7.1 Research Contribution
The overall contribution of this research is to introduce and assess one predictive RTC approach that controls storages during rainfall events and one reactive RTC approach that does not require calibration to utilizing storage capacity for achieving stormwater management objectives that address the research needs related to both predictive and reactive RTC outlined in Chapter 1. Details of specific contributions of this research are as follows:
1. In order to provide a comprehensive assessment of the proof-of-concept predictive RTC approach introduced by Di Matteo et al., (2019a), it was tested under a range of return periods, storm durations and storage sizes for three Australian cities: Adelaide, Melbourne and Sydney (Paper 1).
The optimal peak flow reduction performance for the real-time, smart tank systems approach was compared with the performance of a benchmark approach, where the tanks are emptied prior to a storm event, and behaves as a retention tank during the storm. The results demonstrate that the real-time, smart systems approach has significant potential to mitigate urban flooding problems that require peak flow rate attenuation at the allotment scale. The results showed that by applying an optimal control strategy for each tank, during a storm event, the tanks could provide from 35 to 85% peak flow attenuation of runoff from the roof catchments connected to the tanks where the tank volume to runoff volume ratios range from 0.15 to 0.8, respectively. This performance represented a peak flow reduction improvement in the order of 35 to 50%
compared with the benchmark approach.
2. In order to extend the above predictive RTC approach so that it is applicable at the precinct scale, a two-step approach was introduced to minimising peak flows by first optimising the volumes and locations of distributed storages and then optimising their predictive RTC control strategies (Paper 2). The effectiveness of this approach (including the
150
relative impact of each of its two steps) was tested on a real catchment in Adelaide, South Australia. Results show that distributed storage with optimised layout and control can achieve significantly higher peak flow reductions than more commonly used end-of-system (EoS) storage.
These range from 5% for 100 m3 of system storage up to 40% for 700 m3of system storage - whereas EoS storage achieved no peak flow reduction up to 700 m3 storage. The addition of optimised predictive real-time control to distributed storages is able to achieve a further peak flow reduction, particularly for smaller storage volumes, corresponding to an additional 10% reduction of the peak flows prior to the addition of storage. These results highlight the potential for using optimised distributed storage and RTC as an alternative approach to end-of-system storage to reduce flood peaks.
3. A reactive RTC approach, the Target Flow Control (TFC) approach, was introduced, which is able to maintain system outflows at or below specified target flows (e.g., existing system capacity) for storages at the lot scale (Paper 3). The key features of the approach are that it does not require calibration to catchment specific data, as is the case for existing reactive RTC approaches, and is only based on storage level information measured in real-time during rainfall events. This makes the approach generally applicable to different catchments and able to respond to future changes in rainfall due to land use and/or climate change. The TFC approach is tested on a simple two-storage system for 750 design rainfall events from a range of climates, event durations, rainfall intensities and temporal patterns using a practically achievable control time step of 30 seconds. Results show that the TFC approach can achieve the desired target flows effectively, with 95% of the experiments having less than 10% errors in target flow. This is a significant achievement, given the TFC approach does not require calibration and only requires measurable storage level information. The outcomes highlight the potential of the TFC approach as a practical RTC approach that can maximize the effectiveness of existing stormwater conveyance systems by maintaining stormwater system outflows at
151
desired target flows, thereby potentially avoiding stormwater infrastructure upgrades due to land use and climate change.
4. The Target Flow Control (TFC) approach was extended to the Target Hydrograph Control (THC) approach, so that it can achieve desired target hydrographs, not just limiting peak flows (Paper 4). The utility of the Target Hydrograph Control (THC) approach to achieving desired target hydrographs by adapting to a wide range of inflow hydrographs caused by land use and climate changes was also demonstrated. This was done for three different “future worlds” on a simple example catchment located in Darwin, Australia. The experimental results demonstrate that the THC approach is able to achieve the target hydrograph effectively with less than 3.1% error for all experiments.
This is despite the inflow hydrograph varying significantly as a result of land use and climate change, with the increase in peak flows ranging from 7% to 95% and volumes from 25% to 57%. This study demonstrates that the THC approach has significant potential to adapt to land use and climate change and achieve the desired target hydrographs for environmental flow requirements.
5. The Target Flow Control (TFC) approach was extended to the Target Flow Control Systems (TFCS) approach, so that it is applicable to systems of storages at the precinct scale that are controlled to achieve desired flow target(s) at downstream locations(s) of interest, rather than just a single storage (Paper 5). As is the case for the TFC approach, the TFCS approach does not require calibration to catchment-specific data, unlike existing approaches. This means that the TFCS approach is generally applicable to different catchments and able to respond to future changes in runoff due to land use and/or climate change. In addition, it only requires storage level information measured in real- time with the aid of low-cost pressure sensors. This means the approach is practical and relatively easy to implement. Another key innovation of this study is that the TFCS approach is tested on three case studies, each with different configurations and stormwater management objectives.
152
In addition, the performance of the approach is compared with that of five RTC approaches, including three best-performing advanced approaches from the literature. Results show that the TFCS approach is the only one of the control approaches analyzed that has both the best overall performance and the highest level of practicality. The outcomes highlight the potential of the TFCS approach as a practical RTC approach that is applicable to a wide range of catchments with different stormwater management objectives. By maximizing the performance of existing stormwater storages, the TFCS approach can potentially extend the lifespan of existing infrastructure and avoid costly upgrades due to increased runoff caused by land use and climate change.
7.2 Future Work
Future research should be undertaken to increase the performance, generality and practicality of the proposed approaches, including:
1. Future improvements of the practicality of the proposed ‘calibration- free’ reactive control approach by developing an optimization framework to identify required design storage volumes so as to identify the optimal balance between minimizing required storage volumes (and hence costs) and ensuring storages do not overflow.
2. Testing the ability of the proposed RTC approaches to achieve a range of other hydraulic and environmental objectives, including adaptation to the impacts of climate change (Wu et al., 2020, Culley et al., 2021, Bennett et al., 2021) and improvement of water quality and stormwater harvesting (Campisano et al., 2017, Muschalla et al., 2014, Shen et al., 2020). For example, during non-storm periods, the storage outlet could be closed, and the harvested stormwater used for multiple purposes (Xu et al., 2020), including water supply (Dandy et al., 2019, Di Matteo et al., 2019b) or achieving the downstream environmental flow requirements (Shen et al., 2020, Xu et al., 2020). For street-scale storages, by detaining stormwater in the storage for a particular length of time, downstream water quality can also be improved (Sharior et al.,
153
2019), especially by integrating storages with bioretention systems (Shen et al., 2020).
3. Testing and evaluating the proposed RTC approaches using physical experiments. This is helpful to understand the impact of assumptions made in the modelling. For example, using currently available control technology, an electric actuator can be connected to the orifice system to achieve different opening/closing times depending on the required torque, which can be used to determine a practically feasible control time step for simulations.
4. Future application of the proposed RTC approaches to develop regional storage size guidelines by running continuous simulations.
154