Potentials and Systems in Sustainable Landscape Design
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Potentials and Systems in Sustainable Landscape Design Erica Ko Editor Werner Lang Aurora McClain csd Center for Sustainable Development II-Strategies Site 2 2.2 Potentials and Systems in Sustainable Landscape Design Potentials and Systems in Sustainable Landscape Design Erica Ko Based on a presentation by Ilse Frank Figure 1: Five-acre retention pond and native prairie grasses filter and slowly release storm water run-off from adjacent residential development at Mueller Austin, serving an ecological function as well as an aesthetic amenity. Sustainable Landscape Design quickly as possible using heavy urban infra- structure. Today, we are more likely to take Landscape architecture will play an important advantage of the potential for reusing water role in structuring the cities of tomorrow by onsite for irrigation and gray water systems, for allowing landscape strategies to speak more providing habitat, and for slowing storm water closely to shifting cultural paradigms. A de- flows and allowing infiltration to groundwater signed landscape has the ability to illuminate systems—all of which can inspire new forms the interactions between a culture’s view of for integrating water into the built environ- its societal structure and its natural systems. ment. Water can be utilized in remarkable Landscape architecture employs many of the variety of ways–-as a physical boundary, an same design techniques as architecture, but is ecological habitat, or even a waste filtration unique in how it deals with time as a function system. A large-scale example of an outmoded of design (Figure 2), its materials palette, and approach is the Rio Bravo/Rio Grande, which how form is made. Today, landscape architec- once meandered between the cities of El ture plays a leading role in sustainable design Paso, Texas and Ciudad Juarez, Mexico. This because of its ability to address ecological body of water was rechanneled and defined concerns associated with urban growth and with concrete banks to create a more clearly the built environment. Sustainable ap- delineated geo-political boundary between proaches to landscape strive to create places the two countries. While this intervention has of value and meaning while also respecting maximized the river’s potent physical and vi- and acknowledging the important functions sual ability to demarcate distinct spaces, it has that nature performs. Sustainable landscape also divorced the river from its unique capacity design combines aesthetic and psychological to engage a landscape through the ephemeral advantages while tapping into the enormous ebb and flow of erosion and deposition, and ecological and functional potential of living has removed the habitat potential of a large systems. swath of land. Water is a critical resource for cities in the 21st century, but we can no longer Shaping (the role of) water rely on concrete and heavy-handed engineer- ing to shape its flow. These techniques cause Water is a powerful element which has the critical problems for groundwater recharge, soil ability to shape the organization of a site. erosion, and maintaining native landscapes. Attitudes toward water as a site element have We must integrate water into our site design, changed over the course of the 20th century. rather than pushing it aside, to generate new Water is no longer moved across a site as forms for living in the 21st century. 3 II-Strategies Site Figure 2: Park as a catalyst for new development patterns for the city of Quito through urban tree production. Parque del Lago Competition Design by Dean Almy, Ilse Frank, and Jason Sowell. Water may act as a defining site feature dition permits the use of the water’s edge and ures 2 and 4), by providing an area of natural through various “edge conditions” where a encourages occupants to be in close interac- filtration and helping to break down some of transition occurs between water and land. tion with nature in an urban context where that the harmful substances in the run-off before Soil erosion is an important concern when is especially rare and valuable. the water drains into a stream. considering the interaction of water and land, and various strategies can be used to address Another type of edge condition is a ripar- Consequences of the built environment this issue. The grade or slope of the land may ian buffer, which is the strip of land adjacent be manipulated to protect the edge, and subtle to a stream where the vegetation is closely Rapid sheet flow across impermeable surfaces variations can be designed with this goal in influenced by the presence of water. A buffer at during a storm event and accumulation of mind. Edge conditions have various options to the edge of a creek or river can protect against sediments and pollution from roadways in consider in their design—whether to allow or soil erosion, provide habitat and food for native the storm surge are the two largest problems discourage human engagement with a water species, mitigate non-point source pollu- affecting the built environment’s impact upon body, to develop certain habitats, or to direct tion, and slow stormwater surges. Depend- water quality. Water flows more quickly across the flow of water. In Brooklyn Bridge Park, ing on their width, buffers can serve multiple impermeable surfaces such as buildings and which extends along the East River in Brook- functions, with increasing possibilities where paved areas, than it does across impermeable lyn, New York, some edges were treated in a greater width is available for the buffer area. A surfaces that allow water to infiltrate. The most rough and naturalized manner, with grass and narrow buffer can protect against erosion and critical volume of water in a storm event, with soil ending in a buffer of large irregular rocks supply an important source in the food web, regard to water quality, is the “first flush,” which toward the water. Since public use was also while larger buffers can serve additional func- contains the majority of the pollutants and a primary component of this program, some tions such as providing habitat, flood control, sediments which are washed across imperme- other points received a different treatment, with and sediment control, etc. Buffers can also able areas. As the water runs over these sur- large stone slabs terracing down to provide play an important role in managing non-point faces, it collects impurities and toxic elements seating in close proximity to the river. This con- source pollution, such as street run-off (Fig- left by pollution from cars or other sources. 4 2.2 Potentials and Systems in Sustainable Landscape Design Collecting and slowing this first run-off from a Bioswales retention and detention basins provide an storm event, thus managing pollutants onsite opportunity for stormwater to recharge the as much as possible, is the most important Bioswales are shallowly sloped channels filled groundwater onsite, provide irrigation, and to task that landscape design can undertake with with vegetation, compost or rocks that have supply an amenity on site, whether functional regard to water. Water cannot penetrate imper- been graded to accept run-off and move it or aesthetic. meable surfaces and thus cannot be filtered slowly over their surfaces. They are designed and absorbed by plants and soil. In addition, to maximize the amount of time the water Sediment/infiltration basins the flow of water is not slowed by the absorp- spends in the swale, allowing contaminants tion process and therefore places a greater and silt to be captured and slowing the flow Sediment or infiltration basins also allow water burden on our storm sewer systems. Cities of water to larger bodies. They are commonly to percolate slowly into the ground and are with combined sewer systems are at high used around parking lots and roadways, commonly used in urban conditions as land- risk, since the overflow of combined sewer where run-off tends to be highly polluted. As a scape elements. They can take a variety of systems can cause raw sewage to end up in physical intervention, bioswales can engage forms and can make use of vegetation which natural waterways. When run-off drains rapidly seasonal changes through vegetation, make is able to handle a wide range of moisture in into bodies of water, it causes higher levels of evident the natural processes of vegetation order to survive dry periods as well as times toxicity, erosion problems, and the possibility of interacting with water, and provide a new edge of inundation. A second kind of sediment/ storm surges and flooding conditions. We must condition between streets and buildings. infiltration basin (Figure 3) can be contained design the path of the water, especially the sub-grade which sends storm water for cleans- “first flush,” to mitigate the problems of erosion, Retention and Detention Basins ing through a filtration system composed of non-point source pollution, and overburdening varying grades of fines in a contained area. our municipal storm sewer systems. Retention basins (Figure 1) serve a similar This system can be of particular benefit to purpose but hold water in pools, whose water more urbanized areas where open space is Retention and filtration strategies levels fluctuate with the level of rainfall versus at a premium, and vegetative water-cleansing the rate of absorption. Retention basins can techniques are not feasible. Through all of Allowing the landscape to filter and absorb take on the form of a vegetated pond, similar these retention methods, rainwater can be water naturally is a key strategy for sustainable to a wetland condition, which can engage pub- captured and reused with a pumping system landscapes. Some fundamental approaches lic space as a respite from the day to day ur- for irrigation, thereby greatly reducing overall include bioswales, rain gardens, retention ban built environment.