Resource Management and Geography - Theses
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ItemHydrology of a vegetable raingarden: implications for vegetable yield and stormwater management( 2013)Stormwater runs off the roofs and other impervious surfaces of cities at artificially high rates, and carries with it a range of contaminants. Raingardens, as biofiltration systems, are self-watering garden beds that are designed to capture and filter this urban runoff, using sandy soils and resilient plants. This improves the health of local waterways; reducing both pollution and erosion. Given these benefits, the construction of raingardens is being actively promoted in many cities, including Melbourne. However, raingardens might have another significant benefit; as sites of food production, at least on a small, non-commercial scale, using captured stormwater (urban runoff) for irrigation. The use of stormwater is an increasingly popular practice for overcoming water scarcity issues, which often constrain home vegetable gardening and other forms of urban agriculture. Nonetheless, the use of raingardens for food production has not been explored, and vegetables represent a significant departure from the types of plants that are conventionally used in these systems. As such, this thesis investigates the potential to produce vegetables in raingardens. The focus is on how water availability in a “vegetable raingarden” affects the yield of various common vegetables, as well as the role of raingardens in reducing urban runoff. These issues were explored through a 1.5-year field trial and a greenhouse (pot) experiment. This included an assessment of: 1) the merits of a sub-irrigated raingarden design relative to surface irrigation, 2) two soil types with different water-holding capacities (loamy sand, as used in conventional raingardens, and potting mix, as commonly used in vegetable gardens), and 3) reduction in both the frequency and volume of urban runoff. The results indicate that, if designed and managed effectively, it is possible to productively grow vegetables in raingardens, and the function of raingardens in reducing runoff can be retained. A wide range of common vegetables could be able to survive and produce yield in these systems. Furthermore, whether sub- or surface-irrigated, a vegetable raingarden has the potential to not require any back-up irrigation, particularly in the winter months under Melbourne conditions, and particularly if the sub-irrigated raingarden is fitted with waterproof lining so that it retains water. A lined raingarden would be reasonable for stormwater management; the system tested in the field trial reduced the volume of runoff by 63% and the frequency by 34%. However, an infiltration (unlined) raingarden type was even more effective, reducing both the volume and frequency of runoff by > 90%. Overall, sub-irrigation did not offer any clear advantages over surface irrigation in relation to vegetable growth and yield, or the efficient use of water. A traditional vegetable gardening soil or mix is the preferred soil type, because it provides relatively high water availability, and thereby greater vegetable growth and yield, compared to conventional raingarden media (loamy sand). The use of this vegetable gardening soil or mix precludes a uniform profile design for a raingarden, because a separate layer of “filter” media would be required.