The main building of the irrigation system can be defined as a complex of buildings that are planned along the river or stream to divert water into a network of channels that can be used for irrigation purposes. The main building can reduce excessive sediment load, and measure the amount of incoming water. The main building consists of a weir with energy absorbers, one or two major decision, flush doors, megrim pool, and a bag of mud, flood dikes and building complementary.
a. Weir
Weir on the surface irrigation systems can be divided into two types, namely weir (weir) and motion weir (barrage). Weir is used to raise the water level in the river up to a certain height necessary for water to be flowed into the irrigation channel and tertiary. It will determine the height of the area irrigated. Dam building bending motion is equipped with a door that can be opened to drain the water at the time of the great flood and closed when a small stream.
In Indonesia, dam building motion is most commonly used to divert river water for irrigation purposes.
Figure 9. weir motion
b. Rubber weir
Rubber dam has two main parts, namely the body is made of a rubber dam and a concrete foundation slab concrete shaped as a rubber tube holder and a control room equipped with several equipment (machines) for controlling expand and collapse of the rubber tube. Weir serves elevate the water level by developing the dam body and lowering the water level by means of deflating the weir body is made of a rubber tube can be filled with air or water.
The process of filling air or water from the air or water pump is equipped with air or water control instruments (manometer).
Figure 10. Weir Rubber
c. Decision-free
Free retrieval is building created by the river that drains into the river water irrigation, without set the water level in the river. In such circumstances, it is clear that the water level in the river should be higher than the irrigated area and the amount of water that must be guaranteed sufficient deflected.
d. Decision of the Reservoir
Reservoir (reservoir) is used to store irrigation water in times of excess water in the river that can be used any time there is a shortage of water. Thus, the primary function of the reservoir is to regulate the flow of the river. Large reservoirs often have multiple functions such as for irrigation, hydroelectric power generation, flood control, fisheries and others. Smaller reservoirs used for irrigation purposes only.
e. Pumping stations
lrigasi to be considered when making the pump by gravity was not feasible in terms of technical and economical. In the beginning of irrigation pumps require only little capital, but the cost of exploitation is expensive.