One Tertiary Unit Layout Example of a layout in an area with 400 m tertiary canal distance	A 2 ha field lay-out for one farmer Example for an area mainly depending on rainfall. Two crops rice are possible with some pump irrigation during land preparation. Tertiary canal distance is 400-m. Sub-Tertiary at 200-m distance essential.in this case to improve flows	Rainfed padi field in the Tidal Lowlands. Broad-cast sowing system. See sub-tertiary ditch and field road.

On-Farm Water Management (TAM) is a key factor in developing Coastal Lowland Schemes. It should aim at both satisfying the short-term water supply and the drainage of the crops and the leaching requirements of the soil. It should promote soil ripening and the land development processes in the long-term, including removal of acidity and toxicities. Poor crop growth is often related to stagnant water in the fields and insufficient means for leaching and re-supply. For soils rich in organic matter this quickly leads to anaerobic, toxic conditions and a poor quality of the organic matter suitable for productive growth. Further the absence of an On-Farm Water Management system in combination with proper operation of the water control structures delays the time the soils require to ripen to acceptable levels, becoming no longer problem soils. 

How to translate the water management objectives into a practical, on-farm water management system and a practical day-to-day operation depends strongly on local rainfall, soil, hydrological, topographical and crop/growing stage conditions. It means each location needs an own on-farm water management system and its own suitable operation, often also strongly depending on the lay-out of the fields and its tertiary and secondary canal system. In ISDP (Proyek Pengembangan Rawa Terpadu; IBRD Loan 3762-IND) 12 Model areas were created in three provinces covering in total 1500 ha to implement the new technologies for rice production in Coastal Lowland Schemes. These Model Areas included TDU’s and FSTA’s. 

Sustainability through Farmer Participation

The guiding principle was that all activities in the Model areas should be carried out by the farmers themselves, with only minimal material or financial support from the project. The emphasis was not on quickly installing a perfect Model through high inputs, but by gradually improving conditions together with the farmers, with feedback from the government agencies. 

Conclusions based on the experiences in the Model Areas

The technology to increase rice production in Coastal Lowlands has been proven. On-Farm Water Management (TAM) plays a major role in this technology development. There is a high need to develop Standards for the implementation of TAM in the different environmental and socio-economic conditions in the Coastal Lowlands. Connections with the operation of the main system will be essential.

Design Criteria for On-Farm Watermanagement system (open ditches)

General

Fields with frequent tidal irrigation

Objective is to grow two times rice per year; for the dry season crop some additional pump irrigation might be required for an optimum yield, especially during land preparation for the second crop. The existing conditions for supply of water should never be changed. For all new connections of tertiary and sub-tertiary canals with the secondary canals, care should be taken that all drainage can be controlled by the farmers.

1. The newly-made sub-tertiary canal should be connected to the Secondary canal with a relatively narrow culvert. The drainage outflow should be controlled.

2. When there is no control structure in the Secondary canal: The newly-made connection of the Tertiary canal with Secondary canal needs a sliding gate structure near the houses for supply. When the newly-made connection is far away from the houses, only a culvert with stoplog, or a flapgate with water level control is required to control the drainage from the fields. (hazard of over-drainage!)

3. When there is a control structure in the Secondary canal: The newly-made connection of the Tertiary canal with the Secondary canal needs only a culvert with a stoplog to control drainage from the fields. Existing structures will be re-habilitated.

In principle the quaternary ditches are made at the borders of the fields with a distance of 75-100 m between the ditches. 

Fields with no tidal irrigation (rainfed)

Objective is to grow one rice crop in the rainy season and one dryland crop in the dry season. For that reason improved drainage is required to grow the dryland crop. In the wet season a balance should be found between the need for leaching of the toxic surface soil and to control the waterlevels to grow a wetland rice crop.

1. The newly-made sub-tertiary canal should be connected to the Secondary canal with a culvert with one-way flow (drainage-flapgate). The drainage outflow should be controlled with a stoplog. Bottom (sill) of structure should be one-meter below surface.

2. When there is no control structure in the Secondary canal: The newly-made connection of the Tertiary canal with Secondary canal needs a sliding gate structure near the houses for supply. When the newly-made connection is far away from the houses, a culvert with one-way flow (drainage-flapgate) is required. The drainage outflow should be controlled with a stoplog. Bottom (sill) of the structure should be one-meter below surface.

3. When there is a control structure in the Secondary canal: The newly-made connection of the Tertiary canal with the Secondary canal needs only a culvert with a stoplog to control drainage from the fields. Existing structures should be re-habilitated

Quaternary ditches should be made at a distance of 37 - 50 m, both at the borders and in the middle of the field.

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