Headworks is a facility withdrawing water from irrigation sources to the main canal in the volume and time required for irrigation in accordance with the relevant water use schedule.

Water intake facilities, or headworks, are constructed for withdrawing water from a river (or reservoir) to the main canal. Water intake facilities are usually built along with a dam, sediment tank, river control structures, hydropower plants, etc. The complex of such facilities is called the hydraulic system of water intake facilities, or head hydroscheme.

The water intake facilities of the irrigation system must meet the following requirements:

1. withdrawing water to the main canal at the rate strictly complying the water use schedule irrespective of water level fluctuations in the water source;
2. protecting the canal from getting bed loads of sand and gravel, floating bodies, ice to it, and confining entry of suspended sediments (i.e. transported by the river in suspended state);
3. provide unimpeded passing of flood and storm flows;
4. where necessary, complying with the requirement of navigation, fishery, energy industry, and timber floating;
5. allowing measuring water flow passed through the facilities;
6. making it possible to repair the facilities without ceasing water supply to the canal;
7. being durable, long-run, low-cost, service-strong, and having simple design.

There are two principal types of water intake facilities for gravity water withdrawal from the river to the main canal: river-canal (damless) intake and dam intake.

River-canal intake is applied in the cases when the water level in the river is higher than the full supply level in the main canal by 10-120 cm at the water intake ratio (ratio of the water quantity withdrawn to the canal to the river flow) of not greater than 0.2 and under favorable conditions for laying the canal. River-canal intake is also set if the water level in the river is slightly lower than in the canal, mainly in mountain and submountain sections of the river with the control of water level in low-water seasons by means of water-harvesting dams and spur dikes without building a permanent dam.

At dam intake, the river channel is dammed up; at that, the river water level rises and the water inflows through the head regulator (offtake) to the main canal. Dam intake facilities are installed at a water intake ratio over 20% and if it is necessary to raise the water level, control the flow, withdraw water on both sides of the river, improve navigation conditions, and produce electric power.

At gravity intake, the headworks represents a check structure with a gate; at mechanical intake, a pumping station serves as the water intake facility.