The St. Louis region is defined by the confluence of America’s two great rivers and its unique landscapes. By utilizing an interconnected and multi-functional network of blue, gray, and green infrastructure, the region can enhance water quality and reduce costs to local governments and individual citizens.
Our region has a rich and complex interconnected network of rivers, creeks and streams. When combined with built infrastructure including levees, storm sewers, sewers, water supply, and water treatment systems, along with parks and open spaces, these natural systems can serve as the framework for low-impact, high-performance water infrastructure. This blue, gray, and green natural infrastructure system can help the region improve water quality and mitigate flooding through coordinated watershed planning. At the same time, it can provide recreational amenities and protect and expand natural habitats in the St. Louis region.Blue, Gray & Green Infrastructure Opportunities
Our sewer infrastructure serves residents throughout the region, both by removing waste and by removing stormwater from streets and properties. Point source pollution can emanate from sewer overflows, which often activate when sewer systems are overwhelmed with stormwater runoff. In order to remove sewage from streams, regions across the country are being forced to spend billions of dollars to eliminate sewer overflow systems. St. Louis and peer regions are expected to require $3 to $5 billion each in infrastructure upgrades to attain compliance with federal clean water laws.14
In addition, local sewer districts have been mandated to initiate on-site stormwater detention, which increases development costs. Metropolitan St. Louis Sewer District’s (MSD) new site design requirements are one regional example. Costs for such changes to the system must currently be paid from limited municipal, county and regional resources. In addition, there exists no coordinated regional framework to achieve these requirements. While St. Louis City and County are under the jurisdiction of MSD, the rest of the region is served by a patchwork of many sewer districts and municipalities.
A coordinated regional approach to watershed planning based on blue, gray, and green infrastructure will reduce both public and private sector costs while improving the local environment.15 OneSTL goals to build a regional blue, gray, and green infrastructure are outlined in the sidebar to the right. Along with associated objectives and strategies, they are presented in detail in Chapter 4 of this document.
The first step is to map existing water infrastructure and new blue, gray, and green infrastructure opportunities. 
The region has an extensive network of greenways and recreation trails (the Katy Trail; St. Charles, MO).The map on page 40 illustrates the regional opportunities located along our rivers and streams. This mapping should incorporate regional watersheds, water bodies, and water intake, treatment and outflow facilities. This comprehensive mapping will show the sources, flows, destinations of the water we use. As we understand the relationships between the rivers and streams and the human-built pipes, channels, and treatment facilities, it becomes possible to think creatively to find cost effective solutions to the problems of water quality, erosion and flood prevention. For example, stream buffers along urbanized creeks can help to protect adjacent development from flooding. Within a system of stream buffers, it may, over time, be possible to restore channelized streams to wider, natural channels surrounded by green space. Such improvements will make more room for our rivers. A coordinated regional approach to watershed planning based on blue, gray, and green infrastructure will reduce both public and private sector costs while improving the local environment.Stream buffers can help to reduce the amount of runoff channeled directly to our primary rivers and restored channels can improve water quality because of the filtering capacity of natural, vegetated stream beds.
In addition to flood protection, stream buffers can become habitat corridors for native wildlife, recreational amenities, and greenways as part of the transportation network. The blue and green infrastructure network includes existing assets such as established parks and preserves. Larger scale open space functions as recreational hubs within the greater network. It also provides opportunities for centralized stormwater management facilities and major "carbon sinks" to improve air quality. This multi-functional approach is one of the keys to successful, triple-bottom-line sustainability. The potential of green infrastructure is the ability to create a network that functions as a high-quality natural habitat, an aesthetically beautiful park and recreational amenity, and a high-performance stormwater treatment and runoff management system.
