The Experts below are selected from a list of 108 Experts worldwide ranked by ideXlab platform
William D. Phillips - One of the best experts on this subject based on the ideXlab platform.
-
Dimensionless Units in the SI
Metrologia, 2014Co-Authors: Peter J. Mohr, William D. PhillipsAbstract:The International System of Units (SI) is supposed to be coherent. That is, when a combination of Units is replaced by an equivalent Unit, there is no additional numerical factor. Here we consider Dimensionless Units as defined in the SI, {\it e.g.} angular Units like radians or steradians and counting Units like radioactive decays or molecules. We show that an incoherence may arise when different Units of this type are replaced by a single Dimensionless Unit, the Unit "one", and suggest how to properly include such Units into the SI in order to remove the incoherence. In particular, we argue that the radian is the appropriate coherent Unit for angles and that hertz is not a coherent Unit in the SI. We also discuss how including angular and counting Units affects the fundamental constants.
Ivan Muzik - One of the best experts on this subject based on the ideXlab platform.
-
A MICROCOMPUTER-BASED GEOGRAPHIC INFORMATION SYSTEM FOR HYDROLOGIC SIMULATION
Computer-Aided Civil and Infrastructure Engineering, 2008Co-Authors: Ivan Muzik, Chiadih ChangAbstract:A microcomputer-based geographic information system (GIS) supporting hydrologic simulation is described. The hydrologic model uses the Soil Conservation Service (SCS) runoff curve number (CN) method and a synthetic Unit hydrograph to represent the physical transformation of rainfall into runoff. The standard SCS method was modified to account for randomness of key parameters whose probability distributions can be derived from regional rainfall and runoff data. The GIS, and hydrologic theory and techniques, including the modified SCS method, derivation of a regional Dimensionless Unit hydrograph, and Monte Carlo simulation procedure, are described. Results of hydrologic analysis and simulation by the system implemented for an area of 11,000 km (squared) in the Alberta foothills are presented.
-
Regional Dimensionless hydrograph for Alberta foothills
Hydrological Processes, 2003Co-Authors: Ivan Muzik, Chiadih ChangAbstract:The majority of hydrologic engineering applications deal with ungauged watersheds. Various empirical methods are available for synthesizing Unit hydrographs for ungauged watersheds from information obtained from maps or field inspection of the watershed. An alternative to the employment of generalized synthetic Unit hydrographs is to develop a regional Dimensionless hydrograph to characterize the local rainfall-runoff processes better. The derivation of such a Dimensionless hydrograph is described for Alberta foothills, based on the analysis of 31 basins and 61 rainfall-runoff events. The analysis shows that it is possible to derive a representative Dimensionless hydrograph for the region with reasonable accuracy by averaging the observed direct runoff hydrographs converted into a Dimensionless form. However, considerable uncertainty is associated with the estimation of the excess rainfall duration and the lag time of the events analysed. The lag time is the key parameter needed to convert the regional Dimensionless hydrograph into an ungauged watershed Unit hydrograph. Possible reasons for unexplained lag time variations are discussed. The regional Dimensionless hydrograph developed and lag time curve were used to regenerate the original 61 hydrographs. Results were compared with the generalized Soil Conservation Service Dimensionless Unit hydrograph which tended to produce larger errors in predicted peak flows. Error analysis indicates the limits of accuracy that may be expected from the method.
-
The Method of Derived Distributions Applied to Peak Flows
Engineering Hydrology, 1993Co-Authors: Ivan MuzikAbstract:Random variables which are functionally related have their probability distributions also related in a prescribed manner. Thus, in theory, the probability distribution of peak discharge could be derived from a known probability distribution of rainfall. The rainfall-runoff relationship, however, is a complex one, involving stochastic parameters, precluding analytical solution. Monte Carlo simulation has to be employed instead. The theory of derived distributions is briefly reviewed. Application of Monte Carlo simulation in deriving synthetic flood frequency curves, using modified Soil Conservation Service runoff curve method and Dimensionless Unit hydrograph, is illustrated by examples.
Mario Aristide Lenzi - One of the best experts on this subject based on the ideXlab platform.
-
Field-derived relationships for flow velocity and resistance in high-gradient streams
Journal of Hydrology, 2007Co-Authors: Francesco Comiti, Luca Mao, Andrew C. Wilcox, Ellen Wohl, Mario Aristide LenziAbstract:Summary We measured velocity and channel geometry in 10 reaches (bed gradient = 0.08–0.21) of a predominantly step-pool channel, the Rio Cordon, Italy, over a range of discharges (3–80% of the bankfull discharge). The resulting data were used to compute flow resistance. At-a-station hydraulic geometry relations indicate that in most reaches, the exponent describing the rate of velocity increases with discharge was between 0.48 and 0.6, which is within the range of published values for pool-riffle channels. The Rio Cordon data are also combined with published hydraulics data from step-pool streams to explore non-dimensional relationships between velocity and flow resistance and factors including Unit discharge, channel gradient, and step geometry. Multiple regression analysis of this combined field dataset indicated that Dimensionless Unit discharge ( q ∗ ) is the most important independent variable overall in explaining variations in velocity and flow resistance, followed by channel slope and the ratio of step height to step length. Empirical equations are provided both for Dimensionless velocity and flow resistance, but prediction of the former variable appears more reliable.
Peter J. Mohr - One of the best experts on this subject based on the ideXlab platform.
-
Dimensionless Units in the SI
Metrologia, 2014Co-Authors: Peter J. Mohr, William D. PhillipsAbstract:The International System of Units (SI) is supposed to be coherent. That is, when a combination of Units is replaced by an equivalent Unit, there is no additional numerical factor. Here we consider Dimensionless Units as defined in the SI, {\it e.g.} angular Units like radians or steradians and counting Units like radioactive decays or molecules. We show that an incoherence may arise when different Units of this type are replaced by a single Dimensionless Unit, the Unit "one", and suggest how to properly include such Units into the SI in order to remove the incoherence. In particular, we argue that the radian is the appropriate coherent Unit for angles and that hertz is not a coherent Unit in the SI. We also discuss how including angular and counting Units affects the fundamental constants.
Chiadih Chang - One of the best experts on this subject based on the ideXlab platform.
-
A MICROCOMPUTER-BASED GEOGRAPHIC INFORMATION SYSTEM FOR HYDROLOGIC SIMULATION
Computer-Aided Civil and Infrastructure Engineering, 2008Co-Authors: Ivan Muzik, Chiadih ChangAbstract:A microcomputer-based geographic information system (GIS) supporting hydrologic simulation is described. The hydrologic model uses the Soil Conservation Service (SCS) runoff curve number (CN) method and a synthetic Unit hydrograph to represent the physical transformation of rainfall into runoff. The standard SCS method was modified to account for randomness of key parameters whose probability distributions can be derived from regional rainfall and runoff data. The GIS, and hydrologic theory and techniques, including the modified SCS method, derivation of a regional Dimensionless Unit hydrograph, and Monte Carlo simulation procedure, are described. Results of hydrologic analysis and simulation by the system implemented for an area of 11,000 km (squared) in the Alberta foothills are presented.
-
Regional Dimensionless hydrograph for Alberta foothills
Hydrological Processes, 2003Co-Authors: Ivan Muzik, Chiadih ChangAbstract:The majority of hydrologic engineering applications deal with ungauged watersheds. Various empirical methods are available for synthesizing Unit hydrographs for ungauged watersheds from information obtained from maps or field inspection of the watershed. An alternative to the employment of generalized synthetic Unit hydrographs is to develop a regional Dimensionless hydrograph to characterize the local rainfall-runoff processes better. The derivation of such a Dimensionless hydrograph is described for Alberta foothills, based on the analysis of 31 basins and 61 rainfall-runoff events. The analysis shows that it is possible to derive a representative Dimensionless hydrograph for the region with reasonable accuracy by averaging the observed direct runoff hydrographs converted into a Dimensionless form. However, considerable uncertainty is associated with the estimation of the excess rainfall duration and the lag time of the events analysed. The lag time is the key parameter needed to convert the regional Dimensionless hydrograph into an ungauged watershed Unit hydrograph. Possible reasons for unexplained lag time variations are discussed. The regional Dimensionless hydrograph developed and lag time curve were used to regenerate the original 61 hydrographs. Results were compared with the generalized Soil Conservation Service Dimensionless Unit hydrograph which tended to produce larger errors in predicted peak flows. Error analysis indicates the limits of accuracy that may be expected from the method.