanic eruptions: a quantitative assessment at the Merapi and Semeru stratovolcanoes,Java, Indonesia

Sediment yields were calculated on the ?anks of Merapi and Semeru volcanoes in Java, Indonesia, using two different methods. During the ?rst year following the 22 November 1994 eruption of Merapi, a sediment yield in excess of 1·5 × 10⁵ m³ km^?2 yr^?1 was calculated in the Boyong River drainage basin, based on the volumes of sediment that were trapped by ?ve check dams. At Semeru, sediment discharges were assessed in the Curah Lengkong River from direct measurements on the lahars in motion and on the most signi?cant stream?ows. The calculated rate of sediment yield during one year of data in 2000 was 2·7 × 10⁵ m³ km^?2 yr^?1. Sediment yields are dominated by rain‐triggered lahars, which occur every rainy season in several drainage basins of Merapi and Semeru volcanoes, mostly during the rainy season extending from October to April. The return period of lahars carrying sediment in excess of 5 × 10⁵ m³ is about one year in the Curah Lengkong River at Semeru. At Merapi, the volume of sediments transported by a lahar did not exceed 2·8 × 10⁵ m³ in the Boyong River during the rainy season 1994–95. On both volcanoes, the sediments are derived from similar sources: pyroclastic‐?ow/surges deposits, rockfalls from the lava domes, and old material from the riverbed and banks. However, daily explosions of vulcanian type at Semeru provide a more continuous sediment supply than at Merapi. Therefore, sediment yields are larger at Semeru. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of sediment size on transport capacity of overland flow on steep slopes

Abstract

Sediment transport capacity is a key concept in determining rates of detachment and deposition in process-based erosion models, yet limited studies have been conducted on steep slopes. We investigated the effects of sediment size on transport capacity of overland flow in a flume. Unit flow discharge ranged from 0.66 to 5.26?×?10^-3 m² s^-1, and slope gradient varied from 8.7 to 42.3%. Five sediment size classes (median diameter, d ₅₀, of 0.10, 0.22, 0.41, 0.69 and 1.16 mm) were used. Sediment size was inversely related to transport capacity. The ratios of average transport capacity of the finest class to those of the 0.22, 0.41, 0.69 and 1.16 mm classes were 1.09, 1.30, 1.55 and 1.92, respectively. Sediment transport capacity increased as a power function of flow discharge and slope gradient (R²?=?0.98), shear stress (R²?=?0.95), stream power (R²?=?0.94), or unit stream power (R²?=?0.76). Transport capacity generally decreased as a power function of sediment size (exponent?=??0.35). Shear stress and stream power predicted transport capacity better than unit stream power on steep slopes when transport capacity was <7 kg m^-1 s^-1. Sediment transport capacity increased linearly with mean flow velocity. Critical or threshold velocity increased as a power function of sediment size (R²?=?0.93). Further studies with fine soil particles are needed to quantify the effects of sediment size on transport capacity of overland flow on steep slopes.

Citation Zhang, G.-H., Wang, L.-L., Tang, K.-M., Luo, R.-T. & Zhang, X.C. (2011) Effects of sediment size on transport capacity of overland flow on steep slopes. Hydrol. Sci. J. 56(7), 1289–1299.     

Sediment transport by burrowing mammals,Marin County,California

Field observations suggest that burrowing activity is the primary mode of sediment transport currently active in a small grassland drainage basin in Marin County, California. Spatial concentrations of the 1150 gopher mounds surveyed vary from 0-16 mounds m^?2 on interfluves to 0.32 mounds m^?2 on sideslopes and in the topographic hollow, with localized concentrations of up to 2.88 mounds m^?2 on the margins of the colluvial deposit. Simple models of sediment transport by burrowing activity yield estimates of between 0.91 and 2.33 cm³ cm^?1 yr^?1 for the basin as a whole, with absolute minimum and maximum rates of 0.48 and 631 cm³ cm^?1 yr^?1. These values are similar to those previously estimated for this area (Lehre, 1982) and are nearly an order-of-magnitude less than average long-term sediment transport rates at the same site (Reneau, 1988).     

Flow hydraulics and geomorphic effects of glacial‐lake outburst floods in the Mount Everest region,Nepal

Glacial‐lake outburst floods (GLOFs) on 3 September 1977 and 4 August 1985 dramatically modified channels and valleys in the Mount Everest region of Nepal by eroding, transporting, and depositing large quantities of sediment for tens of kilometres along the flood routes. The GLOF discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff, glacier meltwater, and monsoonal precipitation (referred to as seasonal high flow floods, SHFFs). Specific stream power values ranged from as low as 1900 W m^?2 in wide, low‐gradient valley segments to as high as 51 700 W m^?2 in narrow, high‐gradient valley segments bounded by bedrock. Along the upper 16 km of the GLOF routes, the reach‐averaged specific stream power of the GLOFs was 3·2 to 8·0 times greater than the reach‐averaged specific stream power of the SHFFs. The greatest geomorphic change occurred along the upper 10 to 16 km of the GLOF routes, where the ratio between the GLOF specific stream power and the SHFF specific stream power was the greatest, there was an abundant supply of sediment, and channel/valley boundaries consisted primarily of unconsolidated sediment. Below 11 to 16 km from the source area, the geomorphic effects of the GLOFs were reduced because of the lower specific stream power ratio between the GLOFs and SHFFs, more resistant bedrock flow boundaries, reduced sediment supply, and the occurrence of past GLOFs. Copyright © 2003 John Wiley & Sons, Ltd.     

High rates of bedload transport measured from infilling rate of large strudel-scour craters in the Beaufort Sea,Alaska

Strudel scours are craters in the sea floor as much as 25 m wide and 6 m deep, that are excavated by vertical drainage flow during the yearly spring flooding of vast reaches of shorefast ice surrounding arctic deltas; they form at a rate of about 2.5 km^?2 y^?1. We monitored two such craters in the Beaufort Sea and found that in relatively unprotected sites they fill in by deposition from bedload in 2 to 3 years. Net westward sediment transport results in sand layers dipping at the angle of repose westward into the strudel-scour crater, whereas the west wall of the crater remains steep to vertical. At the bottom the crater traps almost all bedload: sand, pebbles, and organic detritus. As infilling progresses, the materials are increasingly winnowed, and bypassing must occur. Over a 20m wide sector, an exposed strudel scour trapped 360 m³ of bedload during two seasons; this infilling represents a bedload transport rate of 9 m³ y^?1 m^?1. This rate should be applicable to a 4.5-km wide zone with equal exposure and similar or shallower depth. Within this zone, the transport rate is 40,500 m³ y^?1, similar to estimated longshore transport rates on local barrier beaches. Based on the established rate of cut and fill, all the delta-front deposits should consist of strudel-scour fill. Vibracores typically show dipping interbedded sand and lenses of organic material draped over steep erosional contacts, and an absence of horizontal continuity of strata—criteria that should uniquely identify high-latitude deltaic deposits. Given a short 2- to 3-year lifespan, most strudel scours seen in surveys must be old and partially filled. The same holds true for ice gouges and other depressions not adjusted to summer waves and currents, and therefore such features record events of only the past few years. In view of such high rates of bottom reworking of the shallow shelf, any human activities causing turbidity, such as dredging, would have little effect on the environment. However, huge amounts of transitory material trapped by long causeways planned for offshore development would result in major changes in the environment.     

Factors controlling the chemical evolution of travertine‐depositing rivers of the Barkly karst,northern Australia

Groundwaters feeding travertine‐depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major‐ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO₂ outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO₃ per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m³ s^?1) and Carl Creek (Q = 0·50 m³ s^?1) have identical stream gradients, but the loss of CaCO₃ per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m³ s^?1), O'Shanassy River (Q = 0·57 m³ s^?1) and Lawn Hill Creek (Q = 0·72 m³ s^?1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd.     

VERTEX: manganese transport through oxygen minima

Manganese transport through a well-developed oxygen minimum was studied off central Mexico (18°N, 108°W) in October–November 1981 as part of the VERTEX (Vertical Transport and Exchange) research program. Refractory, leachable and dissolved Mn fractions associated with particulates caught in traps set at eight depths (120–1950 m) were analyzed. Particles entering the oxygen minimum had relatively large Mn loads; however, as the particulates sank further into the minimum, total Mn fluxes steadily decreased from 190 nmol m^?2 day^?1 at 120 m to 36 nmol m^?2 day^?1 at 400 m. Manganese fluxes then steadily increased in the remaining 800–1950 m, reaching rates of up to 230 nmol m^?2 day^?1 at 1950 m.Manganese concentrations were also measured in the water column. Dissolved Mn levels < 3.0 nmol kg^?1 were consistently observed within the 150–600 m depth interval. In contrast, suspended particulate leachable Mn amounts were especially low at those depths, and never exceeded 0.04 nmol kg^?1.The combined water column and particle trap data clearly indicate that Mn is released from particles as they sink through the oxygen minimum. Rate-of-change estimates based on trap flux data yield regeneration rates of up to 0.44 nmol kg^?1 yr^?1 in the upper oxygen minimum (120–200 m). However, only 30% of the dissolved Mn in the oxygen minimum appears to be from sinking particulate regeneration; the other 70% probably results from continental-slope-release-horizontal-transport processes.Dissolved Mn scavenges back onto particles as oxygen levels begin to increase with depth. Scavenging rates ranging from ?0.03 to ?0.09 nmol kg^?1 yr^?1 were observed at depths from 700 to 1950 m. These scavenging rates result in Mn residence times of 16–19 years, and scavenging rate constants on the order of 0.057 yr^?1. Manganese removal via scavenging on sinking particles below the oxygen minimum is balanced by Mn released along continental boundaries and transported horizontally via advective-diffusive processes.Manganese appears to be very weakly associated with particulates. Nevertheless, the amounts of Mn involved with sinking biogenic particles are large, and the resulting fluxes are on the same order of magnitude as those necessary to explain the excess Mn accumulating on the sea floor. The overall behavior of Mn observed in this, and other, studies strongly suggests some type of equilibrium occurring between dissolved and particulate phases. This equilibrium appears to shift in direct or indirect response to dissolved oxygen levels.     

A rare landform: Yerköprü travertine bridges in the Taurids Karst Range,Turkey

Two examples of travertine bridges are observed at 8 to 15 m above stream level in the Lower Zamanti Basin, Eastern Taurids, Turkey. Yerköprü‐1 and Yerköprü‐2 bridges are currently being deposited from cool karstic groundwaters with log P_CO2 > 10^?2 atm. The surface area and the total volume of travertine in Yerköprü‐1 bridge are 4350 m² and 40 000 m³, whereas the values for Yerköprü‐2 are 2250 m² and 20 000 m³, respectively. The interplay of hydrogeological structure, local topography, calcite‐saturated hanging springs, algal activity and rapid downcutting in the streambed appear to have led to the formation of travertine bridges. Aeration through cascades and algal uptake causes efficient carbon dioxide evasion that enhances travertine formation. Algal curtains aid lateral development of travertine rims across the stream. Model calculations based on a hypothetical deposit in the form of a half‐pyramid implied that lateral development should have occurred from both banks of the stream in the Yerköprü‐1 bridge, whereas one‐sided growth has been sufficient for Yerköprü‐2. The height difference between travertine springs and the main stream appears to be a result of Pleistocene glaciation during which karstic base‐level lowering was either stopped or slowed down while downcutting in the main stream continued. Copyright © 2002 John Wiley & Sons, Ltd.     

Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data

This study used realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE mission, was applied to CloudSat, CALIPSO and MODIS satellite data thus producing 3D cloudy atmospheres measuring 61 km wide by 14,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances were then computed by a Monte Carlo photon transfer model run in both full 3D and 1D independent column approximation modes. Results were averaged into 1,303 (50 km)² domains. For domains with total cloud fractions A _c  < 0.7 top-of-atmosphere (TOA) albedos tend to be largest for 3D transfer with differences increasing with solar zenith angle. Differences are largest for A _c  > 0.7 and characterized by small bias yet large random errors. Regardless of A _c , differences between 3D and 1D transfer rarely exceed ±30 W m^?2 for net TOA and surface fluxes and ±10 W m^?2 for atmospheric absorption. Horizontal fluxes through domain sides depend on A _c with ～20% of cases exceeding ±30 W m^?2; the largest values occur for A _c  > 0.7. Conversely, heating rate differences rarely exceed ±20%. As a cursory test of TOA radiative closure, fluxes produced by the 3D model were averaged up to (20 km)² and compared to values measured by CERES. While relatively little attention was paid to optical properties of ice crystals and surfaces, and aerosols were neglected entirely, ～30% of the differences between 3D model estimates and measurements fall within ±10 W m^?2; this is the target agreement set for EarthCARE. This, coupled with the aforementioned comparison between 3D and 1D transfer, leads to the recommendation that EarthCARE employ a 3D transport model when attempting TOA radiative closure.     

Understanding of the Common Land Model performance for water and energy fluxes in a farmland during the growing season in Korea

The Common Land Model (CLM) is one of the most widely used land surface models (LSMs) due to the practicality of its simple parameterization scheme and its versatility in embracing a variety of field datasets. The improved assessment of land surface water and energy fluxes using CLM can be an alternative approach for understanding the complex land–atmosphere interactions in data‐limited regions. The understanding of water and energy cycles in a farmland is crucial because it is a dominant land feature in Korea and Asia. However, the applications of CLM to farmland in Korea are in paucity. The simulations of water and energy fluxes by CLM were conducted against those from the tower‐based measurements during the growing season of 2006 at the Haenam site (a farmland site) in Korea without optimization. According to the International Geosphere–Biosphere Programme (IGBP) land cover classification, a homogeneous cropland was selected initially for this study. Although the simulated soil moisture had a similar pattern to that of the observed, the former was relatively drier (at 0·1 m³ m^?3) than the latter. The simulated net radiation showed good agreement with the observed, with a root mean squared error (RMSE) of 41 W m^?2, whereas relatively large discrepancies between the simulation and observation were found in sensible (RMSE of 66 W m^?2) and latent (RMSE of 60 W m^?2) heat fluxes. On the basis of the sensitivity analysis, soil moisture was more receptive to land cover and soil texture parameterizations when compared to soil temperature and turbulent fluxes. Despite the uncertainty in the predictive capability of CLM employed without optimization, the initial performance of CLM suggests usefulness in a data‐limited heterogeneous farmland in Korea. Further studies are required to identify the controls on water and energy fluxes with an improved parameterization. Copyright © 2010 John Wiley & Sons, Ltd.     

Sediment transport in Swiss torrents

Sediment loads have been measured in six Swiss mountain torrents over several decades. Most of these torrent catchments are situated in the prealpine belt. They have catchment areas of between 0·5 and 1·7 km². Bedslopes at the measuring sites vary between 5 and 17 per cent, and peak discharges up to 12 m³ s⁻¹ have been recorded. Geophone sensors installed in the Erlenbach stream allow bedload transport activity to be monitored and sediment volumes associated with each flood event to be determined. A detailed analysis of the measurements in this stream results in an empirical equation in which the sediment load per flood event is expressed as a function of the effective runoff volume (discharges above the threshold for bedload motion) and of the normalized peak discharge. For the total of 143 investigated flood events in the Erlenbach stream, the deviation of the predicted from the measured value is within a factor of two for more than two-thirds of all events. A distinction can be made between summer and winter events in analysing the bedload transport events. The summer events, mainly caused by thunderstorms, transport comparatively larger sediment loads than the winter events. For the other investigated streams, the periods of the deposited sediment volume surveys cover in general several flood events. An analysis is performed analogous to that for the Erlenbach stream. The sediment loads show a similar dependency on the two factors effective runoff volume and normalized peak discharge. However, the exponents of these factors in the power law expressions differ from stream to stream. A comparison of the investigated stream shows that some of the variation can be explained by considering the bedslope above the measuring site. The inclusion of a bedslope factor is in agreement with laboratory investigations on bedload transport. © 1997 John Wiley & Sons, Ltd.     

Nondimensional sediment transport capacity of sand soils and its response to parameter in the Loess Plateau of China

Soil erosion is a major contributor to land degradation in the Loess Plateau in China. To clarify the sediment transport capacity of overland flow influenced by hydraulic parameters, such as shear stress, sand shear stress (hydraulic gradient partition method and hydraulic radius partition method), mean flow velocity, Froude number, stream power, and unit stream power, indoor experiments with eight-unit-width flow discharges from 0.0667 × 10⁻³ to 0.3333 × 10⁻³ m²·s⁻¹, six slope gradients from 3.49 to 20.79%, and two kinds of sand soils (d₅₀ = 0.17 and 0.53 mm) were systematically investigated. A nondimensional method was adopted in data processing. Results showed that there was a partition phenomenon of relation curves because of the different median grain diameters. The correlation between the nondimensional stream power and nondimensional sediment transport capacity was the highest, followed by the correlation between the nondimensional unit stream power and nondimensional sediment transport capacity. However, there was a poor correlation between the flow intensity indices of velocity category and nondimensional sediment transport capacity. Nondimensional stream power, nondimensional unit stream power, and nondimensional shear stress could predict sediment transport capacity well. Ignoring the partition phenomenon of the relation curves, stream power could be used to predict sediment transport capacity, with a coefficient of determination of .85. Furthermore, a general flow intensity index was obtained to predict sediment transport capacity of overland flow. Finally, an empirical formula for predicting sediment transport capacity with a coefficient of determination of .90 was established by multiple regression analyses based on the general flow intensity index. During the analysis between measured sediment transport capacities in present study and predicted values based on Zhang model, Mahmoodabadi model, and Wu model, it was found that these three models could not accurately predict sediment transport capacities of this study because different models are estimated on the basis of different experimental conditions.     

Indirect estimation of ungauged peak discharges in a bedrock channel with reference to design discharge selection

Geomorphological evidence and recent trash lines were used as stage indicators in a step-backwater computer model of high discharges through an ungauged bedrock channel. The simulation indicated that the peak discharge from the 26.7 m² catchment was close to 150m³s^?1 during the passage of Hurricane Charlie in August 1986. This estimate can be compared with an estimate of 130–160 m³s^?1 obtained using the Flood Studies Report (FSR) unit hydrograph methodology. Other palaeostage marks indicate that higher stages have occurred at an earlier time associated with a discharge of 200 m³s^?1. However, consideration of both the geometry of a plunge pool and transport criteria for bedrock blocks in the channel indicates that floods since 1986 have not exceeded 150 m³s^?1. Given that the estimated probable maximum flood (PMF) calculated from revised FSR procedure is at least 240 m³s^?1, it is concluded that compelling evidence for floods equal to the PMF is lacking. Taking into consideration the uncertainty of the discharge estimation, the 1986 flood computed using field evidence has a minimum return period of 100 years using the FSR procedure. This may be compared with a return period for the same event in the neighbouring gauged River Greta of > 100 years and a rainfall return period of 190 years. In as much as discharges of similar order to FSR estimates are indicated, it is concluded (a) that regional geomorphological evidence and flood simulation within ungauged catchments may be useful as a verification for hydrological estimates of recent widespread flood magnitude and (b) that palaeohydraulic computation can be useful in determining the magnitude of the local maximum [historic] flood when determining design discharges for hydraulic structures within specific catchments.     

Step–pool evolution in the Rio Cordon,northeastern Italy

The principle that formative events, punctuated by periods of evolution, recovery or temporary periods of steady‐state conditions, control the development of the step–pool morphology, has been applied to the evolution of the Rio Cordon stream bed. The Rio Cordon is a small catchment (5 km²) within the Dolomites wherein hydraulic parameters of floods and the coarse bedload are recorded. Detailed field surveys of the step–pool structures carried out before and after the September 1994 and October 1998 floods have served to illustrate the control on step–pool changes by these floods. Floods were grouped into two categories. The first includes ‘ordinary’ events which are characterized by peak discharges with a return time of one to five years (1·8–5·15 m³ s^?1) and by an hourly bedload rate not exceeding 20 m³ h^?1. The second refers to ‘exceptional’ events with a return time of 30–50 years. A flood of this latter type occurred on 14 September 1994, with a peak discharge of 10·4 m³ s^?1 and average hourly bedload rate of 324 m³ h^?1. Step–pool features were characterized primarily by a steepness parameter c = (H/L_s)/S. The evolution of the steepness parameter was measured in the field from 1992 to 1998. The results indicate that maximum resistance conditions are gradually reached at the end of a series of ordinary flood events. During this period, bed armouring dominate the sediment transport response. However, following an extraordinary flood and unlimited sediment supply conditions, the steepness factor can suddenly decrease as a result of sediment trapped in the pools and a lengthening of step spacing. The analogy of step spacing with antidune wavelength and the main destruction and transformation mechanism of the steps are also discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

Radiogenic heat production in the lithosphere of Sulu ultrahigh-pressure metamorphic belt

The Chinese Continental Scientific Drilling (CCSD) project is located at the Sulu ultrahigh-pressure metamorphic (UHPM) belt. It offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks. Based on the concentrations of radiogenic elements U, Th and K on 349 samples from main hole of CCSD (CCSD MH), pilot holes and exposures, we determined radiogenic heat productions of all major rock types in the Sulu UHPM belt. Results show the mean values of orthogneiss and paragneiss are respectively 1.65 ± 0.81 and 1.24 ± 0.61 µW m^? 3. Due to different composition and grade of retrogressive metamorphism, the eclogites display significant scatter in radiogenic heat production, ranging from 0.01 to 2.85 µW m^? 3, with a mean of 0.44 ± 0.55 µW m^? 3. The radiogenic heat production in ultramafic rocks also varies within a large range of 0.02 to 1.76 µW m^? 3, and the average turns out to be 0.18 ± 0.31 µW m^? 3. Based on the measurements and crustal petrologic model, the vertical distribution model of heat production in Sulu crust is established. The resulting mean heat production (0.76 µW m^? 3) contributes 24 mW m^? 2 to the surface heat flow. 1-D thermal model indicates that the temperature at the Moho reaches above 750 °C, and the thermal thickness of the lithosphere is ~ 75 km, in good agreement with the geophysical results. The high teat flow (~ 75 mW m^? 2) together with thin lithosphere presents strong support for the extension events during the late Cretaceous and Cenozoic.     

Debris-flow-dominated sediment transport through a channel network after wildfire

Field studies that investigate sediment transport between debris-flow-producing headwaters and rivers are uncommon, particularly in forested settings, where debris flows are infrequent and opportunities for collecting data are limited. This study quantifies the volume and composition of sediment deposited in the arterial channel network of a 14-km² catchment (Washington Creek) that connects small, burned and debris-flow-producing headwaters (<1 km²) with the Ovens River in SE Australia. We construct a sediment budget by combining new data on deposition with a sediment delivery model for post-fire debris flows. Data on deposits were plotted alongside the slope–area curve to examine links between processes, catchment morphometry and geomorphic process domains. The results show that large deposits are concentrated in the proximity of three major channel junctions, which correspond to breaks in channel slope. Hyperconcentrated flows are more prominent towards the catchment outlet, where the slope–area curve indicates a transition from debris flow to fluvial domains. This shift corresponds to a change in efficiency of the flow, determined from the ratio of median grain size to channel slope. Our sediment budget suggests a total sediment efflux from Washington Creek catchment of 61 × 10³ m³. There are similar contributions from hillslopes (43 ± 14 × 10³ m³), first to third stream order channel (35 ± 12 × 10³ m³) and the arterial fourth to fifth stream order channel (31 ± 17 × 10³ m³) to the total volume of erosion. Deposition (39 ± 17 × 10³ m³) within the arterial channel was higher than erosion (31 ± 17 × 10³ m³), which means a net sediment gain of about 8 × 10³ m³ in the arterial channel. The ratio of total deposition to total erosion was 0.44. For fines <63 μm, this ratio was much smaller (0.11), which means that fines are preferentially exported. This has important implications for suspended sediment and water quality in downstream rivers. © 2019 John Wiley & Sons, Ltd.