Early hydrologic and hydraulic numerical modeling of urban drainage systems focused on the minor system (i.e. storm sewer only). Over the past three decades there has been increased interest in the concurrent evaluation of the conveyance capacity of the major system (i.e. overland flow-roadways). More and more, these two systems are being modeled dynamically, using a linked approach known as dual drainage modeling. Dual drainage modeling allows for an improved assessment of the deficiencies in both systems, through integrated assessments which consider the interaction between the two systems.Of key interest in dual drainage models is the representation of inlet capture functions (roadway catchbasins and ditch inlets) since these intrinsically link the two often-parallel flow conveyance systems. The accurate representation of these features is critical, given the potential implications for basement flooding, surface ponding or flooding, and the development of appropriate drainage system designs. This paper describes various methods of modeling these functions and assesses them under different conditions, using models that had been developed for several urban communities. The relative benefits and drawbacks of each method are given and discussed, along with associated considerations for minor and major system design in dual drainage modeling.

Storm sewer systems and their associated utility trenches may strongly influence the effects of urbanization on a groundwater system. This study was undertaken to identify the causes of district‐wide basement infiltration in an aquitard system. It comprised widespread continuous monitoring of utility trench wells and dye tracing from storm sewer system exfiltration tests. The results indicate that a major effect of urbanization on shallow groundwater is related to storm sewer system exfiltration, which is marked by a characteristic pattern of head variations in the aquitard unrelated to distributed surface infiltration. The aquitard constrains flow from storm sewer system exfiltration to the utility trench, creating an urban flow path for groundwater discharge. Temporary buildup of water levels in the utility trench drives relatively high‐velocity flow through the permeable sewer bedding material of the utility trench to a separate foundation drainage collector system, ultimately causing a severe “urban karst” effect that produces system surcharging and widespread basement water infiltration. The main conditions causing the “urban karst” are the large hydraulic conductivity ratio between the utility trench material and the aquitard, and the shallow depth and low gradient of the storm sewer system imposed by a very flat drainage basin.