| Rainwater harvesting (RWH) has traditionally been implemented in areas with (semi-)arid climates or limited access to potable water supplies; however, recent droughts in the humid southeastern United States (US) have led to increased implementation of RWH systems. In this region (including the state of North Carolina (NC)), water is generally not considered a limited resource and sufficient rainfall year-round creates a perception of abundance. Despite recent droughts in the southeast US, this perception of abundance persists. Chapter 2 is an examination of usage characteristics of four RWH systems installed in humid NC, as compared to systems located in arid/semi-arid regions. Results of this research indicated a considerable difference in usage patterns of NC RWH systems compared to systems in (semi-)arid regions and established the need for identifying and implementing secondary objectives for these systems, namely stormwater management. Otherwise, the expense and effort required to implement RWH systems in humid areas will most likely preclude their use.;Rainwater harvesting systems are unique in their ability to provide the dual benefits of (1) acting as alternate water supply sources and (2) providing detention/retention of roof runoff that would otherwise become stormwater runoff. The ability of a RWH system to capture runoff typically relies on the extraction of water from the tank to meet water demands (i.e. to create available storage in the tank for runoff capture). As discussed in Chapter 2, the majority of systems employed in NC are used to meet infrequent, discretionary demands or seasonal demands such as irrigation. Consequently, these systems provide minimal benefits with respect to stormwater management. Chapter 4 presents two innovative methods, passive and active release mechanisms, as a means of enhancing the stormwater management benefits of RWH systems while preserving their water conservation benefits. A passive release mechanism creates a dual-purpose system by dividing a storage tank into two portions: the detention storage volume, which is slowly drained between storm events, and the retention storage volume, which is retained for use. The active release mechanism includes a real-time control device that automatically releases harvested water based on real-time forecasted precipitation and current conditions within the RWH system. Monitoring results indicated that each of these mechanisms substantially increased stormwater runoff volume and peak flow reductions provided by a RWH system, while still allowing the majority of user demands (and, thus, potable water conservation goals) to be met.;RWH systems used for irrigation often provide fewer stormwater management benefits than systems used for year-round, non-discretionary purposes, as there is diminished demand for harvested rainwater during the non-growing season or rainy periods. Thus, identifying demands during these periods would improve the stormwater mitigation potential of these systems. Research presented in Chapter 5 evaluates how irrigating bermudagrass year-round at rates greater than those required by the turf affected the stormwater benefits provided by a RWH system. Results indicated significant increases in runoff volume and peak flow reductions when turf was irrigated at 25 mm/week and 51 mm/week, compared to an evapotranspiration/effective precipitation-based regime. There were no noted increases in soil moisture content, pest occurrences or wet weather contributions, nor were there significant differences in turf quality or soil nitrate movement.;Collecting and storing runoff via RWH systems can potentially provide water quality benefits due to physical and chemical processes that occur within the storage tank. Chapter 3 quantifies the water quality improvement provided by storing rooftop runoff via RWH systems in NC. Results showed that RWH systems can significantly lower nutrient concentrations of incoming roof runoff. A lack of significant TSS reduction was likely attributable to low, "irreducible" concentrations of TSS in the roof runoff. These findings suggest that stormwater benefits associated with RWH are not only limited to hydrologic mitigation, but also include reductions in concentrations of nitrogen and phosphorus species. |
