Hydrological surveys can be carried out by professional surveyors, to identify soil characteristics, water supply and other factors, in order to develop a ‘water budget’ for the site. Models can be drawn up to produce precise information on spacing of ditches, pipes, sluices and so on, to produce particular desired heights of water table.
For small schemes, a simple survey should be carried out to measure the area and ground levels within the site. A knowledge of basic surveying techniques using a surveyors’s level is required. Dig test pits and take soil samples as necessary, to determine ground water levels and soil permeability. Draw a scale plan, marking the position of inlets and outfalls, and design the ditches, drains or supply pipes to fit within recommended gradients.
Mark out the lines of drainage or water supply with pegs, using a surveyor’s level to give the correct heights for each peg to ensure a smooth gradient. Erect a ‘profile’ at each peg to act as a reference point, with the sighting rail at a measured height above the peg.
A ‘traveller’ is useful, cut to the vertical height from the top of the sight rail to the bottom of the ditch. To use the traveller, set it vertically in the bottom of the ditch as it is being dug, and if necessary adjust the ditch depth until the sight rail lines up with the next two profiles. Consult publications on surveying techniques and land drainage for further advice.
