Integrated Water Resources Management: One Street at a Time
Intelligent stormwater engineering can improve drainage while achieving advanced levels of sustainable groundwater recharge. Case in point: The City of Paso Robles has made it a strategy to incorporate LID design elements into prioritized infrastructure improvement projects. By doing so, they have succeeded in capturing grant funds, reducing stormwater runoff impacts to the Salinas River, and recharging their groundwater all while maximizing infrastructure investment dollars. By looking for ways to replicate their initial design efforts, and maximize opportunities for weaving infiltration features into new infrastructure, the City is transforming the way they respond to the water resource portfolio dilemma. This presentation will discuss the Pilot Project and subsequent projects undertaken; provide an overview of the City’s goals and achievements; and share some of the lessons learned from design through construction and maintenance.
21st street was built on land that was once a branch of the nearby Salinas River. Historic runoff from the local watershed, along with subsequent urban development over several decades, caused frequent flooding, poor pavement, and inadequate facilities for bicyclists and pedestrians. Improvements were necessary – not only to address usability and improve drainage, but recharge the local groundwater supply. With these goals in mind, the 21st Street improvements were engineered to combine bioretention for treatment of initial stormwater flush with open-channel flow for larger runoff.
The newly designed 21st Street incorporates open-channel drainage design for conveyance of large-scale stormwater flow. Open channels running down the middle of the street are connected by box culverts at intersections to allow for street traffic passage. Placed in lieu of drain pipes, these channels allow even more water infiltration into the landscape – and the local water supply.
In certain locations, the drainage channels contain infiltration trenches for yet another level of drainage and groundwater recharge. The engineering process included infiltration testing to locate areas with the sandiest – and therefore most permeable – soils beneath the streetscape. Placed in these areas of superior infiltration, the trenches contain perforated piping surrounded by clean rock. This allows storage of large quantities of stormwater as it infiltrates into the underlying soil.
All told, the 21st Street Improvement Project solves a massive flooding issue while not only diverting stormwater into the local groundwater supply but also cleaning the water as it enters the groundwater table. In effect, it promotes sustainable drainage and groundwater recharge by bringing the historic drainage channel in line with its original, more natural form.
Lessons learned from the 21st Street project, and the City’s commitment to using stormwater as a resource led to adoption of Green and LID design features along 12th Street.
The new 12th Street Green Complete Street incorporates specially engineered landscapes (bioretention planters) to manage stormwater runoff. The plants selected for bioretention areas are powerful natural filters that can tolerate both seasonal flooding and periods of drought during Paso’s hot, dry summer months. Many of the plants selected for 12th Street’s landscape are California native species that provide biodiversity, combat climate change, and support wildlife habitats for native pollinators and birds that depend upon specific, local plant species for survival. Other stormwater management features built into the 12th Street corridor include underground infiltration structures (dry wells) and permeable paver surfaces.
Through lessons learned along the 21st and 12th Street Improvement projects, the City has successfully incorporated sustainable design features that enhance public engagement with the streetways.