Combined Optimization of LID Patches and the Gray Drainage System to Control Wet Weather Discharge Pollution

Low impact development (LID) has emerged as an effective management to control urban runoff. However, for storm drainage systems located in high-density old urban areas with scarce land resources and fragmented landscapes, there are difficulties in the application of LID layouts. To solve the waterlogging and wet weather discharge pollution (WWDP), based on the spatial distribution of available land resources, runoff path, ponding area, overflow nodes, and sediments in drainages, a spatial optimized layout method of LID patches combined with gray drainages was proposed and applied to a typical storm drainage system in Shanghai, China. Only 22.9% of the ground surface and 14.0% of the roof, which accounted for the study area were reconstructed to LIDs, and the optimal LID patches combined with 0.4 m storage capacity depth (SCD) could prevent discharge below 6.5 mm rainfall. The optimal LID-gray drainages increased the reduction ratios of suspended substances (SSs) in WWDP by 37–74% compared with only LID patches in 9.1–21.8 mm rainfall. The “LID patches-gray system” could effectively control WWDP in old urban areas with high frequencies of moderate and light rain. The proposed methodology can be instructive for the sustainable reconstruction of storm drainages inappropriately connected with sewage

Editorial Note, Indonesia, volume 51, (April 1991)

<p>a, all data; b, non-rainfall days (≥7 days after rainfall); c, final day of rainfall; d, 1 day after rainfall; e, 3 days after rainfall; f, 5 days after rainfall.</p

Stoichiometric Determination of Nitrate Fate in Agricultural Ecosystems during Rainfall Events

<div><p>Ecologists have found a close relationship between the concentrations of nitrate (NO₃^-) and dissolved organic carbon (DOC) in ecosystems. However, it is difficult to determine the NO₃^- fate exactly because of the low coefficient in the constructed relationship. In the present paper, a negative power-function equation (<i>r</i>² = 0.87) was developed by using 411 NO₃^- data points and DOC:NO₃^- ratios from several agricultural ecosystems during different rainfall events. Our analysis of the stoichiometric method reveals several observations. First, the NO₃^- concentration demonstrated the largest changes when the DOC:NO₃^- ratio increased from 1 to 10. Second, the biodegradability of DOC was an important factor in controlling the NO₃^- concentration of agricultural ecosystems. Third, sediment was important not only as a denitrification site, but also as a major source of DOC for the overlying water. Fourth, a high DOC concentration was able to maintain a low NO₃^- concentration in the groundwater. In conclusion, this new stoichiometric method can be used for the accurate estimation and analysis of NO₃^- concentrations in ecosystems.</p></div

NO₃- concentration as a function of changes in the molar DOC:NO₃- ratio among major ecosystems of the rainfall transport route.

<p>a, all data; b, experimental systems; c, rainfall; d, runoff; e, drainage ditch; f, porewater; g, groundwater; h, river.</p