Drainage Impact Study in Dallas, TX

A drainage impact study is an engineering analysis that shows how a proposed project changes stormwater runoff volumes and flow rates on and around a site. In Dallas, it includes a drainage area delineation, runoff calculations for multiple storm events, and a downstream capacity check to confirm the existing system can handle the added flow.

Most new development and redevelopment projects in Dallas that require a site plan, grading permit, or subdivision plat approval also require a drainage impact study. The City of Dallas Drainage Design Manual sets the thresholds, and the study must be submitted as part of the Development Review Committee process.

Infill redevelopment on parcels smaller than one acre may be exempt from detention requirements under the City of Dallas Drainage Design Manual, though a drainage analysis may still be required depending on the permit type. The specific exemption depends on the project scope, parcel size, and the type of city approval being sought.

Yes, projects near or within a Special Flood Hazard Area in Dallas must comply with the City's floodplain regulations under Article V, Section 51A-5.100, in addition to standard drainage requirements. FEMA flood maps are used to establish base flood elevations, and projects that alter a floodplain may require a No Rise Certificate or additional engineering documentation.

Dallas sits on Blackland Prairie clay soil that becomes nearly impermeable when wet, so rainwater sheets across the surface instead of soaking in. Dense impervious cover from roads, rooftops, and parking lots adds to the runoff volume, and much of the city's drainage infrastructure was designed for a smaller population than exists today.

The City of Dallas Sustainable Development and Construction department reviews drainage studies through the Development Review Committee process, which includes input from Dallas Stormwater Services. The submitted study must be prepared and sealed by a licensed professional engineer to be accepted for review.