Lewisville, TX Environmental Rules: Grading & Drainage (2026)

Lewisville regulates grading and drainage through its development ordinances and engineering standards. A grading permit is required for land-disturbing activities that change the existing grade or drainage patterns. Development projects must submit a drainage study demonstrating that post-development stormwater runoff rates do not exceed pre-development conditions. Detention or retention basins may be required to manage increased runoff from impervious surfaces. The finished grade around structures must slope away from foundations at a minimum of 6 inches of fall within the first 10 feet. Property owners may not alter grading or drainage to direct stormwater onto adjacent properties. Existing drainage easements must remain clear and unobstructed. Construction within drainage easements requires written approval from the Engineering Department. The city maintains public drainage infrastructure including storm sewer pipes, channels, and detention facilities. Private drainage improvements on individual lots are the property owner's responsibility to maintain. Driveway culverts and lot-to-lot drainage swales must remain functional. Report drainage blockages or flooding concerns to the Engineering Department at (972) 219-3590. Major development projects may require a Letter of Map Revision (LOMR) from FEMA if they modify base flood elevations.