Nenad Jacimovic

Stormwater biofilter treatment model (MPiRe) for selected micro-pollutants.

Biofiltration systems, also known as bioretentions or rain-gardens, are widely used for treatment of stormwater. In order to design them well, it is important to improve models that can predict their performance. This paper presents a rare model that can simulate removal of a wide range of micro-pollutants from stormwater by biofilters. The model is based on (1) a bucket approach for water flow simulation, and (2) advection/dispersion transport equations for pollutant transport and fate. The latter includes chemical non-equilibrium two-site model of sorption, first-order decay, and volatilization, thus is a compromise between the limited availability of data (on stormwater micro-pollutants) and the required complexity to accurately describe the nature of the phenomenon. The model was calibrated and independently validated on two field data series collected for different organic micro-pollutants at two biofilters of different design. This included data on triazines (atrazine, prometryn, and simazine), glyphosate, and chloroform during six simulated stormwater events. The data included variable and challenging biofilter operational conditions; e.g. variable inflow volumes, dry and wet period dynamics, and inflow pollutant concentrations. The model was able to simulate water flow well, with slight discrepancies being observed only during long dry periods when, presumably, soil cracking occurred. In general, the agreement between simulated and measured pollutographs was good. As with flows, the long dry periods posed a problem for water quality simulation (e.g. simazine and prometryn were difficult to model in low inflow events that followed prolonged dry periods). However, it was encouraging that pollutant transport and fate parameters estimated by the model calibration were in agreement with available literature data. This suggests that the model could probably be adopted for assessment of biofilter performance of other stormwater micro-pollutants (PAHs, phenols, phthalates, etc.). The model, therefore, could be applied in practice for sizing of biofilter systems and their validation monitoring, when used for stormwater harvesting.

A simple numerical method for snowmelt simulation based on the equation of heat energy

This paper presents one-dimensional numerical model for snowmelt/accumulation simulations, based on the equation of heat energy. It is assumed that the snow column is homogeneous at the current time step; however, its characteristics such as snow density and thermal conductivity are treated as functions of time. The equation of heat energy for snow column is solved using the implicit finite difference method. The incoming energy at the snow surface includes the following parts: conduction, convection, radiation and the raindrop energy. Along with the snow melting process, the model includes a model for snow accumulation. The Euler method for the numerical integration of the balance equation is utilized in the proposed model. The model applicability is demonstrated at the meteorological station Zlatibor, located in the western region of Serbia at 1,028 meters above sea level (m.a.s.l.) Simulation results of snowmelt/accumulation suggest that the proposed model achieved better agreement with observed data in comparison with the temperature index method. The proposed method may be utilized as part of a deterministic hydrological model in order to improve short and long term predictions of possible flood events.

Cellular Automata Approach for 2D Pollution Transport Modelling in Urban Groundwater

Integrated modelling requires many simplifications in order to speed up long time calculations and simulations. Therefore, many non-traditional methods are being widely used. Cellular automata (CA) represents one of these methods. The paper presents the application of the CA approach in modelling of the contaminant transport in unsteady groundwater conditions. It compares the results obtained using the two CA models modified for groundwater problems. Results obtained in this paper show that CA approach can be successfully used for simulations of unsteady groundwater conditions, caused by surface-groundwater interaction, and pollution transport.

Numerical modelling of simultaneous overtopping and seepage flows with application to dike breaching

Dike failures due to overtopping frequently occur during floods, causing serious damage to settlements and the environment. For risk management, it is of great importance to understand the mechanisms of dike failure and predict this process accurately. In this study, a three-dimensional numerical model is developed to simulate both overtopping and seepage flows during dike breaching. The governing equations describing the free water flow are extended and applied to simulate also the filtration through porous media. A non-equilibrium sediment transport model is utilized for simulation of the bed deformation. The numerical model is firstly applied to flows over a solid embankment in order to validate the flow part of the model, and then the dike breaching is simulated such that the bed deformation model is also incorporated. By comparison with the experimental results, it is shown that the developed model reproduces overflow and the dike failure processes reasonably well.

Laboratory investigation of hydraulic characteristics of fly ash as a fill material from the aspects of pollutant transport

Depending on the usage of fly ash, it is necessary to determine its environmental parameters, such as the potential for pollutant transport/leaching after its built-in. This study presents a methodology for determination of transport parameters (filtration coefficient, effective porosity, longitudinal dispersivity, and the mean residence time) from experimental data collected from column experiments with a conservative tracer on different mixtures of fly ash with stabilizers (4.8% lime and 5% cement). The transport parameters are determined using (1) numerical model results and (2) an adapted analytical solution results against measured outflow tracer concentrations. The study shows that the addition of stabilizers decreases the filtration coefficient by an order of magnitude and the effective porosity by half. The longitudinal dispersivity is not influenced by the addition of lime to the mixture, and is increased by 40% by the addition of cement. The pollutant contact time with fly ash increases by six or nine times with the addition of lime and cement, respectively. The adaptation of the analytical solution agrees well with both the numerical solution and the experimental results, and it is anticipated to be of high value for determination of transport parameters for practitioners not familiar with numerical methods.

Consequences of Non Planned Urban Development During Turbulent Times in Serbia — Case Study of Suburb Kumodraz Watershed in Belgrade

Development is usually based on numerous analyses accounting for planning, economy and population assessments as well as urbanism, architectural and civil engineering infrastructure planning and project design. The modern city planning begun during Napoleon in Paris, while modern urban planning in Belgrade started in mid nineteenth century. At the end of twentieth century turbulent times occurred in the area of ex Yugoslavia so that numerous plans of development started being misused or never completely respected. Actually, during 1990s urban development in cities of Serbia became rather uncontrolled. In addition, during 1990s many people moved from rural places to, to their opinion, more promising places, most frequently to the Capital city. This paper presents a series of consequences of non planned urban development on sewer infrastructure operation. Those includes high construction rate including increase of number of inhabitants at suburban part, namely watershed of the brook Kumodraz at the southern part of the city of Belgrade. Those changes were noticed during preparation of preliminary design for the reconstruction and upgrading of the combined waste water system at this part of the city. The design preparation included measurements of wastewater and rainfall runoff at the downstream outlet. During measurement period, which started in 1997, significant differences occurred in the both base flow, i.e. dry weather flow, as well as in peak flows during moderate and severe rainfall events.