Irrigation Surveying
Planning and surveying for irrigation networks. El-Eman Office provides agricultural surveying services.
Canal and Drain Levels and Their Relation to the Ground
The basis of irrigation network design is that, for surface irrigation, the water level in the canal must be higher than the ground to be irrigated, and the drain level must be lower than the ground to collect excess water. This can only be achieved with an accurate level map. Even small differences in level mean large differences in how much water reaches the far end of a field. Work therefore starts with a levelling grid covering the whole area, from which the controlling levels for the main canal and then the branch canals are set.
- Choose the canal gradient so it causes neither silting nor scouring of its banks.
- Check the levels of distribution outlets, gates and bridges.
- Compare the drain level with the final outfall level.
- Make sure canals pass structures without conflict.
Laser Levelling of Farmland
A modern technique is to level a field with a laser unit mounted on tractor equipment, giving a surface with a uniform slope at an accuracy the eye cannot match. Levelling helps distribute water evenly, reduce losses, improve germination and cut the flooded or thirsty patches within one field. It is always preceded by measurements that fix the cut and fill quantities and plan their balance so soil is not carried long distances unnecessarily.
In modern irrigation (drip and sprinkler), the need for slope for surface flow is less, but levels still matter for working out pressure and discharge in the pipes, especially on undulating land.
Route Mapping, Land Acquisition and Documentation
Canals and drains cross land owned by several parties, so routes need precise definition of the canal corridor and property boundaries. Boundaries are surveyed and tables of the affected areas are prepared to organise understandings with owners and the competent bodies. After construction, the as-built route is surveyed to update records and fix responsibility for maintenance.
- Survey the centrelines, culverts and hydraulic structures.
- Calculate excavation quantities to estimate project cost and schedule.
- Check the actual canal dimensions against the design.
- Update the maps after any changes made during construction.
Maintenance and Operation After Construction
Silt builds up and weeds grow in canals, so their capacity falls over time. They therefore need periodic clearing and a review of their levels and structures. Measuring canal cross sections from time to time shows how much silting or scouring has occurred. In closed irrigation networks, valves, filters and pressures are checked regularly to keep distribution efficient.
Frequently asked questions
Why does water collect in one part of a field despite regular irrigation?
Usually because of a local low spot in the ground or poor drainage in that part. A level map reveals these areas and helps correct them by levelling.
Is laser levelling necessary for every farm?
It is not compulsory, but it is useful, especially for surface irrigation, as it saves water and improves distribution. Its worth is judged by the size of the land, the crop and the irrigation method.
Why are agricultural drains important?
They prevent the groundwater level rising and salts accumulating in the soil, which harms crops, and they keep the land fit for farming over the long term.
