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In recent years, high‐molecular‐weight anionic polyacrylamides (PAMs) have been tested on a variety of soils, primarily in temperate climates. However, little information is available regarding the effectiveness of PAM for preventing soil loss through runoff in tropical settings. Screening tests were performed using three negatively charged PAMs and one positively charged PAM on five Hawaii soils (two Oxisols, one Vertisol, and two Aridisols) to determine erosion loss, sediment settling, and aggregate stability. A laboratory‐scale rainfall simulator was used to apply erosive rainfall at intensities from 5 to 8·5 cm h?1 at various PAM doses applied in both dry and solution forms. Soil detachment due to splash and runoff, as well as the runoff and percolate water volumes, were measured for initial and successive storms. The impact of PAM on particle settling and aggregate stability was also evaluated for selected soil‐treatment combinations. Among the PAMs, Superfloc A‐836 was most effective, and significantly reduced runoff and splash sediment loss for the Wahiawa Oxisol and Pakini Andisol at rates varying between 10 and 50 kg ha?1. Reduced runoff and splash sediment loss were also noted for PAM Aerotil‐D when applied in solution form to the Wahiawa Oxisol. Significant reductions in soil loss were not noted for either the Lualualei Vertisol or the Holomua Oxisol. It is believed that the high montmorillonite content of the Lualualei Vertisol and the low cation‐exchange capacity of the Holomua Oxisol diminished the effectiveness of the various PAMs tested. The polymers were also found to enhance sediment settling of all soils and helped improve their aggregate stability. This screening study shows the potential use of PAM for tropical soils for applications such as infiltration enhancement, runoff reduction, and enhanced sedimentation of detention ponds. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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The sustainable management and profitable development of the Pacific island tuna fisheries is the key ocean governance challenge for the Pacific islands region in the short and medium term. Resolving these challenges is fundamental to the long term future of the region and its ability to implement oceans governance across all resource and conservation concerns. 相似文献
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Teo Siew Eng 《Singapore journal of tropical geography》1995,15(2):171-187
This paper examines the perceptual images and residential desirability of public and private housing residents in Clementi housing estate in Singapore. Residents’ mental maps are established in terms of their levels of knowledgeability of activity nodes tied to various aspects of their lives, namely, workplaces, recreational and sports centres, shops and residential areas. The way the mental maps shape residents’ perceptions of what are desirable and non-desirable places to live in are also discussed. The paper highlights the significance of socio-economic differences, length of residence, physical proximity, levels of interaction and cultural leanings in influencing the mental maps and residential preferences of urban residents in Singapore 相似文献
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This study examined perceptions of the impacts of the antinatalist (OPP) and pronatalist (NPP) policies in Singapore. Data were obtained from a sample of 209 men and 280 women under 45 years old who lived in Ang Mo Kio New Town in the center of the island. Findings indicate that 53.4% of women said that fertility decisions were joint ones. 50% of women and 65% of men said that family size was jointly determined. Over 70% were aware of the OPP "stop at 2" policy. Those who gave accurate, detailed knowledge were mostly over 35 years old. Knowledge of OPP did not vary by education, but did vary by awareness of incentives and disincentives. 45.4% of women believed that OPP was a necessary state policy; 25.4% did not. 36.4% thought that OPP was fair; 28.3% did not. 60.3% of women said that OPP did influence family size in society, but 63.8% said it did not influence their individual family size. Finances, education, and child care were explanatory factors in individual planning. OPP is viewed as a successful policy not because of ideology, but because of the value placed on improved socioeconomic standards. 58.2% of women and 55.5% of men knew the details about the NPP. 51.9% of women said the NPP would encourage larger family size, but 87.8% said it would not affect them personally. Findings suggest that personal freedoms and public ideology are not binary, public-private concepts in fertility decision making. 相似文献
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Formula of incipient velocity for flooded vehicles 总被引：3，自引：3，他引：0
With the climate change caused by global warming, the occurrence probability of urban flooding due to flash floods has increased
gradually. Flush floods propagate rapidly, which can lead to significant hazard to human life and property. Flood hazard to
vehicles has become more noticeable and frequent in recent years. Therefore, it is important to investigate the behaviour
of vehicles on flooded streets or roads. In the current study, a formula has been derived to predict the incipient velocity
of flooded vehicles according to the mechanical condition of sliding equilibrium. A series of flume experiments were conducted
using three types of scaled die-cast model vehicles, with two scales being tested for each type of vehicle. The experimental
data obtained for the small-scale model vehicles were used to determine the two parameters in the derived formula, and the
prediction accuracy of this formula was validated using the experimental data obtained for the large-scale model vehicles.
Finally, the corresponding incipient velocities under various incoming depths were computed using this formula for these three
prototype vehicles. It is found that for a specified vehicle, the value of incipient velocity reaches its minimum as the incoming
flow depth approaches the height of the vehicle, and the smaller and lighter vehicle like Mini Cooper is the easiest to start
sliding in floodwaters. The results can be used as a preliminary assessment to define the hazard to vehicles parking on flooded
streets or roads. 相似文献
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The strength of raw ironmaking materials is usually determined by tumble and shatter tests. Although an average result for a bulk sample is determined, the strength index is empirical and its numerical value cannot be used to predict the extent of breakage for a particular material handling circuit. A new experimental procedure has been developed to measure the strength based on the extent of breakage of agglomerates repeatedly dropped from a predetermined height. The drop procedure combined with impact and breakage theories has been used to quantify the effect of particle size and drop height on the extent of breakage of lump materials such as iron ore sinter, coke, coal and iron ore. Results from a plant trial indicated that the drop procedure could also be used to examine the stabilization effect of brittle material due to repeated dropping during handling. 相似文献
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