Real Time Control of Rainwater Harvesting Systems: The Benefits of Increasing Rainfall Forecast Window

Abstract

Use of real time control (RTC) technology in rainwater harvesting systems can improve performance across water supply, flood protection, and environmental flow provision. Such systems make the most of rainfall forecast information, to release water prior to storm events and thus minimize uncontrolled overflows. To date, most advanced applications have adopted 24-hr forecast information, leaving longer-term forecasts largely untested. In this study, we aimed to predict the performance of four different RTC strategies, based on different forecast lead time and preferred objectives. RTC systems were predicted to yield comparatively less harvested rainwater than conventional passive systems but delivered superior performance in terms of flood mitigation and delivery of environmental water for streamflow restoration. More importantly, using a 7-day rainfall forecast was shown to enhance the ability of RTC in mitigating flood risks and delivering an outflow regime that is close to the natural (reference) streamflow. Such a finding suggests that RTC combined with 7-day forecast can enhance the functionality of rainwater harvesting systems to restore and even mimic the entire natural flow regimes in receiving streams. This also opens up a new opportunity for practitioners to implement smart technology in managing urban stormwater in a range of contexts and for a range of stream health objectives. Plain Language Summary "Smart tanks" based on real time control is increasingly used in rainwater harvesting systems to address water shortages, urban flooding, and streams depleted of flow. Smart tanks, controlled by real time control, can use a range of digital information (e.g., rainfall forecast) to make optimal decisions to release some tank water before heavy rain, to reduce flood risks, while still supply water to households. Globally, most uses of this technology use 1-day forecasts of rainfall. To understand the effect of longer prediction window, we compared four strategies using either 1-day or 7-day rainfall forecast and modeled their performance using specialized computer code. We found that smart tanks using 7-day rainfall forecasts are superior in reducing urban flood risks and restoring baseflows to streams. More importantly, they can release the tank water in a pattern that is similar to natural streamflow, thus helping to restore and sustain healthy waterway habitats. Our study is the first reported application of 7-day forecast information in smart control rainwater tanks. It opens up a new opportunity in managing urban water in a range of contexts and for a range of stream health objectives.

Towards Regional Scale Stormwater Flood Management Strategies through Rapid Preliminary Intervention Screening

“…This is of significance when evaluating the differences between urban greening, which is likely to have significant additional ecosystem service benefits to heat reduction, biodiversity and recreation, versus rainwater capture, which is less likely to exhibit these benefits typically associated with urban green space [3,26,29,100,103]. However, it should be noted that recent developments to urban rainwater capture infrastructure, such as community systems, active control and smart technology enabling real time catchment management may also enhance the effectiveness and benefits of capture technology [72,[102][103][104][105][106][107][108], and subsequent research should explore this further.…”

Review on mechanism and technical measures of urban rainwater harvesting

“…The accuracy of precipitation forecast can be improved by refined precipitation simulation. Xu's research showed that the flood peak time could be delayed with the help of a relatively long prediction time window [64]. Process optimization refers to optimizing the rainwater infiltration and storage facilities, such as combination type, layout area, spatial location and water flow path, which aims to maximize the amount of water stored and optimize the water quality.…”

Nature-Based Solutions and Real-Time Control: Challenges and Opportunities

“…In this way, the water stored in the stormwater harvesting system can be used to maintain the green roof through the monitoring of soil moisture and an RTC system, while maintaining optimum points of plant growth, as the green roof can treat the water and increase the possibilities of reuse, as for non-potable demands. The addition of stormwater harvesting reservoirs to green roofs can also benefit from reduced runoff and peak flow, especially when used in RTC [28][29][30] Studies show that green roofs can retain stormwater to reduce peak flow and runoff [31][32][33]. In [20], the application of movable gates with RTC was studied in an urban basin to reduce CSO by comparing scenarios using only RTC and RTC combined with passive green roofs.…”