Tsang-Jung Chang

Inundation simulation for urban drainage basin with storm sewer system

An urban inundation model, combining a storm sewer model SWMM, two-dimensional (2D) diffusive overland-flow model and operations of pumping stations, has been developed to simulate inundation in urban areas caused by the surcharge of storm sewers and outlet pumping stations. The movement of water in the studied urban watershed is characterized by two components, namely, the storm sewer flow component and the surcharge-induced inundation component. SWMM is employed to solve the storm sewer flow component and to provide the surcharged flow hydrographs for surface runoff exceeding the capacity of the storm sewers. The 2D diffusive overland-flow model considering the non-inertia equation with Alternative Direction Explicit numerical scheme is then used to calculate the detailed inundation zones and depths due to the surcharged water on overland surface. Drainage by pumping stations at outlets of the storm sewer system has also been taken into consideration. The parameters of the model are calibrated and verified for discrete storms. The combined model is suitable for analysis of inundation on urban areas due to overflow of storm sewers and flooding caused by failure of pumping stations. Simulated results can be applied to establish flood-mitigation measures.

Dynamic inundation simulation of storm water interaction between sewer system and overland flows

Abstract An improved urban inundation model, coupling a 2D non‐inertia overland flow model with a storm water management model, is adopted to simulate inundation in urban areas. The model computes, not only the overland runoff and the water overflow through manholes where surface runoff exceeds the capacity of storm sewers, but also the bidirectional flow interactions between sewers and overland runoff. The model was verified by a typhoon event in Nov. 2000, which resulted in serious inundation in the Mucha area of Taipei City. The result shows that the present model indeed improves simulation accuracy over the earlier model, and can be used to provide a more reliable flood mitigation design.

Sensitivity analysis of the hydrological response of the Gaping River basin to radar-raingauge quantitative precipitation estimates

Abstract The generation of reliable quantitative precipitation estimations (QPEs) through use of raingauge and radar data is an important issue. This study investigates the impacts of radar QPEs with different densities of raingauge networks on rainfall–runoff processes through a semi-distributed parallel-type linear reservoir rainfall–runoff model. The spatial variation structures of the radar QPE, raingauge QPE and radar-gauge residuals are examined to review the current raingauge network, and a compact raingauge network is identified via the kriging method. An analysis of the large-scale spatial characteristics for use with a hydrological model is applied to investigate the impacts of a raingauge network coupled with radar QPEs on the modelled rainfall–runoff processes. Since the precision in locating the storm centre generally represents how well the large-scale variability is reproduced; the results show not only the contribution of kriging to identify a compact network coupled with radar QPE, but also that spatial characteristics of rainfalls do affect the hydrographs. Editor Z.W. Kundzewicz; Guest editor R.J. Moore Citation Pan, T.-Y., Li, M.-Y., Lin, Y.-J., Chang, T.-J., Lai, J.-S., and Tan, Y.-C., 2014. Sensitivity analysis of the hydrological response of the Gaping River basin to radar-raingauge quantitative precipitation estimates. Hydrological Sciences Journal, 59 (7), 1335–1352. http://dx.doi.org/10.1080/02626667.2014.923969

Evaluating the contribution of multi-model combination to streamflow hindcasting by empirical and conceptual models

ABSTRACT The contribution of multi-model combination to daily streamflow hindcasting was evaluated through the HBV (Hydrologiska Byråns Vattenbalansavdelning) and RNN (recurrent neural networks) models with 100 ensemble members generated with different initial conditions for both. In the calibration phase, the analysis showed that the HBV and RNN models with 20 members have better accuracy and require less calibration time. The combination of two models, however, did not provide significant improvements when 80 more members were added in the combination. In the validation phase, the results indicated that both HBV and RNN models with 20 members not only accurately produce reliable and stable streamflow hindcasting, but also effectively simulate the timing and the value of peak flows. From the consistency of calibration and validation results, the study provides an important contribution, namely, that ensemble size is not sensitive to the type of hydrological model in terms of streamflow hindcasting.

Evaluation of Adaptation Strategies for Urban Flooding in Central Taipei City in Taiwan

The urban areas have been rapidly developed in Taiwan in recent years. The expanding urban areas and the increasing population, especially in the metropolitan Taipei city, result in surface runoff discharge during typhoons or rainstorms. When the surface runoff exceeds the capacity of drainage systems of the city, the urban inundation and property losses occur. The urban flooding risk assessment is a useful tool for the decision-making in flood damage mitigation. In general, hazard and vulnerability are two main factors for the risk assessment. In the present study, the Center Taipei City (CTC) is chosen as the study area. The A1B scenario simulations proposed by IPCC are used to compare the flood risks between the present situation and future condition which is under climate change scenario. The ArcGIS is used to yield the flood potential information and the flood risk for the return period of 10, 25, 100 and 200-year flood. The simulated results revealed that the increasing water storage to meet the regulation of the Taipei City government would effectively reduce the effects of climate change on the decreasing inundation areas. The adaptation strategies will also reduce the high-risk areas in the CTC according to risk assessment. The adaptation strategies composed of increasing the water storage in urban areas and reducing the social vulnerability of flooding area are the effective way for the flood risk reduction in urban area.