LARE Drainage System Design Questions and Answers

Question 1

A landscape architect is designing a storm drain line connecting two catch basins.
Catch Basin 1 (CB-1) has an outlet invert elevation of 152.50 ft.
The two catch basins are 120 feet apart, and the pipe connecting them is specified to have a minimum slope of 1.5%.
What is the required invert elevation for the inlet of Catch Basin 2 (CB-2)?

Accepted Answer

150.70 ft

Answer

154.30 ft

Answer

152.32 ft

Answer

151.00 ft

Question 2

When laying out a storm sewer system, what is the fundamental principle for setting pipe elevations as they pass through a manhole or catch basin to ensure proper hydraulic function?

Accepted Answer

The invert of the outlet pipe must be lower than the invert of all inlet pipes. [26, 27]

Answer

The crown of the inlet pipe must align with the crown of the outlet pipe.

Answer

All pipes entering and exiting a structure must have the same invert elevation.

Answer

The invert of the main trunk line should be at least 24 inches below any lateral lines.

Question 3

A landscape architect is designing a drainage solution for a persistently soggy lawn area at the base of a slope with heavy clay soils. Surface water is already managed by a shallow swale. Which of the following is the most appropriate system to intercept and remove the problematic subsurface water?

Accepted Answer

A French drain system installed across the slope, upstream of the wet area.

Answer

A series of area drains connected to a solid pipe.

Answer

Increasing the surface slope of the lawn to promote faster runoff.

Answer

A dry well filled with coarse aggregate.

Question 4

In storm drain pipe design, specifying a minimum gradient to achieve a 'self-cleansing velocity' is a critical requirement. What is the primary purpose of maintaining this minimum velocity?

Accepted Answer

To prevent the deposition of sediment, sand, and debris within the pipeline. [7, 17]

Answer

To maximize the hydraulic capacity of the pipe during peak flow.

Answer

To reduce the structural load on the pipe from the weight of the water.

Answer

To meet the manufacturer's warranty requirements for the pipe material.

Question 5

A landscape architect is calculating the Time of Concentration (Tc) for a small watershed as part of a drainage study. Which of the following design changes would result in a *decrease* in the Time of Concentration?

Accepted Answer

Increasing the average slope of the overland flow path.

Answer

Changing the primary ground cover from asphalt to a densely vegetated meadow.

Answer

Increasing the length of the longest flow path by adding meanders to a channel.

Answer

Routing the flow through a small detention pond within the watershed.

Question 6

What is the primary function of installing a perforated underdrain pipe with the perforations oriented downwards within a gravel-filled trench?

Accepted Answer

To allow collected subsurface water to enter the pipe from below as the trench fills.

Answer

To distribute water out of the pipe for subsurface irrigation.

Answer

To prevent debris from entering the pipe from the surface.

Answer

To increase the structural load-bearing capacity of the trench.