Some people maintained that a sustainable urban drainage solution (SUDS) or green infrastructure would remove the need for the tunnel. They argue that replacing paved, impermeable surfaces in London with permeable options and implementing green roofs, swales and water butts would promote the infiltration of rain-water, preventing it from reaching the combined sewer system, thus reducing peak flows and limiting the number of CSO overflows. Opponents of the tunnel felt that these measures would provide the level of control required and be cheaper than the proposed tunnel. They also argued that green infrastructure would have further benefits for London in addition to addressing the rainwater overflow problem, such as: