Formative Assessment 3: Cone of Depression

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Use the figures below to complete the exercises that follow then answer the questions.

Cross-section shows effects of pumping and generation of cone of depression in anunconfined aquifer between a lake and a stream.
Figure 35. Schematic cross-section showing effects of pumping and generation of a cone of depression in an unconfined aquifer between a lake and a stream. Pumping and the ensuing cone of depression reverse the hydraulic gradient from pre-development (A) and induce flow from the stream into the groundwater system and to the well (B).
Source USGS: Ground water in the Great Lakes Basin: the case of southeastern Wisconsin.
Potentiometric surface for southwestern Long Island, New York, ca. 1903, 1936 and 1965, described in caption.
Figure 36. Potentiometric surface for southwestern Long Island, New York, ca. 1903 (pre-development), 1936 (near the peak in pumpage for combined municipal and industrial uses), and 1965, well after the municipal supply was switched to the upstate supply system described in Liquid Assets, and after reduction in withdrawals for industrial use.
Source: USGS

Questions:

  1. Sketch a few (~6-8) flowlines on the potentiometric surface maps for Long Island, New York in 1903 and 1936 (lower figure).
  2. Sketch a cross-section of the potentiometric surface (similar to those shown in panels A and B in the top figure) for Long Island in 1903 and 1936 along the red line shown on the map. Superimpose the two cross-sections on top of each other to allow comparison.

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