Presentation Final Project

Final Project CE 505 Environmental Hydrodynamics: 

Final Project CE 505 Environmental Hydrodynamics Evaluating the influence of hyporheic flows in solute transport using a numerical model Angel Monsalve Sepúlveda December 13, 2011

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Contents Motivation Introduction Methods Study Reach Numerical modeling – OTIS Parameter estimation – OTIS-P Modeling and calibration with measured data Results Discussion Conclusion Evaluating the influence of hyporheic flows in solute transport using a numerical model

PowerPoint Presentation: 

Motivation Evaluating the influence of hyporheic flows in solute transport using a numerical model Solute transport has a major importance in water quality, aquatic habitats and the fluvial ecosystem Is a complex phenomena that involves multiple processes, among others hyporheic flows, dead zones, turbulence and the hydrological environment Its properties have been studied for a long time and there exist a solid mathematical and theoretical background that are the base of a family of numerical model and analytical solutions

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Introduction Evaluating the influence of hyporheic flows in solute transport using a numerical model Transport of solutes on rivers and streams is affected by retention of the solutes in transient storages areas. A large amount of water and solute may interchange with hyporheic zone causing retardation of solute. Hyporheic exchanges is one of the several mechanisms of the interaction of the groundwater and surface water. Water that is flowing in the stream channel flows into the subsurface of the streambed and then returns to the stream.

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Introduction Evaluating the influence of hyporheic flows in solute transport using a numerical model A real river or stream is not a pipe or a flume. This fact makes that the mathematical formulation in the solute transport must include effects like transient storage. However, the river system can be simplified and numerical models can explains how is the movement of a solute and what are the most important processes for a given condition. One of the simplest way to study this phenomena is the use of one dimensional model, such as OTIS. This type of model has proved to be very accurate in a wide variety of situations.

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Methods Field Site Evaluating the influence of hyporheic flows in solute transport using a numerical model Bear Valley Creek, Idaho, USA. Reach Length: 271 m Measurement points: 143.45 and 271.34 m Discharges were taken during the injection experiments

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Methods Numerical Modeling Evaluating the influence of hyporheic flows in solute transport using a numerical model OTIS is a one dimensional model (Runkel, 1998) that solves a set of equations that describe the physical processes of advection, dispersion and transient storage

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Methods Numerical Modeling Evaluating the influence of hyporheic flows in solute transport using a numerical model OTIS-P is module that also includes OTIS and is used for parameter estimation. Given a set of guessed values or initial conditions the model, using Nonlinear Least Squares automatically determines a set of optimal parameters. The solution must be checked in order to avoid results that are in unrealistic ranges.

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Methods Calibration Evaluating the influence of hyporheic flows in solute transport using a numerical model Using OTIS-P, the measured concentration upstream and downstream, discharge data and the mean cross sectional area we can look for the best set of parameters that match as good as possible measured with computed concentration. Discharge: 0.927 m 3 /s Cross Sectional Area: 3.27 m 2

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Results Calibration Evaluating the influence of hyporheic flows in solute transport using a numerical model OTIS-P gives found an optimal set of parameters matching as good as possible measured and calculated concentration in the downstream point.

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Discussion Evaluating the influence of hyporheic flows in solute transport using a numerical model The results shows that a one dimensional model is able to capture the main processes of solute transport in a complex river The use a classical advection-dispersion equation can generarate erroneous results, because is not considering the effects of storages zones The set of parameter obtained with OTIS and OTIS-O replicate in a very good way the measured concentration Storage zone cross section area and the exchange coefficient plays a fundamental role in the transport solute process a is in charge of the “velocity” of the interchange of the storage zone and the main channel. High values makes the release to be faster As quantifies the size of the storage area. The Ratio A/As also is determinant, as this ratio increases more solute can be found in the main channel.

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Conclusion Evaluating the influence of hyporheic flows in solute transport using a numerical model The numerical model OTIS was used to study solute transport in the Bear Valley Creek Using the parameter estimation model OTIS-P an optimal set was found, replicating very good the measured concentrations. The use of this type of optimization must be done very carefully and checking that the results are in a realistic range The results of the model shows that the storage area and its interaction with the main channel must be take into account in order to have more realistic results This type of model is a powerful tool to take decision of that affects water quality, aquatic habitats and all the fluvial environment. A next step could be the inclusion of a hydrodynamic module that account at least for roughness and slope.