**Answer:**

**Length of stilling basin = 32.9 feet**

**Height of end sill = 6.58 feet **

**Explanation:**

Discharge = Q = 400 ft^3 /sec

Slope = 2.5 ft

Width = 20 feet

n = 0.013

we will assume the depth of flow as "**d**"

Q = 1/n (R)^2/3 (slope)^1/2 A ( here R is the hydraulic Radius)

by substituting the given data in above formula we get:

400 = 1/0.013 * (R)^2/3 * sqrt (2.5/100) * 20d

R = A/P

here,** A **is the **flow area **and** P **is the **wetted perimeter**

**400*0.013 = (20d/(20+20d))^2/3 * sqrt(2.5/100) * 20d**

<u>**d = 1.42 feet**</u>

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**Depth of stilling channel before the jump will be = d1 = 8 feet**

**Depth of stilling channel after the jump will be = d2 = 1.42 feet **

Length of stilling basin = 5(d2 - d1)

= 5( 8 - 1.42)

<u>**Length of stilling basin = 32.9 feet **</u>

Now calculating the height of end sill:

Jump height = (8 - 1.42)

<u>**Height of end sill = 6.58 feet**</u>