Improving the Multi-Objective Performance of Rainwater Harvesting Systems Using Real-Time Control Technology

Evaluation of uncertain signals' impact on deep reinforcement learning-based real-time control strategy of urban drainage systems

Real-time control (RTC) is a recognized technology to enhance the efficiency of urban drainage systems (UDS). Deep reinforcement learning (DRL) has recently provided a new solution for RTC. However, the practice of DRL-based RTC has been impeded by different sources of uncertainties. The present study aimed to evaluate the impact caused by the uncertainties on DRL-based RTC to promote its application. The impact of uncertainties in the measurement of water level signals was evaluated through large-scale simulation experiments and quantified using measures of statistical dispersion of control performance distribution and relative change of control performance compared to the baseline scenario with no uncertainty. Results show that the statistical dispersion of DRL-based RTC was reduced by 15.48%-81.93% concerning random and systematic uncertainties compared to the conventional rule-based control (RBC) strategy. The findings indicated that DRL-based RTC is robust and could be reliably applied to safety-critical real-world UDS.

Examining How a Smart Rainwater Harvesting System Connected to a Green Roof Can Improve Urban Stormwater Management

This study quantified how a smart rainwater harvesting cistern that collected stormwater runoff from a green roof reduced stormwater flow into a combined sewer system (CSS) during wet-weather flow. The studied smart rainwater harvesting cistern collected runoff from a green roof located in Bronx, New York City; it used the Continuous Monitoring and Adaptive Control (CMAC) smart sensor provided by OptiRTC, Inc., to regulate the water flow from the cistern. The cistern collected stormwater runoff from the roof, usually draining completely after 24 h of dry weather. However, the smart sensor used weather forecasting data, and if additional rainfall was predicted immediately following another storm, the cistern only drained a specific amount, calibrated to mitigate the CSO. Five years of data from the cistern system were used to understand the role of the cistern’s smart sensor in reducing stormwater flow into the CSS during storms. The study results demonstrate that connecting the smart cistern system to the green-roof maximized stormwater collection (compared with the green roof alone) for storm sizes between 2 mm and 25 mm and for antecedent dry-weather periods greater than 2 days. The total of 65.2% of rainfall retained over the monitoring period by the green roof alone increased to 75.6% when considering the total stormwater retained and detained together by the green roof and cistern, thus yielding a 10% improvement. The study results also demonstrate that the smart sensor’s use of weather forecasting data failed to improve system performance.

Moving to a future of smart stormwater management: A review and framework for terminology, research, and future perspectives

Stormwater hazards are a significant threat across the globe. These are continuing to increase in line with urbanisation and climate change, leading to a recognition that the historic paradigm of passive management using centralised infrastructure is insufficient to manage future hazards to our society, environment, and economy. The cross-sector Internet of Things revolution has inspired a new generation of smart stormwater management systems which offer an effective, cost beneficial and adaptive solution to enhance network capacities and reduce hazards. However, despite growing prominence within research, this technology remains under-utilised, in a large part due to fragmented and inconsistent alignment and terminology, obscuring the strategic co-ordination of research. We respond to this through systematically reviewing the terminology, practice and trajectory for smart stormwater management and developing a framework which can be applied to both coordinate and understand the existing research landscape, as well as identifying key research gaps for future development. We find that literature almost universally agrees that smart technology is, or will be, beneficial to stormwater management and that technology has reached partial maturity in terms of quantity management, although this has not yet transferred to water quality. However, research is dominated by proof-of-concept modelling studies, with limited practical application beyond real time control of large assets, individual pilot studies and monitoring. We recommend that future research explores and evidences the substantial benefits likely through expanding current implementation towards a coordinated, decentralised, and optimised catchment-scale approach.

Optimizing the Control of Decentralized Rainwater Harvesting Systems for Reducing Urban Drainage Flows

The practice of rainwater harvesting (RWH) has been studied extensively in recent years, as it has the potential to alleviate some of the increasing stress on urban water distribution systems and drainage networks. Within the field, an approach of real-time control of rainwater storage is emerging as a method to improve the ability of RWH systems to reduce runoff and urban drainage flows. As applying real-time control on RWH tanks means releasing water that could be used for supply, applying controlled-release policies often hinders the RWH system’s ability to supply water. The suggested study presents an approach that has the potential to improve the capability of a distributed network of RWH systems to mitigate peak drainage flows while substantially reducing the impact on harvested rainwater availability. The suggested method uses a genetic algorithm to generate release policies, which are tailored for any given rain event and initial conditions. The algorithm utilizes the modeled drainage system’s response to a given rainfall pattern and manages to substantially reduce peak drainage flows with little impact on available rainwater when compared to the conventional no-release alternative and other active release methods.

Sustainable Urban Water Management in China: A Case Study from Guangzhou and Kunming

In China, the notion of a water sensitive city has gained popularity in urban water management as a result of the detrimental effects of flooding and pollution caused by developmental activities. Urban systems and their interrelationships are critical for long-term urban water management and water sensitivity. This article is a case study considering how a strength, weakness, opportunities, and threat (SWOT) analysis-based approach to urban water management interventions in Guangzhou and Kunming cities (China) enables decision makers to identify solutions for cities to become more water-sensitive and resilient. The similar difficulties and rewards with respect to the contexts of both cities were synthesized using SWOT analysis. The contextual SWOT analysis, in conjunction with the comprehensive inclusion of Sustainable Development Goals (SDGs) in intervention planning in these cities, revealed that a water-sensitive-cities approach requires the establishment of a comprehensively multi-objective rainwater management system; this approach would have the goals of reducing rainwater draining sources, controlling processes and adaptive measures, and governing the system to make it more resilient. The water strategy should be holistic and adaptive, capable of providing a broad range of ecological services and other social benefits consistent with the fulfilment of the Sustainable Development Goals, and adaptable to other Chinese cities seeking to achieve water sensitivity.

Impact of roof rain water harvesting of runoff capture and household consumption

In recent years, the occurrence of floods is one of the most important challenges facing in Hamadan city. In the absence/inefficiency of urban drainage systems, rainwater harvesting (RWH) systems as low-impact development (LID) methods can be considered as a measure to reduce the floods. In this study, three scenarios concerning the RWH from the roof surfaces are studied to evaluate the type of the harvested water on reducing flooding. In the first scenario, which indicates the current situation in the studied area, it is indicated that there is no harvest of the roof surfaces in the studied area. The second scenario is about the use of water harvested from the roof surfaces for household purposes. The third scenario also refers to the use of harvested water for irrigation of gardens. The simulation results of these three scenarios using the Soil Conservation Service (SCS) method in the Hydrologic Modeling System (HEC-HMS) model reveal that if the second scenario is implemented, the runoff volume decreases from 28 to 12% for the return period from 2 to 100 years. However, in the third scenario, this reduction in runoff volume will be 48 and 27% for return periods of 2 to 100 years, respectively. Therefore, the results of this study indicate that the use of harvested water can also affect the reduction on runoff volume.

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

Nature-based solutions (NBS) as green infrastructures to urban drainage are an effective mitigation strategy both in terms of quantity and quality of runoff. Real-time control (RTC) can complement both flood mitigation and improvement of water quality by controlling elements of the drainage and sewage system. This study assessed the improvement opportunities with RTC of three NBS-related techniques commonly applied in urban drainage with different spatial scales: green roof, bioretention and detention basin and the remaining challenges to integrate both methods. Additionally, our investigations showed that the main difficulties reported involve the planning and monitoring stages of the RTC system. All of the studied devices can benefit from RTC. It is possible to observe that, despite the good results reported in the literature, the application of RTC to NBS studies on urban drainage are very recent. There are several opportunities that can be explored to optimize the performance.

Quantifying the performance of dual-use rainwater harvesting systems

Rainwater harvesting systems in urban settings are increasingly relied upon to mitigate pluvial flooding on top of providing an additional water supply. Alternative designs have been proposed to support their dual use. Stormwater management performance is typically evaluated through long-term averages. However, long-term assessment is not aligned with the goal of attenuating the impacts of short duration high-intensity rainfall events. This paper contributes a framework for evaluating the dual-use performance of design alternatives. The framework incorporates a set of stormwater management metrics that provides a robust characterisation of performance during significant rainfall events. To the usual long-term volumetric retention metric, we add: 1) metrics that represent the total volume and duration above predevelopment (greenfield) runoff rates; and 2) robust peak outflow rate and retention efficiencies based on the long-term median of a representative sample of significant rainfall events. Our multi-criteria performance visualisations of alternative dual-use designs highlight the importance of carefully designing the forecast-based controlled release mechanisms built into active systems. This work has direct implications for design guidance standards, which we discuss.

Financial Sustainability of Selected Rain Water Harvesting Systems for Single-Family House under Conditions of Eastern Poland

Recent climate changes limiting the available water resources require careful sustainable water management in the cities, the locations of highest drinking water consumption and sanitary sewage and stormwater generation. Over 50% of water demand in the residential areas of cities cover activities in which non-potable water could be used, e.g., toilets and laundry facilities, cleaning, garden irrigation and washing vehicles. Thus, rain water harvesting (RWH) systems are the sustainable alternative water supply, lowering drinking water consumption, by the usage of non-potable harvested water, and limiting the anthropopressure on natural water reservoirs. However, in many cases the social acceptance of RWH and willingness to pay may be affected by financial sustainability, including the affordability and profitability of the investment. This paper presents a case study concerning the financial sustainability of thirteen designs of RWH systems for a single-family house under the climatic and economic conditions of Eastern Poland, one of the poorest regions of the European Union. The financial sustainability of the tested RWH designs were based on indictors of cost-efficiency: dynamic generation cost, payback period, net present value and benefit–cost ratio. The performed analyses showed the limited profitability of the studied RWH designs and the insufficient governmental financial support which may significantly affect the social sustainability of the designs under the local conditions.

A Critical Evaluation of the Water Supply and Stormwater Management Performance of Retrofittable Domestic Rainwater Harvesting Systems

Rainwater harvesting systems are often used as both an alternative water source and a stormwater management tool. Many studies have focused on the water-saving potential of these systems, but research into aspects that impact stormwater retention—such as demand patterns and climate change—is lacking. This paper investigates the short-term impact of demand on both water supply and stormwater management and examines future and potential performance over a longer time scale using climate change projections. To achieve this, data was collected from domestic rainwater harvesting systems in Broadhempston, UK, and used to create a yield-after-spillage model. The validation process showed that using constant demand as opposed to monitored data had little impact on accuracy. With regards to stormwater management, it was found that monitored households did not use all the non-potable available water, and that increasing their demand for this was the most effective way of increasing retention capacity based on the modelling study completed. Installing passive or active runoff control did not markedly improve performance. Passive systems reduced the outflow to greenfield runoff for the longest time, whereas active systems increased the outflow to a level substantially above roof runoff in the 30 largest events.

Real-Time, Smart Rainwater Storage Systems: Potential Solution to Mitigate Urban Flooding

Urban water systems are being stressed due to the effects of urbanization and climate change. Although household rainwater tanks are primarily used for water supply purposes, they also have the potential to provide flood benefits. However, this potential is limited for critical storms, as they become ineffective once their capacity is exceeded. This limitation can be overcome by controlling tanks as systems during rainfall events, as this can offset the timing of outflow peaks from different tanks. In this paper, the effectiveness of such systems is tested for two tank sizes under a wide range of design rainfall conditions for three Australian cities with different climates. Results show that a generic relationship exists between the ratio of tank:runoff volume and percentage peak flow reduction, irrespective of location and storm characteristics. Smart tank systems are able to reduce peak system outflows by between 35% and 85% for corresponding ranges in tank:runoff volumes of 0.15–0.8. This corresponds to a relative performance improvement on the order of 35% to 50% compared with smart tanks that are not operated in real-time. These results highlight the potential for using household rainwater tanks for mitigating urban flooding, even for extreme events.

Urban stormwater characterization, control, and treatment

This review summarizes over 250 studies published in 2018 related to the characterization, control, and management of urban stormwater runoff. The review covers three broad themes: (a) quantity and quality characterization of stormwater, (b) control and treatment of stormwater runoff, and (c) implementation and assessment of watershed-scale green stormwater infrastructure (GSI). Each section provides an overview of the 2018 literature, common themes, and future work. Several themes emerged from the 2018 literature including exploration of contaminants of emerging concern within stormwater systems, characterization and incorporation of vegetation-driven dynamics in stormwater control measures, and the need for interdisciplinary perspectives on the implementation and assessment of GSI. PRACTITIONER POINTS: Over 250 studies were published in 2018 related to the characterization, control, and treatment of stormwater. Studies cover general stormwater characteristics, control and treatment systems, and watershed-scale assessments. Trends in 2018 include treatment trains, vegetation dynamics, and interdisciplinary perspectives.

Linkages between flow regime, biota, and ecosystem processes: Implications for river restoration

River ecosystems are highly biodiverse, influence global biogeochemical cycles, and provide valued services. However, humans are increasingly degrading fluvial ecosystems by altering their streamflows. Effective river restoration requires advancing our mechanistic understanding of how flow regimes affect biota and ecosystem processes. Here, we review emerging advances in hydroecology relevant to this goal. Spatiotemporal variation in flow exerts direct and indirect control on the composition, structure, and dynamics of communities at local to regional scales. Streamflows also influence ecosystem processes, such as nutrient uptake and transformation, organic matter processing, and ecosystem metabolism. We are deepening our understanding of how biological processes, not just static patterns, affect and are affected by stream ecosystem processes. However, research on this nexus of flow-biota-ecosystem processes is at an early stage. We illustrate this frontier with evidence from highly altered regulated rivers and urban streams. We also identify research challenges that should be prioritized to advance process-based river restoration.

Advanced Operating Technique for Centralized and Decentralized Reservoirs Based on Flood Forecasting to Increase System Resilience in Urban Watersheds

The frequency of inundation in urban watersheds has increased, and structural measures have been conducted to prevent flood damage. The current non-structural measures for complementing structural measures are mostly independent non-structural measures. Unlike the current non-structural measures, the new operating technique based on flood forecasting is a real-time mixed measure, which means the combination of different non-structural measures. Artificial rainfall events based on the Huff distribution were used to generate preliminary and dangerous thresholds of flood forecasting. The new operation for centralized and decentralized reservoirs was conducted by two thresholds. The new operation showed good performance in terms of flooding and resilience based on historical rainfall events in 2010 and 2011. The flooding volume in the new operation decreased from 6617 to 3368 m3 compared to the current operation in 2010, and the flooding volume in 2011 decreased from 664 to 490 m3. In the 2010 event, the results of resilience were 0.831835 and 0.866566 in current and new operations, respectively. The result of resilience increased from 0.988823 to 0.993029 in the 2011 event. This suggestion can be applied to operating facilities in urban drainage systems and might provide a standard for the design process of urban drainage facilities.

Real-Time Integrated Operation for Urban Streams with Centralized and Decentralized Reservoirs to Improve System Resilience

Recently, the number of extreme rainfall events has increased because of climate change. The ever-widening impervious area in urban watersheds also continuously augments runoff volume. Most measures to prevent urban inundation are structural, such as the construction, rehabilitation, and replacement of urban drainage facilities. Because structural measures require time and money, nonstructural measures are also required for the efficient prevention of urban inundation. Current operations in Korea focus on the individual operation of urban drainage facilities while neglecting the status of effluent streams. A study on urban drainage facilities that considers the status of urban streams is necessary to improve the operation of drainage facilities in urban areas. A revised resilience index is suggested to evaluate measures. For the historical rainfall event in 2010, the system resilience for current and integrated operations was 0.199 and 0.238, respectively. For the 2011 event, the system resilience for current and integrated operations was 0.064 and 0.235, respectively. The integrated operation exhibited good performance for the 2010 and 2011 events. Based on the results of this study, an operation as a nonstructural measure for the total management of urban areas is proposed. The revised resilience index could support decision-making processes for flood-management plans.