Landscape Architect Articles

Phoenix Desert Hills Trailhead01-09-18 | Feature

Phoenix Desert Hills Trailhead
A unique habitat of the Sonoran Desert through the Parks Preserve program

Prime Firm: J2 Engineering and Environmental Design, LLC

People reconnoiter at the plaza before venturing off on one of the Sonoran Preserve trails. Lack of water prohibited flush toilets for the restrooms (left). A vault evaporator technology waste disposal system was employed. A three-foot deep concrete vault is beneath the ramada, with an 18-inch diameter pipe around the inside perimeter of the vault. The pipe is slotted in one section to allow liquids to enter and has two vents fitted with fans that force air down the toilet risers and through the pipe. The pipe's large surface area facilitates evaporation of liquids, effectively reducing the volume of vault waste by two-thirds. While the forced air system is designed for evaporation, an added benefit is the waste remains aerobic, which further eliminates odors. The revegetated native flowers (see plant collage p. 69) include yellow poppies, lupines and wild heliotrope. A seed mix of low growing wildflowers, grasses and forbs were placed adjacent to pedestrian areas. A seed mix of grasses, shrubs and trees were placed in larger restoration areas.

Phoenix has spent years and millions of dollars on preserving and making sensitive connections into the Sonoran Desert through their Parks Preserve program. Since 2009, the city has built over 36 miles of new trails in the Sonoran Preserve. The latest connection to the over 27,000 city acres of preserve land, the Desert Hills Trailhead, is at the intersection of Carefree Highway and 7th Avenue, an access point long used by area residents.

J2 Engineering and Environmental Design, LLC (J2) provided overall design project management, site analysis and master planning, landscape architecture, civil engineering design, drainage analysis, traffic engineering, site revegetations and construction management. J2 was supported by a team of subconsultants: surveying by AZTEC Engineering and Kenney Aerial Mapping, geotechnical engineering by RAMM Engineering, electrical engineering by Wright Engineering, structural engineering by Gannett Fleming and Campbell Engineering, building interior architecture by Swan Architects, mechanical engineering by Applied Engineering, and native plant inventory by Native Resources.

A traffic circle at the entrance to the Sonoran Preserve directs equestrians and other trail users to their respective parking areas. A sweep of colored concrete encircles a median of wildflowers and two "Foothill' palo verde trees salvaged on site and relocated. The landscape architect had the topography at the parking sites terraced to "nestle the hardscape" into the site with minimal earth disturbances.

A main pedestrian walkway"?uthe "spine""?uconnects Carefree Highway to the preserve. The design includes a pedestrian bridge that spans one of the preserved desert washes. J2 performed multiple sunshade studies to ensure the gathering space between the ramada and restroom would offer comfort and respite from the desert heat. Built components are rusted steel, integrally colored concrete and a sandblasted pattern of "cholla bones" on the restroom walls that cast intricate patterns on the stabilized decomposed granite floor. Rusted gabion baskets, one of the many stormwater harvest basins, blend into the desert landscape.

The trunk of the cholla, the inspiration for the steel design panels, is used by a host of desert critters to hide from predators or to seek shelter from the desert sun.
*Photo: Western New Mexico University Department of Natural Sciences*

Desert Hills Trailhead
This design aesthetic included working with the contours of the natural land to accommodate, in an inconspicuous manner, 180 plus automobile parking lot spaces and a stabilized granite equestrian parking and staging area. The design of the facilities respect the land and minimized their impact on the site. Extensive site analysis was performed prior to a pen ever touching paper for the design and layout of the new trailhead connection. Analysis included studying the drainage patterns of the native washes, identifying the stands of native vegetation and evaluating the varying terrains to ensure the lightest footprint possible. The extensive analysis determined the ideal area for the new facility would include a burned area with minimal vegetation. Native washes would be preserved. More than 520 plants on site were inventoried and assessed. Only 19 trees required removal, many of which were in serious decline. This "deadfall" went to habitat areas.

The project overcame the challenge of no available water by introducing water harvest swales into all the parking lot islands and other low areas. Any collected stormwater goes to the new trees and existing plants. Lack of water meant the use of vault evaporator (no flush) restrooms, a biological system that is noticeably odor free.

The ramada is made of rusted steel I-beams and board-formed concrete walls. Welded to the steel I-beams are decorative steel panels cut to resemble the trunks ("skeltons") of Sonoran Desert Cholla cacti. Valley Steel laser cut the "cholla bone" panels, which create intricate shade patterns inside the ramada. A circular fan on a timer is set in the square wall space to cool off hikers.
*Photo: Creative Commons Attribution Share Alike.*

Two site specific native seed mixes were developed: one is a wide variety of Sonoran Desert wildflowers, desert grasses and low ground covers around the pedestrian areas. The other mix included seed species of larger native trees, shrubs and cacti that will eventually serve as cover and as a natural nursery for wildlife and new vegetation.

The contractor salvaged the existing pavement to replate disturbed site areas. Techniques and details required extensive mock-ups of hardscape treatments (textures, aggregates and colors). Mock-up panels were either done in place so they could be reused as a final product or repurposed for other uses, such as the mock-up for the restroom walls, which were sand blasted and repurposed for trail wayfinding signage.

Native stands of vegetation and natural drainage ways were preserved in place to minimize the footprint of the site development. The steel pedestrian bridge, supported on concrete foundations, spans a natural desert wash. The bridge and exposed aggregate concrete walk connect the northern parking area to the south and places trail users on the path to the restrooms and ramada plaza. The bridge combines various sized steel angle irons that support steel bar grating. The walking surface is perforated metal panels.

Large areas of desert were roped off and had silt fences installed so that neither construction vehicles nor foot traffic disturbed those areas. The contractor had separate bins so that construction debris could be recycled.Trees were evaluated and trimmed by a certified arborist. Daily sweeps cleared the site of debris.

The design team worked with the city to plan and develop the parking lot design. The challenge was the city's desire to maximize parking. The team initiated extensive ground evaluation and topographic mapping, resulting in a series of parking "nodes" designed out of respect for the wash corridors, surrounding slopes, native vegetation and desert views.

Equestrian needs required accommodating horse traffic, large trailer turning, pull through parking areas and special considerations for parking area surfacing (stabilized decomposed granite) and site drainage.

The site-specific design features required the expertise of multiple specialty contractors. The restrooms and ramada structures alone had multiple complex angles and planes, varying slopes on tops of walls, window pop outs and cantilevered site furnishings.

The tilting rusted I-beams of the ramada and placement of the restroom structure frame views of the Sonoran Preserve. A spreading palo verde tree and wildflowers intersperse the pavements to "ground" the structures to the site.

The site evaluation, planning and design have integrated into the desert landscape over 180 parking spaces, an equestrian staging area for six equine trailers, restrooms, a shade ramada and access to numerous trails. The design directly addressed the challenges of site sensitive planning, grading, pedestrian and automobile access, maximizing but blending parking areas into the site, equestrian trailer movements, wash preservation, desert revegetation and pavement preservation and storm water harvesting. The attention to detail epitomizes the site ethos of "take only memories, leave only footprints."

This board-formed concrete mock-up panel was repurposed as wayfinding signage at the intersection of two hiking paths. The text was sandblasted into the concrete.

Design Team
Owner: Phoenix Parks and Recreation Department: Natural Resources Division
General Contractor/Construction Manager: Valley Rain Construction Corp., Tempe
Prime Design Firm & Civil Engineer: J2 Engineering and Environmental Design, LLC (J2)
Ramada and Restroom Structural Engineer: NSB Group of Gannett Fleming, Inc.
CMC Steel (steel I-beams); Basic Metals (shop fabrication); Caliente Ironworks (field installation/field fabrication).
MEP Engineer: Applied Engineering
Geotechnical Engineer: Ricker, Atkinson, McBee, Morman and Associates
Electrical Engineer: Wright Engineering
Restroom Building Interior Architect: Swan Architects
Restroom Building Interior Structural: Campbell Engineering, Inc.