Question 7 of 21: Question 3, Part 1: Groundwater Zone Cross-Section

Question 3, Part 1: Groundwater Zone Cross-Section (6 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given. A vertical column of ground from the surface down to some depth below the water table.

Find. A labelled cross-section locating all six named features in correct relative vertical order.

Approach. Everything above the water table is unsaturated (the zone of aeration, subdivided top-to-bottom into the belt of soil moisture, an intermediate vadose zone, and the capillary fringe immediately above the water table); everything below the water table is saturated (the zone of saturation, whose water is the groundwater proper).

The belt of soil moisture is the thin, biologically active near-surface layer from which plant roots draw water; the underlying intermediate (vadose) zone is unsaturated pore space through which infiltrating water percolates downward under gravity; the capillary fringe is a thin zone directly above the water table where water is pulled upward by surface tension into partially saturated pores, forming the transition into full saturation. Together these three constitute the zone of aeration (vadose zone, broadly). The water table is the surface where pore-water pressure equals atmospheric pressure (the top of the saturated zone as normally measured in an open well). Below it, the zone of saturation has every pore, fracture, and void completely filled with water – this water is the groundwater proper, which can be extracted by wells or discharge naturally at springs.