Introduction

■ Fluid

Fluid pertains to landscape structures designed to Flexibly accommodate the cyclical and seasonal Fluctuations oF water Flow, as well as the management oF water volume, Frequency, and velocity.

Water is equally a life sustaining and an erosive force. Subject to weather cycles, with seasonal variations ranging from rains to hurricane, and from drought to floods, water flow is unpredictable.

Fluid pertains to landscape structures designed to flexibly accommodate the cyclical and seasonal fluctuations of water flow, as well as the management of water volume, frequency, and velocity. In this chapter, structures and materials are discussed in terms of their capabilities to retain, infiltrate, control-release, and attenuate flows in order to prevent soil erosion, conveyance of pollutants, or flooding. Conversely, the capture and conveyance of water flow is examined in terms of the potential to create habitat, as well as recreational and visual amenities.

Within Living Systems, water as a resource, a medium, and a fluid relates to every chapter topic: Stratify regulates permeability; Digestive biodegrades water pollutants; Translate monitors pollution or storm surges; and Volatile displays water’s ephemeral phases, such as mist and fog.

In this chapter, all of the projects featured are associated with peak flows during storm events. However, each exemplifies a different type of flow dynamic ranging from large water bodies to small streams, from linear river flow to surface flow in urban areas. The projects demonstrate different site conditions and different scales: from urban to coastal riparian, from small lots to entire river sections. Within urban and suburban environments, landscape is typically engineered to convey water rapidly away from built structures to prevent interior flooding and to clear exterior circulation surfaces. Current design, planning and policy regard the dynamic of flows differently due to several major concerns. One concern is the conveyance of polluted surface runoff into water bodies, which necessitates onsite retention and filtration systems. While many sites comply with such municipal requirements, its landscape form is not always integrated as a design intent.

The urban projects featured here demonstrate a retrofit design to inhabit the existing, dimensionally constrained urban fabric and infrastructure, as with Blackstone Stormwater Garden and SW 12th Avenue Green Street Project. The former is composed of a series of bio-swales that are designed to detain a 3-month storm event for 72 hours, consequently capturing and cleansing 90% of annual rainfall, and preventing polluted runoff from entering the nearby river. The latter features a stormwater collection and retention system that has been integrated into the existing sidewalk section. Distributed along the length of the street, the networked containers collect 60% of annual rainfall, and still accommodate circulation and vegetation. Such interventions, if deployed throughout the urban-suburban environment, can have a tremendously positive impact on water quality and flood prevention. Combined with Digestive operations and technologies, such as the newspaper nitrate treatment bioretention medium, researched by Allen P. Davis, the capacity for biofiltration can be highly efficient.

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■ with a majority oF surFaces in the built environment being impervious, these methods oF small-scale, local water retention, and inFiltration begin to compensate For the depletion oF the natural sponge structures (soil, wetlands) that were once widely dispersed to attenuate the volume oF surges, as well as Facilitate ground water recharge.

With a majority of surfaces in the built environment being impervious, these methods of small-scale, local water retention, and infiltration begin to compensate for the depletion of the natural sponge structures (soil, wetlands) that were once widely dispersed to attenuate the volume of surges, as well as facilitate ground water recharge. To regain the sponge infrastructure in urban and suburban developments, the new approach seeks to integrate retention and infiltration into every lot and curbside. Consequently, new landscape typologies that were previously inconceivable arise and become common terminology.

The greenroof is such an example, now seen more frequently, as many landscapes are actually built on top of structures such as underground garages. The landscape design for the Allianz Arena Munich Stadium is an extensive type of greenroof, which sits on top of a parking garage. The surface is composed of a combination of nonporous and porous asphalt, intended to capture the roof’s surface runoff and redirect it to a rain garden for infiltration. While the nonporous asphalt paths facilitate pedestrian movement, the porous asphalt absorbs water and sprout-vegetated islands.

Surface products such as interlocking pavers, concrete, asphalt, as well as structural soils are now designed specifically to manage and attenuate runoff volumes. Various configurations and material compositions allow for a range of retention and infiltration. In the Allianz Arena landscape design, for example, the porous asphalt mix includes lava rock, which increases the surface’s water-holding capacity and slows down its release. Structural soils often include super-absorbent polymers (SAP), which absorb up to 400 times their own weight in water in order to increase the soil’s water retention and availability for tree roots. Engineered to convey fluids via osmotic pressure, the absorbed water (and fertilizer) is released when the soil is dry. In order to contend with the extreme hydrograph of drought and intermittent torrents, the Besòs River employs a series of inflatable dams along the river that are activated throughout the year. These dams inflate to detain the limited flow and convert the dry riverbed into a continuous cascading pool, and deflate during the onset of a storm to accommodate the torrent.

Set within the context of riverbanks or deltas, water velocity can act as a tremendous erosive force. The Delta In-Channel Island case study employs biotechnical wave and flood control structures in the delta to attenuate erosive coastal wave action, control potential flooding, and improve bank stabilization as well as levee protection.

In Shop Creek, six drop structures were embedded along its course to dissipate the forceful energy of the river during storm events. The structures are wide crescents that turn the flow of the stormwater against itself to decelerate the water’s velocity. To prevent erosion of the structures, a mixture of impervious soil cement was applied to form a solidified, protective shell. Other materials discussed within the book, such as geotextiles, bonded fiber matrixes, and cellular soil confinement structures are also frequently applied to prevent erosion, at the same time allowing for vegetation and roots systems to establish and provide stream bank reinforcement.

Fluid // 57 ■