EVALUATING TWO RAINWATER HARVESTING SYSTEMS IN AN URBAN SETTING IN OREGON'S WILLAMETTE VALLEY

INTRODUCTION

The recent trend toward more extreme periods of drought has been a shock to the residents of the Pacific Northwest – many of whom have relied upon heavy water-use in the summer months in order to make a living (i.e. producers of grass seed and sod, berries, or nursery crops), or to maintain their landscapes at high levels (i.e. certain homeowners, recreational facilities, or commercial properties). Furthermore, population growth has reached the point where even an average year of precipitation has proven insufficient for urbanities that had not previously experienced issues with water scarcity (McDonald et al., 2011). This modern climate scenario has forced people of the Pacific Northwest, and people from all around the world, to rethink their water-use strategies, as the global trend has shifted toward greater sustainability (Tilman, 2001; McDonald et al., 2011). One potential mitigation strategy for cool-humid regions, such as Oregon's Willamette Valley, is to utilize rainwater-harvesting systems to alleviate freshwater demand (Kinkade-Levario, 2007). Rainwater harvesting is a logical choice for this climate zone because the average annual precipitation (42.7-in for Corvallis, OR) is sufficient for the majority of its crop production, however, this precipitation occurs almost exclusively in a nine-month period spanning from fall to spring (US Climate Data, 1981–2010). Although annual precipitation is adequate, irrigation is still required for at least three months of every year. This study considered rainwater harvesting to be ideally suited for the cool-humid Willamette Valley; the excess rainfall in the wet season that could be stored for use in the summer months, thus decreasing demand for municipal water by an equivalent amount.

It should be stated that rainwater harvesting is not a novel idea; there have been studies dating back to the 1980's and earlier that have shown significant water-savings when retrofitting homes with new features like rainwater-harvesting systems (Boers et al., 1982, Karpisack et al., 1990). Even before that, golf courses, sporting complexes, and industrial sites alike were making use of this strategy. However, their methods typically consisted of catching rainwater via surface runoff and storing it in retention ponds (Ferguson, 1998), which is a strategy that is less applicable to the small-acreage homeowner who wants to irrigate their property without having to turn half of their backyard into a pond. Fortunately, there are alternative methods of rainwater harvesting that make a lot more sense in a residential setting, where irrigated land is small in relation to the roof-area for which rain can be easily harvested. This study documents the construction of two distinct rainwater-harvesting systems (an aboveground cistern and a belowground AQUABLOX ^™ matrix storage system), and gives insight into their advantages and disadvantages.