1. A small river is proposed to receive water from a new wastewater treatment plant. The width of this river is 3.5m, depth is 0.3m, slope is 0.001 , and the Manning roughness coefficient is 0.032 . To estimate travel time and dispersion coefficient of river flow, an environmental engineer injected 50g of rhodamine dye (a soluble, fluorescent dye considered as an ideal tracer) at the site of the proposed outfall. Because the river is too wide to easily distribute the dye evenly across the channel, the engineer dumped the dye in near the bank and figured that it would spread out soon enough. c. The engineer set up a fluorometer and began making rhodamine measurements 1km downstream. The data, when converted to a spatial (longitudinal) distribution at t=2500 sec after dye release, show the following: 95% of mass lies between 800m and 1200m at t=2500sec (profile in the figure below). Estimate the longitudinal dispersion coefficient for the reach of river between the proposed outfall and the measurement location. [Hint: Recall the 68-95-99.7 rule of normal distribution and the relationship between and dispersion coefficient.] [10 points ]