Proper Sizing of Infiltration Trenches Using Closed-Form Analytical Equations

Infiltration trenches in urban areas are mainly used for the purposes of water balance maintenance and water quality improvement. To ensure that a high enough fraction of runoff from a contributing catchment is infiltrated, trenches are usually sized to provide enough storage capacity so that runoff from a design storm of certain depth can be temporarily stored and infiltrated. Since it is difficult to quantify the actual long-term average runoff reduction ratio provided by individual trenches, their exact long-term average performances are often unknown. In this study, the closed-form analytical equations derived and verified previously for the estimation of the long-term average trench performance are applied in the practical design analysis of infiltration trenches following the detailed design guidelines of Atlanta, Georgia and New Durham, New Hampshire, U.S.. The results demonstrate that the conventional design storm-based design procedure cannot always ensure uniform trench performances because of different site soil and infiltration conditions. Use of the analytical equations (also known as the analytical stormwater models) can facilitate more accurate and consistent design of infiltration trenches because the effects of soil type, trench footprint dimensions, drain time and infiltration conditions on trench performance are all taken into consideration. The analytical equations are recommended as a convenient tool for the proper sizing of infiltration trenches so that a uniform long-term average performance can be achieved for all individual cases.