Given: Sequent depth ratio = 16.48

We know that the sequent depth ratio is given as:

Sequent depth ratio = (y2/y1)^2

where y1 is the depth of the upstream flow and y2 is the depth of the downstream flow.

To find the Froude number of the supercritical flow, we can use the following formula:

Fr = V / (g*y1)^0.5

where Fr is the Froude number, V is the velocity of the flow, g is the acceleration due to gravity, and y1 is the depth of the upstream flow.

Let's solve for the Froude number:

(y2/y1)^2 = 16.48

Taking the square root on both sides, we get:

y2/y1 = 4.06

Now, we can use the continuity equation to find the velocity of the flow:

Q = A1*V1 = A2*V2

where Q is the discharge, A1 and A2 are the cross-sectional areas of the upstream and downstream flows respectively, and V1 and V2 are the velocities of the upstream and downstream flows respectively.

Since the channel is horizontal, we can assume that the cross-sectional areas of the upstream and downstream flows are equal. Therefore, we have:

V1 = V2 / 4.06

Now, we can substitute this value of V1 in the formula for the Froude number:

Fr = V2 / (g*y1)^0.5

Fr = (V1*4.06) / (g*y1)^0.5

Fr = (V2 / (g*y1)^0.5) * 4.06

Fr = Fr_c * 4.06

where Fr_c is the Froude number of the critical flow.

We know that the Froude number of the critical flow is given as:

Fr_c = (g*y1)^0.5

Substituting this value in the above equation, we get:

Fr = 4.06 * (g*y1)^0.5

Now, we can substitute the given value of the sequent depth ratio to find the value of y2/y1:

(y2/y1)^2 = 16.48

y2/y1 = 4.06

Substituting these values in the above equation for Fr, we get:

Fr = 4.06 * (g*y1)^0.5 = 4.06 * Fr_c = 4.06 * (y1*g)^0.5

Hence, the Froude number of the supercritical flow is 12 (option D).