On August $10,1992,$ at $1535,$ a pulse injection of food$-$grade table salt $($sodium chloride, NaCl $)$ was made at a point on an experimental stream in the Bickford watershed $($see Fig. $2\mathrm{.}2)$ in central Massachusetts. The molarity of chloride as a function of time was measured $20m$ downstream at Site $1.$

a$.$ Estimate the average stream velocity in this reach.

b$.$ Estimate a dispersion coefficient for this reach $($assume the cloud is "frozen" as it passes Site $1).$

c$.$ Is the time versus concentration curve expected to be exactly Gaussian in this experiment?