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Many urban flood models employ coarse grids to reduce the computational cost of real‐time forecasting. Such a coarse grid, however, may result in poor predictions of the discharge rate of surface water because of difficulties in representing the detailed features of drainage facilities. In the present study, an urban flood model that consists of a one‐dimensional (1D) river flow model, a two‐dimensional (2D) ground surface flow model, and a 1D sewer network model was developed. A coarse grid is used for the 2D ground surface flow model, and the tail networks of the sewer systems are neglected to reduce computational cost. A novel approach is proposed for determining the integrated water discharge from the ground surface to the trunk sewer network to retain the accuracy of a simplified coarse‐grid system. Numerical experiments were performed to evaluate the performance of the proposed method. Measured water levels at manholes were employed to examine the accuracy of the model. The results show that this approach significantly improves the accuracy of the simulated water level in a sewer network with enhanced computational efficiency. [ABSTRACT FROM AUTHOR]

The article compares and contrast watershed management practices of the United States, Brazil, Japan and Switzerland, and the problems inherent in depending on inadequate natural resources and expensive technologies. It is posited that cooperation between resource-rich and resource-poor nations, and between developed and developing nations, will promote sustainable management practices.

Integrated flood models have been previously developed to simulate diverse inundation situations and combined with models of storm surges and river floods. However, drainage systems, ground elevation, and surface information of human settlements have only been digitized in large cities. Digitization of surface information is essential for developing a drainage system model for pluvial flood analysis. Occasionally, suburban drainage areas exhibit various complex land-use conditions, including residential and green areas, agricultural land with drainage, and irrigation channels. Herein, UAV photogrammetry was applied to obtain high-resolution geospatial data associated with small-scale flood-prone areas whose elevation, land-use, and waterway networks have not been elucidated sufficiently. The resolution of elevation and land-use data ranged from 2.61–5.22 cm/mesh. The measurement accuracy of the width and depth of the open channels was high, and the errors were mostly within 10%. A drainage system model was developed using data on open channel, elevation, and land-use. [ABSTRACT FROM AUTHOR]

Compared to pumping stations, pump gates have small sites and are constructed for a low cost over a short period of time. A new type of horizontal axial submersible pump that is optimal for pump gates has recently been developed. Since the new type of pump can be operated at full speed regardless of water level, it is possible to conduct standby operations in preparation for stormwater runoff inflows. In a simulation comparing the conventional pumps and the new type of pump, there was no serious inundation condition in the new pump up to 70 mm/h, which is 140% of the design's rainfall intensity. As a result, it was clarified that standby operations can keep the peak water level low and maximize the water storage capacity of the drainage channel. [ABSTRACT FROM AUTHOR]

The series of annual flood disasters that struck Japan in recent years pose challenges to urban stormwater management. Japan has been implementing nation-wide hydrometeorological observation through a dense network of rain gauges. Since the recent decade, ground radars have been deployed to observe heavy rainfall with high spatiotemporal resolution as a countermeasure. While commercial software is popular in designing stormwater drainage systems, several integrated urban flood models have been developed domestically and are applicable in stormwater management. A paradigm shift with the rise of Internet of Things (IoT) provides an inexperienced opportunity in hydrological observation, and has been implemented for monitoring sewer network conditions. Despite this broad scope of research works and technological innovations, such advancement is not internationally recognized yet. The present study aims to review the development and role of science and technology in stormwater management in Japan, focusing specifically on rainfall observation, integrated urban flood modelling, and emerging technologies for stormwater monitoring. In addition, the possible future direction of stormwater management is envisioned. Considering the series of record-breaking rainfall events that struck Japan, we will have to face more severe challenges in urban flood management alongside the impact of global climate change. As compared to structural measures, which are subject to budgetary constraints, the relative importance of non-structural measures is increasing; therefore, effective application of numerical modeling techniques is required. A common weakness of the urban flood modeling framework is the limited availability of observations in sewer networks, which can be relaxed by emerging IoT based observations. The fusion of IoT based observations with an integrated urban flood modeling technique appears to the emerging technology for stormwater management. [ABSTRACT FROM AUTHOR]