|Related Agroforestry Livelihood (IIRR, 1992, 30 p.)|
|Small water-impounding technologies|
Small water-impounding refers to structures using readily available materials for the storage and/or diversion of surface water (running water from springs, creeks, streams or rivers) either for the purpose of irrigation or for domestic use. These structures are generally characterized as simple, easy-to-build and maintain, inexpensive and using readily available materials. However, they are less efficient and need to be maintained frequently compared to more permanent structures.
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.
(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.
(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.
(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.
Earth or mixed-material dam -- a structure composed of readily available materials (such as rocks, boulders, logs and earth) and is used to store water for watering and other similar purposes. The structure is usually applied in live or intermittent creeks or streams with up to three meters width and not prone to flash flooding.
Earth or mixed-material dam
1. Earth dam - a structure composed mainly of compacted soil with a base of at least one meter thickness arranged in a pyramidal fashion. It usually has an opening near the base (through a bamboo tube) and at the top (small opening lower in height than the dam) to control the water flow.
To make reservoir area more impermeable to minimize seepage of water, the following should be conducted: a) scrape the bed of rocks until reaching the clay surface; b) line the bed with at least 20 cm thick of fresh leaves, grasses and fine organic matters; c) cover the organic materials with soil of at least 20 cm thick and compact it eliminating air spaces; and, d) allow the organic matter to rot, thus forming a sticky and impermeable layer.
2. Earth and stone dam - a structure composed of compacted earth (soil) and a core of boulders and rocks. The dimension is more or less similar with the earth dam.
Earth and stone dam
3. Earth, Rock, Log Dam - a structure composed of compacted soil rocks and log (wooden) materials. The core is mainly composed of boulders and rocks with interspaces filled up with clay materials. Compacted earth materials cover the core and the logs are arranged either in horizontal or vertical fashion with clay materials as the outer covering.
4. Bamboo and earth dam - a structure mainly composed of bamboo poles and crushed bamboo and earth materials. Two lines of bamboo poles and crushed bamboo culms are constructed at 0.25 m distance between lines. The distance between bamboo poles in a line is approximately one meter. The interspaces between the lines are filled up with rocks mixed with clay. The outer covering is composed of compacted earth.
Bamboo and earth dam
For further storage efficiency of the above mentioned dams, the surface of the structure should be lined with two inches of clay materials. Planting of grasses, such as bermuda grass, can also be done to strengthen the outer surface of the dam.
Bamboo and earth dam lined with two inches of clay materials
Box spring - a structure that encloses a live spring for storing water and or storing and diverting water through a pipe for drinking and other domestic consumption purposes. The structure can be made up of rocks and mud lined with clean river sand or hollow blocks and cement, covered by wooden planks.
1. Site Selection. Locate a live spring which is accessible and preferably 50 meters from the residence. A live spring located higher in elevation than the site of the residence can be tapped through a series of pipes (PVC or bamboo poles) while those located at the same level or lower than the house can be tapped by using water pails or other containers.
2. Preparation of Materials. Prepare sufficient amount of clean river sands, clean clay, polished stones/rocks and wooden planks or sufficient amount of hollow blocks, cement and sands. Piping materials should also be prepared whenever necessary either of bamboo poles or PVC.
3. Construction of Box Spring. Clean the area around the spring at least with a dimension of 0.5 x 0.5 m. Provide a temporary outlet for the water to pass through while the box spring is still under construction. Line the area with clean clay with at least two inches thickness and enclosed it with stones/rocks mixed with clay forming a box structure with a dimension of at least 0.5 x 0.5 x 0.5 m. Line the base of the box with clean river sand and cover the top of the structure with wooden planks. Allow an opening near the top for piping or to allow the flow of excess water.
4. Operation and Maintenance. The box spring is allowed to store water a day or two after construction by plugging the temporary water outlet. Check and repair leakages. Conduct regular maintenance of the box spring by cleaning it of insects, leaves and other materials that get into the box spring.
Note: For health safety, water from this structure should be passed through a clean cloth screener and boiled before drinking. A water purifier tablet is also recommended.