Chapter 9 Quadratic Relations and Conic Sections - 9.2 Graph and Write Equations of Parabolas - 9.2 Exercises - Problem Solving - Page 625: 58

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The equation has the form $x^2=4py$ The focus is $F=0.36\times diameter\\=0.36\times 25\\=9$ Since the parabola is opening upwards, the focus is located at $(0,9)$. Hence, the equation becomes $x^2=36y$. Since the diameter is 25 meters, we know $x=\pm 12.5$. Find the depth: $x^2=36y\\(\pm 12.5)^2=36y\\36y=156.25\\y\approx4.34$