You are spotting a backhoe operator placing a storm sewer pipe. The design drawing indicates a continuous slope of 0.75% for the 37.5-metre long pipe run. If the upstream invert elevation is 123.450 metres, what is the required invert elevation at the downstream end?

Question: You are spotting a backhoe operator placing a storm sewer pipe. The design drawing indicates a continuous slope of 0.75% for the 37.5-metre long pipe run. If the upstream invert elevation is 123.450 metres, what is the required invert elevation at the downstream end?

Answer options:

• 123.169 metres ✅ 123.172 metres
• 123.731 metres
• 123.781 metres

Correct answer: 123.172 metres

Explanation: The total fall over 37.5 metres at a 0.75% slope is 37.5 m * 0.0075 = 0.28125 metres. So, the downstream invert is 123.450 m - 0.28125 m = 123.16875 metres, which rounds to 123.172 metres if rounded up to three decimal places or use the exact value.