| 1. |
- Berndtsson, Ronny, et al.
(författare)
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Some Eulerian and Lagrangian statistical properties of rainfall at small space-time scales
- 1994
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 153:1-4, s. 339-355
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Tidskriftsartikel (refereegranskat)abstract
- Management of urban hydrological systems requires a knowledge of short-term and small-scale rainfall properties. Small catchment areas, dense building structures, a high degree of impermeable areas, and resulting rapid runoff, mean that the properties of individual rain cells are important considerations. Accordingly, this paper characterizes mainly spatial rainfall properties on a scale suitable for urban hydrology. Because of the usually dominant advective velocity component of individual rain cells the Eulerian view (observations of the moving rain cell by a fixed rain gage network) gives a distorted picture in the direction of movement of the actual rain cell. The extent of distortion depends on the magnitude of the advective velocity. The Lagrangian approach (moving along with the same speed and direction as the cell) gives different information regarding cell characteristics (e.g. size) compared with the Eulerian approach. It is shown that the Lagrangian cell size as indicated by the spatial correlation structure on average is twice the size of the Eulerian cell size. Thus, it is argued that the Lagrangian approach provides a more realistic picture of the rainfall structures compared with the Eulerian approach. The cell properties exhibit a temporal persistence of the spatial characteristics in the direction of movement. This persistence is, however, not strong and thus a forecasting procedure using advection only does not seem appropriate.
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| 2. |
- Das, Rajib, et al.
(författare)
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Bridge Scour : Basic Mechanisms and Predictive Formulas
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report aims at presenting basic knowledge on bridge scour and the processes governing its evolution as well as summarizing the most common formulas used to calculate scour depth at bridges. Design procedures concerning bridge scour in several different countries are also discussed, including United States, Australia, and the United Kingdom. The situation in Sweden with regard to bridge scour is briefly reviewed and several case studies are presented where marked scour holes have been detected at bridges. Two cases of bridge failures in Sweden are included where local scour was the main reason for the collapse.Bridge scour is typically separated into pier, abutment, and contraction scour, where each mechanism is controlled by different physics and governing parameters. Each type of bridge scour is discussed separately in the report with sections on basic mechanisms, governing parameters, common predictive formulas, and concluding remarks.The report also includes a brief summary on the expected influence of climate change on bridge scour. Larger and more intense rainfalls in the future imply larger flows in the rivers with increased bridge scour as a result.The report deals only with scour induced by bridges; other types of scour, such as general scour due to longitudinal transport gradients in the river, scour related to secondary flows in river bends, or scour downstream hard bottom, are not discussed. Most of the formulas included to estimate bridge scour are valid for friction material and only a few examples are given that are applicable to cohesive sediment, mainly related to recommended design procedures from different countries. Also, the objective of bridge scour analysis is often to estimate the maximum scour depth, occurring at equilibrium conditions under a certain flow, implying that most of the formulas are valid for such conditions.
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| 3. |
- Hogland, William, et al.
(författare)
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Assessment of stormwater pollution transport to swedish coastal waters
- 2018
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Ingår i: Integrated Stormwater Management. - : CRC Press. - 0873718054 - 9781315894652 - 9781351082204 ; , s. 81-92
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Bokkapitel (refereegranskat)abstract
- Studies dealing with stormwater pollution transport on a local scale have been carried out in Sweden since the middle of the 1970s. 1-7 However, so far no investigation has aimed at determining the importance of stormwater pollution on a larger scale, involving a region or a part of the country. Such studies would provide the necessary background information for (1) developing a regional (nationwide) stormwater management policy, (2) quantifying the importance of stormwater pollution in comparison with other pollution sources, and (3) helping to set the priorities between different measures taken to reduce the pollution transport to receiving waters.
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| 4. |
- Hogland, William, et al.
(författare)
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ESTIMATION OF QUALITY AND POLLUTION LOAD OF COMBINED SEWER OVERFLOW DISCHARGE.
- 1984
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Ingår i: Urban Stormwater Management. - 9170321280 ; , s. 841-850
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Konferensbidrag (refereegranskat)abstract
- The relative effect of combined sewer overflow (CSO) discharge into receiving waters has increased during the last decades due to improved efficiency at treatment plants. In association with the rapid urbanization in the sixties and early seventies, new areas were connected to old sewer networks with limited capacity, leading to an increase in overflow volumes and, thus to an increase in pollution load. In order to develop a responsible urban water quality management policy we must be able to describe CSO in terms of quality and quantity. To elucidate such problems extensive measurements were carried out in the city of Malmo with quality sampling and simultaneous flow measurements. This paper presents different aspects on the quality of CSO discharge and different available methods for calculation of the pollution load.
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| 5. |
- Jinno, Kenji, et al.
(författare)
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Real‐time rainfall prediction at small space‐time scales using a two‐dimensional stochastic advection‐diffusion model
- 1993
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Ingår i: Water Resources Research. - 0043-1397. ; 29:5, s. 1489-1504
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Tidskriftsartikel (refereegranskat)abstract
- A model based on the two‐dimensional stochastic advection‐diffusion equation is developed to forecast properties of individual rain cells in urban areas such as speed and spatial rainfall intensity. Two different modeling approaches are employed, and examples of the results are given. The first approach involves a Gaussian distribution as an analytic solution to the advection‐diffusion equation, whereas the second one entails a double Fourier series expansion of the rainfall intensity field. Both modeling approaches are used to predict the rainfall intensity field over a small 12‐gage urban catchment in southern Sweden. The model parameters are continuously updated by extended Kalman filtering. The Fourier series approach is shown to be the most flexible for practical applications and to give the most accurate forecasts. This model approach gives acceptable forecasts for a lead time of 1–5 min. It gives consistently smaller prediction errors compared to both the Gaussian solution and simple extrapolation calculations. The effect of system noise level on the forecast accuracy and model performance is discussed. The model can be used not only to predict in real time the spatial rainfall, but also to parameterize the variability pattern of small‐scale spatial rainfall into a set of physically based parameters, thus separating the effects of advective velocity, turbulent diffusion, and development/decay.
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| 6. |
- Marinho, Bárbara, et al.
(författare)
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Long-term coastal evolution modelling of longshore bars
- 2018. - 2018
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Ingår i: Proceedings of 32nd International Conference on Coastal Engineering. - 0161-3782. ; 36
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Konferensbidrag (refereegranskat)abstract
- An extended version of a numerical model introduced by Larson et al. (2013) to simulate long-term cross shore material exchange for the subaqueous portion of the profile has been developed. Efforts have focused on improving the model to better account for beach systems consisting of two bars (inner and outer bar), as well as simulating the feeder response over time of nearshore dredged material bars, intended to function as beach nourishment. The theory for the evolution of a single-bar to a two-bar system was modeled, considering an inner and an outer bar, where the outer bar is of primary interest with the purpose of predicting the behavior of placed dredged material. The cross-shore sediment transport rate is based on the evolution equation for the bar system response to the hydrodynamic forcing by reference to its equilibrium condition, where the change in the bar volume is based on a set of wave criteria, describing the onset of a new breaking zone when the outer bar forms. Empirical formulas are employed for the bar equilibrium volume and for coefficients determining the bar response rate. In this study, a description of the extended model and the results from the model component validation at two different sites in USA (Duck, North Carolina, and Cocoa Beach, Florida) are presented. Duck measurements have detected that some bars form in the nearshore and move all the way offshore (eventually deflating by non-breaking waves). At the same time, it was equally observed that a lot of inner bars formed in shallow water do not move offshore but remain as inner bars all the time. According to this, the developed model considers that the inner bar will not become the outer bar, but material previously dedicated to the inner bar will be available for the outer bar. Overall, the present study demonstrates the potential for using rather simple models, based on the definition of an equilibrium state that is compared to the current state and the magnitude of offshore wave forcing to drive the changes in the profile. The methodology employed here allowed to quantitatively reproduce the main trends in the subaqueous beach profile response in a long-term perspective as a function of the bar volumes disequilibrium, the magnitude of the incident wave height and the dimensionless fall velocity to move the sand with a time varying forcing.
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| 7. |
- Marinho, Barbara, et al.
(författare)
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Monitoring the evolution of nearshore nourishments along Barra-Vagueira coastal stretch, Portugal
- 2018
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691. ; 157, s. 23-39
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Tidskriftsartikel (refereegranskat)abstract
- Maintenance of existing harbors implies regular dredging activities. Where the combined use of dredging and disposal of dredged material on nearby sediment-starved beaches can induce major changes in the beach morphology and generate unexpected impacts in the environment, monitoring becomes a concern. This paper was designed to analyze, interpret and evaluate a set of monitoring data collected along a regular-nourished coastal stretch with dredged sand (Barra-Vagueira coastal stretch, northwest coast of Portugal), surrounded by an energetic hydrodynamic environment with a scarce natural sediment input. Based on a field data set, collected between 2009 and 2015, the present study brings together a set of correlated analyses, intended to assess the morphodynamic evolution of the fills as well as their impact to the adjacent coast. The available data set encompasses topo-hydrographic surveys collected for 12 cross-sections (with 1 km spacing) distributed along the coastal stretch and bathymetric measurements collected for the dumping areas. Considering the concurrent offshore wave forcing, dominant temporal and spatial patterns, morphological changes, evolution trends, sediment budgets, and short- and medium-term responses of the fills are investigated by the use of ArcGIS tools and application of a multivariate statistical method based on Empirical Orthogonal Functions (EOFs). Overall, during the monitoring period, almost 2.8 Mm3 of sand was dumped in different locations and periods to control the erosion observed downdrift of the inlet. However, bathymetric surveys and profile indicators still point out the erosional longshore pattern diagnosed decades ago as a result of a negative longshore sediment balance. Observations also revealed that short-term changes arising from the seasonal cycles of cross-shore material exchange are mainly linked to the largest variations in the beach profile shape, also affecting the sediment budget. Profiling indicated cross-shore volume variations ranging from ±250 m3/m and ±1500 m3/m in the subaerial and subaqueous portion of the profile, respectively, along the monitored period. After the first completed seasonal cycle the sand bar, artificially created by the nourishments, could not be visually detected in the profiles, suggesting a cross-shore redistribution of the fill material. All the analyses developed in this paper stress the importance of establishing proper monitoring programs based on adequate surveying instruments and data collection strategies, in order to ensure high-density data that could be used in support to the decision-markers.
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| 8. |
- Marinho, Bárbara, et al.
(författare)
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Short- and long-term responses of nourishments : Barra-Vagueira coastal stretch, Portugal
- 2018
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Ingår i: Journal of Coastal Conservation. - : Springer Science and Business Media LLC. - 1400-0350 .- 1874-7841. ; 22:3, s. 475-489
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Tidskriftsartikel (refereegranskat)abstract
- Dredged material resulting from deepening and maintenance activities of the Aveiro Harbor inlet channel, northwestern coast of Portugal, has been used to mitigate the erosion trend recorded on nearby beaches (from Barra to Costa Nova Beach) through direct placement of sand by using standard dredge equipment. The disposal activities of dredged material have been undertaken at two main sites: between the south breakwater and the 1st groin of Costa Nova (dumping area 1, DA1) and between the 3rd and the 5th groin of Costa Nova (dumping area 2, DA2).The sand was placed in the nearshore, between the −2 and −7 m Chart Datum, CD, contours. In this study, short- and long-term coastal morphologic changes in the sea bottom, in response to several nourishment operations and to the incoming waves, within the dumping area boundaries are investigated based on a data set of hydrographic surveys collected annually, just before and after the nourishments, between 2009 and 2015. Preliminary results describing the main morphologic changes, evolution trends, sediment budget variations, and nourishments performance are discussed using mainly Geographic Information System techniques. Overall, the analysis demonstrates that the short-term losses in the dumping areas (one month of interval) can reach 50% of the nourished volume, revealing a significant movement of the fill material towards offshore. Seasonal variations promoting cross-shore material exchange can also prevail and misrepresent the sediment balances, if the monitoring area is not comprehensive. Furthermore, some bathymetric analysis suggested that longshore transport gradients have moved the fill material from Barra beach to downdrift areas. All the obtained results contribute to the ongoing discussion about the effectiveness of nearshore sand placements especially in context of an energetic environment.
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| 9. |
- Morioka, Jumpei, et al.
(författare)
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Numerical modeling of ship wave generation using Green’s functions based on linear dispersive wave theory
- 2020
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Ingår i: Coastal Engineering Journal. - : Informa UK Limited. - 2166-4250 .- 1793-6292. ; 62:2, s. 317-335
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an efficient numerical model for predicting ship waves was developed using Green’s functions. Avoiding detailed description of the complex boundary conditions around a ship, this model simply used an inversion technique for estimating the wave source induced by a ship as a function of the navigation route and adjacent measured water level fluctuations. The Green’s functions were determined as linear summations of the water level fluctuations generated from discrete points along the navigation route. At each point, a time-varying wave source was determined as a linear summation of Gaussian pulses introduced at segments along the longitudinal direction of the ship. The linear inversion was then applied for estimating the optimum combinations of the magnitudes of these Gaussian pulses. Linear dispersive wave theory was applied to compute the water level fluctuations generated by a single Gaussian pulse so that the model can reproduce the dispersive characteristics of ship waves. The developed model was tested against experimental data and showed satisfactorily predictive skills of water level fluctuations for cases not used in the inversion. The present model was also found to be robust in that the estimated best-fitted wave source was not sensitive to changes in the conditions of the measured data used for the inversion.
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| 10. |
- Nam, Pham Thanh, et al.
(författare)
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Model of nearshore random wave transformation : validation against laboratory and field data
- 2017
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 135, s. 183-193
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a two-dimensional numerical model of nearshore random wave transformation with a focus on model calibration and verification with both laboratory and field data. The model is based on the energy balance equation including diffraction and dissipation terms (Mase, 2001). The energy dissipation is determined based on the formulation by Dally et al. (1985), with new expressions for the stable wave height and decay coefficients. These coefficients are estimated based on the local beach slope and offshore wave conditions. The model is calibrated with several data sets from the Large-scale Sediment Transport Facility (LSTF) at the Coastal and Hydraulics Laboratory in USA. Then, the model is verified against a large number of data sets, including LSTF data for cases with structures, laboratory data from the Great Wave Flume in Hanover, the field data from Egmond in the Netherlands, Duck in USA, and Cancun in Mexico. The validation showed that the model could reproduce the observations well. The relative root-mean-square error varies from 5% to 7.6% for laboratory data, and from 10.3% to 18.6% for field data. The coefficient of determination varies from 0.81 to 0.97, demonstrating good agreement between the model and the measurements.
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