Impacts of system modifications on time-dependent rainwater flow conveyance in property level systems
Wickramasinghe, Simanmahadura A.N.S.
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This thesis establishes the impacts of systems modifications on time dependent rainwater flow conveyance across complete flow pathways in a property level system. A numerical model called ‘Residence Time Estimator’ was developed to establish the relationship between system modifications and residence time of rainwater within the whole system. Property level water supply and drainage systems are often designed as individual system components due to their seemingly isolated performance. However, for sustainable management of water, different flows at property level; potable water, rainwater and greywater need to be used efficiently. This involves storing, reusing water, often by interconnecting different system components and pathways and modifying the characteristic flow profiles. Hence, changes in time dependent flow conveyance, from the upstream to the downstream of a property, which can be quantified in residence time; is based upon the overall impact of different system modifications. Establishing this relationship in property level systems, informs better estimating time dependent flow characteristics for designing the wider urban setting. Simulation of rainwater conveyance across three flow pathways, including storage and reusing to supply non-potable water demand for WC usage, under two rainfall events, was established using the numerical simulation model in 5-second time steps. Using a reference of 1 litre sized flow parcels, residence time within the system, in relation to the amount of inflow, system characteristics and also inflow characteristics was established. The results indicate that, the residence time of rainwater within the selected property under the selected rainfall event, which was less than 25 seconds, can be increased up to 100 seconds or more by the integration of a rainwater attenuation tank of 300 litres. It can be further increased up to one day or more, if a RWH system with an underground storage tank of 1200 litres and a header tank of 125 litres is integrated to the system. ‘Residence Time Estimator’ can be used as a tool in urban planning and design, to select the appropriate system modifications for SWM and hence to achieve the required flow attenuation capacity within system components, individual properties or the wider urban scale.