Application of indices to evaluate LID facilities for sediment and heavy metal removal

Heavy metal and sediments transported from the urban catchment are the prime interest among researchers these days due to its toxic behaviour and hazardous effect on the animals, plants and human. The inflow from urban catchments and outflow from the Low impact development technologies (LID) were evaluated using different types of indices. Indices like f_d, f_p and K_d showed that heavy metals like Pb, Cd and Ni were dominantly observed in the dissolved form. These metals possess higher threat to the water bodies receiving urban runoff without any treatments. The state of heavy metal was highly dependent on the particle size which was directly affected by the TSS EMC in urban area. The indices like f_d, f_p and K_d were good enough to understand the behaviour, nature and state of metal in urban inflow and outflow from the system. On the other hand, calculated MPI and PERI indices showed that runoff from urban areas without any treatment bare very strong risk to the environment. LID technologies were found to be the better option in reducing the risk of urban areas to the receiving water bodies. These indices could be valuable for the decision making before the selection of applicable LID types, plants and filter media. Furthermore, indices like these can be devised to measure the impact of LID system to the environment as well as the decision making tool before discharge of outflow to the nearby streams.