Groundwater Hydrology & Resources Analysis

Groundwater Hydrology & Resources Analysis.

1 Questions about Lecture 1

This sequence of questions is designed to develop a better understanding of structural geology. Aquifers are contained within the lithological units that make up the geological sequence. These geological beds can be deformed, deforming the matrix that carries the aquifer. Most geological maps use a fairly standard sequence of keys to indicate different geological rock types (Fig 1). 1. (7 marks) In Fig. 2 [Bennison, 1975] the ground surface contours are shown along with some partial mapping of the horizontal units. Complete the following tasks:

(a) Draw a cross-section from A to B using the same scale as the map.

(b) Complete the geological map and indicate an interface which is likely to develop a spring line.

(c) Complete the cross-section as a geological section.

(d) What thickness are the various geological units? 2. (8 marks)

In Fig 3 [Bennison, 1975] show strike lines on the geological boundaries.

(a) Give the gradient of the beds (dip angle).

(b) Draw a section from east to west along line Y-Z.

(c) Calculate the thickness of beds B, C, D and E.

(d) Indicate on the map the position of an inlier and an outlier.

Note: Information about strike and dip can be found here.

Information about inliers and outliers can be found here. Hyperlinks only work when this document is viewed on a screen. 3. (5 marks) A sequence of horizontally lying sandstones and shales is known to exist beneath a site. The surface topography is varied with hills and valleys. Four bores have been drilled at the locations shown in

Table 1. The bores have each been completed as a piezometer with a screen set in a sandstone unit. The sandstone unit is known to be 3 m thick but unfortunately, all other records have been lost!

Answer the following:

(a) Draw a sketch to show the relationship of the bores in plan (x-y)

(b) Draw a sketch section to show the main aquifer (x-z)

(c) What is the hydraulic gradient and the direction of flow in the main aquifer?

(d) If the transmissivity of the sandstone unit is 500 m2/day what is the flow through a 1000 m wide section of this sandstone unit?

Table 1: Bore details for the layered system in Question 3 Piezometer A B C D x-location (m) 1500 1500 2000 3232 y-location (m) 4000 2000 3000 3000 Elevation of the top of the bore (m) 213 275 337 240 Depth of the bore (m) 108 170 150 135 Depth to water inside the bore (m) 33 85 63 40

Groundwater Hydrology & Resources Analysis

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