Both the flow and quality solved problems in hydrology pdf water are commonly studied using hydrologic models. MODFLOW, a computational groundwater flow model based on methods developed by the US Geological Survey.
Model scope and complexity is dependent on modeling objectives, with greater detail required if human or environmental systems are subject to greater risk. Scale models offer a useful approximation of physical or chemical processes at a size that allows for greater ease of visualization. Yet, maintaining some properties at their natural values can lead to erroneous predictions. Properties such as viscosity, friction, and surface area must be adjusted to maintain appropriate flow and transport behavior. A two-dimensional scale model of an aquifer.
Groundwater flow can be visualized using a scale model built of acrylic and filled with sand, silt, and clay. Water and tracer dye may be pumped through this system to represent the flow of the simulated groundwater. Some physical aquifer models are between two and three dimensions, with simplified boundary conditions simulated using pumps and barriers. An early process analog model was an electrical network model of an aquifer composed of resistors in a grid.
Voltages were assigned along the outer boundary, and then measured within the domain. The frequency of extremal events, such as severe droughts and storms, often requires the use of distributions that focus on the tail of the distribution, rather than the data nearest the mean. With respect to hydrologic modeling, convolution can be used to analyze stream discharge’s relationship to precipitation. Convolution is used to predict discharge downstream after a precipitation event.
Many hydrologic phenomena are studied within the context of historical probability. Within a temporal dataset, event frequencies, trends, and comparisons may be made by using the statistical techniques of time series analysis. The questions that are answered through these techniques are often important for municipal planning, civil engineering, and risk assessments. The event must be dependent, such as rainy weather. The conceptual model is used as the starting point for defining the important model components. The Nash Model uses a cascade of linear reservoirs to predict streamflow. The model combines continuity and storage-discharge equations, which yields an ordinary differential equation that describes outflow from each reservoir.