Project is designed to mimic the function of natural desert riparian corridors using native soils, rocks and vegetation to slow and cleanse storm water.
Sarah Buente and Heather Venhaus
BioCycle December 2016
The University of Texas at El Paso’s (UTEP) Campus Transformation Project (CTP) was awarded Silver certification under the Sustainable SITES Initiative (SITES) rating system, and is the first project to certify under SITES v2 (Version 2). The project has transformed the heart of the UTEP campus by redeveloping acres of sloping streets and parking space into a beautiful, pedestrian-oriented, accessible green space. By converting an automobile-centric environment dominated by asphalt to an inviting community landscape, the CTP also strengthens the connection between the city, campus and land.
Owned and administered by Green Business Certification Inc. (GBCI), SITES is the first program of its kind to offer a systematic, comprehensive rating system that aligns land design and development practices with the functions of healthy ecosystems to protect, restore and enhance ecosystem services. The SITES rating system draws on the experience gained from a two-year pilot program involving more than 100 projects. Forty-seven of these pilot projects, located at corporate headquarters, national and city parks, academic campuses, private homes and elsewhere, have achieved certification. Site design categories included in the SITES rating system include Water, Soil and Vegetation, Materials Selection, and Human Health and Well-Being.
Whether in a nature preserve or a built landscape in an urban environment, the SITES rating system emphasizes the importance of healthy soil, the essential foundation for healthy vegetation and ecosystems. Healthy soil is also necessary for supporting the many other critical ecosystem services, such as filtering pollutants, sequestering carbon, mitigating floods, regulating water supply, controlling erosion and creating wildlife habitat, which is why protecting or restoring soil function is a critical first step in sustainable site design and management. SITES-certified projects must ensure degraded soil has been restored to meet certain criteria relevant to reference soils that include soil organic matter, compaction and infiltration rates, biological function and chemical characteristics.
The first step for any SITES project is to assess the existing soil on the site and conduct a detailed analysis that includes investigation of vegetation, materials, climatic and cultural conditions, and both the existing on-site soils and reference soils. With input from an integrated design team, which must include a professional with soil expertise in order to properly identify any healthy soil or degraded soil found on-site, the analysis precedes design and is a tool for optimizing site performance. To restore degraded soils, the team must identify the site’s reference soils during the predesign site assessment stage, which fall into one of the following categories:
• Soils native to the site as described by the Natural Resources Conservation Service soils surveys
• Undisturbed native soils within the site boundary
• Undisturbed native soils within the site’s region that support appropriate native plants or appropriate plant species similar to those intended on the new site.
These assessments aim to protect any existing healthy soil rather than having to recreate what is already functioning, and also inform the site design and support the project’s sustainability goals.
To ensure that soil has been restored, SITES requires that a soil management plan is created and communicated to contractors, and that post-restoration soils tests are also conducted. Any soil disturbed as a result of the project’s construction will need to be restored to the predetermined criteria, which is only required for areas that will be revegetated. This performance-based benchmark ensures the team and the client that healthy soil will serve as the foundation of the project landscape. Often overlooked in the development process, these critical steps can provide both environmental and economic benefits, such as conserving water, reducing runoff, protecting water quality, improving plant health and decreasing long-term maintenance.
Campus Transformation Project
One of the main goals of UTEP’s CTP was to change storm water from a waste product that was quickly removed from the landscape to a valuable resource that provides benefits to the site and surrounding region. This is especially important as the Chihuahuan desert ecoregion where UTEP is located receives an average of 9.6 inches/year of precipitation. To manage storm water, the project team looked to natural desert riparian corridors for guidance.
The CTP design process began with a detailed site assessment, which focused on the movement of water across the landscape from the mountains in the upper watershed to natural arroyos that ultimately lead to the Rio Grande River. Prior to the project’s implementation, storm water was handled in a conventional manner, flowing across asphalt parking lots or through underground pipes. Flooding of intersections and buildings occurred after large storm events.
The green infrastructure storm water system was designed to mimic the function of natural desert riparian corridors using native soils, rocks and vegetation to slow and cleanse storm water. From upper portions of the watershed, storm water is directed through a series of arroyo and acequia bioswales, which reconnect historic arroyos that were filled during UTEP’s construction. Carefully woven into the topography, visitors can experience the artful management of storm water from surrounding pedestrian corridors, bridges, benches and gathering areas.
The sandy native soils have high infiltration rates of approximately 10 inches an hour and andesite rock collected on-site form check dams and basins that slow the flow of water and encourage infiltration. Compost from local vendors was added to the soils where needed to increase organic matter levels to 2 to 3 percent, representing desert garden soils. The compost provides additional water retention, as well as feeds soil biota. During construction, special attention was given to the bulk density of the soils with a goal of not exceeding 1.57 g/cm3 or 85 percent maximum dry density. Infiltration rates were tested to verify performance. The native vegetation planted in and around the bioswales is equipped for both arid conditions, as well as the summer monsoons.
In addition to the focus on storm water and soils, the CTP project included creation of the Centennial Plaza and Centennial Green, richly detailed outdoor gathering spaces that features a performance lawn and a 130-seat amphitheater, desert gardens, walking paths and a diverse array of native trees, shrubs and perennial plants. Since its official opening in April 2015, the Centennial Plaza has been used as a living classroom, event venue and outdoor space for students, faculty and staff to gather.
Sarah Buente is Marketing & Communications Project Manager at U.S. Green Building Council. Heather Venhaus, principal of Regenerative Environmental Design, is a SITES project consultant. To get started with SITES and register your project, go to sustainablesites.org.