US-CHINA WORKSHOP ON ADVANCED COMPUTATIONAL MODELLING IN HYDROSCIENCE & ENGINEERING September 19-21, Oxford, Mississippi, USA MODELING HYDRODYNAMICS, CHANNEL MORPHOLOGY, AND WATER QUALITY USING CCHE1D
CCHE1D is a one-dimensional model for the simulation of unsteady flows, sediment transport, and water quality in stream networks. The model can be applied to a variety of engineering problems, but it is particularly useful in the determination of channel–watershed system responses to natural and man-made changes in both channels and upland areas. The model can be used in combination with the watershed model AGNPS in the analysis of watershed hydrology and nonpoint source pollution problems caused by erosion or pollutants such as nutrients and pesticides. CCHE1D’s flow module – CCHE1D-FL – computes one-dimensional unsteady flows in dendritic channel networks of arbitrary cross-sectional shapes. The sediment transport module – CCHE1D-ST – simulates the transport of sediment mixtures using a nonequilibrium approach, predicting sediment yields and channel morphological changes. The recently developed water quality module – CCHE1D-WQ – simulates transport and fate of pollutants in streams for continuous, unsteady flow conditions. The model computes advective-dispersive transport of a number of pollutants, simulating the biogeochemical processes of the main nutrient cycles, phytoplankton growth, and the process of eutrophication. GIS-based graphical software complements the modeling system, providing automated methods for watershed delineation, channel network generation, data transfers and conversions, and visualization.
One-dimensional numerical model for nonuniform sediment transport under unsteady flows in channel networks
In this study, the proposed one-dimensional model simulates the nonequilibrium transport of nonuniform total load under unsteady flow conditions in dendritic channel networks with hydraulic structures. The equations of sediment transport, bed changes, and bed-material sorting are solved in a coupling procedure with a direct solution technique, while still decoupled from the flow model. This coupled model for sediment calculation is more stable and less likely to produce negative values for bed-material gradation than the traditional fully decoupled model. The sediment transport capacity is calculated by one of four formulas, which have taken into consideration the hiding and exposure mechanism of nonuniform sediment transport. The fluvial erosion at bank toes and the mass failure of banks are simulated to complement the modeling of bed morphological changes in channels. The tests in several cases show that the present model is capable of predicting sediment transport, bed changes, and bed-material sorting in various situations, with reasonable accuracy and reliability.
On the validity of area-based income measures to proxy household income
BackgroundThis paper assesses the agreement between household-level income data and an area-based income measure, and whether or not discrepancies create meaningful differences when applied in regression equations estimating total household prescription drug expenditures.MethodsUsing administrative data files for the population of BC, Canada, we calculate income deciles from both area-based census data and Canada Revenue Agency validated household-level data. These deciles are then compared for misclassification. Spearman's correlation, kappa coefficients and weighted kappa coefficients are all calculated. We then assess the validity of using the area-based income measure as a proxy for household income in regression equations explaining socio-economic inequalities in total prescription drug expenditures.ResultsThe variability between household-level income and area-based income is large. Only 37% of households are classified by area-based measures to be within one decile of the classification based on household-level incomes. Statistical evidence of the disagreement between income measures also indicates substantial misclassification, with Spearman's correlations, kappa coefficients and weighted kappa coefficients all indicating little agreement. The regression results show that the size of the coefficients changes considerably when area-based measures are used instead of household-level measures, and that use of area-based measures smooths out important variation across the income distribution.ConclusionThese results suggest that, in some contexts, the choice of area-based versus household-level income can drive conclusions in an important way. Access to reliable household-level income/socio-economic data such as the tax-validated data used in this study would unambiguously improve health research and therefore the evidence on which health and social policy would ideally rest.