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Xia J.,Wuhan University | Zhang Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Xiong L.,Wuhan University | He S.,CPG Consultants Pte Ltd | And 2 more authors.
Science China Earth Sciences | Year: 2017

Waterlogging is one of the major water issues in most cities of China and directly restricts their urbanization processes. The construction of Sponge City is an effective approach to solving the urban water issues, particularly for the waterlogging. In this study, both the urban issues emerged at the stage of rapid urbanization in China and the demands as well as problems of Sponge City construction related with the water issues were investigated, and the opportunities and challenges for the Sponge City construction in the future were also proposed. It was found that the current stormwater management focused on the construction of gray infrastructures (e.g., drainage network and water tank) based on the fast discharge idea, which was costly and hard to catch up with the rapid expansion of city and its impervious surface, while green infrastructures (e.g., river, lake and wetland) were ignored. Moreover, the current construction of Sponge City was still limited to low impacted development (LID) approach which was concentrated on source control measures without consideration of the critical functions of surrounding landscapes (i.e., mountain, river, wetland, forest, farmland and lake), while application of the integrated urban water system approach and its supported technologies including municipal engineering, urban hydrology, environmental science, social science and ecoscape were relatively weak and needed to be improved. Besides, the lack of special Sponge City plan and demonstration area was also a considerable problem. In this paper, some perspectives on Good Sponge City Construction were proposed such as the point that idea of urban plan and construction should conform to the integral and systematic view of sustainable urban development. Therefore, both the basic theoretical research and the basic infrastructure construction such as monitoring system, drainage facility and demonstration area should be strengthened, meanwhile, the reformation and innovation in the urban water management system and the education system should also be urgently performed. The study was expected to provide a deeper thinking for the current Sponge City construction in China and to give some of suggestions for the future directions to urban plan and construction, as well as urban hydrology discipline. © 2017 Science China Press and Springer-Verlag Berlin Heidelberg

Kog Y.C.,CPG Consultants Pte Ltd. | Kho C.,CPG Consultants Pte Ltd. | Loh K.K.,CPG Consultants Pte Ltd.
Journal of Performance of Constructed Facilities | Year: 2015

The modulus of subgrade reaction is not a unique fundamental soil property that can be readily measured, and its magnitude is an outcome from a soil-structure interaction. But it is required by structural engineers for the structural design of a tunnel. The adoption of an appropriate magnitude for the modulus of subgrade reaction is crucial to ensure that the structural design of the tunnel will be adequate. Some engineers inappropriately rely on the plate load test to determine the magnitude of the modulus of subgrade reaction of the underlying stratum for the structural design of the tunnel. This paper will discuss an appropriate approach to estimate the magnitude of the modulus of subgrade reaction of weak sandstones and siltstones underlying a 2-km tunnel. This tunnel was completed and extensive cracks were noted prior to the opening of the tunnel. This prompted an investigation that included a design review that identified the important issue of an appropriate method for determining the magnitude of the modulus of subgrade reaction for the tunnel design. Typical values for the moduli and Poisson's ratios of weak sandstones and siltstones required for the soil-structure interaction analysis will be discussed based on a review of the existing literature and the results of plate load tests, pressuremeter tests, and unconfined compression strength tests of the soil investigation report for the tunnel project. © 2014 American Society of Civil Engineers.

Chua L.H.C.,Nanyang Technological University | Tan S.B.K.,CPG Consultants Pte Ltd. | Sim C.H.,WaterWays | Goyal M.K.,Nanyang Technological University
Ecological Engineering | Year: 2012

This study investigated the performance of a floating wetlands system (FWS) planted with Chrysopogon zizanioides (Vetiver grass), Typha angustifolia and Polygonum barbatum as treatment units to remove nutrients contained in the baseflow to the Kranji reservoir in Singapore. Phase 1 of the study consisted of controlled experiments with a perspex floating wetland test cell of dimensions 2.5m×2m×1m. Separate experiments were carried out using the inflows from Sungei Kangkar, Sungei Tengah and Sungei Peng Siang, which drain into Kranji reservoir. Tests were conducted for each plant species using water taken from each of the tributaries in turn. Water samples were collected from the experimental and control tanks during the experiment and analysed for total nitrogen, TN (mg/L), total phosphorus, TP (mg/L), orthophosphate, OP (mg/L) as PO 4 and ammoniacal nitrogen, AN (mg/L) as NH 4+. The net nutrient reduction (%) for Vetiver, Typha and Polygonum were 19.1, 39.2 and 46.0 for TP, and 40.8, 67.5, 7.8 for TN, respectively. The rate of decrease of nutrients was found to be significant within the first few days and reached steady state after approximately 10 days. The removal coefficient (day -1) for Vetiver, Typha and Polygonum were 0.66, 0.87 and 1.06 for TP and 0.64, 0.68, 0.87 for TN, respectively. The removals of OP and AN could not be ascertained due to the low concentrations of these parameters contained in the waters tested. In Phase 2, field experiments were carried out with the FWS installed in Sungei Peng Siang with the same plant species that were used in the controlled experiments. The growth of Vetiver and Typha was monitored while all three plant species were tested for plant nutrient content. Plant TN and TP content increased rapidly during the initial rapid growth stage, reached a maximum after approximately 1 month and decreased. Typha achieved the highest rate of increase in nutrient content compared to Vetiver and Polygonum. The uptake of TN by Typha, Vetiver and Polygonum was estimated to be 16.2, 1.74 and 2.82 (mg/daym 2). The corresponding uptake for TP was 1.57, 0.16 and 0.4 (mg/daym 2). For Typha, the mat size required for 50% removal of TN and TP from the baseflow was estimated to be 0.056 and 0.031ha of mat/ha of catchment area. This is a conservative estimate since nutrient uptake by the root system was ignored. © 2012 Elsevier B.V.

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