30 Tex. Admin. Code § 299.31
The owner of a proposed dam or a dam proposed to be reconstructed, modified, enlarged, rehabilitated, altered, or repaired shall have the professional engineer of record establish one or more permanent reference mark(s) for future use near, but separate from, the project. Accurate location(s) and elevation(s) above mean sea level for the permanent reference mark(s) must be shown on the record drawings. Horizontal and vertical measurements recorded with a global positioning system (GPS) receiver must be based on the North American Datum of 1983 and the North American Vertical Datum of 1988 horizontal and vertical reference datums. Elevation data must be recorded using a survey instrument or survey grade GPS receiver. Latitude and longitude measurements must be provided in decimal degrees to six decimal places.
30 Tex. Admin. Code § 299.31