Assessment of rainwater detention basins located in the municipality of São Carlos (SP), Brazil

ABSTRACT The accelerated urbanization process, together with a disordered occupation of the land, causes changes in the water balance, generating a greater percentage of surface runoff and increasing the frequency and magnitude of floods. As a measure to mitigate these impacts, detention basins (DB) are implemented in the urban environment to reduce the peak flow. This study aimed to evaluate the DB built in São Carlos (SP), Brazil, through established variables related to physical as well as management and urban integration aspects (position, insulation, conservation, use, filling/emptying, construction processes, maintenance, costs). For this purpose, on-site visits were made to each of the 26 identified units, with or without precipitation events. Drainage projects were also consulted and interviews were conducted with agents involved in the issue. Results showed that all units serve only a hydrological function, through the filling and subsequent emptying of stored water by means of a bottom hole in less than 24 hours (except in three cases where there is only soil infiltration). There is no concern about integration with the urban space or about finding other uses for the space occupied by the units. There is a tendency of lack of frequent maintenance, with excessive vegetation growth, especially in units under public management. The costs of implementation vary around values mentioned in the literature (between R$ 50 and R$ 25/m3). Although hydrological control is being provided, improvements in maintenance are recommended, as well as a paradigm shift in design that allows for multiple uses for DB.

摘要 加速的城市化进程与无序土地侵占共同引发水平衡改变，致使地表径流量占比提升，洪水发生频率与量级均有所增加。作为缓解此类影响的措施，滞留塘（detention basins, DB）被应用于城市环境中，以削减洪峰流量。本研究旨在评估巴西圣保罗州圣保罗卡洛斯市已建成的滞留塘，选取与物理特性、管理及城市融合相关的既定变量（位置、隔离度、养护状况、使用情况、充放水流程、施工工艺、维护成本）开展分析。为此，研究人员对已确认的26处设施开展实地走访，调研覆盖有降水与无降水两种场景；同时查阅排水工程规划资料，并对相关领域从业人员开展访谈。结果显示，所有设施均仅发挥水文功能：通过底部孔道将储存水体在24小时内完成排空（仅3处设施仅依靠土壤入渗实现排水）。当前未考虑与城市空间的融合利用，亦未探索设施占地的其他潜在用途。公共管理的设施普遍存在维护频次不足、植被过度生长的问题。建设成本大致处于文献提及的区间内（每立方米50至25雷亚尔（R$））。尽管目前已实现水文调控功能，但研究建议优化维护工作，并转变现有设计范式，使滞留塘能够具备多种用途。