Micro-Scale Hydrology Modelling for Multipurpose Rainwater Management

Abstract

Most of the world hydrological problems such as flooding, drought, water shortage, water pollution and groundwater depletion are all related to rainwater. By proper rainwater management (RWM), we can resolve the hydrological problems and enhance the resilience. This dissertation is to develop micro-scale hydrology modelling for multipurpose rainwater management. Traditional methods of draining rainwater from rooftops, based on the Rainfall-Discharge (R-D) model, are challenged. By storing some of the rainfall that falls on building rooftops, flooding of nearby sewer systems can be mitigated, and the reduction of peak runoff can then calculated using the Rainfall-Storage-Discharge (R-S-D) model. The dissertation proposes and develops numerical modellings for innovative RWM systems with controlled measures as a resilient and sustainable flood mitigation approach. Conventional rainfall-runoff analysis was found to be unreasonable for micro-scale of building rooftops. In the Seoul area, 10% probability in the second quartile was set as the time distribution appropriate for determining the tank retention volume. By utilizing stored rainfall in or near a building, flooding can be further mitigated while conserving water, and the reduction of peak runoff and amount of used rainwater can also be calculated using the Rainfall-Storage-Utilization-Discharge (R-S-U-D) model. By controlled pumping, which is developed by the R-S-P-D (Rainfall-Storage-Pump-Discharge) model, runoff flows can be neutralized and thus mitigate flooding in case of heavier rainfall. Further, The R-S-I-D (Rainfall-Storage-Infiltration-Discharge) model, which incorporates with infiltration can be used for multipurpose, working towards not only further flood mitigation but also water conservation and groundwater enrichment. The reduced peak flow and increased design return period for a combination of tank volume and utilization, pumping or infiltration rates can be calculated and presented by TP, TUP, TUD, TPP, TPD, TIP, and THP curves, which can be used in the design and operation of sewer systems. Results from these models can help in designing methods to reduce the flooding risk in existing sewer systems without increasing their capacity, thus reducing expenses. Additionally, total annual water conservation and groundwater recharge in R-S-U-D and R-S-I-D systems can be calculated as a supplement of existing water supply systems. The dissertation also develops novel modellings for RWM system to resolve the world water shortages. Getting a detailed and suitable rainfall data to have a good design of RWH system is a challenge in developing countries. In RWH system performance predictions, direct use of monthly rainfall data may lead to considerable error instead of using daily rainfall data. This dissertation proposes a simple and reasonable design method of RWH systems from available limited data. The proposed model that employs the designed rainfall which generate daily rainfall for each month with distribution of uniformly number of wet days in the last days of month as its input gives performance predictions quite similar to that of using actual daily rainfall. Further, the seasonal variatiion of rainfall was found to be other hydrological problem in RWM which caused droughts in dry sreason, and thus prohobits the use of RWM. This dissertation develops the novel variable demand model taking rainfall variance into determination of daily demand which can result an optimal performance of RWH system and ensure water saving in even dry seasons. From the model, the TRRC curves and water supply chart are developed. These curves can be used to suggest an optimal design and operation of RWM system. The developed modellings in the dissertation can be used to resolve the current world water shortage problem and the mitigation of urban flooding, which are working towards increasing the resilience of existing systems against urbanization and climate change, and thus resulting in a solution for Sustainable Development Goals (SDGs 6 and 11).