Seven-Year Running Effect Evaluation and Fate Analysis of Rain Gardens in Xi’an, Northwest China

Abstract

Rain gardens have recently been studied as important low-impact development (LID) facilities that play a critical role in runoff volume reduction and pollutant purification. Approximately 16-40 rainfall events were monitored from March 2011 to October 2017 in order to determine the running effect of three rain gardens with respect to runoff volume reduction and pollutant purification. In particular, running fate analysis of rain gardens is the key focus in this study. Combined analyses revealed three key points. Firstly, performance assessment demonstrated that rain gardens effectively cut inflow volumes through the filter media; when the confluence area ratio was 6:1-20:1 (confluence ratio = roof area or road/garden area) and the rainfall was approximately 2.8-39.9 mm, the runoff volume reduction rate ranged from 9.8% to 100.0%. However, the average annual runoff reduction rate presented an initially increasing and then gradually decreasing trend with monitoring time. Secondly, according to water quality data in 54 rainfall events, the annual average concentration removal rate of NH 4 + -N was relatively good, but generally decreased with monitoring time. The concentration removal rate of NO 3 − -N and total phosphorus (TP) is unstable; however, the removal rate of total suspended solids (TSS) is better than that of total nitrogen (TN). Combined with runoff reduction, the pollutant load reduction by rain gardens is greater than 50%, although this decreases with increasing monitoring time. Thirdly, through the study of 7-year running effect on runoff reduction and pollutant purification, the "three-stage purification (TSP) concept" (periods of purification growth, stability, and attenuation) with respect to pollutant load reduction processes was finally proposed, and a curve chart was drawn for pollutant load reduction and rain garden operating fate (the "P-F" curve chart).

The Composition of Urban Storm-water Runoff Pollutants in Sediment and Loess Soil in Rain Garden

“…A total of 47 rainfall events were monitored of RG2, and only eight rainfall events produced the overflow from the system. The annual average runoff volume reduction rate of RG2 was more than 97.3% [6]. Because of the special structure of RG3 with 0.5 m aquifer, no overflow occurred in case of RG3-E from 2012 to now.…”

“…Water Quality of the Inflow Forty-two rainfall events about rain garden of RG1 were monitored during the period from March 2011 to August 2018. The runoff volume reduction ranged from 9.80% to 100.0%, and the flood peak flow reduction rate varied from 20.3% to 100.0%.The NH 3 -N, NO 3 -N, TN, TP and TSS concentration reduction rate varied from 7.83%~94.22%, -583.50%~58.65%, -119.30%~85.06%, -467.40%~48.89%, -18.60%~100.0% [6]. A total of 47 rainfall events were monitored of RG2, and only eight rainfall events produced the overflow from the system.…”

“…Because of the special structure of RG3 with 0.5 m aquifer, no overflow occurred in case of RG3-E from 2012 to now. The runoff volume reduction rate of RG3-E was 100.0%, so all the pollutants carried in the rainfall runoff entered the system [6]. The pollutant EMC concentration and the load of inflow were shown in Table 2.…”

“…Stormwater nitrogen and phosphorus are present in a number of chemical forms, including ammonium (NH 3 -N), nitrate (NO 3 -N), nitrite (NO 2 -N), dissolved organic N (DON), particulate organic N (PON), soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP), and dissolved phosphorus (DP), etc [5]. The pollutants composition varies with land use and hydrologic conditions [6]. Nitrogen and phosphorus behavior in stormwater runoff are therefore complex because of the biogeochemical complexity of their species.…”

The Urban Environment Impact of Climate Change Study and Proposal of the City Micro-Environment Improvement

“…The decision on suitable sites therefore needs a detailed knowledge of current and historical conditions. Urban areas are characterized by a high proportion of impermeable areas (e.g., roads, roofs of buildings), which in urban centers reaches 70% or more [61]. Water raining on the surface of a river basin during precipitation cannot naturally infiltrate the groundwater collector.…”