Quantifying the performance of dual-use rainwater harvesting systems

Robust optimisation of combined rainwater harvesting and flood mitigation systems

Combined large-scale rainwater harvesting (RWH) and flood mitigation systems are promising as a sustainable water management strategy in urban areas. These are multi-purpose infrastructure that not only provide a secondary, localised water resource, but can also reduce discharge and hence loads on any downstream wastewater networks if these are integrated into the wider water network. However, the performance of these systems is dependent on the specific design used for its local catchment which can vary significantly between different implementations. A multitude of design strategies exist, however there is no universally accepted standard framework. To tackle these issues, this paper presents a two-player optimisation framework which utilises a stochastic design optimisation model and a competing, high-intensity rainfall design model to optimise passively-operated RWH systems. A customisable tool set is provided, under which optimisation models specific to a given catchment can be built quickly. This reduces the barriers to implementing computationally complex sizing strategies and encouraging more resource-efficient systems to be built. The framework was applied to a densely populated high-rise residential estate, eliminating overflow events from historical rainfall. The optimised configuration resulted in a 32% increase in harvested water yield, but its ability to meet irrigation demands was limited by the operational levels of the treatment pump. Hence, with the inclusion of operational levels in the optimisation model, the framework can provide an efficient large-scale RWH system that is capable of simultaneously meeting water demands and reducing stresses within and beyond its local catchment.

Impact of residential rainwater harvesting on stormwater runoff

Population increase, climate change and soil impermeability are factors causing floods in large urban centres. Such places also always have water shortage problems. This research aims to evaluate the influence of rainwater harvesting in residential buildings on stormwater in a basin located in southern Brazil (Rio Cachoeira Basin). Urbanised and non-urbanised areas, soil types, curve numbers and time of concentration of each sub-basin were taken into account. Through the HEC-HMS programme, it was possible to calculate hydrographs for the base scenario (when there is no rainwater harvesting). Then, rainwater tanks for the residential buildings were sized using the computer programme Netuno. In the second scenario, there is rainwater harvesting in all residential buildings. Thus, the hydrographs for the second scenario were also calculated. The peak flow reduction potentials for the sub-basins ranged from 2.7% to 14.3%. The highest percentage (14.3%) did not occur in the sub-basin with the most extensive roof area; such highest peak flow reduction occurred in Bom Retiro sub-basin. In Bom Retiro sub-basin, there are more houses than multi-storey residential buildings. Even when considering the full potential of rainwater harvesting for roof areas of all existing buildings in the Rio Cachoeira Basin, the average potential reduction in peak flow was 7.2%. The conclusion is that rainwater tanks in residential buildings have little influence on stormwater runoff, and the stormwater runoff will be less affected when the area of the hydrographic basin is larger. Thus, the reduction in peak flows is insignificant when considering the flooding in the region.

Changes in the Amount of Rainwater in the Roztocze National Park (Poland) in 2001–2020 and the Possibility of Using Rainwater in the Context of Ongoing Climate Variability

Data for the years 2001–2020 on changes in the amount of rainwater in the Roztocze National Park (RNP) in the catchment area of the Świerszcz River (Poland) were investigated to evaluate the possibility of using rainwater in the park for various purposes in the context of ongoing climate variability. An analysis of data from the RNP’s Integrated Monitoring of the Natural Environment showed that the average annual air temperature increased by 2.1 °C over the 20-year period, while the amount of precipitation decreased, especially in the winter seasons. These changes periodically led to a negative hydrological balance. As an effect, the groundwater table was gradually lowering, the flow of the Świerszcz River was reduced, and there were periodic shortages of water feeding the Echo Ponds. Water shortages also negatively affected the flora and fauna of the RNP. In order to quantitatively protect the Park’s water resources, a proposition was made to build a rainwater management system at the Animal Breeding Centre in Florianka to provide water for watering Polish Konik horses, flushing toilets, washing cars and agricultural equipment, and fire-prevention purposes. The excess water would be discharged to a nearby pond, which is an amphibian breeding site. It was estimated that the system was capable of meeting 100% of the demand for lower-quality water in the summer period. Moreover, it was determined that 9109 m3 of rainwater could be obtained annually from the roofs of all public utility buildings located in the RNP.

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.

Management of Urban Waters with Nature-Based Solutions in Circular Cities—Exemplified through Seven Urban Circularity Challenges

Nature-Based Solutions (NBS) have been proven to effectively mitigate and solve resource depletion and climate-related challenges in urban areas. The COST (Cooperation in Science and Technology) Action CA17133 entitled “Implementing nature-based solutions (NBS) for building a resourceful circular city” has established seven urban circularity challenges (UCC) that can be addressed effectively with NBS. This paper presents the outcomes of five elucidation workshops with more than 20 European experts from different backgrounds. These international workshops were used to examine the effectiveness of NBS to address UCC and foster NBS implementation towards circular urban water management. A major outcome was the identification of the two most relevant challenges for water resources in urban areas: ‘Restoring and maintaining the water cycle’ (UCC1) and ‘Water and waste treatment, recovery, and reuse’ (UCC2). s Moreover, significant synergies with ‘Nutrient recovery and reuse’, ‘Material recovery and reuse’, ‘Food and biomass production’, ‘Energy efficiency and recovery’, and ‘Building system recovery’ were identified. Additionally, the paper presents real-life case studies to demonstrate how different NBS and supporting units can contribute to the UCC. Finally, a case-based semi-quantitative assessment of the presented NBS was performed. Most notably, this paper identifies the most typically employed NBS that enable processes for UCC1 and UCC2. While current consensus is well established by experts in individual NBS, we presently highlight the potential to address UCC by combining different NBS and synergize enabling processes. This study presents a new paradigm and aims to enhance awareness on the ability of NBS to solve multiple urban circularity issues.

Revealing the Challenges of Smart Rainwater Harvesting for Integrated and Digital Resilience of Urban Water Infrastructure

Smart rainwater harvesting (RWH) systems can automatically release stormwater prior to rainfall events to increase detention capacity on a household level. However, impacts and benefits of a widespread implementation of these systems are often unknown. This works aims to investigate the effect of a large-scale implementation of smart RWH systems on urban resilience by hypothetically retrofitting an Alpine municipality with smart rain barrels. Smart RWH systems represent dynamic systems, and therefore, the interaction between the coupled systems RWH units, an urban drainage network (UDN) and digital infrastructure is critical for evaluating resilience against system failures. In particular, digital parameters (e.g., accuracy of weather forecasts, or reliability of data communication) can differ from an ideal performance. Therefore, different digital parameters are varied to determine the range of uncertainties associated with smart RWH systems. As the results demonstrate, smart RWH systems can further increase integrated system resilience but require a coordinated integration into the overall system. Additionally, sufficient consideration of digital uncertainties is of great importance for smart water systems, as uncertainties can reduce/eliminate gained performance improvements. Moreover, a long-term simulation should be applied to investigate resilience with digital applications to reduce dependence on boundary conditions and rainfall patterns.

Uptake and Dissemination of Multi-Criteria Decision Support Methods in Civil Engineering—Lessons from the Literature

The SCOPUS and Wed of Science bibliometric databases were searched for papers related to the use of multi-criteria methods in civil engineering related disciplines. The results were analyzed for information on the reported geographical distribution of usage, the methods used, the application areas with most usage and the software tools used. There was a wide geographical distribution of usage with all northern hemisphere continents well represented. However, of the very many methods available, a small number seemed to dominate usage, with the Analytic Hierarchy Process being the most frequently used. The application areas represented in the documents found was not widely spread and mainly seemed to be focused on issues such as sustainability, environment, risk, safety and to some extent project management, with less usage on other areas. This may be due to individual engineer’s choices in relation to if and how to disseminate the results of their work and to their choice of keywords and titles that determine if their publications are selected in bibliographic searches and thus more visible to a wider readership. A comparison with more topic focused searches, relating to Bridge Design, Earthquake Engineering, Cladding, Sewage Treatment, Foundation design, Truss design, Water Supply, Building Energy, Route selection and Transport mode showed very different results. Analysis of the papers in this area indicated that the full range of supporting software available for multi-criteria decision analysis (many listed in this paper) may not be fully appreciated by potential users.