On the efficiency of stormwater detention tanks in pollutant removal

Abstract

In the design of a stormwater detention tank is important to guarantee a sufficient retention time for the sedimentation of suspended solids, the biological uptake of nutrients and the die-off of bacteria carried in rainwaters. Long retention times increase the capacity of pollutant removal, but also the possibility of spills in downstream receivers and the risk of environmental pollution. In this paper, an analytical probabilistic approach, to estimate the probability distribution function of the average retention time and the efficiency in pollutant removal of stormwater tanks has been proposed. The possibility of water mixing from consecutive runoff events and storage carryover due to successive rainfall events has been considered. The method has been applied to a case study in Milano, Italy.

Vegetation Survival in Green Roofs without Irrigation

“…Table 2 contains correlation index among rainfall variables. With reference to correlation index, it's evident that correlation between rainfall depth and interevent time and correlation between interevent time and rainfall duration is negligible while correlation between rainfall depth and rainfall duration is high; effects on this assumption on results have been discussed in previous works [32]. Potential evapotranspiration and water content at saturation have been assumed respectively equal to Et=0,131 [mm/hour] and =0,58 [-] [8]; growing medium thickness zg has been varied between 50 [mm] and 500 [mm].…”

Performances and Uncertainty of Temperature Methods for Illicit Infiltrations and Inflows Assessment in Stormwater Sewers

“…Case A1: Q 1 = 50 l/s, Q 3 = 100 l/s, T 1 = 20°C, T 3 = 18°C  Q 2 = 50 l/s, T 2 = 16°C Case B1: Q 3 = 100 l/s, T 1 = 20°C, T 2 = 30°C, T 3 = 25°C  Q 1 = 50 l/s, Q 2 = 50 l/s Case C1: Q 1 = 50 l/s, T 1 = 20°C, T 2 = 30°C, T 3 = 25°C  Q 2 = 50 l/s, Q 3 = 60 l/s Then, through eqns (5) and (6) and considering the uncertainty values assumed for the measured quantities, relative uncertainties for Q 2 and T 2 in the three cases A1, B1 and C1 have been estimated (Table 1).…”

“…Many regulations all over the world stress the importance to limit illicit flows into the stormwater sewers; it is very important not only to detect the so-called Infiltration & Inflow (I&I) into the drainage networks but also to understand their sources, trying to locate and quantify them. This knowledge is fundamental for the estimation of peak runoff [1] and the proper size of stormwater detention facilities [2]- [6] and Sustainable Urban Drainage Systems (SUDS) as like permeable pavements [7] and rainwater harvesting systems [8]- [10].…”

Performance of Green Roofs for Rainwater Control

“…Moreover, they are not influenced by a specific place, but can be applied to different basins and climates all over the world. In recent years, different applications of the analytical probabilistic approach have been proposed in literature for the modelling of stormwater detention facilities (Raimondi and Becciu 2017;Raimondi 2014, 2015); rainwater tanks Becciu 2011, 2014;Becciu et al 2018); infiltration trenches (Guo and Gao 2016); permeable pavements (Zhang and Guo 2014a); bioretention systems (Zhang and Guo 2014b), and green roofs (Guo 2016;Guo and Zhang 2014;Zhang and Guo 2013). In these works, the modelling of green roofs, does not take into consideration the possibility that the retention capacity could be partially pre-filled from more than one previous event at the beginning of the considered rainfall; this aspect is not negligible for this kind of systems, since outflows from green roofs are limited to evapotranspiration from vegetation and soil.…”