Storm Water Master Plan Development Employing An Integrated 1D/2D Model For The Redwood Basin In Josephine County

By Ryan Retzlaff, Cardno and Anthony Kuch, XP Solutions

The use of two-dimensional (2D) storm water models has increased in recent years primarily due to advances in software, hardware and the availability of surface data. These advances allow for robust and diverse applications including basin-wide storm water assessments. Storm water master planning is a critical element for the development of state and local agency comprehensive plans, capital improvement projects, and associated budgets.

The Josephine County Public Works Department in Josephine County, Oregon, used an integrated one-dimensional/two-dimensional (1D/2D) model for storm water master plan assessment. When a storm water conveyance system is under capacity, a 1D schematization alone cannot accurately model flow once it surcharges out of the 1D elements. The linkage of 1D and 2D models allows water to move out of a 1D element then return to the same or another 1D element. This complete description eliminates model losses due to surcharging and inaccurate 1D description of surface storage. For example, flows leaving an irrigation canal, defined with cross sections in 1D, can flow overland via the 2D grid cells to a downstream irrigation canal or stream.

The results of this comprehensive hydrologic and hydraulic analysis include the discovery of overland flow routs between open channel elements during surcharge and 2D map results which include depth, volume, and the spatial extent of flooding.