Drainage Basin Characteristics Research Articles

Predicting streamflow regime metrics for ungauged streamsin Colorado, Washington, and Oregon

Streamflow prediction in ungauged basins provides essential information for water resources planning and management and ecohydrological studies yet remains a fundamental challenge to the hydrological sciences. A methodology is presented for stratifying streamflow regimes of gauged locations, classifying the regimes of ungauged streams, and developing models for predicting a suite of ecologically pertinent streamflow metrics for these streams. Eighty-four streamflow metrics characterizing various flow regime attributes were computed along with physical and climatic drainage basin characteristics for 150 streams with little or no streamflow modification in Colorado, Washington, and Oregon. The diverse hydroclimatology of the study area necessitates flow regime stratification and geographically independent clusters were identified and used to develop separate predictive models for each flow regime type. Multiple regression models for flow magnitude, timing, and rate of change metrics were quite accurate with many adjusted R 2 values exceeding 0.80, while models describing streamflow variability did not perform as well. Separate stratification schemes for high, low, and average flows did not considerably improve models for metrics describing those particular aspects of the regime over a scheme based on the entire flow regime. Models for streams identified as ‘snowmelt’ type were improved if sites in Colorado and the Pacific Northwest were separated to better stratify the processes driving streamflow in these regions thus revealing limitations of geographically independent streamflow clusters. This study demonstrates that a broad suite of ecologically relevant streamflow characteristics can be accurately modeled across large heterogeneous regions using this framework. Applications of the resulting models include stratifying biomonitoring sites and quantifying linkages between specific aspects of flow regimes and aquatic community structure. In particular, the results bode well for modeling ecological processes related to high-flow magnitude, timing, and rate of change such as the recruitment of fish and riparian vegetation across large regions.

Stratigraphic variability due to uncertainty in model boundary conditions: A case-study of the New Jersey Shelf over the last 40,000 years

Prediction of stratigraphy by numerical sedimentary models is influenced by a series of geological boundary conditions: paleo-bathymetry, sediment supply, sea level, ocean storm climate, and tectonics. These boundary conditions evolve non-linearly over time and have considerable uncertainty. This study explores the impact of the uncertainty of complex boundary conditions on stratigraphic prediction. Two numerical models are sequentially run: the climate-driven hydrological model, HydroTrend, generates a time series of discharge and sediment load at the river mouth, which then feed into the process-based stratigraphic model, SedFlux-2D. SedFlux disperses sediment in the fluvio-marine domain; the bedload fluxes drive floodplain and mouthbar deposition, while suspended sediment is dispersed in the ocean through hypopycnal plumes. Seafloor sediment is reworked by ocean storms, failures and subsequent transport as sediment gravity flows. SedFlux records the thickness of the deposited sediment and the grain size preserved over time along a longitudinal profile. One ‘base-case’ simulation and 20 sensitivity tests of the New Jersey shallow margin over the last 40,000 yr serve to explore the impact of uncertain boundary conditions. Initially, the shelf is exposed and Arctic conditions prevail in the drainage area. Paleo temperature and precipitation estimates differ significantly between different Community Climate System Model realizations, impacting river sediment flux predictions. Subsequently, high sediment supply from the rivers draining the melting Laurentide Ice Sheet has a dominant impact on the shelf stratigraphy. Drainage basin characteristics are strongly controlled by the hard to define details of the Laurentide Ice Sheet dynamics. Over the last 10,000 yr the shelf becomes sediment-starved and storm-dominated, but the paleo storm conditions are uncertain and thus require a wide range of values. Shallow seismic data have been used to validate the large-scale deposited thicknesses of the SedFlux prediction. The ‘base-case’ SedFlux prediction for the sedimentary architecture of the New Jersey Shelf is consistent with the acoustically observed distribution of major sediment wedges, due to the strong forcing of the relatively well-constrained sea-level changes. The range in thickness predictions over the sensitivity tests is well within the lateral variations reconstructed from the observed seismic data. SedFlux predictions and a data set of 654 seafloor samples taken on the New Jersey Shelf between 50 and 150 m water depth shows a subtle fining towards deeper water. SedFlux systematically overpredicts the component of fine sediments at the seafloor, likely because the model does not predict shell hash. Paleo-storm climate is found to have a high uncertainty and strongly impacts the predicted grain size distributions. We advocate a modeling approach which couples a series of sensitivity experiments to a predicted “base-case” experiment. In that way the stratigraphic variability caused by uncertainty in the boundary conditions is evident for later users.

Efeitos das mudanças do uso da terra na biogeoquímica dos corpos d'água da bacia do rio Ji-Paraná, Rondônia

Este trabalho discute os efeitos das mudanças do uso do solo na biogequímica dos rios da bacia de drenagem do rio Ji-Paraná (Rondônia). Nesta região, a distribuição espacial do desmatamento e das propriedades do solo resultam em sinais diferentes, possibilitando a divisão dos sistemas fluviais em três grupos: rios com águas pobres em íons e baixo impacto; rios com conteúdo iônico intermediário e impacto médio e rios com elevados conteúdo iônico e impacto antropogênico. As características biogeoquímicas dos rios têm relação significativa com a área de pasto, melhor parâmetro para prever a condutividade elétrica (r² = 0,87) e as concentrações de sódio (r² = 0,75), cloreto (r² = 0,69), potássio (r² = 0,63), fosfato (r² = 0.78), nitrogênio inorgânico (r² = 0.52), carbono inorgânico (r² = 0.81) e carbono orgânico (rain ² = 0.51) dissolvidos. Cálcio e magnésio tiveram sua variância explicada pelas características do solo e pastagem. Nossos resultados indicam que as mudanças observadas na micro-escala constituem "sinais biogeoquímicos" gerados pelo processamento do material nas margens dos rios. A medida em que os rios evoluem para ordens superiores, os sinais persistentes nos canais fluviais estão mais associdados às características da bacia de drenagem (solos e uso da terra). Apesar dos efeitos das mudanças observadas no uso do solo não serem ainda detectáveis na macro-escala (bacia amazônica), a disrupção da estrutura e funcionamento dos ecossistemas é detectável nas micro e meso escalas, com alterações significativas na ciclagem de nutrientes nos ecossistemas fluviais.

Climatic controls on alluvial-fan activity, Coastal Cordillera, northern Chile

Abstract A description of the distribution, drainage basin characteristics, surface morphology, depositional process and age of 64 alluvial fan systems from both flanks of the hyper-arid Coastal Cordillera of northern Chile between 22°15′S and 23°40′S is presented. The coastal fans on the western flank of the Coastal Cordillera are dominated by debris-flow deposits fed from steep catchments. Two drainage basin types are recognized: type A drainage basins are small (10–30 km 2 ) and do not cut back beyond the main coastal watershed; and type B drainage basins are large (up to 400 km 2 ) and cut inland beyond the coastal watershed. The western Central Depression fans on the eastern flank of the Coastal Cordillera are characterized by sheetflood deposition fed from relatively shallow catchments in small drainage basins (10–50 km 2 ). The surface morphology, sedimentation rates, a luminescence date and regional cosmogenic radionucleide data suggest that these fans have been inactive for at least the last 230 000 years and probably for much of the Neogene. The principal control on fan activity in the study area is climate. The Coastal Cordillera forms an orographic barrier to recent El Niño-related precipitation events that are restricted to the western flank of the Coastal Cordillera. These events did not penetrate into the Central Depression as indicated by the inactive nature of the western Central Depression fans located 25 km east of the active coastal-fan catchments. This scenario is considered to have prevailed for much of the Neogene. Climate also controls rates of weathering on alluvial-fan surfaces. The coastal fog results in rapid salt weathering of clasts on coastal fans resulting in the production of fines, but does not penetrate into the Central Depression. Fault activity is important in controlling drainage basin size. The larger (type B) drainage basins are commonly focused on active faults that cut the coastal watershed, facilitating drainage basin expansion. Source-area lithology is not important in controlling depositional processes. Fans on both sides of the cordillera have the same basaltic andesite and granodiorite source lithologies, yet coastal fans are dominated by debris-flow and western Central Depression fans by sheetflood deposition. A combination of chemical weathering and stream power related to gradient are considered to account for the differences in process.

Recent Changes in Areal Extent of the Devon Ice Cap, Nunavut, Canada

Image data from the years 1959/1960 and 1999/2000 reveal a 2.4% decrease in the surface area of the Devon Ice Cap, Nunavut, over the last 40 yr. This has resulted primarily from extensive retreat of tidewater glacier margins on the eastern side of the ice cap, and shrinkage of its near-stagnant southwestern arm. Thinning of the ice cap has also increased bedrock exposure in the ice cap interior. However, since 1960 the northwestern margin of the ice cap has advanced slightly. Volume loss associated with these changes was estimated at −67 ± 12 km3 as calculated from two independent techniques. A digital elevation model (DEM) of the ice cap surface was used to delineate interior ice divides allowing patterns of change to be investigated at the drainage basin scale. Strong correlation between the hypsometric characteristics of drainage basins and the observed changes in ice-cap geometry suggests that these changes reflect interbasin differences in the inherent sensitivity of glacier mass balance to recent climate forcing. Response time calculations indicate that most of the ice cap is responding to recent climate warming, whereas the northwestern region is likely still responding to cooler conditions that prevailed during the Little Ice Age (LIA).

Pre-industrial and contemporary fluxes of nitrogen through rivers: a global assessment based on typology

This paper provides a global synthesis of reactive nitrogen (Nr) loading to the continental landmass and subsequent riverine nitrogen fluxes under a gradient of anthropogenic disturbance, from pre-industrial to contemporary. A mass balance model of nitrogen loading to the landmass is employed to account for transfers of Nr between atmospheric input sources (as food and feed products) and sub- sequent consumer output loads. This calculation produces a gridded surface of nitrogen loading ulti- mately mobilizable to aquatic systems (Nmob). Compared to the pre-industrial condition, nitrogen loading to the landmass has doubled from 111 to 223 Tg/year due to anthropogenic activities. This is particularly evident in the industrialized areas of the globe where contemporary levels of nitrogen loading have increased up to 6-fold in many areas. The quantity of nitrogen loaded to the landscape has shifted from a chiefly fixation-based system (89% of total loads) in the pre-industrial state to a het- erogeneous mix in contemporary times where fertilizer (15%), livestock (24%) and atmospheric de- position (15%) dominate in many parts of the industrialized and developing world. A nitrogen transport model is developed from a global database of drainage basin characteristics and a comprehensive compendium of river chemistry observations. The model utilizes constituent delivery coefficients based on basin temperature and hydraulic residence times in soils, rivers, lakes and reservoirs to transport nitrogen loads to river mouths. Fluxes are estimated for total nitrogen, dissolved inorganic nitrogen, and total organic nitrogen. Model results show that total nitrogen fluxes from river basins have doubled from 21 Tg/year in the pre-industrial to 40 Tg/year in the contemporary period, with many industrialized areas of the globe showing an increase up to 5-fold. DIN fluxes from river basins have increased 6-fold from 2.4 Tg/year in the pre-industrial to 14.5 Tg/year in the contemporary period. The amount of nitrogen loading delivered to river mouth as flux is greatly influenced by both basin temperatures and hydraulic residence times suggesting a regional sensitivity to loading. The global, aggregate nitrogen retention on the continental land mass is 82%, with a range of 0-100% for individual basins. We also present the first seasonal estimates of riverine nitrogen fluxes at the global scale based on monthly discharge as the primary driver.

04/00118 Producing hydrocarbons and non-hydrocarbon containing materials from a hydrocarbon containing formation including oil shale: Vinegar, H. J. et al. PCT Int. Appl. WO 03 35,801 (Cl. C10G) 1 May 2003, US Appl. PV 374,970

The northern Great Plains of western Canada, a vast region stretching from the Precambrian Shield east of Winnipeg, Manitoba, westward for some 1600 km to the foothills of the Rocky Mountains, contains literally millions of lakes and wetlands. Although often characterized as a saline, Na-SO4 system, in fact the wide range of water chemistries exhibited by the lakes results in an unusually large diversity of sediment composition. Despite a long history of limnogeological study, it is only recently that the spectrum of carbonate minerals and sedimentological processes in these lakes has been realized. About 30 species of carbonate minerals have been reported from the modern and Holocene sediment of about 50 basins in the region. The ubiquity of detrital calcite and dolomite is a legacy of the carbonate bedrock and carbonate-rich glacial sediments. Elevated salinities of the lakes, together with high alkalinities, productivity, and pH values, act in concert to create thermodynamically saturated or supersaturated conditions with respect to many carbonate minerals. The most common non-detrital components are Mg-calcite, aragonite and non-stoichiometric dolomite. Many of the basins whose brines have very high Mg/Ca ratios also contain hydromagnesite, magnesite, and nesquehonite. Although not common, sodium carbonates, including trona, natron and nahcolite, also occur in some of the hypersaline lakes.Because of their great range of formative conditions, carbonates have been the workhorse for much of the physical and geochemical paleolimnology in the Canadian Great Plains. However, the often-difficult task of distinguishing endogenic lacustrine carbonates from allogenic and authigenic minerals has limited the use of carbonate stratigraphy in the region. Despite this problem, the carbonates have been useful in deciphering (i) past changes in hydrology and drainage basin characteristics, (ii) lake level and water column stratification fluctuations, and (iii) water chemistry and salinity variations.

04/00121 Synergic effect of sulfur on activated carbon-catalyzed hydrocracking of di(1-naphthyl)methane: Ni, Z.-H. et al. Energy & Fuels, 2003, 17, (1), 60–61

The northern Great Plains of western Canada, a vast region stretching from the Precambrian Shield east of Winnipeg, Manitoba, westward for some 1600 km to the foothills of the Rocky Mountains, contains literally millions of lakes and wetlands. Although often characterized as a saline, Na-SO4 system, in fact the wide range of water chemistries exhibited by the lakes results in an unusually large diversity of sediment composition. Despite a long history of limnogeological study, it is only recently that the spectrum of carbonate minerals and sedimentological processes in these lakes has been realized. About 30 species of carbonate minerals have been reported from the modern and Holocene sediment of about 50 basins in the region. The ubiquity of detrital calcite and dolomite is a legacy of the carbonate bedrock and carbonate-rich glacial sediments. Elevated salinities of the lakes, together with high alkalinities, productivity, and pH values, act in concert to create thermodynamically saturated or supersaturated conditions with respect to many carbonate minerals. The most common non-detrital components are Mg-calcite, aragonite and non-stoichiometric dolomite. Many of the basins whose brines have very high Mg/Ca ratios also contain hydromagnesite, magnesite, and nesquehonite. Although not common, sodium carbonates, including trona, natron and nahcolite, also occur in some of the hypersaline lakes.Because of their great range of formative conditions, carbonates have been the workhorse for much of the physical and geochemical paleolimnology in the Canadian Great Plains. However, the often-difficult task of distinguishing endogenic lacustrine carbonates from allogenic and authigenic minerals has limited the use of carbonate stratigraphy in the region. Despite this problem, the carbonates have been useful in deciphering (i) past changes in hydrology and drainage basin characteristics, (ii) lake level and water column stratification fluctuations, and (iii) water chemistry and salinity variations.

Surge potential and drainage-basin characteristics in East Greenland

AbstractWe introduce a new glacier inventory of central East Greenland and use the collected data to test proposed theories on surging. The glacier inventory contains 259 glaciers, of which 10 have observed surges and a further 61 are inferred surge-type. The total glaciated area is 5.5×103km2. The inventory was created from a combination of remote-sensing data and maps, and some 24 glacial and geological inventory parameters were collected for each glacier. A multivariate logistic analysis is used to test which combination of glacial and environmental data is conducive to surging behaviour in East Greenland. Three different models suggest that glaciers with a large complexity, low slope and oriented in a broad arc from northeast to south are most likely to be of surge type. Geological conditions, and hence substrate character, appeared not to be related to surge potential. On the basis of these results and the surge dynamics in this region, we suggest a hydrologically controlled surge mechanism operates in central East Greenland.

Geoindicators for river and river-valley monitoring in the humid tropics

Geoindicators for rivers and river valleys in the humid tropics are suggested to indicate environmental change during periods of up to a century. Geoindicators suggested for upland areas of supply are rainfall-runoff relations, rates of soil movement and slope failure, and analyses of drainage density. Data applicable to sediment storage in lowlands are rates of sediment deposition as shown by monuments, short-lived radioisotopes, and pollen. Discharges of water, sediment, and dissolved solids are basic geoindicators for large streams, especially when analyses include flood frequency, stage-discharge relations, flow duration, sediment-rating curves, and comparisons of dissolved loads to sediment loads. The utility of geoindicators in the humid tropics may be greatest if observation sites are selected with a network design to permit comparisons of sites with similar conditions of climate and drainage-basin characteristics.

River flow mass exponents with fractal channel networks and rainfall

An important problem in hydrologic science is understanding how river flow is influenced by rainfall properties and drainage basin characteristics. In this paper we consider one approach, the use of mass exponents, in examining the relation of river flow to rainfall and the channel network, which provides the primary conduit for transport of water to the outlet in a large basin. Mass exponents, which characterize the power-law behavior of moments as a function of scale, are ideally suited for defining scaling behavior of processes that exhibit a high degree of variability or intermittency. The main result in this paper is an expression relating the mass exponent of flow resulting from an instantaneous burst of rainfall to the mass exponents of spatial rainfall and that of the network width function. Spatial rainfall is modeled as a random multiplicative cascade and the channel network as a recursive replacement tree; these fractal models reproduce certain types of self-similar behavior seen in actual rainfall and networks. It is shown that under these modeling assumptions the scaling behavior of flow mirrors that of rainfall if rainfall is highly variable in space, and on the other hand flow mirrors the structure of the network if rainfall is not so highly variable.

Regional calibration of a watershed model

As watershed models become increasingly sophisticated and useful, there is a need to extend their applicability to locations where they cannot be calibrated or validated. A new methodology for the regionalization of a watershed model is introduced and evaluated. The approach involves calibration of a watershed model to many sites in a region, concurrently. Previous research that has sought to relate the parameters of monthly water balance models to physical drainage basin characteristics in a region has met with limited success. Previous studies have taken the two-step approach: (a) estimation of watershed model parameters at each site, followed by (b) attempts to relate model parameters to drainage basin characteristics. Instead of treating these two steps as independent, both steps are implemented concurrently. All watershed models in a region are calibrated simultaneously, with the dual objective of reproducing the behaviour of observed monthly streamflows and, additionally, to obtain good relationships between watershed model parameters and basin characteristics. The approach is evaluated using 33 basins in the southeastern region of the United States by comparing simulations using the regional models for three catchments which were not used to develop the regional regression equations. Although the regional calibration approach led to nearly perfect regional relationships between watershed model parameters and basin characteristics, these “improved” regional relationships did not result in improvements in the ability to model streamflow at ungauged sites. This experiment reveals that improvements in regional relationships between watershed model parameters and basin characteristics will not necessarily lead to improvements in the ability to calibrate a watershed model at an ungauged site.

Environmental geological investigations at the Van open dump site, southeastern Turkey

This study evaluates the geological, hydrogeological and hydrological conditions at the open waste dump site of the Van municipality in eastern Anatolia, Turkey. A geological map and a three-dimensional view of the project site have been prepared. All lithological units exposed at and near the dump site have been determined and their boundary relationships identified. Drainage basin characteristics of the dump site along with the water bearing properties of different lithological units have been assessed. For the rehabilitation of the existing dump site, material availability (clay as a liner, cap, and daily cover material; granular soil as a filter material) has been researched. Based on the geological, hydrogeological, morphological and hydrological conditions of the existing waste dump site, recommendations to minimize its environmental impact are presented.

A Shape Definition for Geographic Applications Based on Edge, Elongation, and Perforation

An expanded definition for measuring shape in a geographic context is presented. Shape analysis is important in many geographic contexts such as studying the effects of urban development, measuring geographic characteristics of drainage basins, and examining the patterns of geologic formations.This research implements and tests an approach to expand the current mathematical definition of shape and to measure shape for geographic applications, called the trivariate shape definition. The expanded definition involves identifying three characteristics to define shape: edge, elongation, and perforation. Indices to measure these characteristics were identified and applied to two different data sets. Analysis of results from these data sets suggests that the trivariate index clustered groups of objects based on shape similarity. The trivariate approach provides more flexibility to measure shape by relying on a more specific definition of shape.

Flow Balances in St. Andrew Bay Revealed through Hydrodynamic Simulations

The circulation patterns in St. Andrew Bay, Florida are revealed through the application of a well-tested, extensively used three-dimensional hydrodynamic model. A high resolution grid resolving both the horizontal and vertical directions is used with a systematically developed set of forcing functions to simulate conditions over a full year. Water levels at the three open boundaries are deduced from a year-long deployment of pressure gauges, and freshwater loadings are based upon drainage basin characteristics and precipitation measurements. Model validation involves comparisons with hydrographic casts taken at twelve stations distributed throughout the bay at monthly intervals. The relative average error between the observed and model-predicted salinity is 15% for the surface of the water column and 4% for the bottom. The annual net flow balance consists of an influx of water at the two Intracoastal Waterway open boundaries, with that water exiting to the Gulf of Mexico. An average of about 100 m3 s−1 enters from East Bay and about 40 m3 s−1 enters through West Bay. On shorter time scales, the flow balance is quite variable both in terms of magnitude and direction. This study also presents methods to overcome the paucity of data that is usually available for the development of such a model. These include techniques to take bottom pressure data sets with short gaps and create reliable sea surface elevation boundary conditions and to take precipitation data and drainage basin characteristics and produce estimates of freshwater inflows.

A comparative study of regression based methods in regional flood frequency analysis

Reliable estimates of flow statistics are needed for water resources management and flood forecasting purposes. However, the location of gaging station seldom coincides with the site of interest, or the available record becomes too short to make meaningful statistical inferences. Thus regional regression models, such as power-form model of Thomas and Benson (Thomas, D.M., Benson, M.A., 1970. Generalization of streamflow characteristics from drainage-basin characteristics, US Geological Survey, Water Supply Paper, 1975), which relate regional physiographic characteristics to streamflow statistics are developed to estimate the streamflow statistics where data are needed but not available. Depending upon the postulated model type and nature of the data, there are several ways of estimating model parameters. This paper compares the performances of nine methods of estimating parameters of the power-form model that expresses flood quantile as a function of basin area. The performance of each method is assessed based upon its quantile prediction ability from an ungaged site in the region. A jacknife procedure is used to simulate the ungaged site condition in the region. Based upon a case study using the hydrologic and physiographic data from Quebec, Canada, nonlinear models outperformed the log-linearized (or linear) models. Despite the differences in the parameter estimation techniques and suitability for different data type, the quantile prediction abilities of all of the linear models were not different from each other. Most of the linear models had higher bias and higher root mean squared error and they under-predicted floods from large basins.

A cross-scale comparison of drainage basin characteristics derived from digital elevation models

The feasibility of using small-scale digital elevation models (DEMs) to extract various drainage basin characteristics was evaluated by comparing basin parameters derived from the 1:250 000 DEMs with those from the 1:24 000 DEMs. Twenty basins ranging approximately from 150 km2 to 1000 km2 in West Virginia, a geologically complex region, were examined in this study. The basin parameters examined included those commonly used in hydrology and geomorphology such as elevation, slope, stream length, drainage density, relief ratio and ruggedness number. Our results suggested that the 1:250 000 DEMs can provide accurate estimates for elevation-based and stream-length-based basin parameters, but not for slope-based parameters. After examining the differences between the DEM-derived basin parameters from the two different scales, we found that the performance of the 1:250 000 DEMs was not significantly influenced by basin size, while terrain complexity seems to be an important factor of accuracy of the estimated basin parameters. Copyright © 1999 John Wiley & Sons, Ltd.

A cross‐scale comparison of drainage basin characteristics derived from digital elevation models

A cross‐scale comparison of drainage basin characteristics derived from digital elevation models

Fractal dimensions of suspended solids in streams: comparison of sampling and analysis techniques

Fluvial suspended sediment typically consists of a variety of complex, composite particles referred to as flocs. Floc characteristics are determined by factors such as the source, size and geochemical properties of the primary particles, chemical and biological coagulation processes in the water column and shear stress and turbulence levels in the stream. Studies of floc morphology have used two contrasting methods of sampling and analysis. In the first method, particles settle on a microscope slide and are observed from below using an inverted microscope. The second method uses filtration at no or low vacuum and particles deposited on the filter are observed with a microscope. Floc morphology can be quantified using fractal dimensions. The aims of the present study were to examine the effect of the two sampling methods on the fractal dimensions of particle populations, and to evaluate for each method how well the fractal dimensions at the various sampling sites reflect basin conditions. Suspended solids were collected in triplicate on inverted microscope slides and on 0·45 μm Millipore HA filters in two southern Ontario streams with contrasting riparian zones during a minor runoff event resulting from the melt of a freshly fallen snowpack. An image analysis system was used to determine area, longest axis and perimeter of particles. The morphology of the particle population of each sample was characterized using four fractal dimensions (D, D1, D2 and DK). Systematic differences in fractal dimensions obtained with the two methods were observed. For the settling method, outlines of larger particles were frequently blurred because of the distance between the focal plane (the top of the inverted microscope slides) and the plane of the particle outline. In this method, the blurring of large particles can cause an increase in the projected area and length of the particle. The effect on the particle perimeter is unpredictable because it depends on the amount of detail lost through blurring and its effect on the apparent increase in particle size. Because of blurring, D and D1 tend to be systematically lower for the settling method, whereas the net effect on D2 is unpredictable. Particle size distributions derived from settling are typically coarser because small, low density particles may remain in the water column and all particles may not deposit on the slides. This loss of fines results in systematically lower DK values for the settling method compared with the filtration method. Fractal dimensions and particle size distributions obtained with the filtration method were sensitive to and clearly indicated differences between drainage basins and between sites within each basin. These differences were explained by basin characteristics and conditions. Fractal dimensions and particle size distributions obtained with the settling method were less sensitive to drainage basin characteristics and conditions, which limits their usefulness as process indicators. Copyright © 1999 John Wiley & Sons, Ltd.

Estimation régionale de quantiles de crues par l'analyse des correspondances

In this study, the problem of regional flood estimation at ungauged sites is examined in the metric space defined by the application of correspondence analysis to physiographic and climatic characteristics of drainage basins. The selection of this technique was dictated by its highly descriptive ability and the stability of the results it yields. The transposition of flood quantiles at an ungauged site is carried out via the corresponding weighted averaged quantiles observed at s neighboring sites (s fixed). The fundamental question regarding the optimal size of the neighborhood to be used in flood estimation at a particular site is addressed in the discussion of results obtained from the application of the methodology to the drainage basins in the province of Ontario, Canada. In addition to identification of dependence structures between the characteristics of the drainage basins considered, the correspondence analysis allows to identify homogeneous groups within which floods at an ungauged site are represented satisfactorily by the weighted averages of floods observed at neighboring sites. Comparison between results obtained and those from multiple regressions on the ensemble of basins shows that the proposed methodology can be adequately used to estimate flood quantiles.