Browsing by Author "Mtega, Narsis Anton Leonard"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Mathematical modeling and simulation of spread of pollutants between Mkuyuni area and the Saanane Island: the effect of re-suspension.
    (University of Dar es Salaam, 1998) Mtega, Narsis Anton Leonard
    Water pollution resulting from enormous increasing waste discharge to Lake Victoria, threatens not only the lake ecosystem but also the socio-economic applicability of the lake to the population. The mathematical model we have formulated is based on the principle of conservation of mass and it has been used to study the concentration of pollutants at shallow areas of the lake. The mass balance equation of this model consist of a system of seven first-order non-linear differential equations for substrate, dissolved oxygen, organic nitrogen, ammonia, nitrate, inorganic phosphorus and detritus. Sampling validated the model and analyses done for the named pollutants were used to compute the re-suspension from the benthic layer of the lake. Since it is rather difficult to obtain a closed form, analytical solution, a fourth order Runge-Kutta method was employed to solve the model and it .vas implemented using the MAPLE software package. Simulation of the model showed that much of the pollutants observed at the area of study (MSI) resulted from re-suspension. The model is intended for the use as a tool for prediction and evaluation of relationships between loading rate and resultant concentration of pollutants at areas resembling MSI. Also the model is intended for the use as a tool for prediction and evaluation of concentration of pollutants at areas resembling MSI after considering different physical characteristics, environmental constraints and the size of the concerned area.
  • No Thumbnail Available
    Item
    Mathematical modelling and numerical solution of run-up waves on a sloping beach extended with an artificial bottom
    (University of Dar es Salaam, 2005) Mtega, Narsis Anton Leonard
    Beaches in Tanzania are constantly dynamic resulting to an enormous loss of property and investments, flora and fauna and even the natural beauty. Such a phenomenon requires attention and action to rectify it. This study has developed a model that focuses on the swash zone as part of a bigger study intended to get the general understanding of the beach erosion problems Tanzania is facing. The model comprises of two dimensional depth-averaged nonlinear shallow water equations (NSWE) with forcing teens. For the numerical implementation of the model an artificial viscosity term has been introduced. The computational domain is extended with an artificial layer of constant depth, (ε) which alleviates a great complication of modeling swash zone flows characterized by both intermittency and occurrences of motions with different scales. Several assumptions are considered and the model is solved and simulated using Finite Element Laboratory (FEMLAB) commercial software. A solution (w) has been found which permits an evaluation of flows on a sloping beach that is cut-off at a level below that of a maximum run-up creating a flat artificial distance (Lo). Simulations have been done for both alongshore bottom independent and dependent cases. In both cases it has been shown that the solution converges as ε- O and also we found the smallest distance Lo which can be altered without significantly changing the solution. Observations on simulations fit very well with the general knowledge and experimental/field results. The simulation results can directly be an input to the sediment transport and profile evolution modules not only to Tanzania but also to other areas with similar problems. Finally, we are convinced that the results presented in this thesis can be very helpful and guiding to other researchers from other disciplines and to decision makers.