Feifei Zheng

Urban drainage pipes face increasing risk of sediment deposition, which reduces drainage capacity and increases blockage potential. This study experimentally investigated sediment deposition using a laboratory-scale drainage pipe system with a roughened pipe wall and an image-recognition-based monitoring method. 130 experiments were conducted by varying flow velocity, pipe slope, sediment concentration (loading conditions), and sediment type. Under the tested conditions, sand deposition development exhibited critical hydraulic thresholds, with critical pipe slopes of approximately 6 and 3‰ under low and high concentration conditions, respectively, and a critical flow velocity of 0.4–0.5 m/s. Higher sediment loading conditions promoted deposition, particularly at larger pipe slopes and flow velocities. Compared with sand, cohesive sediments produced longer and more spatially distributed deposits, while mixed sediments exhibited interaction effects rather than simple superposition. Sediment deposition was concentrated in the upstream pipe region, with the maximum deposition thickness occurring at approximately 2% of the pipe length, and generally followed a two-stage temporal evolution from rapid accumulation to quasi-equilibrium. These findings provide improved, empirically grounded understanding of sediment deposition processes, including the experimental identification of critical hydraulic thresholds and sediment-type interaction effects, offering practical guidance for drainage pipe design, targeted sediment removal, and proactive blockage management.

Urban drainage network models (UDNMs) have been widely used to facilitate flood management. Typically, a UDNM is developed using data from Geographic Information Systems (GIS), and hence it consists of many short pipes and connection nodes or manholes. To improve modeling efficiency, a GIS‐based model is generally skeletonized by removing many elements. However, there has been surprisingly a lack of knowledge on to what extent such skeletonization can affect the model's simulation accuracy, resulting in uncertainty in flood risk estimation. This paper makes the first attempt to quantitatively evaluate multidimensional impacts of different skeletonization levels on hydraulic properties of UDNMs. This goal is achieved by a new evaluation framework comprising of eight existing and new metrics that make use of hydrographs, main pipe hydraulics and flood distribution properties. A real‐life UDNM is used to illustrate the new framework under various rainfall conditions and different skeletonization levels. The new framework is also used to compare the performance of two compensation methods in mitigating impacts caused by model skeletonization. Results obtained show that: (a) model skeletonization can significantly affect the magnitude of peak flow at the outfall, with a maximum overestimation of up to 20%, (b) hydraulics in main pipes can also be affected by model skeletonization with the maximum flow increasing up to 35%, and (c) model skeletonization may significantly alter the flood distribution properties which has been largely ignored in past studies. These findings provide guidance for UDNM skeletonization, where their associated impacts should be aware in engineering practice.

Draining processes through a bottom orifice of a water tank under different ventilation conditions were studied experimentally. The water pressure fluctuations at the tank bottom and the air pressure in the headspace were measured simultaneously, based on which the air–water flow features were analyzed. From the experiments, three drainage modes were identified, including a periodic draining mode with periodic bubble generation at the orifice, a full-flow draining mode without bubble formation in the tank, and a combined draining mode with bubbles generated when the water level fell to a certain water depth. The drainage efficiencies varied among the three modes, resulting from the different conditions of bubble generation at the bottom orifice and the negative pressure in the headspace due to limited ventilation. The mechanism for bubble generation at the orifice was analyzed theoretically, and the effect of the negative pressure on drainage efficiency was discussed. The transition criteria among the modes were developed by a mathematical model. This study provides new knowledge on the drainage from a water tank under different degrees of ventilation.

Bursts in water distribution systems (WDSs) lead to water wastage and negative environmental impacts. Optimizing pressure sensor placement (PSP) for effective burst detection is crucial for prompt response and adverse event mitigation. While many optimization methods are available for this purpose, their resulting PSP strategies often exhibit large variability caused by background noise or metering accuracy, representing low robustness. This consequently hinders the wide application of existing PSP methods for burst detection in WDSs. This study proposes a novel multi‐objective PSP method aimed at maximizing burst detection while minimizing the number of sensors. Within this method, a new threshold metric is introduced to quantify the minimum detectable burst outflow across all pipes. The metric has the key advantage of taking into account the fact that the relative magnitude of the detectable threshold for different pipes is independent of noise, thereby addressing the low robustness issue. The proposed method is applied to three WDSs, and results show that it can consistently achieve robust optimal PSP strategies across diverse noise conditions. Comprehensive comparisons between the proposed method and the other benchmark approaches are conducted using five metrics, including detection performance and layout characteristics. These comparisons reveal the properties of each optimization method and show how detection performance is affected by various placement features. It is anticipated that the proposed method can be useful in engineering practice due to its great robustness in determining the optimal PSP strategies for burst detection in WDSs compared to other alternatives.