Wash-off Process Research Articles

Assessment of radiocaesium washoff transport from a pilot catchment in the first period after nuclear contamination

As part of the EC-funded project SPARTACUS a GIS-embedded radionuclide redistribution model was developed based on the existing LISEM soil erosion model. It simulates lateral radiocaesium transport and exchange in the active top soil layer and runoff water in catchment during a rainstorm event. The model was applied for the assessment of the relative extent of radiocaesium transport from the Mochovce catchment following an accidental nuclear contamination using selected rainfall intensity scenarios. In this case, a 15 mm rainfall event during 30 minutes with a maximum rainfall intensity of 75 rnm/h during 8 minutes was selected to assess the effect of ploughing on 137 Cs transport. The model results demonstrate that particulate transport contributes considerably to the IJ7 Cs transport within and from the Mochovce catchment. The l37 Cs transport from unploughed soils appears to be a factor of 35 larger than the transport from ploughed soils. The implications of the model results for selecting appropriate mitigating measures to reduce l37 Cs following a nuclear accident are discussed. measurements in soil samples were conducted in the pilot catchment to test the soil erosion LISEM and the developed radiocaesium redistribution model. Soil samples were collected to determine radiocaesium exchange distribution parameters for the developed model. Radionuclides deposited on the soil surface after a nuclear power plant accident could be a significant source of secondary contamination induced by a heavy rainstorms and subsequent wash-off processes. The extent of radionuclide wash-off transport depends on the character of the first rainstorm events and prevailing soil conditions with respect to fixation and remobilisation of radionuclides from the topsoil layer. Within the frame of the national part of the SPARTACUS project the main focus was devoted to use of the tested model for assessment of wash-off transport characteristics for the pilot catchment in relation with a hypothetical nuclear contamination. To conduct such assessment it is necessary to select appropriate rainfall intensity and soil erosion scenario that conservatively represent the expected worst- case situation. Design block rain intensity curves are available for about 70 Slovakian hydro- meteorological stations (4). They represent the maximum precipitation intensity period within a real rainfall event based on statistical frequency distributions and seem to be appropriate for the simulation of ,37 Cs wash-off. The intensity curves are commonly used in the civil engineering for the design of for example run-off channel dimensions.

A preliminary model for predicting heavy metal contaminant loading from an urban catchment

The toxicity of heavy metals to biota in urban catchments has been regarded as a very important non-point source pollution issue. Numerous studies on heavy metal pollution in urban receiving waters have found that metal transport by surface runoff is closely correlated to the partitioning of the metal forms between dissolved and particulate phases, where sediment plays an important role in the transport process. Sediment cycling on urban streets, metal binding form, and rainfall character in the catchment area are considered to be the key factors for metal transport. A preliminary model is developed based on these considerations. Starting from classical build-up and wash-off processes for the suspended sediment (SS) on the urban impervious surface, the model links the transport of suspended sediment to the transport of metal species. Monitoring data from a small highway catchment were used in the model development. A total of 47 rain events over 1 year were monitored intensively at short time intervals (5–10 min) for hydrological data, rainfall intensity, and stormwater quality. In developing the model, lead was used for the metal load prediction, as it has been a common fuel additive for urban transportation. Agreement between model results and monitoring data indicates that the model can be used in predicting metal load from impervious urban areas, such as streets and roadways, on a long-term basis.

Printing of nylon 6,6 with reactive dyes part I: preliminary studies

Conventional and Coloursafe® modified nylon 6,6 fabrics were printed with reactive dyes from various commercial ranges. Maximum colour yield was achieved using saturated steam as fixation medium and pH 4–5. The colour yield obtained on Coloursafe fabric was higher than that achieved on conventional nylon 6,6. A simple wash-off process was used to remove unfixed dye and print paste from the printed fabrics. The prints displayed excellent fastness to repeated wash testing and to cold water contact fastness. The print paste was stable after up to 3 months storage.

Modeling Storm-Water Runoff Quantity and Quality from Marine Drydocks

Storm-water runoff from a floating marine drydock can be a major source of pollution for the waterway in which the drydock is located. Significant amounts of pollutants build up over drydock surfaces because of intensive industrial activity. During periods of rainfall these pollutants can be washed off and quickly transported into the receiving water. In this study, a mathematical model has been developed to simulate the quantity and quality of storm-water runoff from marine drydocks. The mathematical model is based on the two-dimensional kinematic-wave and convective transport equations for total suspended solids. An empirical formula is used to model the wash-off process. An implicit finite-difference scheme is employed to solve the governing equations of the model numerically. In support of the modeling effort, the quantity and quality of storm-water runoff from a private drydock was monitored under actual rainfall-runoff conditions. The samples collected were analyzed in the laboratory to determine the pollutant loading of the runoff, and these data were subsequently used to calibrate and verify the mathematical model.

Use of Regression Models for Analyzing Highway Storm-Water Loads

Storm-water data collected from an expressway in the Austin, Tex. area were used to develop regression models for predicting loads for a number of constituents commonly found in highway runoff. The goal of the model development was to identify the processes that affect the quality of highway runoff. Linear regression was selected as the most appropriate technique for analyzing the data because of its ability to identify constituent specific causal variables. The regression equations indicate that the majority of variations observed in highway storm-water loading can be explained by causal variables measured during the rainstorm event, the antecedent dry period, and the previous rainstorm event. Loads for each of the constituents were dependent upon a unique subset of the identified variables, indicating that processes responsible for the generation, accumulation, and washoff of storm-water pollutants are constituent specific. Loads of some constituents, such as total suspended solids, were dependent on the characteristics of the current storm, antecedent dry period, and the preceding storm indicating the importance of buildup and washoff processes. Other constituents, such as oil and grease, were dependent only on conditions during the current storm, such as runoff volume and number of vehicles during the event. The identification of constituent-specific explanatory variables suggests the type of mitigation that would be appropriate for specific constituents in non-point-source pollution control.

5725655 Method for new concrete from old concrete

Current urban washoff models still rely on empirical catchment-scale functions, that have not been substantially updated during the last 40 years. This paper introduce a new approach using the physical model FullSWOF to evaluate urban washoff process. The modelling approach is performed for a Parisian road catchment. Water flow simulation is validated by outlet discharge measurements and local observations of water depth. Water quality modelling of three classes of particles (d50 = 7 μm, 70 μm, and 250 μm) is applied using the Hairsine-Rose model. Analysis of the washoff process at the catchment scale indicates that most (> 90%) of the finest particles are removed at the beginning of a rainfall event, about 10%–20% of medium-sized particles are moved over the latest part of the event, and almost no coarse particles can be transferred into the sewer inlet. Spatial analysis of washoff process reveals that the concentration of suspended solids on road and sidewalk surface is more sensitive to rainfall intensities than that on gutter surface, while coarser particles tend to accumulate in the gutter over the later part of a rainfall event. Investigation of the driving force behind the detachment process indicates that rainfall-driven effects are two orders of magnitude higher than flow-driven effects. Moreover, it is observed that rainfall-driven detachment is considerably decreased with the rising water depth, while flow-driven detachment occurs only in gutter areas. Finally, several controversial arguments on the use of physical models for assessing the washoff process, and perspectives on development of physical urban washoff models are discussed.

Modelling of storm wash-off of suspended solids from impervious surfaces

A mathematical model of suspended solids discharge from impervious surfaces during storm events has been developed. The model continuously simulates two major processes of different time scales; solids build-up at impervious surfaces between two storm events, and solids wash-off from the surfaces during storm events. Buildup is modelled using the Sartor and Boyd equation (21) in which the amount of' solids available on the surface is an exponential function of antecedent dry weather period duration. The spatial distribution of solid particles over the street surface is also modelled, which is an innovation. The wash-off process is divided into three subprocesses that are modelled consecutively. A kinematic wave model is used for overland flow modelling. The particle entrainment into suspension is estimated by two methods. In one, the rainfall and overland flow effects are not separated and the total shear stress is used to predict entrainment. In the other, the rainfall and overland flow effects are treated separately and then summed. An original equation was developed for this method. The model is applied on two small experimental catchments, one at Miljakovac-Belgrade, Yugoslavia and the other in Lund, Sweden. The description and verification of the model are presented and discussed in the paper.