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Elysian Park Case Study

LANDSCAPE ARCHITECTURE

The ongoing global issues related to human sprawl, resource depletion, and environmental degradation are reflected in the current landscape design of Elysian Park in Los Angeles, CA.

The goal of this case study was to explore innovative landscape architecture methods that would help elevate the sustainability and productivity of urban landscapes. The project aimed to demonstrate how initial assessment and evaluation of the environmental system performances of an existing site can be used to help guide regenerative design decisions that will increase landscape productivity, leading to a greater storage of carbon and energy and an increased production of oxygen.

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Final Site Design.

The final site design achieved the case study's environmental objectives by incorporating regenerative design principles and practices throughout the project area. By replacing vast areas of turfgrass with native, drought-tolerant plantings and expanding the size of the urban forest canopy, carbon sequestration and energy conservation levels were elevated. The new design also provided habitat and wildlife restoration. Rainwater capture, harvesting, and bioremediation were achieved with rain gardens, wetlands, and cisterns, all while preserving its precious historical and cultural elements.

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Site Design:
Upper Zone.

The design elements of the Upper Zone feature: (1) crushed stone plazas for resting or gathering; (2) rain gardens for stormwater infiltration into natural cisterns; (3) a pavilion with a solar panel roof to generate power for the drip irrigation system; (4) a stormwater catchment wetland that overflows into the rain garden below; (5) a rain garden for stormwater infiltration into an underground natural cistern.

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Site Design:
Lower Zone.

The design elements of the Lower Zone feature: (6) crushed stone plazas for resting or gathering; (7) a vernal pool created from the overflow of the main wetland; (8) a constructed landform filled with land cut to create cisterns and wetlands; (9) the main wetland which is the final stormwater collection point for the entire site, infiltrating water into a large underground natural cistern that extends underneath the constructed landform.

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Conceptual Design Layers.

The exploded axonometric diagram below highlights the hierarchical layers of the conceptual design. It shows the integrated analysis of pedestrian circulation with stormwater collection coupled with tree placement in order to illustrate dual and complementary functionality between each design aspect. The new design aimed to create a softer, more natural flow of both humans and water, accented with lush trees and native vegetation.

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Conceptual Design Renderings.

The images below show a "before" photo next to a rendering of the new design. These "after" images illustrate how the wetlands, rain gardens, and cisterns were designed to convey a natural look in which water flows and collects into aesthetically pleasing pools of water surrounded by lush vegetation and weaving pedestrian paths. 

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Project Location.

Elysian Park is the oldest and second largest park in Los Angeles, encompassing 575 acres, and largely covered in water-demanding turfgrass, exotic trees, shrubs, and groundcovers. An area of land within the park covering 22 acres was selected for this case study in which a portion of this site is home to Chavez Ravine Arboretum. Founded in 1893 by the Los Angeles Horticultural Society, Chavez Ravine Arboretum is the oldest arboretum in Los Angeles and many of the trees are the oldest and largest of their kind in California and the United States.

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Site Analysis:
Plant Inventory

This precious historical collection of tree specimens deserves to be preserved and celebrated. However, unfortunately, the overall design of the arboretum currently lacks purpose, flow, and a cohesive concept in general. It is extensively and unnecessarily planted with turfgrass across the site, covering the majority of the 22 acres. Mixed understory plantings of some California natives and mostly exotic species occupy the outer hillside. The tree canopy is an eclectic mixture of tree specimens from around the world in the old arboretum area including a great deal of eucalyptus as well as oaks, pines, and ficus throughout the rest of the site. The graphic below illustrates the tree locations, species proportions, and tree origin abundance.

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Planting Design.

The new planting design was organized into zones based on the origins of the existing arboretum's tree species. Both the tree canopy and understory plantings were selected for their compatibility and for their aesthetic qualities that associate with various themed areas, from continental origin to symbolism to native plant communities. Plants were also selected based on their adaptive ability to the Los Angeles region and their water requirements.

The plant palette diagram below illustrates the various colors that can be enjoyed during blooming periods throughout the seasons for prominent species within the design.

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Site Analysis:
Environmental Data

Another step of the site analysis involved gathering data and information for the environmental systems analysis of the existing site, summarized in the graphic below with photos of existing conditions. These metrics include the following: of the 22 total acres, 15.4 acres are covered in turfgrass; there are over 70,000 square feet of hardscape which produces almost 530,000 gallons of water in runoff during a 1" rainstorm; 4,000 pounds of fertilizer are used per year; 680 gallons of gas are used per year to mow; and over 30,000,000 gallons of water per year are used to irrigate, mainly the turfgrass.

Utilizing this data, the environmental systems analysis was conducted to determine the existing site's biomass, oxygen production, carbon dioxide sequestration, and energy use. These metrics are illustrated in the graphic below.

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Site Analysis:
Topography

The site analysis concluded with topographic studies to assess the general shape, slopes, and physicality of the park. A combination of GIS, Rhino, and Grasshopper was used to generate a heightmap analysis, slope analysis, watershed flowlines, and topographic map with 2' contours. These 3D maps were used to determine the flow of surface water on landforms and aided in locating ideal areas for creating stormwater catchment, retainment, and re-use for the new design.

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Hydrologic Analysis.

Using the topographic and watershed analyses above, hydrologic zones were located for water catchment, filtration, retainment, and reuse. As illustrated in the graphics and maps below, the park exhibits a generally declining slope with areas in Zone "1" being the higher elevation points, and Zone "3" being the lowest elevation point. These three hydrozones featured a combination of rain gardens, wetlands, and underground "natural" cisterns made of sand and clay. Additionally, the square footage of each zone area was determined by calculating the amount of surface rainwater to be captured during a typical one-inch rain event.

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Hydrologic Design: Zones.

As illustrated by the graphics below, the hydrologic design began with Zones 1a, 1b, and 1c, in which rain gardens capture and filter surface stormwater before entering an underground cistern. Any overflow stormwater travels to Zones 2a and 2b which feature wetlands to capture and filter water, then rain gardens that catch spill-over from the wetlands, ending with an underground cistern for retainment and re-use. Zone 3 is the final catchment point and features the largest wetland and underground cistern to filter and store stormwater from the surrounding areas as well as spillover from Zones 1 and 2.

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Hydrologic Design: Natural Cisterns.

Specific cistern sizes for each hydrologic zone within the design were carefully calculated, as shown below. Sizes were determined based on the square footage of micro-watersheds and the estimated amount of stormwater runoff that can be collected during a one-inch rain event.

Additionally, the figure below exhibits a comparative analysis of the major energy savings gained by using "natural" cisterns versus traditional concrete cisterns. "Natural" cistern design is composed of a hardpan, bentonite clay base, about two feet of sand for water holding, then eight inches of stone, topped with one to three feet of soil.

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Site Re-Analysis: Environmental Benefits.

The environmental systems analysis of the new site was compared to the original site analysis as illustrated in the graphs below. From biomass to carbon dioxide sequestration to oxygen and energy production, each metric was almost doubled in the new design. Therefore, this case study demonstrated that integrating these regenerative design practices into the existing urban fabric can provide environmental benefits, elevate sustainability, and increase landscape productivity.

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