Which of the following is NOT an effect of incorrect disconnection of branch drains?

The correct choice highlights that increased flow efficiency is not an effect of incorrect disconnection of branch drains. In fact, when branch drains are disconnected improperly, it typically leads to a variety of issues that compromise the overall efficiency and function of the drainage system.

Incorrect disconnection can create blockages or cause drains to function less effectively, leading to inefficiencies in how wastewater is managed. For instance, if drains are misconfigured or poorly connected, water flow may become impeded, leading to backup or slow drainage.

In contrast, the other outcomes listed—such as infiltration of groundwater, vermin entering the drain, and leakage of sewage into the surrounding ground—are direct consequences of improper disconnections. These issues result from failures in the integrity of the drainage system, causing water and waste to escape from the intended path and create environmental or health hazards. This reinforces that while the system may exhibit issues when not functioning correctly, it cannot simultaneously achieve increased flow efficiency.