Robert Deegan Presents
May 7, 2013
In February, Robert Deegan
, Senior Associate at Norris Design's Austin office
, had the opportunity to present to the University Landscape Manager’s Associate of Texas at their annual conference. Below is an entry written by Robert about his presentation.
"Back in February, I had the opportunity to present to the University Landscape Manager’s Associate of Texas at their annual conference. I chose to talk about water in the landscape, going beyond simply ways to conserve water and looking at ways to capture, utilize, and treat water that comes to the site through both natural and mechanical processes.
Water is a resource that is increasingly scarce; I think that’s fairly indisputable at this point. The problem is we still build infrastructure for our sites that treats water as an abundant resource when we pipe it in and a waste product as we pipe it out. My presentation focused on ways to use water more efficiently on the way in, replace potable supply with on-site water sources, and when possible find ways to cycle water back through so that the same water can be used multiple times for different purposes.
To increase efficiency of landscape water use, I focused on both improving irrigation practices and plant selection. Irrigation efficiency can be improved by converting to drip irrigation (even in turf areas), regulating pressure, and utilizing ET based controllers. ET controllers calculate water loss due to evapotranspiration by measuring temperature, wind, and humidity and automatically adjust the run times for the irrigation system to put back only the amount of water the plants need.
Plant selection is summed up by getting rid of high water-use turf, especially St. Augustine, and replacing it with native / adapted plant beds, native grasses, or even more efficient turf grass. Zoysia for shady areas and buffalo grass for sunny areas are the most water efficient turf grass choices. In a school campus setting, buffalo grass can offer an additional benefit. It’s ability to go dormant during drought periods gives campuses the option to turn off the irrigation during the hot, dry summer months when most students are not present, allowing the grass to go dormant and turn brown through the summer, then fire the irrigation back up in late summer to green things back up for the fall semester. This practice would also serve as an organic weed control as most weeds do not share buffalo grass’s extreme drought tolerance. It is important to note that buffalo grass is not appropriate for the highest traffic areas of college campuses and other sites.
The efficiency approach was best illustrated in my presentation by one of my past projects completed with another firm, the landscape renovation of the Teacher’s Retirement System in downtown Austin, Texas. This project features both a baselilne condition prior to the renovation (mostly turf, spray irrigation), and a post-renovation condition that utilizes most of the strategies discussed above: conversion of all turf to landscape native / adapted planting beds, conversion of all spray irrigation to drip, and ET-based irrigation control. Based on calculations detailed in this chart, total water use was reduced from 357,000 gallons per year (and probably more because the timer-based irrigation controller likely watered more than was needed) to 175,000 gallons / year, a better than 50% reduction.
A 50% reduction in water use is great, but as water becomes increasingly scarce, it may be that we need to go even further. Once we’ve reduced the amount of water needed to feed the landscape, alternate water sources including recycled water, rainwater, grey water, and especially condensate water become increasingly practical as alternate water sources.
Rainwater can be challenging to collect economically because you need irrigation water most in the hot, dry summer months when the rain is not falling. This leads to demands for large (and expensive) storage tanks to collect enough rainwater to get through dry months. However, there are situations where rainwater starts to make more sense economically. The Blue Moon Gardens, a Norris Design project in Tuscon, Arizona, had the benefit of an existing building with a large collection area and an existing 15,000-gallon storage tank. For the relatively small cost of a booster pump and some additional piping and controls, they were able to convert these existing assets into 45,000 gallons / year of rainwater for this community vegetable garden.
Condensate water, which is water that condenses from the air onto the cold coils of an air conditioning system, is in many ways the opposite of rainwater from a storage requirement perspective. Because we run our air conditioners most when it is hot and sunny, the condensate water supply literally scales with irrigation demand, with the maximum supply generated in July and August when it’s needed most. This allows for much smaller storage tanks, as the water can essentially be used on a daily basis as it’s generated. While an average home AC unit only generates about 5-20 gallons of condensate water per day during the summer, not enough to make much of an impact on the landscape water demand of the average residential lot, these numbers can turn far more favorable in high-density urban areas where the ratio of air conditioned space to landscaped space is much higher. For one project I worked on in San Antonio, Texas, the AC units for a 4-story, 320-unit apartment building generated up to 4,000-gallons of condensate water / day in peak months, enough to irrigate an entire 2.5-acre park, provide make-up water for a small pond, and run a small water feature. Water that most projects drain away to the sanitary sewer instead fueled a variety of landscape amenities for the project’s residents with minimal impact on City water supplies, and all with only 10,000 gallons of storage.
It’s worth noting that the best water harvesting systems capture both rainwater and condensate water. The condensate water is the primary supply in the warmer months when the air conditioning is running constantly, while the rainwater supply covers the cooler months, when air conditioning use is minimal but rainfall is typically more than sufficient to supply for the landscape’s reduced water demands. This graph shows the water supply and demand calculations for the rainwater / condensate water capture system I designed for Texas A&M’s new Liberal Arts building in College Station, Texas. It perfectly illustrates how, by combining rainwater and condensate water, total water supply exceeds landscape demand in every month, while it would frequently fall short with just rainwater or just condensate water. (All numbers are in gallons.)
The talk covered several additional areas, including recycled water, grey water, cooling tower blowdown, and stormwater as well, but I think I’ve prattled on long enough. Hopefully some of what I’ve written has inspired you to look a little deeper for ways to conserve and/or reuse water on your next project. For more information, here are some useful links. The San Antonio Water System (SAWS) is also currently developing a manual for condensate water collection which should become available later this year.
http://texaset.tamu.edu/ (ET and Rainfall data for Texas)
http://www.twdb.state.tx.us/publications/reports/rainwaterharvestingmanual_3rdedition.pdf (Texas Rainwater Harvesting Manual)
www.allianceforwaterefficiency.org (General info on water conservation)