Structures for diverting surface water for irrigation purposes

1. Tambak I is a series of interconnected tripod structures, usually made up of wooden poles or piles and/or bamboos arranged in a slightly diagonal position across a stream or river with moderately running surface water. It usually covers 3/4 of the width of a stream or river with the main function of raising the water level and directing it into a drainage canal located immediately upstream of the structure.

Procedures

(a) Site selection. Select a portion of a stream or river that is higher in elevation than the area to be irrigated. The site should have a moderately running surface water, with normal water level of from knee up to waist deep and with more or less even stream or river bed and the area is free of flash flood. It is also necessary that the selected site can be connected by a diversion canal to the proposed area to be irrigated.

Tambak I

(b) Preparation of Materials. Materials needed for the structure are: for each tripod structure, three pcs of 1.5-2 meter wooden poles or piles or bamboo, three pcs of 1 meter bamboo poles; for connecting the tripod structures, bamboo poles sufficient to cover 3/4 of the width of the stream or river; sufficient quantity of split bamboos with one inch width; and tying materials.

(c) Construction of Tambak I. Mark the location of the tripod at approximately two-meter interval, slightly diagonal across the stream or river and covering 3/4 of its width. On these sites, construct the tripod structure with two legs in the upstream and the other in the downstream at approximately one meter distance. Bury the legs at 0.25 meter in the river bed, strengthen the legs of the tripod by forming a small triangle using bamboo poles at the base of the tripod at 0.25 meter from the bed. Add rocks and boulders at the legs and at the small triangle to weigh down and strengthen the tripod structure. Interconnect the top of the tripods with bamboo poles and with the use of bamboo splits line the upstream portion of the tripod with one inch interspaces from the base up to the top of the tripod.

(d) Construction of the Diversion Canal. Immediately upstream of the tripod structure, construct a diversion canal with at least 0.26 meter width and depth and connect K to the area to be irrigated.

(e) Operation and Maintenance. Cover the interspaces between the bamboo splits with leaves, sacks and other materials starting from the bottom up to the top, to raise the water level to reach the level of the diversion canal. When not in use, remove the leaves and other materials to allow free flow of water between the interspaces. All large debris, such as logs and drift wood, should be guided to pass through the opening of the structure to minimize damage to it. Regularly check and repair the structure and the diversion canal.

2. Tambak II is a heap structure, composed of rocks boulders and river sands covering the entire width of the stream or river with a height of up to 0.5 meter. Its function is to store water, slightly raise the water level and divert K to a diversion canal located at its side.

Tambak II

Procedures

(a) Site Selection. a portion of a stream or river that is higher in elevation than the area to be irrigated. The site should have slow to moderately running surface water with normal water level up to knee deep and preferably with even river or stream bed. It should also be free from flash flood. It is necessary that the selected site can be connected by a diversion canal to the proposed area to be irrigated.

(b) Preparation of Materials. Materials needed for the construction are those available in the site, such as boulders, rocks and river sands. The amount of materials depends on the width of the stream or river and the height of the heap to be constructed.

(c) Construction of Tambak II. With the use of bare hands, shovel and crowbar, construct the heap in a linear fashion at least half a meter wide and up to half a meter high. Rocks and boulders should be placed at the core with river sands used to cover and fill up interspaces between them as well as the outside cover of the heap. Diversion canal should also be constructed at the side of the heap.

(d) Operation and Maintenance. Unlike Tambak 1, the structure will automatically raise the water level, store and divert it to the diversion canal. Leakages can be minimized by additional boulders, rocks and sands. Constantly check and repair the structures for leakages. When not to be used, allow a portion of the heap to open or close the diversion canal and allow the water to overflow the heap structure.