Storm Water Management by Pervious Concrete

pervious_handPervious concrete is a mixture of cement, water, and coarse aggregate, and little to no sand. It also frequently contains chemical admixtures. Pervious concrete creates a very porous medium that allows water to drain to the underlying soils. 它通常允许5加仑/英尺²/分钟通过混凝土主体. 

By allowing rain events to penetrate the pavement to the underlying soils, the first flush of the paved surface is contained on site. The natural infiltration of the area remains unchanged so the water can recharge the water table. 这避免了地表径流必须保持在池塘或添加到暴雨水面径流, which must then be treated before it is returned to the local streams. 在许多情况下,路面也可以在路面下面设计一层粗颗粒材料,以增加系统的存储潜力. 这已被证明是一种有效的工具,以增加项目的可用路面面积,并满足当地的水管理法规.

See technical information on pervious concrete.


Hydrologic Design of Pervious Concrete

Pervious concrete has been used in some areas of the country for decades.  然而,最近对可持续发展的兴趣以及美国环境保护署承认透水路面是雨水管理的最佳管理办法,使人们对使用透水路面更感兴趣. 它的使用支持了国家倡议,如EPA的热岛减少倡议和低影响发展,并为可持续建筑建设的领先能源与环境设计(LEED®)评级系统提供了潜在的信用.

Pervious concrete can improve water quality by capturing the “first flush” of surface runoff, reduce temperature rise in receiving waters, increase base flow, and reduce flooding potential.  The pavement creates a short-term storage detention of rainfall. In order to fully utilize these benefits, the hydrological behavior of the pervious concrete system must be assessed. 在决定将这种材料作为雨水管理的最佳管理实践(BMP)时,水文性能通常是一个关键参数,也是颁发许可证的机构最感兴趣的特征.

Passive and Active Mitigation Systems

In many situations, 使用透水混凝土代替不透水表面可以被认为是管理径流的一个足够的管理标准. In others , 法规可能要求开发后的径流量不超过开发前径流量的百分比. These two applications are termed passive mitigation and active mitigation, respectively. In the latter case, 透水混凝土路面系统必须专门设计以应付比路面本身降下的更多的降雨. For example, 停车场可以用来收集落在自身和周围地区的雨水的剩余径流, including, the rain collected and discharged through roof drains of nearby buildings.


Passive Mitigation

"被动"缓解因素仅用于通过将不透水表面替换为透水表面来减少给定区域的不透水表面数量. A passive mitigation element might also capture much, if not all, of the “first flush,” providing additional hydrological benefit, but is not intended to accommodate excess runoff from adjacent surfaces.

Active Mitigation

An “active” mitigation system, on the other hand, 设计是为了在具有几种特征的特定地点将总径流维持在某个特定水平. 在主动缓解系统中使用的透水混凝土必须从现场的其他区域捕获相当大一部分径流,以及自身“足迹”下的雨水.” Typically, such areas include buildings, areas paved with conventional pavement, and traffic islands and buffer zones. 主动缓解系统特别适合于恢复现有的不透水地区,以便对城市径流进行补救控制,因为它们可以设计成从邻近地区收集径流. Depending on the size, geometry, and porosity of the pervious concrete system, the excess surface runoff from the site can be kept at or returned to pre-development levels. 主动透水混凝土路面系统也可以设计为与传统路面结合使用的边界特征,以创建一个局部活跃, but site wide passive feature.

                                                    pervious_15883

Figure 1. Pervious concrete sections in this parking lot (Finley Stadium, Chattanooga, Tennessee) help control runoff. (Photo courtesy of L. Tiefenthaler.)

For example, a pervious concrete system can be designed to capture and temporarily store much, if not all, 通过将一个相对狭窄的透水混凝土带放置在一个深的, clean stone base along the edges of the parking lot (see Fig. 1).

透水混凝土边界用于树井或植被交通岛可以被设计为活跃的元素, helping maintain the net runoff from the entire parking area at desired or constrained levels. 透水混凝土路面系统的一个重要的好处是,有植被的岛屿或树井的足够的水分可以用最小的, if any, need for irrigation. 这在有最低树木密度要求或保护大型树木时尤为重要, existing trees on the site. The active mitigation design approach is very flexible and can be used for a variety of applications. 因此,透水混凝土在积极缓解作用中的主要应用包括商业停车场, boundary features of commercial development sites, 以及设计用于在进入排水渠道之前拦截至少一部分地表径流的围堵装置.

The limiting factor for active mitigation applications are poorly draining soils (generally those, with infiltration rates considerably less than 0.1 inches per hour, 因为透水混凝土系统必须在合理的时间内(通常五天或更短)清空,并恢复全部的存储容量。. 在这些类型的土壤的被动缓解应用中,恢复时间通常不是一个主要问题,因为渗透缓慢,即使是自然覆盖的土壤,径流也相对较高(见图). 2.)

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Figure 2. 降雨渗入土壤增加了透水混凝土路面系统的有效蓄水能力.

Design Storms

在设计透水混凝土系统时,另一个重要的考虑因素是要储存的雨水量. Clearly heavier rains result in more runoff. 不同大小的风暴会产生不同数量的径流,选择合适的设计风暴是很重要的. 较大的风暴发生的频率平均较低,风暴通常是根据它们的重现期来指定的. For example, 一场平均20年发生一次的风暴被称为“20年风暴”,它将比“10年风暴”更大,产生更多的降雨.” Often local authorities choose the design storm, such as city or county water boards. 在小流域的水文设计中,最受关注的风暴通常是两年风暴和十年风暴. 两年风暴常被用作分水岭的“服务负荷”风暴,以提高水质. The 10-year storm has traditionally been used in the design of storm water collection systems. Rainfall estimates for many areas are available online at NOAA's National Weather Service

Resources

Overview of pervious concrete pavement is available though the National Ready Mixed Concrete Association.

Tennis, P. D., Leming, M. L., and Akers, D. J., Pervious Concrete Pavements, EB302, Portland Cement Association, Skokie, Illinois, and National Ready Mix Concrete Association, Silver Spring, Maryland, 2004, 25 pages.