46.3.2. Lacey’s Theory (1930)

Try these first

1. 1.

   What does the 'Q' represent in Lacey's equations?

   Hint

   Think about water flow in a channel.

2. 2.

   What is the purpose of the wetted perimeter equation?

   Hint

   Consider how water interacts with a channel's geometry.

3. 3.

   What is the primary assumption of Lacey's Theory?

   • Regime channels are in full equilibrium
   • Eddy suspension is the only factor
   • Sediment load is irrelevant

   Hint

   Think about the main goal of channel stability.

4. 4.

   True or False: The hydraulic radius is the area of flow divided by the wetted perimeter.

   • True
   • False

   Hint

   Recall the formula we discussed for hydraulic radius.

5. 5.

   Using Lacey’s velocity equation, if the flow discharge (Q_f) is 210 cumecs, calculate the mean velocity.

   Hint

   Insert the value of Q_f into the velocity equation.

6. 6.

   Calculate the hydraulic radius when Q is 120 cumecs and V is previously calculated as 1.2 m/s using Lacey’s formula.

   Hint

   Use the hydraulic radius formula and ensure you have f before attempting.