Generate a schematic pencil architectural sketch depicting how river water is drained using gardens. This sketch should display a clever design of gardens and green areas that act as natural drainage systems to channel and filter rainwater. Focus on depicting terraces, permeable beds, and strategically placed garden zones to capture and absorb water efficiently. Additionally, include elements such as conduits, specific vegetation, and details showcasing how the environment is leveraged for sustainable water management. The sketch aims to convey the creativity and functionality of gardens as eco-friendly solutions for stormwater drainage.