Which method of landfill is most commonly used in big cities?

The valley or ravine method is commonly used in big cities for landfilling because it takes advantage of natural depressions in the landscape, which are often more cost-effective and environmentally efficient for waste disposal. This method involves filling these natural low-lying areas with waste material, allowing for effective space utilization and minimizing the need for extensive excavation or grading. By using valleys or ravines, cities can manage large volumes of waste while maintaining the surrounding topography and reducing the visual impact of landfills.

In urban settings, where land availability is limited and real estate is valuable, this method allows for the efficient disposal of waste without requiring extensive land alteration. Additionally, the valley/ravine method often incorporates features that help manage leachate and gas emissions more effectively, which is crucial in densely populated areas to ensure environmental safety and compliance with regulations.