by Michael Igo, PE, LEED AP, Affiliate ASLA
Water conservation is an important topic in landscape architecture, as its professionals are stewards of the built and natural environment for society. Without a balanced water supply, drinking water, sanitation, ecological balance, and safety cannot be secured for our existence. Thus, when we speak of water conservation, what we really mean is freshwater or domestic water conservation.
Furthermore, some of the areas of water conservation discussed below are not only about water quantity conservation, but also water quality conservation in our natural surroundings. The adage “an ounce of prevention is worth a pound of cure” is true in water conservation in the sense that not only does saving and using less water in landscapes reduce the quantity of water consumed, but it also prevents poor quality water for reuse or filtering site water from being reintroduced into the environment and conserves existing precious clean freshwater for domestic uses and for habitats.
Below are some of the major areas of concern that the ASLA Water Conservation Professional Practice Network (PPN) and ASLA members should keep in mind in their practice.
Stormwater
When a site is altered from its natural or previously disturbed state, the patterns of rainfall runoff and infiltration are also altered. Natural areas that were once reliant on ample infiltration can be deprived of recharge from paved and developed sites by sealing off underground soils from the atmosphere or just by increasing the velocity of water movement across a site such that runoff does not have time to infiltrate. High velocity, unmitigated stormwater flow can cause erosion of valuable land areas, transport sediment that could fill in and cause eutrophication of natural water bodies, cause damage to sites and structures downstream, and serve as a massive heat exchanging liquid as rain falls on, passes across, and carries away the latent heat trapped in urban pavement—polluting otherwise ecologically-balanced freshwater supplies and habitats.
Understanding how stormwater moves through, how to control its velocity, and its impacts leaving a site are critical to water conservation. With properly designed controls, stormwater can also be reintroduced as groundwater recharge to mimic the infiltration a site would have received if it were not developed.
However, despite how much of a concern stormwater can be, it can serve as an alternate to domestic potable water for site uses such as irrigation, water features, toilet flushing, and cooling towers. By capturing runoff and sequestering it in storage facilities prior to site discharge, it is possible to store sufficient amounts of water for non-potable water uses—further conserving freshwater. Stormwater is an important water conservation topic not only to preserve domestic water for human consumption, but also to conserve the natural water balance of a site or regional ecology.
Irrigation
In order to keep our planted landscapes healthy and thriving, irrigation is required not only at the very least to establish roots, but also to help plants achieve maturity. Irrigation is one of the major loose ends in not only water conservation in landscape architecture, but also regional water supply and watershed management. In years past, landscape irrigation has been uncontrolled, especially at the residential level. Controls are set to dispense water to cover the peak summer day plant consumption every day, whether it is spring, summer, fall, hot, cold, dry, or raining.
However, weather-based and soil moisture-based irrigation controls are within reach of any budget today. Soil moisture sensors only allow irrigation if the soil is acceptably dry. Weather-based controls automatically adjust irrigation running times to run shorter on cooler days and longer on hotter days. In fact, controllers that receive data from local weather stations via the Internet can forecast when rainfall will occur and start to taper or suspend irrigation in order to take advantage of the natural watering cycle to come. In addition to controls, water conserving irrigation design involves understanding plant species, water movement through soils, and application uniformity to use the least amount of water and still achieve healthy plants.
Water Features
It has been said that humans are attracted to gold because its shine is like that of a shimmering stream of water in the sun. It may be that the vision and sound of running water soothes humans’ deep-rooted fears when we were hunter-gatherers. There is no doubt that water features, fountains, spillways, flumes, and pools can provide endless enjoyment and recreation as centerpieces or accents to a built landscape. However, pass-through, or once-through systems, without recirculation waste substantial amounts of water—especially with water features that operate continuously. A small pass-through water feature that uses 10 gallons per minute from a municipal water supply will dump 14,400 gallons into the sewer or storm drain system per day! Even recirculating fountains with misaligned and over-pressurized nozzles, excessive wind drift, and poor maintenance can lead to substantial water waste where spray or mist falls outside the recirculation loop and domestic makeup water will have to be continually added in order keep reservoirs full.
Opting for recirculating systems with proper water quality management for aesthetics and preventing the spread of waterborne diseases dramatically reduces the amount of freshwater that could be used for local drinking water and sanitation systems. Moreover, designers should select water features and nozzles that are appropriate for a site depending on prevailing wind, human contact, and spatial constraints. Water features can be automatically controlled for various conditions such as weather (wind and rain) and actual interaction by people through motion sensing—saving water while no one is around. Design, construction, and maintenance of water features today has to come under more scrutiny from a water conservation perspective. Even for pass-through systems, there is ample opportunity to capture the outflow for non-potable water users such as irrigation, cooling and heating buildings, and toilet flushing.
Building Water Waste and Reuse
In the built environment, there are many mechanical processes that consume water. While a landscape architect may not be privy to or responsible for these processes, it is important to understand that they can provide an opportunity to capture and reuse water within the landscape. For example, a great source of non-potable water for irrigation and water features is condensate from large-scale air conditioning units. Water extracted from air through the dehumidifying interior air can be directed from these units to storage facilities located indoors or outdoors. It is highly recommended and, in many cases, legally required to filter and disinfect this water prior to reuse in a landscape as waterborne diseases like Legionella can be transported from condenser coils and other mechanical systems during the harvesting process.
Another potential source of non-potable water from buildings is basement dewatering systems via sump pumps or under-drain systems. In areas with a high groundwater table, a building’s dewatering system can generate continuous supplies of water available for capture or reuse that would otherwise be discharged to sewer, stormwater drains, or nearby streams and wetlands. A simple 20 gallon per minute basement dewatering system can generate nearly 30,000 gallons of water per day that could be used for any number of landscape or building non-potable water use.
By finding opportunities to capture water that would otherwise be wasted and discharged to the environment and building projects, substantial freshwater can be conserved for more important uses locally and regionally.
Wetlands
Wetlands are nature’s filters for runoff. In addition to providing a habitat to many insects and animals that provide ecological balance, they serve to capture water that must percolate through mineral-rich and well-graded soils and also to hold water for various plant material to use and transpire—maintaining water flows, drawing dissolved pollutants into their root systems, and preventing erosion. However, the built environment can infringe upon a natural wetland’s functionality when the watersheds and areas immediately surrounding them change dramatically—such as natural woodlands to parking lots or meadows to lawns.
Site plan designs that incorporate “buffer zones” and “no disturbance areas” around their edges can help to maintain a natural wetland’s integrity. In addition, designing a new stormwater management system to slowly release water off site to wetlands and mimic natural flows can further increase their viability post-construction. Proper site stormwater design also prevents erosion that would otherwise fill in wetlands with soil and nutrients transported during rainstorms.
While natural wetlands are necessary to conserve for ecology balance, constructed or artificial wetlands on a site can be used to slow down and store stormwater prior to re-entry into the environment, serve as a groundwater recharge point for infiltration, and be used to filter stormwater for reuse in irrigation, water features, and interior mechanical non-potable water uses. Using the natural processes shaped by evolution, we can create and harness the filtering capability of wetlands for the built environment. Reintroducing filtered water back to aquifers and streams helps to offset our water demands from these resources.
Summary
Water conservation in landscape architecture is not just about using less water that could be used for human consumption. It is also about recognizing and understanding how water works, the technological advances in systems automation, and working with other disciplines to find ways to capture water that would otherwise be wasted to the surrounding environment.
Michael Igo, PE, LEED AP, Affiliate ASLA, is President of Aqueous Consultants, LLC. He will be presenting a live ASLA Online Learning presentation, hosted by the ASLA Water Conservation Professional Practice Network (PPN), this upcoming March—stay tuned for more details.