2015 Asia Pacific Stormwater Conference OPTIMISATION OF BAFFLES FOR SEDIMENT RETENTION PONDS Arash Farjood, Bruce W. Melville, Asaad Y. Shamseldin The University of Auckland, Auckland, New Zealand ABSTRACT Effective treatment of the polluted stormwater runoff from earthworks sites is a major concern for water authorities. Sediment retention ponds provide a quiescent place for settling the suspended particles in runoff. However, improper design of ponds can lead to significantly low treatment efficiency. As a retrofit practice, baffles have been utilised to improve the rate of settling of the suspended particles. Yet there is limited information in the design guides about the optimum configuration and type of baffles. This study investigates the effect of porous and submerged solid baffles on the hydraulic performance and trap efficiency of a model sediment retention pond. Several configurations were tested using four different metal meshes (with different aperture size and open area) as porous baffles, and acrylic sheets as solid baffles. The porous baffles were more effective in improving the overall hydraulic performance than the solid baffles. For 4 and 5 baffles, the medium-fine mesh with 1 mm aperture size and 42% open area was the best. The two porous baffles with same aperture sizes but different open areas had different hydraulic performance which highlights the importance of aperture size in addition to the total open area. The trap efficiency for the tested configurations was consistent with the result of hydraulic performance analysis. The present paper is continuation of the work presented at the Water New Zealand’s 2014 Stormwater Conference. KEYWORDS Sediment retention ponds, Baffle, Hydraulic performance, Trap efficiency, Residence time PRESENTER PROFILE Originally from Iran, I hold bachelor’s degree in Irrigation and Drainage Engineering from Shiraz University, Iran. I did my masters in Urban Water Engineering and Management at the University of Sheffield in the UK, in 2010. I’m currently at the last year of my PhD at the University of Auckland. 1 INTRODUCTION Land development and earthwork significantly contribute to soil erosion and accelerated transport of sediment into water ways and reservoirs. In the Auckland region in New Zealand, it is estimated that unprotected earthworks sites could produce up to 66 tonnes of sediment/hectare/year (ARC 1999), which is hundreds of times the yield from a vegetated land. The major concern associated with soil erosion is movement of the soil off site during rainfall events and its subsequent severe (and sometimes irreversible) impact on the sediment budget and aquatic ecosystem of the receiving waters. Therefore, incorporation of effective practices for controlling the suspended sediments in the runoff from disturbed lands is vital for protecting receiving environments. Among practices for treatment of sediment laden runoff, sediment retention ponds (also known as sediment basins or settling ponds) are one of the most important ones. Sediment retention ponds are built (usually temporarily) near construction sites and