Frans Van De Ven (Netherlands) 1; Toine Vergroesen (Netherlands) 2; Wenxing Zhang (Netherlands) 3; Hsuan-Yu Lin (Taiwan) 4; Wen-Shiang Chung (Taiwan) 4; Chen-Wuing Liu (Taiwan) 5; Jin-Jing Lee (Taiwan) 5; Yueh-Tan Lee (Taiwan) 5
1 - Deltares / TU Delft; 2 - Deltares; 3 - TU Delft / Deltares; 4 - Sinotech Engineering Consultants, LTD; 5 - Taoyuan Government, Department of Water Resources
The climate in Taiwan brings Taoyuan city very extreme rainfall events every now and then. The sponge capacity to avoid flooding in districts and streets hence is an important design target that is to be used to evaluate adaptation options. The storage capacity is relevant for both the designers of the drainage system and the urban planners and landscape architects responsible for designing the district, as the sponge capacity requires space for implementation. This sponge capacity is to be determined in the earliest phases of the district’s planning and design process, as all designers and engineers need to take this into consideration when making their final designs.
The storage capacity needed to avoid flooding is related to the capacity to drain / discharge water from the district to its surrounding environment; the larger the capacity to drain, the less storage is required, but the larger the risk of flooding downstream. To find an acceptable equilibrium between storage and discharge capacity we use Storage – Discharge – Frequency (SDF) curves. A water balance model is used to transform multi-annual hourly rainfall data series into a multi-annual series of stored volumes, given a specific discharge capacity of the system. In the next step, the series of stored volumes is subject to extreme value analysis to find out how much storage capacity is exceeded once every X years. These values are calculated and plotted for a series of discharge capacities to construct the SDF curves.
A water system analysis at the larger (basin) scale is used to find an acceptable maximum discharge capacity Qmax that avoids problems downstream and gives realistic sizes of the drainage system. The required storage (sponge) capacity can now be chosen for a specific return period (= frequency) for a discharge capacity that is smaller than Qmax.
Our contribution addresses the method and model that is used to assess the SDF-curves, the required input data, the output and the way the SDF curves are used in practice to assess the required sponge capacity. The same water balance model is used to estimate peak flow reduction due to the application of a specific package of Sustainable Drainage Solutions (SuDS) in a district. This approach will be illustrated using a case in Taoyuan, Taiwan.