Runoff generation characteristics of urban building areas considering the effect of wind fields
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Abstract:
With the rapid pace of urbanization in the past few decades, both the height and density of buildings within cities experienced a noticeable surge. This transformation not only altered the skyline but also introduced new dynamics to natural processes, notably in the interplay between wind fields and rainfall runoff. This study delved into the intricate relationship between wind fields and their influence on runoff within built environments. Under the action of wind, raindrops tend to fall obliquely with an angle and form inclined rainfall. Inclined rainfall is intercepted by buildings with large heights. Meanwhile, part of the area behind the building is shielded due to the existence of the building. According to the phenomenon discussed above, this study endeavored to improve the existing methods of runoff calculation specific to building areas.The proposed formula includes five terms, which are ground runoff, building wall runoff, roof runoff, ground infiltration and evaporation during rainfall period. To improve the accuracy of the proposed formula, the dynamic characteristics of wind field and the characteristics of building areas were considered. The dynamic characteristics of wind field were reflected by adopting reduction factors. The characteristics of building areas were reflected by including the shielding effect between buildings. The shielding effect between buildings existed when the building distance is smaller than the length of shielded area. Rainfall runoff experiments were conducted to validate the soundness of the improved formula. Different scenarios with different inclined rainfall angle and building environments were designed. The experimental results closely mirrored the outcomes predicted by the formula, underscoring its effectiveness in capturing the flow characteristics unique to building areas. This correlation served as a testament to the formula's reliability. Buoyed by this success, the study embarked on an extended exploration of runoff patterns within urban construction zones.In the case of single-family dwellings and sparsely constructed areas, the angle at which rainfall descends exhibited a palpable influence on runoff generation. As the incline of precipitation increased, a discernible decrease in runoff within these areas was observed. This phenomenon was possibly the result of the increasing building shielding effects when the inclined rainfall angle increases. Conversely, complex mechanisms of runoff calculation were found in densely populated urban areas. Here, the building coverage ratio exerted a direct influence on water flow within the vicinity. As the number of buildings grew, accompanied by an escalation in building density, a twofold effect emerged. On one hand, this surge amplified the expanse of building wall runoff, as a greater surface area was exposed to the rainfall. Concurrently, the proliferation of buildings enhanced their collective shielding effect, thus instigating a nuanced trend in runoff dynamics. Initially, there was an upswing in runoff, as the augmented surface area contributed to a surge in water collection. However, this trend exhibited a tipping point, after which the runoff gradually receded.In summary, a formula for runoff calculation of building areas considering the impact of wind fields was proposed. Rainfall runoff experiments were conducted to testify its rationality. Based on the formula proposed, the runoff producing characteristics of different building areas were explored. In sparse distributed building area, the runoff producing is mainly influenced by the inclined rainfall angle; while in dense distributed building area, the runoff producing is not only influenced by the inclined rainfall angle but also the feature of building areas.
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