Team:Cornell/project/drylab/modeling/deployment

Deployment

Theory

If S.A.F.E.B.E.T. is too far downstream from a chemical source then the chemical will be too dilute to detect. Therefore, S.A.F.E.B.E.T. needs to be at most some distance $L$ downstream of a chemical source in order to detect the chemical. So for a given river width $W$, how do we find the distance $L$ to place our biosensor? One way to determine $L$ is to go to the river in question, measure its height, width, length and volumetric flow rate and numerically solve for bulk motion. Unfortunately, the Alberta Oil Sands are roughly 4,000 km away from Cornell, so going to Alberta is out of the question. A simpler solution is to use dimensional analysis to estimate what the value of $L$ would be for each river that may be effected by Oil Sands operations. First, the time scale $\tau$ which is the time scale for bulk motion can be written as: $$\tau = \frac{L}{u}$$ where $u$ is the average velocity of the river and $L$ is the length scale for bulk motion. Second, a time scale for turbulent mixing can be written as: $$\tau= \frac{l^2}{D}$$ where $l$ is the length scale for mixing and $D$ is the turbulent mixing coefficient. Since bulk motion and turbulent mixing are happening at the same time, time scales can be set equal to each other allowing $L$ to be solved for: $$L= \frac{ul^2}{D}$$ The average velocity $u$ can be rewritten as: $$u = \frac{Q}{wh}$$ where $Q$ is the volumetric flow rate of the river, $w$ is the width of the river and $h$ is the depth of the river. Next, the turbulent mixing coefficient can be rewritten as: $$ D=kh \sqrt{ghs}$$ where $s$ is the slope of the river, $g$ is the acceleration due to gravity and $k$ is an experimentally determined constant. This constant differs for turbulent mixing across a river (horizontal) and turbulent mixing within a river (vertical). Since we want to place our biosensor at the point where the chemical is completely mixed in the river, we need to take into account both horizontal and vertical turbulent mixing. Putting both of these definitions into our equation for $L$ gives us $$L= \frac{Ql^2}{kwh^2\sqrt{ghs}}$$ Finally, we need to define what $k$ and $l$ are. If we want to know how far downstream the chemicals will be mixed horizontally across the river ($L_Y$) then $l$ = $w$ and $k$ = 0.6 [1]. If we want to know how far downstream the chemicals will be mixed vertically in the river ($L_Z$) then $l$ = $h$ and $k$ = 0.067 [1]. The larger of these $L$ values will determine where we need to place our biosensor for a giver river. This gives us the following two equations $$L_Y= \frac{Qw}{0.6h^2\sqrt{ghs}}$$ $$L_Z= \frac{Q}{0.067w\sqrt{ghs}}$$

	$\mathrm{Athabasca\ River}$	$\mathrm{Tar\ River}$	$\mathrm{Steepbank\ River}$	$\mathrm{Muskeg\ River}$	$\mathrm{Jackpine\ Creek}$
$L_Y$	$71.233 \ \mathrm{m}$	$1.683 \cdot 10^{-4} \ \mathrm{m}$	$0.1639 \ \mathrm{m}$	$0.0091 \ \mathrm{m}$	$12.2495 \ \mathrm{m}$
$L_Z$	$198.621 \ \mathrm{m}$	$0.2893 \ \mathrm{m}$	$22.1028 \ \mathrm{m}$	$9.5927 \ \mathrm{m}$	$1.582 \cdot 10^{-4} \ \mathrm{m}$