Rainfall-run-off modelling could estimate the surface water discharges according to the rainfall data record. The incremental rainfall derives the reliable rainfall in many probabilities, and then it becomes reliable discharges after rainfall-run-off modelling processes. The standard models to derive rainfall to discharges are F.J. Mock and NRECA. Both models use rainfall, meteorology, and climatology data as the primary information. Location of this research was in the Ciujung watershed, Banten province. The objective of this research was estimating the potential surface water in Ciujung watershed. Rainfall data recording from January 1997 until December 2018 will derive the reliable rainfall of 50%, 70%, 80%, 90% and 99% probability. The meteorology and climatology information were following the days of rainfall, sunshine ratio, wind velocity, air temperature, and relative humidity. The results give information about the potential of reliable discharges in the Ciujung watershed. As the agricultural planning and developing purpose, the 80% reliable discharges Q80 becomes the fundamental consideration. It forecasts maximum discharges in a range of 60 m3/s to 80 m3/s and the minimum discharges in the range of 0.1 m3/s to 0.6 m3/s. These values become the threshold in agricultural planning and development. The advance analysis is quantifying the human needs of water, and the remaining value can be as the potential discharges for agricultural purpose. Further research will accommodate these analyses.
Seawater intrusion is one of groundwater quality problem which in this problem, the mixing between freshwater and saltwater in the coastal aquifer occurs. Mathematical modelling can be formulated to describe the mechanism of this phenomena. The main objective of this research is to develop the mathematical model of groundwater flow and solute transport that applicable to seawater intrusion mechanism. This mechanism is arranged as a differential equation and distinguished into 3 equations. The first equation is groundwater flow equation in dependent-density. It means that the density of groundwater (ρ) changes in spatial and temporal domain due freshwater and seawater are mixed in the coastal aquifer. The second equation is solute transport. Like as groundwater flow equation, in solute transport equation there is a change of solute concentration (С) in the spatial and temporal domain. The last equation is the relationship between groundwater density (ρ) and solute concentration (С). Special case for the third equation, in which this equation is adopted from USGS Seawat model. The first equation and second equation are governed by Eulerian mass conservation law. The main theoretical consideration of governing groundwater flow equation is such as fluid and porous matrix compressibility theory, Darcy's law for groundwater in motion theory and some properties of soil. In other hands, solute transport is involving advection transport and hydrodynamic dispersion transport. Hydrodynamic dispersion is arranged by diffusion Fick's law and dispersion in porous media theory and it depends on transversal and longitudinal dispersivity. Using Jacob Bear's theory which states that fluid density as temperature, concentration and pressure function, authors obtain three primary variables in this model. Those variables follow fluid density (ρ), total head (h) and concentration (С). In this model, isotropic and isobar condition is considered, hence fluid density (ρ) is a function of concentration (С) only. Finally, from this research, authors wish this mathematical model is applicable to modelling, describing and predicting seawater intrusion phenomena theoretically.
Groundwater quality is one of water resource problem. This problem is driven by contaminant transport phenomena and can be described as a mathematical model. Contaminant transports equation usually is composed by advection and dispersion flux. In the porous medium or aquifer, contaminant meet tortuosity effect, therefore hydrodynamic dispersion must be considered as the development of dispersion flux. This paper explains the mathematical model of groundwater contaminant on fully saturated condition. It starts from governing equation of contaminant transport. Advection flux is based on groundwater velocity. In steady state condition, groundwater velocity can be determined as certain value. In another hand, in the transient condition, groundwater velocity must be determined based on the solution of groundwater flow model. Dispersion flux is calculated through first Fick’s law and this component is distinguished into two parts follow mechanical dispersion and molecular diffusion. Mechanical dispersion affected by groundwater velocity and dispersivity. Contaminant transport equation is solved numerically using Finite Difference Method (FDM). This final model is validated theoretically and then this model is simulated into transient condition. The result of the simulation is described and explained graphically. Based on this research, the result of FDM model has similar physical behavior to FEM model from CTRAN example.
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