Green Infrastructure Siting Using Robust Efficient Procedure

Abstract Robust siting of Green Infrastructure (GI) application can achieve high reduction in peak discharge rates of runoff during storm events and improve water quality, all while creating additional green space benefits. While designing and implementing GI has become more mainstream, retrofitting GI into developed areas still poses challenges due to existing utilities and infrastructure, lack of suitable soils or suitable slopes, and several other potential surface and subsurface issues. To identify and evaluate favorable potential GI locations, we developed a four step GIS site-screening approach that reduces engineering process and leads to optimized GI application programs. Arcadis developed a GIS site screening approach that uses readily available infrastructure data. Much of this work would have previously been done by sending field staff out to inspect and gather data. The goal of this approach is to provide a tool for the planner/ designer that represents a continuum of GI suitability across the project area from which individual locations are evaluated and ranked before the sites are sent for further field confirmation. This approach reduces time in the field by prioritizing which areas may be better suited for GI implementation and as such can provide a defensible baseline for Capital Improvement Program (CIP) project selection and design. The approach was developed and used successfully in several cities across the US, in Columbus, OH, Los Angles, CA, DC and Richmond, VA. Objective The developed approach depends on 4 steps to locate most efficient sites that include flow availability, site availability, site suitability and GI performance scoring. These four steps address the sites secretion, the location of the GI (in public parcels or within the public corridor), the type of GI (Bioretention cells or pervious pavement) existing surface and subsurface utilities and project goals. The objective is to consider all the prementioned factors using readily available data and produce a short list of sites that provide highest benefits and reduces the required flied work Stepping through each phase sequentially enabled the screening of large number of potential public parcels and right-of-way sites and reduce to a viable number of sites with the highest benefits. The evaluation process also enabled the GI Ranking approach to provided results at a faster rate as lesser number of sites are being evaluated in each new phase. Finally, the process helped to simplify reviews for each phase and prevented re-examination of sites that were already excluded if/when the performance criteria was modified Figure 1 shows the workflow diagram of the selection phases and the objective/target of each step. Methodology The GI Ranking Tool evaluation and analysis process includes the following steps: 1. Flow Availability. The flow availability process involved locating runoff catchments and city owned parcels with adequate surface runoff. The process included identifying flow routing mechanisms and calculating directly connected impervious area (DCIA) within both City owned parcels and runoff catchments. 2. Site Availability. In this step, the availability for adequate space for various GI types within sites with high flow runoff identified in step 1. Site availability analysis depends on the minimum requirements for each of the considered GI types. In public parcels, pervious pavement, Bioretention cells in open spaces, and/ or converting part of the parking lot to bioretention are considered. In public corridors within the right-of-way, permeable pavement is considered for low traffic areas, like local roads, collector roads, and alleys with curbs. Bioretention sites are considered along sidewalk away from intersections and driveways 3. Site Suitability. Steps 1 and 2 determine the availability of flow to mitigate and space to place GIs. In step 3, sites are then screened for suitability based on potential conflict with surface functions and potential conflict with subsurface structures like tress, utilities, etc. 4. Score GI Performance. The fourth step is ranking the GIs using scoring criteria that meet the study target goals. Criteria include amount of runoff/flow reduction, impervious area reduction, maintenance of the selected GI types, socioeconomic benefits, minimization of known local flooding condition, improvement of urban tree canopy and improvement of water quality. Different benefits could be used for the ranking based on the project goals Case Study Results The siting procedure was applied to different cities including Columbus Ohio, Los Angles California, DC and Richmond VA. The Richmond, VA GI Master Plan is used in this presentation to detail the procedure. The objective was to identify opportunities to incorporate green infrastructure in public parcels and in the right-of-way to reduce stormwater quantity and improve water quality. The key objectives that are critical to the project's success include: - Reduce stormwater volume in the combined sewer system. - Reduce impervious area and increase green space. - Reduce amount of nitrogen, phosphorus, and sediment delivered to James River. - Address existing drainage/flooding concerns where possible. - Implement easily maintainable GI where possible to minimize future maintenance (since maintenance in perpetuity will be required of any GI). The study area included over 500 public parcels and the impervious area within the public corridor was more than 3,860 acres. The final site selection show that Bioretention in open areas of public parcels and the space between curb and sidewalks in the public right-of-way had the highest number of qualified sites for incorporating GI, while bioretention in parking lots and green alleys had significantly smaller numbers of qualified sites. The public parcels contained 169.75 acres of DCIA. The applied procedure identified the top 110 parcels with the highest score. GI application to these 110 parcels would control up to 154 acres (91%) of the public parcels DCIA. The public corridor contained 3,862 acres of DCIA. The applied procedure identified the top sites with the highest score that would control 536 acres (14%) of the DCIA within the public corridor. Tables 1 through 6 show an example of the siting procedure results for each step and Figures 4 and 5 show an example for the final site selection and ranking.