Sand Box Modeling

From GeoMod

Goal: To construct a scaled sand box model capable of modeling ground water/surface water interactions. Water will percolate up from below a porous medium to simulate an aquifer discharging into a fluvial network. The box model will allow for adjustable aquifer head pressure as well as discharge area. The box will be capable of handling multiple layers of varying porosity and composition. Box Construction: Dimensions: 1.0 m * 1.0 m * .1m

The box will be constructed of an outer wooden box frame with a fiberglass coating for waterproofing. One of the 1 m ends will have a drainage lip with a central notch 1 cm in depth. The other 1 meter end will have a reservoir with a variable depth drain spout to allow for multiple head levels. The bottom of the box will have 1.5 cm risers spaced in 10 cm intervals in grid format. A 1 cm mesh screen will be placed on the risers with an additional .2 mm mesh screen on top of it. A schematic drawing is attached.

Testable hypothesis utilizing Sand Box: 1. Ground water discharge creates low spots in river systems due to destabilization of riverbed and therefore increasing erosion rates at this point.

2. River water velocity increases in areas of ground water discharge due to reduced bed friction

3. Variations in thin confining layer thickness creates windows through which ground water discharges at higher rates. These higher rates increase erosion rates of surrounding streambed, widening the river near the window.

4. Groundwater discharge spikes occur where aquifer outcrops are separated by a thin confining bed.

5. River channels migrate towards aquifer discharge outcrops. Procedure for testing hypothesis:

1. An even layer of sand, 4 cm thick, will be placed in the box. An overland flow component will be created in the box by means of tube supplying constant water volume to the surface of the sand. Natural waterways will be allowed to form and the water channel depths will be checked for varying depth. An artesian water pressure will then be applied to the ground water in the box and natural waterways will be allowed to form. The channels will be checked at regular time intervals for varying depth. The results form no ground water pressure will be compared to those of positive ground water pressure for variance.

2. An even layer of sand, 4 cm thick, will be placed in the box. An overland flow component will be created in the box by means of tube supplying constant water volume to the surface of the sand. Natural waterways will be allowed to form. A drop of dye will be added to the upstream end of the box and timed as it moves across the box. Water volume of the current situation will be logged as well. An artesian groundwater component will be added. A second drop of dye will be added to the upstream end of the box and timed once again as it moves across the box. The water volume will be checked again and dye velocity will be corrected for the additional water volume added by groundwater. Results from each run will be compared for variance.

An alternative method will be to create a 10 cm thick layer of sand. An artificial channel, 8 cm deep will be created. Overland flow will be created and water velocity cross sectional profile will be checked using dye tests. An artesian component can then be added and checked again at varying locations in the cross section and compared to the previous test.

3. An initial layer of sand will be randomly applied in the box to an average of 2 cm thickness. A layer of dry powdered clay will be randomly applied to the surface of the sand to an average of 1 cm thickness. An additional layer of sand will then be randomly applied on top of the clay layer. A surface flow will be initiated to create natural waterways. Path and channel depth will be documented. An artesian flow will then be created from below. Channel path and depth will then be documented at an even interval and compared to the non-artesian state.

4. Sand and dry clay powder will be placed in the box in such a way as to simulate a dual aquifer system separated by a 1 cm thick confining bed. A surface flow will then be created to allow a natural waterway to form. Artesian flow will then be applied to the system. Flow rates along the waterway will then be documented at even spacing to locate any high discharge areas.

5. A plastic sheet will be placed in the box covering half the screen to block flow laterally from the artesian source. An even layer of sand, 4 cm thick will be placed in the box. An overland flow component will be created in the box by means of tube supplying constant water volume to the surface of the sand. Natural waterways will be allowed to form. The artesian source will then be initiated. Only one lateral half of the box will receive ground water discharge. The channels will then be allowed to change positions naturally and pre-artesian river position will be compared to artesian positioning.

Expected Results 1. The box will form a meandering river system of low sinuosity. Cannel width will be approximately 1 cm and channel depth will be .2 cm. When groundwater flow is added, sinuosity will increase and channel depth will become less uniform and from several low spots where groundwater discharge is randomly higher. 2. It is expected that the dye travel time will be faster with the artesian component added. 3. Water channels will migrate towards random thin spots in the clay layering. This will create a more sinuous river with a more random meander. 4. Flow volume increase will be highest at the point where the two aquifers converge. It is possible that the river may try to follow the clay confining layer outcrop for this reason. 5. The river will migrate to the groundwater discharging half of the sand box. Given enough time, the entirety of the river channel will be in the artesian half of the box.

Budget:

Cost of Materials: 1. wood for frame $30

2. fiberglass resin and cloth $20

3. Tubing $5

4. fittings $10

5. Graduate Student’s precious time Priceless

Total Cost Estimate $65