Quantification of bedform dynamics and bedload sediment flux in sandy braided rivers from airborne and satellite imagery     

Robert J.P. Strick  Philip J. Ashworth  Gregory H. Sambrook Smith  Andrew P. Nicholas  James L. Best  Stuart N. Lane  Daniel R. Parsons  Christopher J. Simpson  Christopher A. Unsworth  Jonathan Dale 《地球表面变化过程与地形》2019,44(4):953-972

Images from specially-commissioned aeroplane sorties (manned aerial vehicle, MAV), repeat unmanned aerial vehicle (UAV) surveys, and Planet CubeSat satellites are used to quantify dune and bar dynamics in the sandy braided South Saskatchewan River, Canada. Structure-from-Motion (SfM) techniques and application of a depth-brightness model are used to produce a series of Digital Surface Models (DSMs) at low and near-bankfull flows. A number of technical and image processing challenges are described that arise from the application of SfM in dry and submerged environments. A model for best practice is presented and analysis suggests a depth-brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low-turbidity and shallow (< 2 m deep) water. The aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18 km reach and three ~1 km long reaches respectively. Dune and unit bar migration rates are highly variable in response to local variations in planform morphology. Sediment transport rates for dunes and unit bars, obtained by integrating migration rates (from UAV) with the volume of sediment moved (from DSMs using MAV imagery) show near-equivalence in sediment flux. Hence, reach-based sediment transport rate estimates can be derived from unit bar data alone. Moreover, it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2D imagery, including from satellite images, so long as informed assumptions are made regarding average bar shape and height. With recent availability of frequent, repeat satellite imagery, and the ease of undertaking repeat MAV and UAV surveys, for the first time, it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low-turbidity rivers that currently have sparse information on bedload sediment transport rates. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Optical depth,size distribution and flux of dust from Owens Lake,California     

Tezz C. Niemeyer  Dale A. Gillette  John J. DeLuisi  Young J. Kim  William F. Niemeyer  Trevor Ley  Thomas E. Gill  Duane Ono 《地球表面变化过程与地形》1999,24(5):463-479

A joint United States/Russian/French collaborative experiment was undertaken in March 1993 and March 1996. Projects LODE I and II (Lake Owens Dust Experiments) took place on the anthropogenically desertified playa (dry lakebed) and surrounding regions of Owens Lake, in east-central California. One of the five parts of Project LODE was to determine relationships between optical depth and flux of dust emitted from the dry lake. Project LODE II included subsequent dust plume measurements and size distributions obtained through April 1996, to further refine the flux measurements for distinct mineral aerosol source regions at Owens Lake. Size distributions of dust aerosol were determined and aerosol optical depths were calculated from sunphotometer solar extinction measurements taken downwind in plumes coming from the emissive areas of Owens Lake. This source was visually observed for 10 measured dust storms. The plume mass was calculated to be 1·5 × 10⁹ g using ground-based measurements and ≥1·6 × 10⁹ g from satellite data. Project LODE II results were found to be consistent with LODE I results for the south end of the playa, but flux values were found to be reduced for the northeastern portion of the playa by comparison. Vertical flux values estimated by sunphotometry were found to be consistent with values estimated via a micrometeorological method. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Size distributions of saltating grains: an important variable in the production of suspended particles     

Dale A. Gillette  Weinan Chen 《地球表面变化过程与地形》1999,24(5):449-462

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Genetic diversity and population connectivity of the sea urchin Tripneustes gratilla along the South African coast     

M Brink  R Dale Kuys  C Rhode  BM Macey  KW Christison 《African Journal of Marine Science》2018,40(2):149-156

The collector sea urchin Tripneustes gratilla has been identified as a species with potential for aquaculture production in South Africa. The species’ roe is considered a culinary delicacy in Asia and Europe. However, T. gratilla remains genetically uncharacterised in South Africa. Therefore, the purpose of this study was to provide baseline genetic information consisting of estimates of genetic diversity and population stratification, which may aid in future sustainable use of this urchin resource. A total of 22 species-specific microsatellite markers were used for the genetic characterisation of T. gratilla samples from along the South African coast, at Haga Haga, Coffee Bay, Hibberdene, Ballito Bay and Sodwana Bay. A moderate level of genetic diversity was observed, with an average number of alleles of 7.89 and an average effective number of alleles of 6.57, as well as an average observed heterozygosity of 0.55. Population differentiation tests suggest that the geographically representative samples form part of a single, large interbreeding population, with a global F_st estimate of 0.02 (p > 0.05). This finding is likely explained by high levels of gene flow between these locations caused by extensive larval dispersal during the planktonic larval stage. The panmixia observed within these natural populations of T. gratilla indicate that they could be managed as a single genetic stock.  相似文献   

Distribution and retention of Petrolisthes armatus in a coastal plain estuary: The role of vertical movement in larval transport     

Charles E. Tilburg  Jennie E. Seay  T. Dale Bishop  Harlan L. Miller III  Christof Meile 《Estuarine, Coastal and Shelf Science》2010

Since transport of planktonic larvae is essential to the maintenance and expansion of many marine species, we examined the spatial and temporal distribution of green porcelain crab Petrolisthes armatus (Gibbes, 1850) larvae and the possible underlying physical and behavioral mechanisms using a combination of field observations and numerical modeling. The field study consisted of observations of larval abundance and distribution as well as hydrographic surveys of the Satilla River estuary on the east coast of the USA in August 2006. Larvae were found throughout the water column within the tributaries but primarily at depth in the main river. A numerical model was used to examine the effect of flow and possible larval behavior responsible for the observed distribution and the consequences for larval retention in the estuary. Model results that included downward larval movement are consistent with the field observations, supporting the hypothesis that P. armatus larvae vertically migrate within the water column, which aids in their retention within the estuary.  相似文献   

Rapid movement of wastewater from on-site disposal systems into surface waters in the Lower Florida Keys     

John H. Paul  Molly R. McLaughlin  Dale W. Griffin  Erin K. Lipp  Rodger Stokes  Joan B. Rose 《Estuaries and Coasts》2000,23(5):662-668

Viral tracer studies have been used previously to study the potential for wastewater contamination of surface marine waters in the Upper and Middle Florida Keys. Two bacteriophages, the marine bacteriophage ϕHSIC and theSalmonella phage PRD1, were used as tracers in injection well and septic tank studies in Saddlebunch Keys of the Lower Florida Keys and in septic tank studies in Boot Key Harbor, Marathon, of the Middle Keys. In Boot Key Harbor, both phages were detected in a canal adjacent to the seeded septic tank within 3 h 15 min of the end of the seed period. The tracer was then detected at all sampling sites in Boot Key Harbor, including one on the opposite side of U.S. Highway 1 in Florida Bay, and at an Atlantic Ocean beach outside Boot Key Harbor. Rates of migration based on first appearance of the phage ranged from 1.7 to 57.5 m h⁻¹. In Saddlebunch Keys, ϕHSIC and PRD1 were used to seed a residential septic tank and a commercial injection well. The septic tank tracer was not found in any surface water samples. The injection well tracer was first detected at a site most distant from the seed site, a channel that connected Sugarloaf Sound with the Atlantic Ocean. The, rate of tracer migration from the injection well to this channel ranged from 66.8 to 141 m h⁻¹. Both tracer studies showed a rapid movement of wastewater from on-site sewage treatment and disposal systems in a southeasterly direction toward the reef tract and Atlantic Ocean, with preferential movement through tidal channels. These studies indicate that wastewater disposal systems currently in widespread use in the Florida Keys can rapidly contaminate the marine environment.  相似文献   

Y2K and Other Stories     

Sergei A. Gourevitch  Dale Kyle 《GPS Solutions》1999,3(1):2-4

GPS technology will face not one but two critical rollover dates over the next eight months. One is the millennium (Y2K) rollover. The other is the GPS week 1024 rollover also known as the GPS End of the Week (EOW). Each rollover dat has the potential to cause severe problems in GPS receivers and related software. This article expolres the reasons why these dates are a problem and describes choices that must be made as to their solution. The paper also describes some verification methods that may be used to test GPS receivers and software. ? 1999 John Wiley & Sons, Inc.  相似文献   

The Uranian satellites: Water ice on Ariel and Umbriel     

Dale P. Cruikshank  R. Hamilton Brown 《Icarus》1981,45(3):607-611

New near-infrared reflectance spectra are presented for Ariel and Umbriel. Water ice on the surface of Ariel and Umbriel is verified from spectral signatures in the 2-μm region. However, the weaker bands in Umbriel's spectrum indicate that its surface is significantly different from Ariel either in degree of contamination with dark material or in microstate. Umbriel may have a lower albedo than Ariel, Titania, and Oberon and, therefore, may have a diameter comparable to that of Titania.  相似文献   

River ice as a taphonomic agent: An alternative hypothesis for bone “artifacts”     

Robert M. Thorson  R. Dale Guthrie 《Quaternary Research》1984,22(2):172-188

The annual freezeup and violent breakup of temperate and high-latitude rivers produces unique geomorphic features that can be recognized in ancient sediments. The forces and materials involved in the breakup process could modify entrained bones in ways similar to those attributed to human activity. An intuitive taphonomic model is developed to explain how river ice may affect bones, and to predict the modifications expected. Partial testing of the model by experiments designed to simulate river breakup produced bone modifications such as fractures, flakes, facets, striations, isolated cuts, and polish. The taphonomic effects of river ice must be discounted prior to the interpretation of such features as human in origin.  相似文献   

Comment on “late Wisconsinan glaciation models of northern Maine and adjacent Canada”     

Thomas V. Lowell  J.Steven Kite  Dale Becker  Harold W. Borns 《Quaternary Research》1983,19(1):136-137

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