Ground water and surface water Over-use of ground water leads to subside(沉降) of land H H Figure 16.3 The Leaning Tower of Pisa, built cen- turies ago, slowly acquired a deviation from the vertical of about 4.6 meters as a result of groundwater withdrawal The towers foundation has been sta- bilized by groundwater withdrawal management and the tower should remain stable for years to comeGround water and surface water • Over-use of ground water leads to subside (沉降) of land