Physical Scale Modelling of Urban Flood Systems

Urban flooding is defined as ‘an overflowing or irruption of water over urban pathways which are not usually submerged’. Current economic, climatic and social trends suggest that the frequency, magnitude and cost of flooding are likely to increase in the future. Hydraulic models are commonly used by engineers in order to predict and mitigate flood risk. However full scale calibration and validation datasets for these modelling tools are scarce. The main research objective of this thesis was to design and construct a physical model in order to provide datasets useful to verify, calibrate and validate computer model results in terms of energy losses in manholes. To address these issues, an experimental facility has been constructed to enable the investigation of energy losses under steady and unsteady flow conditions in a scaled sewer system. Originally the model was composed of six manholes and three main pipes and then it was modified into a single pipe linked to an urban surface through a single manhole. Experiments involved the measurement of flow rates, velocity, pressure and water depth within the physical models under different hydraulic scenarios. Steady flow tests were conducted to quantify energy losses though manhole structures with different inlet/outlet configurations under a range of hydraulic conditions. Unsteady flow tests were conducted to examine the performance of different computational hydraulic models. These tests have shown that the performance of the SWMM hydraulic model could be improved by including local losses in the calibration process. After modification the model was used to quantify sewer to surface and surface to sewer flow exchange through a single manhole during pluvial flooding. The work has demonstrated the feasibility of using weir and orifice equations within modelling tools to quantify this exchange under steady conditions. The model was used to empirically quantify discharge coefficients for energy loss equations which describe flow exchange for the first time.