High Sloped Mountainous Area Various Saturated Groundwater Finite Element Method Simulation in

Upper Sheep Creek, Reynold Experimental Watershed, Idaho.

 

Groundwater flow modeling has been studied as one of the main subject of hydrogeology, and many groundwater flow simulation computer codes have been developed since then.  Although many studies have examined groundwater flow, the hydrologic processes are still not well understood to simulate highly sloped multiple layers.  The Upper Sheep Creek Watershed, located in southwestern Idaho, a typical mountainous watershed, has simulated groundwater flow using a three-dimensional finite element computer program (FLAMINCO).  The watershed is 64.3 acre in size and varies in elevation from 6035 to 6678 feet (Figure 1).  Annual precipitation is approximately 20 inches, most of which is snow (Flerchinger, 1993).  Shang (1995) simulated groundwater flow of part of the watershed (5.5 acre) from H11 to N15 point in Figure 1.  The simulation results showed reasonable agreement with measured data, but the simulated groundwater tables were not very sensitive to given boundary conditions.  Therefore, the enlarged model watershed area (22.3 acre, G1 to N19) was constructed with more head and flux boundary conditions.  It covered most of Upper Sheep Creek watershed area, and was shaped as a real watershed perimeter, including a seepage face line (Figure 1).  However the simulated groundwater head was over estimated and still had disagreement with observed well data as Figure 2.  It seemed that the given seepage face, which played a role discharging groundwater, had not clearly responded, and the multiple confined layers had a complex relationship with groundwater flow direction.  Twelve different cases which contained unsteady conditions, a impermeable layer, a leaky layer, flux, seepage face, and sloped condition, were simulated for analysis for FLAMINCO code applicability. 

FLAMINCO successfully simulated horizontal rectangular soil column with various boundary conditions.  Flux boundary conditions made the water table increase or decrease, and seepage faces played a role of discharge of the column.  On the contrary, flux boundary conditions on the impermeable layer did not change the water table of the lower part of the layer.  For the leaky aquifer simulation, these were needed to apply not only leaky layer soil properties, but also proper head boundary conditions.  In other words, the semi-confined aquifer part should have been assumed as an independent model, and applied modified head boundary conditions as an independent model.  For sloped model simulation, FLAMINCO code had several finite element construction limitations.  The finite elements must be arranged normal to the plane, and shaped square, rectangular, or triangular not a diamond or a parallelogram.  Rectangular and triangular shape elements can not be meshed together in one simulation model.

 

 

Upper Sheep Creek Watershed                                                                       FLAMINCO Model Simulation

 

 

    Leaky Aquifer Water Table Simulation                                                              Moisture Characteristic Curve

 

 

Evaporation Measuring by Tensiometer and VS2D Numerical Simulation in Rio Grande Bosque Area

 

 Soil water evaporation rate estimation is the important factor for unsaturated groundwater research.  The magnitude of evaporation rate may be significant in terms of the bosque water balance, and should be related with precipitation and surface water level, and external meteorological conditions of the study area.  The purpose of this project is to estimate the evaporation rate around the Middle Rio Grande bosque with filed measurements, and to compare with numerically simulated results.  There are three main objectives in this project.  Estimate steady state evaporation rate with field measurements.  Numerical simulate evaporation rate by VS2D computer model.  Compare between estimation and simulation results.

The VS2D simulated evaporation rates are different with measured evaporation rate.  As contrary the evaporation rate was simulated the maximum 3.9 mm/day for 8 m2 surface simulated area, the measured value varied from 0.1 mm/day to 2410 mm/day for the elevation.  The saturated hydraulic conductivity is the most important factor for estimating evaporation rate with filed measurements by assuming steady state conditions and the Buckinham-Darcy law.  The Rio Grande bosque area soil type is the silty sand as defined, but the saturated hydraulic conductivity of the silt 6 cm/day is different 210 cm/day of the fine sand, and it makes much different evaporation rate between them.  For future study, more field measuring is needed include the soil properties classifying and tensiometer measuring.  It is recommended to measure the suction head for all simulation area, not only one place near the river.  It is required also the VS2D model applicability for the evaporation rate simulation.  Even the VS2D model can simulate the evaporation rate the result accuracy and limitation could be considerable.

 

 

       Matric Potential Head Measuring with Tensiometer

 

 

  

VS2D Model Application                                                                           VS2D Model Simulation Results - Infiltration

 

 

Simulated Evaporation with Precipitation