The next stage in the wet-rice season is the building of dams, called ma faaj which is again a compound term of Karen and Northern Thai (faaj, “dam” or “weir”). Before the dams are erected in the Huai Thung Choa, irrigation canals have to be checked and cleared of leaves and sediment, their walls rebuilt if they have been eroded, and their entrances to wet-rice terraces cleared if they are blocked, and so on. The dams are erected every year because they are not permanent structures. They consist of logs, branches and pieces of wood which are thrust into the stream bed, or placed firmly among rocks, at appropriate places and built up in this fashion in order to raise the level of the stream until it reaches the level of the land where the irrigation canals begin. In some cases, trees may be felled across the stream so that they act as a kind of retaining wall against which branches and pieces of wood are placed in order to erect the dam.

There are five dams across the Huai Thung Choa serving the total of twelve plots of wet-rice terraces. Each dam is shared by a number of households (ranging from two to four per dam) and the work of making the dams is also shared by these households. The ritual that is performed at the dam after its construction is usually led by the oldest cultivator, that is, the household that first made use of a dam. The ritual is not necessarily held immediately after the dam has been built however; it is usually held after the rice seedlings have been transferred from their nurseries into the terraces, in the middle of the wet season. The ritual is conducted as much to propitiate the spirit of the stream as to ensure the successful growth of the wet-rice crop.

Once the dams are built, the water is allowed to flow into the wet-rice terraces via irrigation canals which are cut along contour lines leading to the fields that are fed by the stream. The irrigation canals enter the fields at their upper-most terraces and, from here, the water is directed to lower terraces by means of sluices which are embedded in the dikes or bunds which separate the terrace plots in the field. The sluices are made from a short section of bamboo which is open at one end and closed at the other by the node in the bamboo but which has a small opening cut just before and above the node. The sluices are set in the bunds in such a way that the open ends life in the higher terrace, while the other end leads out to the lower terrace with the opening facing upwards. The sluices thus act as valves which impede the water flowing through them so that the seedlings, when they are planted, around the sluices are not damaged or uprooted by the gush of water entering the lower terraces.

The inundation of terraces at this stage of the season is essential before work can commence in them. The reason for this is that in the dry season the earth in the terraces has dried up and become hard and compact. It is also held together by the roots of the stubble from the previous harvest which are left in the fields although buffaloes are let in to graze when the fields lie fallow. The condition of the earth in terraces before and at the onset of the rainy season thus makes ploughing an impossible task, hence the necessity to inundate the terraces first in order to make the earth soft enough to plough (see also Kunstadter [1978:93]) or to hoe.