Lot Infiltration Trenches Impacts on Water Quality

A comparison between lot scale infiltration trenches and a catchment scale detention basin was modelled using a case study catchment in EPA SWMM. The literature review established the need for comparing source control WSUD against larger traditional scale catchment measures for treatment. In WSUD manuals the concept of source control is encouraged over catchment scale infrastructure. The implementation of WSUD is identified as a strategy with proven potential to deliver environmental flows, restore stream baseflow and remove key pollutants through the replication of natural catchment elements which are removed through the urbanization typical in the Anthropocene Various modelling software was analysed it was found EPA SWMM had key advantages over MUSIC. It is said that EPA SWMM is more suitable for detail design objective and accurately depicting stormwater infrastructure within the conveyance network. Additionally, the open source license of EPA SWMM met that it was freely available. The literature review found a deficiency of case studies for EPA SWMM in an Australian context, with modelling standards and extensive case studies completed using the more widely adopted industry standard, MUSIC. The literature review identified that EPA SWMM could be used to directly compare the performance of different treatment measure place at different scales in the catchment, making it a suitable choice for delivering the desired simulation outcomes. Furthermore, EPA SWMM contained processes by which Build-up and Wash-off could be assigned to land-use which meant it showed potential for future long-term simulations when compared to simple EMC estimates which are specific to isolated rainfall events The case study location was selected balancing data availability and proximity. Where data was available, it was incorporated in the case study catchment. Any parameters which were not available were taken from literature and other case studies. Additionally, key simplifications were required to ensure that the project could meet the required timeframes. The dissertation aim was achieved using three distinct model runs. Model run 1 to simulate unmitigated development, without the implementation of treatment measures. Model run 2, with the same parameters as model run 1 except a detention basin placed at the catchment outlet. Model run 3, same as model run 2 except with infiltration trenches installed at each lot of the catchment. Model run 2 and 3 were each compared against model run 1 to assess the pollutant reduction afforded by the different treatment measures. The results showed that the infiltration trench (model run 3) achieved a 55% TSS reduction compared to a 4% TSS reduction observed in the detention basing treatment simulation. A sensitivity analysis reveal that the detention basin was sensitive to the selected geometry, in addition to the settling velocity adopted in the treatment function. For the infiltration trench model run, the most sensitive parameter related to treatment is the BMP removal efficiency, which requires calibration and significant research to be applied. The BMP removal efficiency established in a Tetra tech study (2010) showed that the treatment observed is a function of the runoff depth treated and the 50% of the soil in-situ saturated hydraulic conductivity. The selected catchment for the case study did not have such performance curves developed, which meant that value adopted for the catchment studied by Tetra Tech in Prince George County, USA, were used for the case study catchment developed in Darling Heights, Toowoomba. Therefore, while the results show that infiltration trenches at lots outperform a regional detention basin, further work is required to ensure the relevance of the model conclusion. Data is required to calibrate hydrologic and quality results, in addition to the development of BMP performance curves that give an accurate representation of TSS treatment performance for the case study catchment