Hydrogeologic Mapping - University of Texas at Dallas



Hydrogeologic Mapping

The goal of this lab is to investigate the basic hydrology of a site, mapping the groundwater table through direct measurement, and estimating flow paths in the area. This type of mapping is important whenever groundwater resources and water quality are an issue at a location, e.g. when you try to find water for your new cabin in the Rocky Mountains...

Parameters to be measured and mapped:

- Surface water elevation and ground water level in several locations.

Field procedures:

1. Gather at site of new Science Center (north of Heard Museum Visitor Center). In the center of the traffic circle is Point 1 (Fig. 1).

2. Assemble your team and make a site reconnaissance using the material handed to you

3. First observation will be done at the hand-dug well (Point 1, Fig. 1), in the parking lot. Use the beeper tape or stadia rod to measure the height above the ground of the top of the concrete housing of the well. Then use the tape to measure the depth to water from the top of the housing. The water table elevation can be determined using the formula Z = Zo - (depth to water) + (height of concrete housing)

4. Go to next points (#2, 3, 4 ,?. on the map) and evaluate the surface water level using the hand-leveling technique shown in Fig. 2. Record all the values in the data table (Table 1).

5. Measure the groundwater level at the point Wind Mill well using the beeper tape.

a) Determine the elevation of the base of the concrete housing of the well using the leveling technique

b) measure the height of the concrete housing above the ground using the beeper tape or stadia rod

c) using the beeper tape, measure the depth to water from the housing top

d) the water table elevation can be determined using the formula Z = Zo - (depth to water) + (height of concrete housing)

Mapping and interpretation

1. Draw ground water table contours on Fig. 1 in colored pencil using a 10 foot contour interval. Where data is absent, follow the topography. Water table contours should meet topographic contours only where water is at the surface! Save a pristine copy of Fig. 1 in case of errors.

2. Draw representative ground water flowlines (4-5)(perpendicular to the contour lines). The flowlines show the probable path of groundwater. In red, draw the most likely path that a groundwater nitrate plume coming from the Golf Course feeding Bullfrog Pond would follow. Also draw the most likely path for a chemical spill from the location of Point 1.

3. Draw a topographic cross section which passes through the hand-dug well (Point 1), the canoe trail (Point 7), the Wind Mill (Point 8) and Wilson Creek (Point9)) and draw on it the ground water table. Things like scale, horizontal distance, elevations and orientation of the cross section are mandatory.

4. When you finished, gather at the Visitor Center and wait for a final discussion.

5. Turn in your final lab report by July 29th. to the TA or Geosciences office. Other group's data need not to be reported in this lab. Your hydrogeologic map will serve as the required graphical summary. Discuss general trends in probable groundwater movement at the Museum, and how that movement differs from surface water movement and storm-related overland flow.

Table 1: Benchmark elevation (Zo), survey data (I, h) and calculated water levels (Z).

|Point |Location Name |Zo (ft) |I |h |Z |

|1 |Handdug Well (Sci. Center) |593 | | | |

|2 |Bull Frog Pond |548 | | | |

|3 |Stagnant Pond |533 | | | |

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|4 |Mallard Marsh Lagoon |528 | | | |

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|5 |WoodDuck Lagoon |528 | | | |

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|6 |Wilson Creek (upper) |528 | | | |

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|7 |Canoe Trail (upper) |525 | | | |

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|8 |Wind Mill |525 | | | |

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|9 |Wilson Creek (middle) |525 | | | |

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|10 |Wilson Creek (lower) |522 | | | |

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|11 |Canoe Trail (lower) |522 | | | |

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Fig. 1: Heard Museum topography (black contours, labeled in feet), sample points (open circles with numbers) and hydrologic features (ponds hachured, Wilson Creek is thicker meandering line). The class will measure water levels at each point 1-11 in succession.

Figure 2: Surveying procedure. Measure eye-height (I) of surveyor using stadia rod, determine elevation at surveyor's location (Zo) using table above. Using hand-level, surveyor then reads height h on stadia rod, calculating elevation (Z) at location of stadia rod using formula in figure. For elevation differences greater than height of rod, or distances too far to read stadia rod with hand level, surveyor determines Z at an intermendiate location, then moves to that location and repeats these steps as needed. In this case the formula for elevation Z becomes: Z = Zo + (I - h)1 + (I - h)2 + ...

Fig. 3: Heard Museum orthophoto showing water-level measurement locations (red dots, yellow numbers) and major features. North is to the right, science center located just northeast of point 1. Large white area to north of points 7-9 (across Wilson Creek) is McKinney landfill.

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