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These moments can then be used to determine an appropriate frequency distribution, which can then be used as a probability model. Statistical moments (e.g., mean, standard deviation, skewness, kurtosis) are used to describe the information content of data. Using statistical methods, hydrologists develop empirical relationships between observed variables, find trends in historical data, or forecast probable storm or drought events. Statistical models are a type of mathematical model that are commonly used in hydrology to describe data, as well as relationships between data. Electrical conductivity paper can also be used instead of resistors. Voltages were assigned along the outer boundary, and then measured within the domain. The analogs to hydraulic conductivity are electrical conductivity, thermal conductivity, and the solute diffusion coefficient.Īn early process analog model was an electrical network model of an aquifer composed of resistors in a grid. The corresponding analogs to fluid potential are voltage, temperature, and solute concentration (or chemical potential). The analogs to fluid flow are the flux of electricity, heat, and solutes, respectively. Process analogs are used in hydrology to represent fluid flow using the similarity between Darcy's Law, Ohms Law, Fourier's Law, and Fick's Law. Some physical aquifer models are between two and three dimensions, with simplified boundary conditions simulated using pumps and barriers. Water and tracer dye may be pumped through this system to represent the flow of the simulated groundwater.
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Groundwater flow can be visualized using a scale model built of acrylic and filled with sand, silt, and clay. Two general categories of analog models are common scale analogs that use miniaturized versions of the physical system and process analogs that use comparable physics (e.g., electricity, heat, diffusion) to mimic the system of interest.Ī two-dimensional scale model of an aquifer.
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Unlike mathematical models that use equations to describe, predict, and manage hydrologic systems, analog models use non-mathematical approaches to simulate hydrology. Prior to the advent of computer models, hydrologic modeling used analog models to simulate flow and transport systems. Systems modeling can be used for building conceptual models that are then populated using mathematical relationships. Model scope and complexity is dependent on modeling objectives, with greater detail required if human or environmental systems are subject to greater risk. Sediments, nutrients, pathogens), and events (e.g., low-, flood-, and mean-flow conditions). The conceptual model would then specify the important watershed features (e.g., land use, land cover, soils, subsoils, geology, wetlands, lakes), atmospheric exchanges (e.g., precipitation, evapotranspiration), human uses (e.g., agricultural, municipal, industrial, navigation, thermo- and hydro-electric power generation), flow processes (e.g., overland, interflow, baseflow, channel flow), transport processes (e.g.,
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The conceptual model is coupled with scenarios to describe specific events (either input or outcome scenarios).įor example, a watershed model could be represented using tributaries as boxes with arrows pointing toward a box that represents the main river. These components describe the important functions of the system of interest, and are often constructed using entities (stores of water) and relationships between these entitites (flows or fluxes between stores). Conceptual models are commonly used to represent the important components (e.g., features, events, and processes) that relate hydrologic inputs to outputs.