Kathy M. DeBusk

Urban rainwater harvesting systems : research, implementation and future perspectives

While the practice of rainwater harvesting (RWH) can be traced back millennia, the degree of its modern implementation varies greatly across the world, often with systems that do not maximize potential benefits. With a global focus, the pertinent practical, theoretical and social aspects of RWH are reviewed in order to ascertain the state of the art. Avenues for future research are also identified. A major finding is that the degree of RWH systems implementation and the technology selection are strongly influenced by economic constraints and local regulations. Moreover, despite design protocols having been set up in many countries, recommendations are still often organized only with the objective of conserving water without considering other potential benefits associated with the multiple-purpose nature of RWH. It is suggested that future work on RWH addresses three priority challenges. Firstly, more empirical data on system operation is needed to allow improved modelling by taking into account multiple objectives of RWH systems. Secondly, maintenance aspects and how they may impact the quality of collected rainwater should be explored in the future as a way to increase confidence on rainwater use. Finally, research should be devoted to the understanding of how institutional and socio-political support can be best targeted to improve system efficacy and community acceptance.

Bioretention Outflow: Does It Mimic Nonurban Watershed Shallow Interflow?

Bioretention, a key structural practice of low impact development (LID), has been proved to decrease peak flow rates and volumes, promote infiltration and evapotranspiration, and improve water quality. Exactly how well bioretention mimics predevelopment (or “natural”) hydrology is an important research question. Do bioretention outflow rates mirror shallow groundwater interevent stream recharge flow associated with natural or nonurban watersheds? Streamflow from three small, nonurban watersheds, located in Piedmont, part of central North Carolina, was compared with bioretention outflow from four cells also in North Carolina’s Piedmont region. Each benchmark watershed drained to a small stream, where flow rate was monitored for an extended period of time. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream interevent flow. Results indicate that there is no statistical difference between flow rates in streams draining unde...

Bioretention Outflow: Does It Mimic Rural Water Interflow?

Bioretention, a key structural practice of Low Impact Development (LID), has been proven to decrease peak flow rates and volumes, promote infiltration and evapotranspiration and improve water quality. Exactly how well bioretention mimics pre-development (or natural) hydrology is an important research question. Do bioretention outflow rates mirror shallow groundwater inter-event stream recharge flow associated with natural or non-urban watersheds? Streamflow from three small, non-urban watersheds, located in the Piedmont of central North Carolina, was compared to bioretention outflow from four cells also in North Carolinas Piedmont region. Each benchmark watershed drained to a small stream, where flow rate was monitored for an extended period of time. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream inter-event flow. Results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 hours following the commencement of flow. Similarly, there is no statistical difference between the cumulative volumes released by the two systems during the 48 hours following the start of flow. These results indicate that bioretention cells behave comparably to watersheds in natural or non-urban conditions with respect to both flow rates and flow volumes and suggest that bioretention outflows may mirror post storm event shallow groundwater inter-event stream recharge flow. Solely considering bioretention outflow as a conjugate to runoff may be a misinterpretation of a flowrate that actually resembles shallow interflow.

Bioretention Outflow: Does it Mimic Non-Urban Watershed Shallow Interflow?

Bioretention, a key structural practice of Low Impact Development (LID), has been proven to decrease peak flow rates and volumes, promote infiltration and evapotranspiration and improve water quality. Exactly how well bioretention mimics pre-development (or natural) hydrology is an important question that continues to be researched. Do bioretention outflow rates mirror shallow groundwater inter-event stream recharge flow associated with natural watersheds? Three small, undeveloped watersheds, located in the piedmont of central North Carolina, were chosen to represent natural hydrology. These watersheds ranged from 50 to 78ha and were comprised primarily of forest and pastureland. Each drained to a small stream, where flow rate was monitored for an extended period of time. Data collected from the natural watersheds was compared to outflow rates from four bioretention cells. The cells selected are located within the piedmont region and drain predominantly urban watersheds ranging from 0.2 to 0.9ha in size. Flow rates and cumulative volumes were determined for each site at the following intervals after stormflow/outflow began: 3, 6, 12, 18, 24, 30, 36, 42 and 48 hours. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream inter-event flow. Nonparametric statistical analyses were performed on the datasets using the Wilcoxon signed rank test. Results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 hours following the commencement of flow. Similarly, there is no statistical difference between the cumulative volumes released by the two systems during the 48 hours following the start of flow. These results indicate that bioretention cells behave comparably to natural, undeveloped conditions with respect to both flow rates and flow volumes and that bioretention outflows somewhat mirrow post storm event shallow groundwater recharge.

Certifying the Landscape Community in Rain Garden Installation: The North Carolina Experience

Low Impact Development (LID) stormwater practices are being utilized to a greater extent in new construction to mitigate pollutant loads and hydrologic impacts associated with development. However, many cities are faced with existing non-LID developments, and may be forced, through legislation, to implement stormwater retrofits. Homeowners are often interested in improving water quality in their neighborhood, and backyard rain gardens are one practice that have become popular in North Carolina. Few homeowners have the technical knowledge to size and construct a rain garden; therefore, they often hire a landscaper to complete these tasks. Faculty at N.C. State University and extension agents in the N.C. Cooperative Extension have developed a 1.5 day certification course that offers landscapers a detailed understanding of how to properly site, design, install, and maintain a residential rain garden. Attendees listen to six hours of presentations on rain gardens, and then take a two hour tour of local rain gardens that have previously been installed. On the second day of the workshop, attendees take both an in-class and a field exam. Four workshops have been delivered in the past 9 months, with a total of 73 people certified. Some of these landscapers are actively advertising their certification. Similar programs could easily translate to other communities throughout the country. Rain gardens help to control runoff at its source, and may make meeting watershed-wide LID hydrology goals easier to obtain.

Demonstration and Monitoring of Rainwater Harvesting Technology in North Carolina

Water conservation has grown in importance across North Carolina, as much of the state has recently suffered moderate to severe drought conditions. In addition to meeting water conservation needs, rainwater harvesting systems (cisterns) have an important application in low impact development (LID) as innovative stormwater management practices. A total of four cisterns were installed in each of the main physiographic regions of North Carolina: Craven County (coastal plain), Cumberland County (sandhills), Guilford County (piedmont), and Watauga County (mountain). These systems demonstrate above ground and in-ground applications. Uses for the captured stormwater include irrigating landscapes and gardens, washing vehicles, an additive for brine applied to icy streets and flushing kennels at an animal shelter. Each site is being monitored for water quantity and usage, and one system is monitored for water quality. Results will help establish the water quantity and quality benefits of rainwater harvesting systems and will influence design recommendations to be incorporated in the State of North Carolina’s new Stormwater BMP Design Manual.

Alternative Site-Assessment Hydrologic Metrics for Urban Development

Urban development increases surface runoff volumes and peak flows, which result in water quality degradation and the impairment of surface water bodies. The concept of low impact development (LID) arose in response to the negative impacts of development and traditional stormwater management. This paper discusses two novel approaches for evaluating a site’s adherence to LID principles. The first approach includes an evaluation of the pre- and post-development hydrologic components for a site and establishing a set of percentages that indicates how much of the total precipitation leaves the site as runoff, infiltration and evapotranspiration. Experimental data were used to generate representative percentages for various land use types in North Carolina. The second approach applies the SWMM model to a specific location and calculates a watershed stream’s flow volume and duration for a given curve number. The change in the curve number from pre- to post-development conditions is determined and the corresponding change in duration and/or volumes is calculated relative to a target number for duration/volume. This percent decrease is then assigned a point value which a developer may use for credit. These methods will provide developers with a tangible, numeric goal for post-development hydrology while allowing flexibility in how that goal is achieved.