Designing Water-Conserving Landscapes

The design of water-conserving landscapes follows the same time-tested process inherent to all landscape architecture a simultaneous consideration of site factors and program needs and the cyclical process of matching physical landscape features to the most appropriate land uses, and vice versa. However, water-saving landscape design is best achieved by placing a greater degree of emphasis on two areas: the physical ecology of plants and plant communities in relation to micro site conditions, and the human ecology of land uses in relation to potential need for additional water or irrigation above that which naturally occurs.

The second concept – the human ecology of water use – adds a new twist to the design process in that it requires the site to be analyzed according to predicted or planned human use intensity. The underlying assumption is that water is most “needed” in the landscape in places where people use the land most intensively for practical or esthetic reasons. By examining areas within the site according to the potential frequency and types of human activity, areas of water-use intensity, or “hydrozones”, can be established to enable the designer to maximize the functional efficiency and psychological effect of water and energy applications to the landscape. Through hydrozonic landscape planning and design, the water use within a given site is varied in proportion to the varying use intensities of different portions of the site. In this way, energy is also conserved, because saving water saves the energy inherent to water delivery systems, pruning and mowing, and other maintenance factors. Detailed land use, space utilization, circulation patterns, and other variables that determine water needs are important factors in the design program and must be considered throughout the planning process of the hydrozonic approach is to succeed. The hydrozone concept can be applied at any scale, and give designers and land use planners a powerful means of understanding and explaining the relationship between water and human use intensity.

Hydrozones

The principal hydrozone represents the area within the site that experiences both the greatest human impact upon the land and the largest subsequent water and energy use. On the residential scale, the principal hydrozone is generally coincidental with the backyard lawn area where people have the most direct contact with the landscape – where they play, run, sit, or lie down to relax. On the community scale, the principal hydrozone is found in local parks and gathering places such as urban plazas and spaces around well-used public buildings. Intensive human activity in the principal hydrozone justifies the greatest water and energy use here. The principal hydrozone can be thought of as a “mini-oasis”.

Areas that are visually important but less physically manipulated by human activity are contained in the secondary hydrozone; often including areas for passive recreation, space delineation, or focal interest. In the residence, this might be a prominent shrub and flower bed near the main entrance; in the community, this often includes focal plantings within parks or around public buildings, entrance plantings, or other moderately water-intensive landscape accents. The secondary hydrozone, while not as directly contacted by the users, has enough significance to merit some water and energy inputs.

Finally, the elementary hydrozone describes the area of the site that receives only natural rainfall and no supplementary water supply. Here the human use intensity is lowest. At the regional scale, the elemental hydrozone is represented by the natural or undeveloped landscape, with little or no human influence. At the residential level, utility areas, mulched parkways, unirrigated plants, or naturally existing vegetation belong to the elemental hydrozone.

By differentiating the site into its principal, secondary, minimal, and elementary hydrozones, the designer or planner is able to put the water where it is needed and to avoid extravagant use of water in areas little used or appreciated. Inherent to the hydrozonic planning concept is the need to carefully evaluate the area required for each zone and to limit the size of the principal and secondary hydrozones (which consume the most water and energy) to what is absolutely necessary for the fulfillment of the designer’s program. The attached illustration shows a matrix used to evaluate potential hydrozones.

Thus, wasting water on the areas where people have little contact, impact, or exposure to the landscape is unnecessary. Utilizing water where it is most needed and appreciated results in little change in esthetic potential or loss of visual quality. The principal hydrozone – the area of water expenditure on such things as turf, fountains, swimming pools, or well-irrigated crops – becomes more dominant and visually precious in the landscape. Water features, areas of turfgrass, or productive vegetable gardens are visually emphasized “water use nodes” of human activity.

Implementing the Hydrozone Concept

The designer wishing to save water can use the concept of “down-zoning”: When in doubt, relegate a certain landscape area to the next lowest hyrozone. For example, if a rural highway interchange only receives sporadic auto traffic and no direct human contact (by other than perhaps an occasional hitchhiker), it need not be included in the principal or secondary hydrozone, but instead should be assigned to the minimal hydrozone.

Indeed, skillful application of the hydrozone concept may enable landscape architects to transform the problem of water and energy shortage into an opportunity. By identifying areas of greatest human impact, and designing them with plant and landscape materials that invite and encourage human activity, designers can provide people with a more visually understandable and “readable” space. Today, the typical urban or suburban setting gives no clue regarding human use intensity. The front lawn, punctuated by shrubs and trees, looks exactly the same and requires exactly the same water and energy inputs as the heavily utilized private garden in the rear, yet is little used. The front lawn exists primarily as a status symbol, a visual badge of suburban confederacy. By downzoning the front yard from a primary to a secondary or minimal hydrozone, it can be designed to more accurately reflect its traditional purpose as a visual complement to the house and a reflection of the homeowner’s way of life. In other applications as well – the subdivision, the public gathering place, the community and the regional land use study – the hydrozone concept can bring diversity and visual clarity to the landscape. If water savings are less important, energy savings can be realized through differentiation of the designed landscape. For example, a large turf area may, with sufficient rainfall, remain entirely as turf, but be zoned into areas of close mowing and unmowed meadow, according to human use intensity. The closely mown area will also receive supplemental irrigation when necessary, frequent fertilization, maintenance, and other energy inputs. The unmown area, because it is less used, would be classified as a less intensive maintenance zone. Thus, hydrozoning saves maintenance energy and brings diversity into the landscape, even in situations where dramatic water savings are not sought. The hydrozone concept does not dictate design, but presents a defensible, rational process by which a water-conserving landscape design can be achieved.

Conclusions

Attaining real landscape water savings is a tremendously complex task, involving social, political and economic decisions on all levels. Yet designers and planners can encourage water savings while simultaneously shaping public attitudes toward water conservation. Landscape architects e pride themselves in being stewards of the land and its resources, but in terms of sitescale design to save water, landscape architects have failed in practice to live up to what they believe themselves to be in theory. The public and the industry need a new process, a new aesthetic, based more on design and resource integration and less on romantic nostalgia. The hydrozone concept provides both a framework for rational design and a foundation for new landscape imagery. From this, an honest and lasting landscape tradition reflecting conservation values will emerge.

Robert Thayer is Professor of Landscape Architecture and Chair of the Department of Environmental Design at UC Davis. His research and professional practice emphasizes resource-conserving practices in landscape planning and design. He has published numerous articles and won several awards for his research work.

Thomas Richman is a landscape architect and campus planner for Stanford University. His previous professional work includes design of landscape developments in California and northern India. He received degrees in classical literature from Stanford University and in landscape architecture from UC Davis.

Thayer and Richman are authors of “Water-Conserving Landscape Design, Chapter Ten in Energy Conserving Site Design, E. G. McPherson, Editor, published in 1984 by the American Society of Landscape Architects, Washington, DC.