Modeling of LIDs in Context of Sustainable Urban Drainage System

Abstract

Urban cities in developing countries often suffered from water logging induced by stormwater runoff due to the underperformance of their existing drainage networks, influenced by changed land use and climate, with an inappropriate solid waste management system and the absence of wastewater networks. Although traditional drainage design is seen as accommodating runoff volume, runoff quality and drainage design amenities are often overlooked. Therefore, a drainage network constructed with conventional methods failed to address sustainability aspects that give equal importance to quantity, quality, and amenity. In this context, sustainable urban drainage systems, or low impact development (LID), open the windows of drainage design by integrating all the above aspects with cost-effectiveness. Although several studies on the quantity, quality, and amenity of drainage networks exist on separate scales, an integration of all of these along with cost-effective implementation is yet to be studied in detail. The aim of the study is to evaluate the performance of LID components, including quantity, quality, and amenity aspects, at a watershed scale under different climatic scenarios in the context of stormwater management using the Chaktai-Rajakhali watershed, which serves as significant stormwater drainage outlets for Chattogram city. The Personal Computer Storm Water Management Model (PCSWMM) software was used to simulate the rainfall-runoff and runoff quality derived from three different LID scenarios (S2-S4) addressing sources to the destination of runoff through the canal. Basic statistical analyses including principal component analysis (PCA) were performed using Statistical Package for the Social Sciences (SPSS v. 23). In addition, Sustainable Technologies Evaluation Program (STEP), a life cycle costing tool v. 3.0., has been used to evaluate the cost-effectiveness of proposed LIDs. The study revealed that the incorporation of LIDs into drainage systems can reduce peak discharge by 14% to 60% with an increase in lag time to peak flow of 30 to 105 minutes in comparison to the scenario without LID implementation. Based on runoff quality in existing or no LIDs, the event mean concentrations (EMC) of TSS, TN, TP, Zn, BOD, and COD in various land uses such as residential, industrial, commercial, and institutional were found to range from 275–1085 mg/L, 2.2–7.3 mg/L, 0.33–1.14 mg/L, 0.02-0.19 mg/L, 21–71 mg/L, and 57–201 mg/L, respectively. Moreover, the incorporation of LID techniques, while incorporating the proposed LIDs, exhibits a substantial reduction of pollutants’ amount in runoff ranging from 23 to 80%, depending on the LIDs choices. Considering the cost of installation, operation, and maintenance of proposed LIDs, it has been found that the LCA values of different LIDs vary in a wide range of 15 to 1252 US$ per square meter. While a single LID is not found to provide an effective solution (S2: vegetative swale), the S4 (combination of S2 and S4) appeared to be the most effective, followed by S2 and S3 in terms of quantity, quality, and amenity. It is hoped that the outcomes of this study can be a wakeup call to adopt sustainable urban drainage for addressing multiple benefits in future drainage design and to assist engineers, architect and city planners to manage stormwater runoff in effective ways.