$4545$ : "What are the primary functions of drainage systems in civil engineering? Analyze the importance of proper drainage in preventing water$-$related damage to infrastructure. Discuss the key components and design considerations of effective drainage systems, including surface drainage, subsurface drainage, and stormwater management. Explore the principles of hydraulics and hydrology governing the flow of water in drainage networks. Evaluate case studies illustrating successful drainage solutions and their impact on mitigating flooding, erosion, and soil instability in urban and rural areas."