Glossary of terms

Ground level

Ground level is the elevation of the ground surface at a point along the route, given in metres relative to the vertical datum. In a longitudinal profile the ground line runs above the pipe invert line; the vertical distance to the invert is the installation depth, and the distance to the pipe crown is the cover. Ground levels come from survey data or a digital terrain model and govern how deep the pipe must be laid. When checking a profile, compare ground levels with survey data at characteristic points and watch the minimum cover over the pipe — too little risks frost and mechanical damage.