Using the flow net shown below, $(1)$ determine the seepage underneath the $1,000$ foot wide concrete dam, and $(2)$ the velocity at point $"a"$ in feet$/$hour$,$ where the height of the net's square is $19$ feet. The soil has a $G_S=2\mathrm{.}67,D_{10}=0\mathrm{.}01mm.$ Overestimate the flow by using Hazen's coefficient $C=15$ to determine the permeability $k.$