News Articles
Communal irrigation system gives quality water source for farmers
by Engr. Leandro BagaoisanSenior Science Research Specialist
NTA Industrial Research Department
LARGE areas in the tobacco-growing regions are suit¬able for quality tobacco production. Unfortunately, some of these areas produced inferior quality of tobacco leaf or not planted with the desired tobacco type, like the full flavor tobacco. These areas lack sufficient irrigation wa-ter from groundwater aquifers, rivers, creeks, and other tributaries during the growing period of the tobacco, which coincides with the dry months of the year.
At present, nearly all parts of the tobacco-growing areas in Region 1 are dependent on groundwater as the alternative source to sustain the crop demand for irrigation water.
To pump out water for irrigation, farmers use the Shallow Tube Well Irriga¬tion System (STWIS) or Open Well Irrigation System (OWIS), powered by either 5 to 8 Hp gasoline engine or 8 to 10 Hp diesel engine, respectively. STWIS is con¬structed by drilling G.I. pipe into the ground until it reaches the shallow aqui¬fer or water saturation point with a drilling depth of 10 to 20 meters.
OWIS operates with the same principle. The only dif¬ference is the material used in the construction. OWIS utilizes concrete casings or culverts with an ideal size of 20 inches in diameter instead of G.I. pipes. These are laid down into the soil column until the shallow aquifer is reached through digging and excavation. The open well is more advantageous than the shallow tube well because it has a wider space for under¬ground storage.
System hazards
Today, extraction of groundwater for irrigation in the tobacco-growing areas in Region 1 is apparently in¬creasing in volume as shown by the progressive increase in the number of shallow tube wells that are installed in the area due to lack of wa¬ter source for irrigation and abnormal weather condition coupled with the occurrence of El Niño. This situation poses danger in the preser¬vation of quality groundwa¬ter reserve of the area, es¬pecially if the rate of water withdrawal is greater than the rate of replenishment or groundwater recharge from other water sources.
If this condition prevails, excessive groundwater de¬pletion occurs which can reverse the normal seaward gradient of the groundwater causing saltwater intrusion which can cause massive groundwater salinization.
This is a very alarming threat, not only to the agri¬cultural sector, but also to the people who depend mostly from this resource for their household consumption. In most irrigation situations, the primary water quality concern is the salinity level since salts can affect both soil structure and crop yield.
The amount of salts in groundwater may vary from one location to another, espe¬cially during the dry season due to the material composi¬tion and minerals present in the groundwater aquifer like lime, gypsum, and weathered soil and rocks. Excessive amount of these substances affect the quality of irriga¬tion water in this area, and, therefore, not suitable for shallow tube well and open well irrigation system.
Similarly, areas with high topography (highly elevated areas) are also not adaptable for shallow tube well and open well irrigation system. These do not have the kind of aquifer, bearing potential yield of groundwater and therefore cannot sustain the year-round crop water re¬quirement due to the nature of rock formation present.
The aquifer present in this area is usually described as perched aquifer, which are held between rocks beneath the ground where water is temporarily trapped and stored through deep percola¬tion during rainy season and eventually dries up during the dry season.
Communal Irrigation
With the above scenario, the National Tobacco Ad¬ministration (NTA), along with its priority program, Development of Irrigation System in Support of High Quality Full Flavor Tobacco Production, was encouraged to look for another source of high quality irrigation water and that is the Communal Irrigation System (CIS). This type of irrigation sys¬tem stores sufficient amount of low salinity water which can be described as qual¬ity irrigation water because these are mostly coming from rain, spring, mountain seepage, rivers, and creeks.
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Small reservoir irrigation system in Patpata Weste. Balaoan, La Union |
High quality irrigation water promotes the produc¬tion of high quality tobacco leaf. Based on the previous results of an NTA study on Water Suitability Testing, conducted in Region 1 in 1998 to 2000, water from these sources has salinity level ranging from 256 to 458 mg/L of total dissolved salts which is relatively lower than groundwater sup¬plied by shallow tube well and open well irrigation sys¬tem which have 480 to 768 mg/L dissolved salts.
In terms of acquisition cost, the CIS is more expen¬sive than the STWIS and OWIS, but can irrigate a large hectarage of farm lands up to 100 hectares. Given a climate change-resilient structure and proper mainte¬nance, the CIS can last more than 30 years.
Types of CIS
The CIS can be a Small Water Impounding Project (SWIP) or Small Diversion Dam (SDD). The SWIP is usually made of earthfill constructed across a narrow depression or valley to develop a reservoir that will harvest and store rain¬fall or runoff for immediate and future uses. This has several advantages. SWIP can be used as soil and water conservation structure, as a source of supple¬mental irrigation during wet season and main source during dry season, as fish and livestock production site, as recreation site, and as a research area.
The SDD, on the other hand, is a concrete structure construct¬ed across a channel or river with continuous flow to raise the wa¬ter level and allows diversion of water by gravity from the river source to the point of use. Its advantages include: use for irri¬gation, protection of river bank against erosion, retardation of flood flows, reduction of the eroding power of water, and use as recreation site.
The Philippines has adequate rainfall, but not uniformly dis¬tributed throughout the year in all parts of the country. Big vol¬ume of rain water is often wast¬ed through excessive runoff and high flood causing soil erosion during rainy season. Thus, there is a need to impound the exces¬sive rain water as major source of irrigation during dry season.
With the joint effort of the Agricultural Engineers of the NTA with experts from the Na¬tional Irrigation Administration and the Bureau of Soils and Wa¬ter Management, this project is expected to be implemented in year 2014-2015.
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