LOVE AND HAIGHT - GREENING THE STREETS OF SAN FRANCISCO Thomas M. Sweet, PE, LEED AP BD+C Senior Engineer, AECOM, San Francisco Amir Ehsaei, PhD Project Engineer, AECOM, San Francisco Purpose: Case study of the first green infrastructure (GI) Early Implementation Project (EIP), constructed under the Sewer System Improvement Program (SSIP) by the SF Public Utilities Commission. The SSIP is a 20-year multi-billion dollar citywide investment required to upgrade the aging sewer infrastructure to ensure reliable and seismically safe sewer system. San Francisco has eight distinct urban watersheds; three on the Westside where stormwater flows towards the Pacific Ocean, and five on the Bayside where stormwater flows towards the San Francisco Bay. This paper discussed the Oak Street and Fell Street Streetscape Enhancement Project, which was the first phase of the Wiggle Neighborhood Green Corridor Project located in the Channel Watershed, as illustrated in Figure 1 below. North Shore Watershed Figure 1 SSIP Watersheds (Source: SFPUC) A key part of the SSIP is to use performance-based green infrastructure within the EIPs to demonstrate the ability for GI to attenuate runoff and reduce flows to the combined sewer, especially during the rainy season, when the combined sewer capacity can be exceeded and result in combined sewer discharges (CSDs) to the San Francisco Bay and/or Pacific Ocean. The Oak Street and Fell Street Streetscape Enhancement Project was initially solely a San Francisco Municipal Transit Authority (SFMTA) project, which SFMTA began to envision including GI in response to neighborhood public input. As a result, SFMTA requested SFPUC fast-track design of GI for the project and AECOM was retained to serve as engineer of record. The Oak Street and Fell Street Streetscape Enhancement Project is located at the northwest corner of the SFPUC Wiggle Neighborhood Green Corridor (WNGC) EIP as illustrated in Figure 2 below. 1
Figure 2 Phasing of the Wiggle Neighborhood Green Corridor Project (Source: SFPUC) The project area is just east of the Golden Gate Park, which is along the route of Bay to Breakers and is dominated by high traffic streets Oak and Fell. Both streets have some sidewalk trees; down-sloped driveways and stairs at residences; areas of distressed sidewalks; and, adjacent narrow side streets with under-utilized sidewalk areas. Images in the project vicinity are included as Figure 3 below. 2
Figure 3 Conditions in the Project Vicinity (early 2014, Source: AECOM) Content: The design team recommended a combination of permeable pavers and raingardens to conform to SFPUC GI guidance on performance (capture of the first ¾ of runoff) and identified 10 candidate areas for GI. The team identified performance metrics and rated each location, which yielded rankings for the sites. Through input from SFMTA and SFPUC, the project ended up with four streets. As part of the broader WNGC project public involvement and internal SFPUC inreach, the team prepared renderings to give the public (and SFPUC staff) an idea of how the raingardens and permeable pavers would look when constructed. Two renderings are included below in Figure 4. Figure 4 Project Renderings (Source: SFPUC) Methodology: Lessons learned from designer's perspective siting GI in urban environments, included: Since project was fast-tracked potholing for existing utilities was not able to be performed. This caused project delays during construction to allow relocation of waterlines and redesign of specific elements of the permeable pavers and raingardens, as illustrated in Figure 5 below. 3
Figure 5 Existing Utilities Avoidance (late 2014, Source: AECOM) Looking for opportunities to expand the planned raingardens along parking strip and into sidewalk areas yielded larger raingardens at SW and NW Broderick which improved function, aesthetics and provided additional storage as illustrated in Figure 6 below. Figure 6 Expanded Raingardens into Previously Under-Utilized Sidewalk Areas (2016, Source: AECOM) Deepening the permeable paver underground reservoirs and raingardens as compared to SFPUC GI design guidance yielded on the order of twice the retention volume as compared to similarly sized guidance-compliant features. Setting raingarden outlet elevations to match existing catch basin rim elevations (and opening areas) ensured similar post-project hydraulic performance and reduced potential for changes to street flooding. Performance during heavy rainfall events to date has limited surface ponding to areas outside vehicle travel lanes, as illustrated in Figure 7 below, where inflow depths of on the order of 3-inches were accommodated. 4
Figure 7 Winter 2015 Heavy Rainfall Gutter/Inlet Performance (early 2016, Source: AECOM) Reinforced curbing/walls with grade beams to transfer loads allowed curbs to withstand vehicle impact loads as drivers became accustomed to the revised bulb-out configurations as illustrated in Figure 8 below. Figure 8 Damage to Divisadero Railing (early 2015, Source: AECOM) Use of underdrains at raingardens as backup to highly infiltrative soils and segregated infiltration zones under permeable pavers maximized infiltration. Use of low fencing to inhibit pet entry into raingardens also provided an effective means of keeping pedestrians from cutting-through the raingardens, even during the annual Bay to Breakers running race (except as used for daycare) as illustrated in Figure 9 below. 5
Figure 9 NW Broderick Raingarden (early 2015, Source: Burt Tanoue) Use of inlet permeable weir allowed for capture of leaf litter and smaller debris prior to entry into the raingardens as illustrated in Figure 10 below. Figure 10 Inlet Detailing and Performance Image (Source: AECOM) Use of piezometers in the inlets, raingarden areas and outlets coupled with v-notch weirs allowed for flow monitoring. Results: Integral to both the pavers and raingardens were features to monitor water levels and measure inflows and outflows to document the effectiveness of the proposed improvements. Construction was completed in early 2015 and overall the GI is performing well. For the 2015/2016 rainy season, the overall system has been attenuating over 90% of inflows. Below, Figures 11-14 show photos from early 2015, shortly after planting and early 2016 which illustrate the grow-in period improvements in plant coverage and generally improved aesthetics. 6
Figure 11 Divisadero Raingarden (Source: AECOM) Figure 12 SW Broderick Raingarden (Source: AECOM) 7
Figure 13 NW Broderick Raingarden (Source: AECOM) Figure 14 Baker Raingarden (Source: AECOM) Importance: With the ongoing drought, the installed drip irrigation system has provided the needed moisture for native and adapted plant grow-in. Thankfully the touted El Nino delivered a more typical rainy season and the GI performance has been able to be documented and the percentage of runoff diverted from the combined sewer system exceeded expectations. 8
Biosketches: Thomas M. Sweet, PE, LEED AP BD+C, Senior Engineer, AECOM Tom Sweet has more than 30 years of experience in civil and environmental engineering. His work has focused on utility infrastructure evaluation and design, with an emphasis on integrating sustainable features into reuse of existing facilities. His work includes identification and evaluation of alternatives related to upgrading existing water, sanitary sewer, storm drainage, and electrical systems. His passion is working with diverse design teams to include green infrastructure in projects, including permeable pavements, raingardens and other infiltration features. Most recently Tom completed: integrating green infrastructure into a "ready for reuse" SoCal Superfund site that is now being used for utility-scale solar PV; post-construction monitoring of the first full-width permeable paver street in Berkeley, CA Allston Way, which is attenuating upwards of 90% of inflows; and, evaluation of expanding stormwater reuse in a regional park Orange County Great Park, in Irvine, CA. Amir Ehsaei, Ph.D., is a Civil Engineer with the AECOM office in San Francisco and is specialized in Green Infrastructure and Low Impact Development Design. With 7 years of experience working on LID/GI projects across the nation, he has been an active part of multiple projects in different stages (research and pre- and Post- construction monitoring, planning, design, construction inspection, and post construction maintenance planning). Amir has worked on Early Implementation projects for the San Francisco Public Utilities Commission (SFPUC), demonstration project for the Louisville Metropolitan Sewer District (MSD) CSO130 watershed, Chicago HUD Resiliency on quantifying benefits of green infrastructure as part of a benefit cost analysis, and working with County of Los Angeles Department of Public Works on developing a Sustainable Infrastructure Guidelines document. He has been a part of USEPA Office of Research and Development doing extensive research on performance and maintenance of permeable interlocking concrete pavements. 9