Odyssey Engineering Group performed a Drainage Impact Analysis for subdivision drainage improvements to Runneburg Estates, an existing subdivision in the Crosby community in east Harris County, Texas. The project area has experienced repetitive structural flooding, with structural flood events documented on at least eight occasions between 1979 and 2017. The Harris County Engineering Department’s (HCED) Recovery and Resiliency Division selected the project area for a subdivision drainage improvement project to reduce the risk of flooding.

The existing Runneburg Estates subdivision faced several significant drainage issues and constraints. The roadside ditches within Runneburg Estates are shallow, and the subdivision has numerous driveway culverts of substandard size. The entire 30-ac subdivision drains through a single 18-inch HDPE culvert to Ramsey Road. The subdivision is immediately north of Runneburg Road, which has insufficient capacity for the large offsite drainage area it serves. Due to this insufficient capacity, excess runoff spills into and through the Runneburg Estates subdivision. The proposed improvements will relieve some of these issues and reduce flood inundation depths in the area.

Due to the complex nature of the flooding condition, Innovyze’s XP-SWMM software was used to perform a 1D/2D analysis of discrete 1D elements (like roadside ditches, culverts, and channels) and 2D analysis for the significant sheet flow areas. Using XP-SWMM software, the existing and proposed drainage conditions were modeled for the 50%, 10%, and 1% AEP 24-hour storm events (based on Atlas 14 rainfall data). The proposed drainage improvements include excavating a proposed detention system and roadside ditch drainage improvements meeting HCED criteria. The analysis demonstrated no adverse impacts and flood depth reductions of as much as 2.2’ in the project area.