Large Braided River Research Articles

The paleoenvironment of the Olympia beds based on fossil beetles from Discovery Park, Seattle, Washington, U.S.A.

Two fossil insect assemblages with ages of 17,959 and 19,786 cal BP are reported from cross-laminated silts and sands within the Olympia beds at Magnolia Bluff, Discovery Park, Seattle, Washington (N 47° 39′, W 122° 25′). The silts accumulated during MIS 2 at a time when the Puget Lobe of the Cordilleran Ice Sheet was advancing southward. Eventually the Olympia beds were buried sequentially by lacustrine beds, outwash sands and gravels and finally till. The depositional environment based on paleoecology and sedimentary facies was a floodplain of a large braided river. The fossils are disarticulated skeletal parts representing a diverse fauna of 132 beetle species, all extant. The habitats represented by fossils include sparsely vegetated sand and gravel bars (Opisthius richardsoni), open muddy areas (Elaphrus californicus), and vegetation-shaded banks (Elaphrus clairvillei and Elaphrus purpurans). Outside of the floodplain, the habitat was grassland (Carabus taedatus) with occasional stands of coniferous trees indicated by scolytids (bark beetles). Large mammals probably used the river as a watering hole, based on the abundance of dung-feeding Aphodiinae (scarabs) and staphylinid beetles (Tachinus). Most of the beetle species have modern geographic ranges which include northern Washington State. Notably, however, species characteristic of the temperate rainforest of the Pacific Northwest are absent. For the older of the two fossil assemblages, mean summer temperature is estimated to be 17 °C, or similar to Seattle today. The climate was more continental and winters would have been colder than at Seattle today. The occurrence of the northern species Pelophila borealis and Olophrum boreale in the younger of the two assemblages indicates a colder climate estimated to represent a lowering of mean summer temperature by 1–2° C. The climatic cooling is possibly associated with the advance of the Puget Lobe. Both pollen and fossil beetle evidence are in agreement that there was less available moisture, possibly one half of today's precipitation. Palynologists have referred to the MIS 2 vegetation as tundra, cold steppe, or subarctic parkland. None of the Discovery Park fossils are obligate tundra species, and because the majority of taxa have ranges which overlap in northern Washington State today, we prefer to use the term prairie for the temperate to cold-temperate MIS 2 grassland.

Study of the Fluvial Facies Reservoir Sedimentary Characteristics of an Oil Field in China

In this paper, 6 kinds of reservoir sedimentary microfacies distribution model-conceptual model have been established by the use of reservoir sedimentology theory and methods, namely, large sandy braided river sand body sedimentary model, large meandering river sand body sedimentary model, low bending-straight distributary channel sedimentary model, crevasse splay (crevasse river) sedimentary model, heart beach sedimentary model, flood plain and distributary plain sheet sand body sedimentary model. On this basis, the sedimentary facies figures of four sedimentary units have been painted, putting forward the evolution law of sedimentary environment in the research zone, thus providing basic data for the facies control modeling.

Control of tectonic-paleogeomorphology on deposition: A case from the Shahejie Formation Sha 3 member, Laizhouwan Sag, southern Bohai Sea

Abstract Based on seismic and logging data, the characteristics of tectonic-paleogeomorphology of the Laizhouwan sag during the sedimentation of the Paleogene Shahejie Formation Sha 3 member (E 2 s 3 ) were restored and the control of tectonic-paleogeomorphology on sedimentary systems was analyzed. During the sedimentation of E 2 s 3 , the Laizhouwan sag can be divided into eight tectonic units, including the eastern fault-slope zone, northeastern slope, northern slope zone, western slope zone, southern slope zone, central uplift belt, northern sub-sag and southern sub-sag; gullies occur in the western and southern slope zones. Controlled by the tectonic-paleogeomorphology, the fan delta was developed in the eastern Laizhouwan sag and the braided river delta was formed in the south and west of the Laizhouwan sag in the sedimentary period of E 2 s 3 , and the developmental place of the main part of the deltaic depositional system was significantly controlled by sub-sags. The fan delta sand body, controlled by the Eastern fault ramp, the braided river delta sand body controlled by the Western and Southern gentle slopes and the gullies, and especially the large braided river delta sand body in the northern sag controlled by the western gentle slope, are important exploration targets for oil and gas.

Medium-deep clastic reservoirs in the slope area of Qikou sag, Huanghua depression, Bohai Bay Basin

Abstract To get a better understanding of the distribution pattern of favorable reservoir belts in the medium-deep clastic rocks in the Qikou sag of the Huanghua depression, and find out premium reservoir zone, the characteristics and controlling factors of the medium-deep reservoirs in the Qikou sag were analyzed. Comprehensive study into the structural setting, provenance, depositional system, and reservoir properties shows that the Paleogene in the Qikou sag has multi-sags and multi-slopes, with slopes accounting for over 70% of the total sag area. A number of large braided river (fan) delta front - gravity flow sand bodies matching with multi-slope zones lay a good material foundation for the formation of medium-deep effective reservoirs there. Generally buried at over 2500 m, the medium-deep clastic rocks are lithic feldspathic sandstone, with secondary pores and cracks as major reservoir space. Being in the medium diagenesis evolution stage, the medium-deep clastic rocks in the Qikou sag span over a large depth. Nine major factors affecting reservoir properties have been identified by mathematical geology. Although the medium-deep clastic rock interval is poor in physical properties and complex in pore structure, high sedimentation rate, medium geothermal field, high fluid pressure, high feldspar content, relatively high dissolution rate and early oil and gas charge have given rise to three to four belts with abnormally high porosity in it, which are all favorable hydrocarbon reservoir zones.

Relationship between observed liquefaction at Kaiapoi following the 2010 Darfield earthquake and former channels of the Waimakariri River

The Darfield earthquake caused widespread damage in the Canterbury region of New Zealand, with the majority of damage resulting from liquefaction and lateral spreading. One of the worst hit locations was the small town of Kaiapoi north of Christchurch, an area that has experienced liquefaction during past events and has been identified as highly susceptible to liquefaction. The low lying town sits on the banks of the Kaiapoi River, once a branch of the Waimakariri, a large braided river transporting gravelly sediment. The Waimakariri has been extensively modified both by natural and human processes, consequently many areas in and around the town were once former river channels.Using historical accounts and maps of the region, areas of land reclamation and old channels that had been cut off from the river since the beginning of European settlement in the 1850s were identified. These areas correlated well with many of the areas having significant liquefaction damage following the Darfield event. Substantial lateral spreads and sand boils developed in areas of reclamation along the current river path, causing significant damage to stopbanks and structures along the river, with fissures up to 2m deep and 1m wide. Much of the residential housing was damaged by lateral spreading, with cumulative displacement offsets up to 3m parallel to old channel beds that had aggraded over time due to river shifts. In former channel areas that were free of lateral spreading, large volumes of ejecta were present over wide areas, with depths of up to 400mm in places. Houses in these regions were damaged as a result of settlement and tilting. In all these areas underground services and roadways were severely impacted as a result of ground deformation. The severity of this damage indicates the importance of knowing the location of old channels when defining liquefaction prone regions.

Role of Land–Water Classification and Manning's Roughness Parameter in Space-Borne Estimation of Discharge for Braided Rivers: A Case Study of the Brahmaputra River in Bangladesh

The proposed Surface Water and Ocean Topography (SWOT) mission will provide global, space-based estimates of water elevation, its temporal change, and its spatial slope for terrestrial water bodies. Using derivations of water slope from the Shuttle Radar Topography Mission (SRTM) elevation data, river bathymetry and Manning's equation, the potential of SWOT for discharge estimation of large braided rivers in humid climates, such as the Brahmaputra river, was found to be promising (Jung , in Earth Surface Processes and Landforms, 2010). In this study we extend the work on assessing SWOT for braided rivers to understand the sensitivity of two river hydraulic parameters to discharge estimation: 1) section factor (AR2/3) derived from land-water classification and in situ river bathymetry and 2) Manning's roughness coefficient. For braided rivers, the first parameter, is intimately dependent on how braided rivers are classified of the multiple channels (water) and in-stream braided bars (land) that consequently dictates the accuracy of wetted perimeter and area of flow estimation from water elevation data. We show that the use of the minimum water elevation data at a river cross section minimizes estimation of section factor which consequently minimizes outlier discharge estimation reported in the Jung study. We also show that by treating roughness coefficient “flexible” as a calibration parameter, discharge estimation from SRTM elevation data can be further improved through trial and error manual optimization. Our sensitivity study illustrates the value of treating section factor and roughness coefficient as calibration parameters for data assimilation systems that use SWOT observables to estimate river discharge in braided rivers.

Quantification of braided river channel change using archival digital image analysis

AbstractHistorical archives of grey‐scale river channel imagery are extensive. Here, we present and test a methodology to extract detailed quantitative topographic data from such imagery of sand‐bed rivers. Extracting elevation information from rivers is difficult as they are characterized by a low relative relief (<4 m); the area of interest may be spatially extensive (e.g. active channel widths >500 m in large braided rivers); the rate of change of surface elevation is generally low except in the vicinity of individual channel banks where the rate of change is very high; there is the complication that comes from inundation; and there may be an added complication caused by blockage of the field of view by vegetation. Here, we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand‐bed braided river dynamics, illustrated for a 500 m wide, 3 km long reach of the South Saskatchewan River, Canada. Digital photogrammetry was used to quantify dry areas and water edge elevations. A methodology was then used to calibrate the spectral signature of inundated areas by combining established two media digital photogrammetric methods and image matching. This allowed determination of detailed depth maps for inundated areas and, when combined with dry area data, creation of complete digital elevation models. Error propagation methods were used to determine the erosion and deposition depths detectable from sequential digital elevation models. The result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of rivers without needing associated calibration data, provided that imagery is of the necessary scale to capture the features of interest. We use these data to highlight several aspects of channel change on the South Saskatchewan River, including bar movement, bank erosion and channel infilling. Copyright © 2010 John Wiley & Sons, Ltd.

Generation of synthetic seasonal hydrographs for a large river basin

Summary This paper describes a methodology for the generation of synthetic seasonal stage hydrographs with a number of flood waves for a large braided river basin based on statistical analysis of the historical stage records. The synthetic seasonal hydrographs in a river is required for different purposes such as assessing the hydraulic performances of various river training structures, morphological predictions, environmental impact analysis. The typical stage hydrograph of such a river has two components: flood waves and seasonal (monsoonal) response. Using historical stage records, flood waves in a seasonal stage record were identified and their characteristics were approximated using Maxwell distribution. The extracted characteristics of flood waves such as time of occurrence and successive flood lifts were analysed with various probability distribution function to find out their best distribution. The frequency analysis of the annual maximum flood lift was carried out. Beside this, seasonal responses were also approximated using Maxwell distribution. A relationship between the seasonal lift and total monsoonal rainfall was established. For a given total seasonal rainfall and return period of annual maximum flood wave lift, synthetic seasonal hydrograph is generated by superimposing both seasonal response and flood waves. The generated hydrographs are evaluated by comparing the cumulative frequency function of river stage and relative frequency of daily stage changes (rise/fall) for three seasons with different flood wave return periods, at two river gauging stations for the river Brahmaputra, India.

Quantifying channel planform and physical habitat dynamics on a large braided river using satellite data—the Brahmaputra, India

AbstractThis paper presents the results of a trialling of the use of Indian Remote Sensing (IRS) satellite imagery for mapping the geomorphology and physical habitat of the Brahmaputra River in Assam, India. The study was undertaken on a 110 km reach as the river emerges out of the Himalayas; a reach with a complex braid pattern and high levels of channel instability. Image analysis on four sets of IRS data encompassing a period of 13 years (1990–2002) was undertaken to detect basic changes in the extent and pattern of low flow channels, vegetated islands, exposed sand bars and floodplain vegetation. Simple unsupervised classification techniques were applied to the images. The water surface of the low flow braided channel network, however was mapped more accurately using the GROW facility within ENVI 4.1; a technique based upon mapping areas within a given number of standard deviations in terms of pixel values within a training area. Subsequent to this unsupervised classification of the water surface area allowed classification of the water in to three water types based on depth and separation of isolated pools and backwaters from the channels conveying flow. Overall classification accuracies of 82.5% were achieved in relation to mapping physical habitat; varying between 86 and 95% for the four different dates. Analysis of the nature of channel planform and habitat change showed that there has been a 3.7% increase in the active channel area consisting of exposed sediment and water within the river corridor. This substantiated a general awareness of an increase in the width and reduction in depth of the Brahmaputra River over the last few decades. The analysis also depicts the occurrence of a major avulsion and the highly dynamic nature of the braided channel network and sand bars.Overall the study demonstrated that simple classification methods when applied to satellite data, capturing imagery in the visible and near infra‐red, can be used to measure important changes in the geomorphology and physical habitats that make up the fluvial system of the Brahmaputra River. The approach may also be more widely applicable to large river systems comprising a mosaic of water, exposed sediment and spectrally different vegetation communities. Copyright © 2008 John Wiley & Sons, Ltd.

Hydraulic characteristics of the Jamuna River gauging section, Bangladesh

The Jamuna is a large braided river in Bangladesh, characterised by high seasonal variability in flow, with a mean discharge of nearly 20 000 m3/s. Hydraulic characteristics of the gauging section have been investigated by analysing the cross-sectional parameters, velocity, discharge and local water surface slope data based on two consecutive years of intensive measurements. The water surface width was more than 8 km during high flood conditions in both years. The gauging section is not stable because of severe erosion and deposition during monsoon. The stage–discharge relationship varies from year to year as well as within the year. The geometric and resistance characteristics during decreasing flow can differ from those during increasing flow. The resistance to flow at flood stage is quite small compared with that at low stage. The stage–discharge curve for a flood wave forms a clockwise loop which is in contrast with the familiar anticlockwise loop. An improved fit of the yearly stage–discharge relationship can be obtained by dividing the annual data set into four subsets to represent different hydraulic conditions.

Hydraulic characteristics of the Jamuna River gauging section, Bangladesh

The Jamuna is a large braided river in Bangladesh, characterised by high seasonal variability in flow, with a mean discharge of nearly 20 000 m3/s. Hydraulic characteristics of the gauging section have been investigated by analysing the cross-sectional parameters, velocity, discharge and local water surface slope data based on two consecutive years of intensive measurements. The water surface width was more than 8 km during high flood conditions in both years. The gauging section is not stable because of severe erosion and deposition during monsoon. The stage–discharge relationship varies from year to year as well as within the year. The geometric and resistance characteristics during decreasing flow can differ from those during increasing flow. The resistance to flow at flood stage is quite small compared with that at low stage. The stage–discharge curve for a flood wave forms a clockwise loop which is in contrast with the familiar anticlockwise loop. An improved fit of the yearly stage–discharge relationship can be obtained by dividing the annual data set into four subsets to represent different hydraulic conditions.

Hydraulic characteristics of the Jamuna River gauging section, Bangladesh

The Jamuna is a large braided river in Bangladesh, characterised by high seasonal variability in flow, with a mean discharge of nearly 20 000 m3/s. Hydraulic characteristics of the gauging section have been investigated by analysing the cross-sectional parameters, velocity, discharge and local water surface slope data based on two consecutive years of intensive measurements. The water surface width was more than 8 km during high flood conditions in both years. The gauging section is not stable because of severe erosion and deposition during monsoon. The stage–discharge relationship varies from year to year as well as within the year. The geometric and resistance characteristics during decreasing flow can differ from those during increasing flow. The resistance to flow at flood stage is quite small compared with that at low stage. The stage–discharge curve for a flood wave forms a clockwise loop which is in contrast with the familiar anticlockwise loop. An improved fit of the yearly stage–discharge relationship can be obtained by dividing the annual data set into four subsets to represent different hydraulic conditions.

Fluvial Architecture of the Hawkesbury Sandstone (Triassic), Near Sydney, Australia

ABSTRACT The Hawkesbury Sandstone has long been assumed to represent the deposits of a large braided river system, comparable in style and magnitude with the modern Brahmaputra River of Bangladesh. Such an interpretation is based mainly on the common occurrence of very large-scale crossbedding, but no architectural studies of the unit have hitherto been carried out. This paper represents a first attempt to estimate the magnitude of Hawkesbury channels and bars on the basis of the preserved architectural evidence. Photomosaics were constructed of two cliff sections south of Sydney, one 5.6 km in length. On the basis of these profiles we estimate that characteristic channel-scale architectural elements are at least 2.7 km wide, and individual macroforms are 5-10 m high, indicating the constructional depth of typical channels. Hollow elements (scoop-shaped units interpreted to have formed at channel confluences) are up to 20 m deep. These magnitudes are large, but measurably smaller that those of channels and bars in the modern Brahmaputra River of Bangladesh.

Methodological sensitivity of morphometric estimates of coarse fluvial sediment transport

The estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest. The revival of the ‘morphological method’ reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high-precision, high-resolution topographic monitoring. Remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys. However, while photogrammetry presents the opportunity to acquire survey data over large areas, data precision and accuracy, particularly in the vertical dimension are lower than in traditional ground survey methods. This paper presents results of recent research in which digital elevation models (DEMs) have been developed for a reach of a large braided gravel-bed river in Scotland using both digital photogrammetry and high-resolution RTK GPS ground surveys. A statistical level of change detection is assessed by comparing surfaces with independent check points. The methodological sensitivity of the annual channel sediment budget (1999–2000) to the threshold is presented. Results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing, moderate precision DEMs of channel topography (RMSE=±0.21 m), the remaining errors imply significant limits on reliable change detection which lead to important information losses. Tests at a 95% confidence interval for change detection show that over 60% of channel deposition and 40% of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements. This bias reflects the difficulty of detecting the topographic signature of widespread, but shallow deposition on bar tops.

Radio‐tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by Einstein

AbstractHans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio‐tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain‐diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain‐diameters and 6·1 m or 120 grain‐diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd.

Particle size characteristics of suspended sediment in hillslope runoff and stream flow

This paper presents results from one of the few scientific studies to examine the physical characteristics of aeolian sediment transport in an alpine area, where topographically reinforced foehn winds initiate dust storm events. The major objective of this study is to improve knowledge of aeolian processes in mid-latitude alpine regions experiencing extreme wind speeds. Of particular interest is the role of surface characteristics in contributing to the unusually deep saltation layer which is seen to form over fluvio-glacial deposits in the Southern Alps of New Zealand. Sediment was collected at several heights (05, 1, 2 and 4 m) and locations over a large alpine braided river delta, and standard laboratory techniques used to examine grain size characteristics. An image processing technique was also used to evaluate grain roundness. Grains filtered from the airstream at 05 m and 1 m above such surfaces were found to display a mean grain size of approximately 300 to 435 m, resembling grain size characteristics of saltation clouds previously observed in high latitude, cold climate locations, in contrast to desert and prairie environments. Samples collected at 2 and 4 m above the surface were found to consist of 60 to 65 per cent sand-sized material, with some grains exceeding 1-15 mm in diameter. Grain shape analysis conducted on silt- and clay-sized grains filtered from the airstream above mixed sand and gravel surfaces showed such grains to display an increase in grain roundness with height. This characteristic is thought to reflect the airstream's shape-sorting ability and has important implications with respect to the often observed increase in grain roundness in aeolian deposits with increasing distance from source areas. Namely, if more rounded grains are preferentially carried higher into the airstream and therefore into regions of higher wind speed, they should theoretically be transported further from the entrainment zone before being deposited. The high wind speeds observed, often exceeding 30 m s-1, are seen to transport significantly larger sediment than reported in the literature for desert and prairie environments. In addition, the mixture of grain sizes, and especially the pebble- and cobble-sized clasts that dominate the fluvio-glacial deposits associated with the braided rivers in this mountain region, also appear to increase significantly the trajectory height of saltating sand grains. As a result of these two factors, the depth of the saltation cloud often exceeds 1 m. Observations made in this study therefore highlight the need for field and laboratory aeolian process studies to be extended to examine grain transport over coarse-grained beds during much higher wind velocities than typically reported in the literature. Such studies would provide a valuable insight into aeolian processes in high latitude/altitude environments, such as loess genesis. © 1997 by John Wiley & Sons, Ltd.

Scour in large braided rivers and the recognition of sequence stratigraphic boundaries

Alluvial scour into shallow marine sediments may be caused by the incision of a river adjusting to a new base level1–4 following a fall in sea level. The identification of such erosion surfaces1–3 has therefore been pivotal in the reconstruction of past sea-level changes from ancient sedimentary sequences1–14. Here we report data from a study of the Jamuna river, Bangladesh, one of the world's largest modern braided rivers15, which illustrate that bed scour associated with channel confluences and bends alone can be substantial—as much as five times greater than the mean channel depth. Indeed, the basal erosion surfaces produced by such deep scours have characteristics similar to those of boundaries in some ancient sedimentary sequences that have been assumed to result from sea-level fall1–14, potentially leading to radically different interpretations of past variation in base level and climate. We suggest that, to discount unambiguously the influence of fluvial scour in ancient sediments, the erosive boundary should be greater than five times the mean channel depth and extend for distances greater than the floodplain width. Ideally, it should be traceable between different basins.

The Holocene evolution of a well nourished gravelly barrier and lagoon complex, Kaitorete “Spit”, Canterbury, New Zealand

Morphological, stratigraphical, micropaleontological and radiocarbon dating investigations of the gravelly Kaitorete “Spit” system, Canterbury, New Zealand show that a barrier/spit system has existed at this site for the last 8000 yr. Kaitorete “Spit” developed as a true spit extending north from near the Rakaia river mouth, during sea level rise in the Late Pleistocene and Early Holocene. This produced an estuarine coastline along the southwestern flank of Banks Peninsula. The spit extended to Banks Peninsula sometime in the early mid-Holocene creating a barrier lake complex behind the spit. Since the mid-Holocene, there have been at least three fluctuations between lacustrine and estuarine/lagoonal conditions in the barrier blocked system. The most recent fluctuation, which resulted in the present barrier lake complex, occurred within the last 200–500 yr.These fluctuations are associated with the avulsion of a large braided river, the Waimakariri, to and from the Lake Ellesmere basin. When the river flows through the basin, a permanent channel is maintained to the ocean with estuarine conditions present. When the river flows elsewhere, the barrier closes and a freshwater lake system forms behind it. This study emphasises the importance of fluvial control on the evolution of gravelly coastlines where sediment supply is not the limiting factor. Both the sediments and the water in the back barrier area are predominantly derived from the terrestrial catchment. We highlight the absence of true marine influence in the back barrier area, except in the vicinity of the tidal channel, even when such a channel is present. Marine processes have been limited to the gradual re-orientation of the barrier system from drift to swash alignment.

Estimation of Discharge From Three Braided Rivers Using Synthetic Aperture Radar Satellite Imagery: Potential Application to Ungaged Basins

Analysis of 41 ERS 1 synthetic aperture radar images and simultaneous ground measurements of discharge for three large braided rivers indicates that the area of active flow on braided river floodplains is primarily a function of discharge. A power law correlation is found between satellite‐derived effective width We and discharge Q, where We is the water surface area within a braided reach divided by the reach length. Synthetic values of We and Q generated from a cellular automata model of stream braiding display a similar power law correlation. Power functions that are fit through plots of We and Q represent satellite‐derived rating curves that can subsequently be used to estimate instantaneous river discharge from space, with errors ranging from tens to hundreds of cubic meters per second. For ungaged rivers, changes in relative discharge can be determined from satellite data alone to determine the shape and timing of annual flows in glacierized basins. Absolute discharge can probably be estimated within a factor of 2. More accurate estimates will require either (1) one or more ground measurements of discharge acquired simultaneously with a satellite image acquisition, or (2) successful parameterization of known morphologic controls such as total sinuosity ∑P, valley slope, bank material and stability, and braid channel hydraulic geometry. Values of total sinuosity ∑P derived from satellite imagery and field measurements from two rivers of braid channel width, depth, velocity, water surface slope, and bed material grain size indicate that while the shape of satellite‐derived We‐Q rating curves may be influenced by all of these variables, the sensitivity of flow area to changing discharge is most dependent upon the degree of braiding. Efforts to monitor river discharge from space will be most successful for intensely braided rivers with high values of total sinuosity. Subsampling of existing daily discharge records from the Iskut River suggests that satellite return times of about 1 week are sufficient for approximating the shape and timing of the seasonal hydrograph in large, glacierized basins. Although errors are large, the presented technique represents the only currently available way to estimate discharge in ungauged braided rivers.

Loess Ecosystems of Northern Alaska: Regional Gradient and Toposequence at Prudhoe Bay

Loess—dominated ecosystems cover ≈14%(11 000 km2) of the Arctic Coastal Plain and much of the northern portion of the Arctic Foothills. Knowledge of this poorly known ecosystem is important for sound land—use planning of the expanding developments in the region and for understanding the paleoecological dynamics of eolian systems that once dominated much of northern Alaska. A conceptual alkaline—tundra toposequence includes eight common vegetation types and associated soils that occur near the arctic coast. A model of the regional loess gradient describes soils and vegetation downwind of the Sagavanirktok River. The addition of calcareous loess affects numerous soil properties, including bulk density, pH, water retention properties, concentrations of soil nutrients, and seasonal thaw depths. Many plant taxa, particularly cryptogams, increase in abundance downwind of the river, apparently in response to higher amounts of nutrients and moisture associated with finer soil—particle sizes and greater organic content. For example, the highest extractable P values (8—12 µg/g) occur in areas with circumneutral pH and finer grained soils, and low P values (<2 µg/g) occur in acidic soils north of the loess region. Early, minerotrophic stages of tundra succession are maintained by loess blown from the Sagavanirktok, Canning, and other large braided—river floodplains. Areas downwind of these rivers provide analogues for vegetation that existed in unstable areas of the Alaskan Coastal Plain during and following full glacial conditions. Total aboveground phytomass in wet acidic sites at Prudhoe Bay (163 ± 21 g/m2) is close to values from similar sites at Barrow and Devon Island. Only a small amount of data is available for alkaline areas, but there is indication of lower biomass near the major rivers, suggesting a response to lower nutrient regimes. Properties of loess tundra important for land—use planning include: (1) its high ice content, which contributes to its susceptibility to thermokarst; (2) high salinities, which hamper revegetation efforts; and (3) presence of certain plant species such as Dryas intergrifolia, which are particularly sensitive to disturbance. The loess gradient provides a natural analogue for road dust, an extensive disturbance associated with oil—field development.