Construction of Irrigation Systems

1. Types of systems 
2. Types of scheme of development
3. Status of irrigation development

Types of systems 
There are three categories of irrigation systems: national, communal, and private. National irrigation systems (NIS) are large and medium schemes. These are basically operated and maintained by NIA where beneficiaries are charged irrigation service fee for the services rendered in the delivery of water. In the 1980s, joint management of portions of national systems with irrigators associations (IA) was effected. 
Communal irrigation systems (CIS) are small-scale schemes and constructed with the participation of farmer-beneficiaries thru their IAs. The operation and maintenance (O&M) of CIS is turned over to IAs upon project completion subject to a cost recovery arrangement. Farmers amortize the chargeable cost for a period not exceeding 50 years at 0 percent interest. The repayment scheme is pre-arranged and acceptable to both NIA and the IA. 
Private irrigation systems are those constructed, operated and maintained by private individuals or groups with or without technical assistance by NIA or other government agencies. 

Types of scheme of development 
The three schemes of development of irrigation systems are run-of-the river diversion, storage or reservoir, and pump irrigation. Diversion projects entail the drawing of water under controlled conditions directly from the flow of rivers or streams. Storage or reservoir projects involve the construction of storage dams to impound water and released as needed to be drawn from a diversion dam downstream. Reservoir projects are usually multi-purpose to include other functions like power generation, flood control, fishery and recreation. In pump projects, water is lifted from underground or from rivers and streams. Pump systems are also common in some storage or diversion schemes to lift water to irrigate areas on higher elevation or pump groundwater to supplement available supply from the river. Environmental protection and conservation is a key consideration in the design of various schemes. 

Status of irrigation development 
The Philippines has about 10.3 million ha agricultural lands. Out of this, around 3.1 million ha are considered irrigable, with up to 3 percent slope, and primarily devoted to rice and corn. A study by the World Bank, however, identified more than 6.1 M ha as irrigable, including areas that are relatively more difficult to irrigate and up to 8 percent slope. 
As of December 2009, about 1.54 million ha or 49 percent of the 3.1 million ha have been developed for irrigation. Of the total area under irrigation, about 764,980 ha or 50 percent are under NIS; 557,630 ha or 36 percent under CIS that are farmer-managed; and 217,330 ha or 14 percent under privately owned systems that are constructed through private initiatives.