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Receiving water quality concerns associated with increased construction activities in recent years in the Greater Toronto Area has prompted the Toronto and Region Conservation Authority (TRCA) to evaluate design criteria for sediment control ponds employed during the construction period. Stormwater management ponds located in the towns of Richmond Hill and Markham were monitored to obtain stormwater runoff quantity and influent-effluent quality data during site development. The ponds were designed and constructed in accordance with the Ontario Ministry of the Environment Stormwater management planning and design manual 2003 for an enhanced level of protection (i.e., 80% total suspended solids removal). A hydrodynamic and sediment-transport model was used to examine the effect of pond geometry on sediment removal efficiency under varying storm events. The monitoring data and the modelling results clearly demonstrate the importance of proper pond size and geometry design. This paper focuses on the effect of the ratio of pond length to pond width in minimizing the short-circuiting effect and improvement of the sediment removal efficiency of stormwater management ponds. The results of this study will be useful in updating the design criteria for stormwater management ponds. [ABSTRACT FROM AUTHOR]