Dynamically coupling enhanced 1‐D sewer network and 2‐D surface routing for urban drainage

Hazem Gheith and Qiuli Lu


Hydraulic models have been used to investigate model hydrological processes in urban environments in many years. The most commonly used urban drainage modeling uses traditional 1‐Dimensional (1‐D) surface hydrology routing. In this traditional approach, runoff from impervious and pervious surfaces uses aggregated parameters that overlook several surface routing constraints. Usage of these models is limited in terms of predicting flood extent or estimating the surface flows that can be captured by lowimpact development (LID) structures which many municipalities are actively placing in the system. This constraint can be resolved through two stepped approaches, enhanced 1‐D platform, and a 2‐D enhancement to focused areas.

Enhanced 1‐D modeling aims to better represent the dynamics of urban storm drainage. It makes use of advancement in digital elevation data and processing application tools to achieve a high‐resolution urban stormwater planning model that improves planning quality at reduced cost. In this approach, similar hydrologic components like houses, lawns, and streets are modeled separately with appropriate physical parameters. Streets are modeled as open channels to route the surface flow to the storm inlets. Depress areas are modeled as storages to track local flooding severity. The enhanced 1‐D modeling is appropriate for LID planning to study water quality, water quantity, and stormwater drainage compliance.

For identified flooding zones, a 2‐dimensional (2‐D) overland flow routing is added. In this step, overland flow and infiltration are applied on a 2‐D grids which has the proper hydrological parameters defined based on its physical properties. The 2‐D flow is routed into the overall 1‐D enhanced model. The 2‐D modeling assists to further understand the surface flooding route, flooding depth and spreading. 2‐D modeling is applied only at focused areas due to its large size. Model efficiency and simulation times are considered when adding 2‐D portion. 2D answer questions that help the design that 1D cannot answer, like the flow escape from the street to between the houses to another street. Depending on the planning and design levels Enhanced 1D or 2D is used at the right mix. The objective of this study is to improve the urban drainage systems modeling approaches to cope with the ongoing stormwater management. Enhanced 1‐D and local 2‐D models are dynamically coupled, allowing for flow to be exchanged between the two models throughout the simulation. This approach provides a more accurate prediction of flow to LID units, surface flooding, and network flow.

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