Activity 13.3 Using Data to Map the Flow of Groundwater Name: Course/Section: Date: Learning GOAL You will construct contours of equal total head along a line of section and use them to determine the flow of groundwater below the water table. We want to understand how groundwater flows below the water table as viewed in a vertical plane through an unconfined aquifer. At several locations along the line of section, a set of piezometers was installed that extended to different depths. This set is called a nest of piezometers. The elevation of the open (screened) base of each of the piezometers was determined--the elevation head. The height to which the water rose in each piezometer was also measured-the pressure head. The total head can be determined by add- ing the elevation head and the pressure head. The profile of the ground surface, the water table (marked by the triangles), and the total head at dozens of points along the line of section are given in Fig. A13.3.1. Elevations and heads are given in feet. 260 ground surface 255 3 -260 250 245 water -250 table $260.5 piezometer 260- 240 235 Δ 251.8 256.0 235 D 257.0 250- 230 230 A 244.0 248.7 252.8 -230 -220 -210 -200 elevation (ft above sea level) 231.4 231.5 ⚫229.5 $235.0 239.5 $236.0 241.2 245.8 249.8 251.0 250--A 254.0 240- 25 ft 230- 243.8 $247.2 $231.9 ⚫249.0 220- $232.0 231.4 $235.0 239.0 242.5 245.2 210- ⚫233.2 233.4 ⚫233.2 234.8 -235 235.8 238.9 242.0 235.0 225 ft above 200- 190 ⚫235.0 236.8 239.2 236.2 ⚫236.4 total head at that point sea level 190- ⚫236.6 ⚫238.0 •237.8 ⚫238.0 238.0 total head = elevation at base of piezometer + height of water column in piezometer Figure A13.3.1 A A Examine the piezometer on the right side of the section at whose base is point A. 1. What is the pressure head for point A? Refer to Fig. 13.4 if you need help. 2. What is the elevation head for point A? 3. What is the total head for point A? ft ft ft B Using the total head for point A and all of the other total head values noted on the section, construct contours of equal total head at a contour interval of 5 ft, similar to the contours shown as dashed red curves in Fig. 13.5. It is best to start contouring in pencil and then go over your contours in pen after you are confident about your work. Parts of the 235 ft and 250 ft contours are provided in Fig. A13.3.1 to help you get started. C The contours you just constructed are part of 3-dimensional equal total-head (or potentiometric) surfaces. Groundwater flows perpendicular to these potentiometric surfaces from high total head to low total head (Fig. 13.3). Draw a flow line from each of the labeled points-A, B, C, and D-and continue the flow lines until they end at the water-table surface or reach the edge of 356 the cross-section.

Activity 13.3 Using Data to Map the Flow of Groundwater Name: Course/Section: Date: Learning GOAL You will construct contours of equal total head along a line of section and use them to determine the flow of groundwater below the water table. We want to understand how groundwater flows below the water table as viewed in a vertical plane through an unconfined aquifer. At several locations along the line of section, a set of piezometers was installed that extended to different depths. This set is called a nest of piezometers. The elevation of the open (screened) base of each of the piezometers was determined--the elevation head. The height to which the water rose in each piezometer was also measured-the pressure head. The total head can be determined by add- ing the elevation head and the pressure head. The profile of the ground surface, the water table (marked by the triangles), and the total head at dozens of points along the line of section are given in Fig. A13.3.1. Elevations and heads are given in feet. 260 ground surface 255 3 -260 250 245 water -250 table $260.5 piezometer 260- 240 235 Δ 251.8 256.0 235 D 257.0 250- 230 230 A 244.0 248.7 252.8 -230 -220 -210 -200 elevation (ft above sea level) 231.4 231.5 ⚫229.5 $235.0 239.5 $236.0 241.2 245.8 249.8 251.0 250--A 254.0 240- 25 ft 230- 243.8 $247.2 $231.9 ⚫249.0 220- $232.0 231.4 $235.0 239.0 242.5 245.2 210- ⚫233.2 233.4 ⚫233.2 234.8 -235 235.8 238.9 242.0 235.0 225 ft above 200- 190 ⚫235.0 236.8 239.2 236.2 ⚫236.4 total head at that point sea level 190- ⚫236.6 ⚫238.0 •237.8 ⚫238.0 238.0 total head = elevation at base of piezometer + height of water column in piezometer Figure A13.3.1 A A Examine the piezometer on the right side of the section at whose base is point A. 1. What is the pressure head for point A? Refer to Fig. 13.4 if you need help. 2. What is the elevation head for point A? 3. What is the total head for point A? ft ft ft B Using the total head for point A and all of the other total head values noted on the section, construct contours of equal total head at a contour interval of 5 ft, similar to the contours shown as dashed red curves in Fig. 13.5. It is best to start contouring in pencil and then go over your contours in pen after you are confident about your work. Parts of the 235 ft and 250 ft contours are provided in Fig. A13.3.1 to help you get started. C The contours you just constructed are part of 3-dimensional equal total-head (or potentiometric) surfaces. Groundwater flows perpendicular to these potentiometric surfaces from high total head to low total head (Fig. 13.3). Draw a flow line from each of the labeled points-A, B, C, and D-and continue the flow lines until they end at the water-table surface or reach the edge of 356 the cross-section.

Applications and Investigations in Earth Science (9th Edition)

9th Edition

ISBN:9780134746241

Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Chapter1: The Study Of Minerals

Section: Chapter Questions

Problem 1LR

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I need help with part c

Transcribed Image Text:Activity 13.3 Using Data to Map the Flow of Groundwater Name: Course/Section: Date: Learning GOAL You will construct contours of equal total head along a line of section and use them to determine the flow of groundwater below the water table. We want to understand how groundwater flows below the water table as viewed in a vertical plane through an unconfined aquifer. At several locations along the line of section, a set of piezometers was installed that extended to different depths. This set is called a nest of piezometers. The elevation of the open (screened) base of each of the piezometers was determined--the elevation head. The height to which the water rose in each piezometer was also measured-the pressure head. The total head can be determined by add- ing the elevation head and the pressure head. The profile of the ground surface, the water table (marked by the triangles), and the total head at dozens of points along the line of section are given in Fig. A13.3.1. Elevations and heads are given in feet. 260 ground surface 255 3 -260 250 245 water -250 table $260.5 piezometer 260- 240 235 Δ 251.8 256.0 235 D 257.0 250- 230 230 A 244.0 248.7 252.8 -230 -220 -210 -200 elevation (ft above sea level) 231.4 231.5 ⚫229.5 $235.0 239.5 $236.0 241.2 245.8 249.8 251.0 250--A 254.0 240- 25 ft 230- 243.8 $247.2 $231.9 ⚫249.0 220- $232.0 231.4 $235.0 239.0 242.5 245.2 210- ⚫233.2 233.4 ⚫233.2 234.8 -235 235.8 238.9 242.0 235.0 225 ft above 200- 190 ⚫235.0 236.8 239.2 236.2 ⚫236.4 total head at that point sea level 190- ⚫236.6 ⚫238.0 •237.8 ⚫238.0 238.0 total head = elevation at base of piezometer + height of water column in piezometer Figure A13.3.1 A A Examine the piezometer on the right side of the section at whose base is point A. 1. What is the pressure head for point A? Refer to Fig. 13.4 if you need help. 2. What is the elevation head for point A? 3. What is the total head for point A? ft ft ft B Using the total head for point A and all of the other total head values noted on the section, construct contours of equal total head at a contour interval of 5 ft, similar to the contours shown as dashed red curves in Fig. 13.5. It is best to start contouring in pencil and then go over your contours in pen after you are confident about your work. Parts of the 235 ft and 250 ft contours are provided in Fig. A13.3.1 to help you get started. C The contours you just constructed are part of 3-dimensional equal total-head (or potentiometric) surfaces. Groundwater flows perpendicular to these potentiometric surfaces from high total head to low total head (Fig. 13.3). Draw a flow line from each of the labeled points-A, B, C, and D-and continue the flow lines until they end at the water-table surface or reach the edge of 356 the cross-section.

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