What Is an Underdrain?

In the hills or plains, low-lying areas form small wetlands due to rainwater accumulation all year round, and obtain abundant shallow groundwater, which overflows and forms small rivers. With the development of human society, in the process of urban construction, some small rivers have been included in densely populated downtown areas. The origin of these small rivers was damaged due to the hardening of the tarmac road, the construction of the sewer network, and the real estate development to reshape the original terrain. Shallow groundwater has dried up, wetlands have disappeared, and rivers have dried up to become natural drainage channels.