In regions where the rainy (monsoon) season is short and limited to only a few months, which sewerage system is generally recommended for urban drainage and wastewater collection?

Introduction / Context:
Choosing an appropriate sewerage system depends on rainfall pattern, cost, operation, and public health. Where rainfall is brief or infrequent, designers prefer arrangements that keep foul sewage flows in smaller, more economical conduits.

Given Data / Assumptions:

• Rainy season lasts only a few months.
• Objective: recommend a suitable sewerage system.
• Systems considered: combined, partially separate, and separate.

Concept / Approach:
A combined system carries sanitary sewage and storm water together, requiring large pipelines sized for storm peaks all year. A separate system carries sanitary sewage and storm runoff in separate conduits, allowing the sanitary sewer to be sized only for wastewater (plus infiltration), reducing cost and avoiding storm-induced overflows. This is ideal when stormwater loads are seasonal or small.

Step-by-Step Solution:
Assess rainfall duration → short season implies most of the year only sanitary flows occur.Economics and hydraulics → separate system keeps sanitary sewers small and efficient.Storm drainage can be handled by open channels or separate storm sewers used mainly during rainy months.

Verification / Alternative check:
Compare life-cycle costs and overflow risks: combined systems risk combined sewer overflows; separate systems minimize pollution during storms and allow targeted stormwater controls.

Why Other Options Are Wrong:

• Combined: oversizes pipes year-round and risks overflows.
• Partially separate: reduces but does not eliminate combined issues.
• None of these: there is a standard solution—separate system.
• Combined with detention only: still conveys foul flow with stormwater.

Common Pitfalls:
Assuming combined systems are always cheaper. In short rainy seasons, they often are not due to large diameters and treatment burdens during storms.

Final Answer:
Separate system (sanitary sewage and storm water in different sewers).