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Discussion Development
Environmental Impacts
Management inputs
Land Qualities
These tables cover hydrological land qualities and soil characteristics with important effects on design and the potentials. The Land Qualities are also subject to dynamic processes, not in the least because of changes in the canal lay-out and design, upgrading of canals and infra-structure, or by environmental changes, such as the disappearance of peat domes. It is hoped that the tables will contribute to a better understanding of the required needs and the expected effects of upgrading of the Tidal Lowland Schemes. The Tables should be used in SID's (Surveys, Investigations and Design) both at Micro as at Macro level.
A Land Unit in the Tidal Lowlands will be a combination of two Hydrological Land Qualities with one Flooding Type Land Quality , one Drainability Land Quality and one Soil Type Land Quality. So far little experience exists to define land units based on the land qualities as described in the tables below. Experience will learn what will be the most relevant combinations of land qualities.
Limits of land qualities based on Canal Distances as mentioned in the tables below are arbitrary. They depend in fact on design and lay-out of the system and are strongly influenced by the tidal range of the near-by river. Modeling of the each canal system is possible and would be recommended to determine the limits for each hydrological land quality. For practical reasons I introduce hereunder the canal distance limits based on experience. It should be realised that for each area and scheme lay-out they might be different and the limits should be used as an indication only.
The classification of the Land Qualities takes into account only the present land conditions. But in cases of flooding problems it assumes that in the present conditions there is already flood protection or there might be dike construction planned in the future. See Land Quality 1.2.1 and 2.1.2
Hydrological land qualities for developed Tidal Lowlands
| Hydrological qualities in developed areas | Hydrological/ Distance qualities | Recommendations and Potentials for Use |
| 1.1 Saline Intrusion Areas | 1.1.1 Areas with 3-6 months saline intrusion in canals | Potential for only one crop rice per year. Extra attention should be given to domestic water supply. Tree crops might be preferred here in areas with sufficient effective drainage depth. In areas with a small tidal range : fish/shrimp ponds can be recommended. |
| 1.1.2. Areas with 3 months or less saline intrusion in canals | Potentials for two rice crops per year. These lands cover the largest area in the developed Tidal Lowlands. | |
|
1.2 Areas with small
tidal range of <30 cm during wet season in adjoining Primary/Secondary
canal; Distance to canal< 1.5 km (When distance to Primary/Secondary canal is more than 1.5 km the area is not considered to belong to the developed Tidal Lowlands.) |
1.2.1. Areas
with canal distance <8 km from tidal river Small tidal ranges in well maintained canals at less than 8 km canal distance from river means usually that you are in the upper reaches of the tidal stretch of the river, close to the floodplain river stretch. |
Areas usually bordering Lebak (floodplain) areas which need dike for flood protection. Adapted cropping calendar. Great care should be taken on acid sulphate soils. Pump irrigation essential on these soils. One-way flow in canals essential |
|
1.2.2. Areas
with canal distance >8 km from tidal river A small tidal range here usually means you are still in the tidal stretch of the river, but only too far away from river. Extra inputs for controlled water flow in the canals are required. |
Special care should be taken on acid sulphate soils. Determine if there is a source to keep the soil wet in the dry season (Flooding Type 2.2) Pump irrigation is usually essential when lands are not subject to surface flows from forest/upland. Major Primary canal required parallel to rivers with controlled one-way flow. | |
| 1.3 Areas with a tidal range of >30 cm during wet season in adjoining River/Primary / Secondary Canal; Distance to canal < 1.5 Km | 1.3 Areas bordering the Tidal Stretch of the rivers | Most Tidal Lowland Schemes are found in these areas. |
Flooding Type Land Quality for developed Tidal Lowlands
|
Hydrological qualities FLOODING TYPE |
Hydrological/ Distance qualities | Recommendations and Potentials for Use |
|
2.1 Tidal Irrigation Tidal Flooding type A/B Canal distances will influence the potentials for tidal irrigation and the type of tidal irrigation.
|
2.1.1. Areas with a canal distance <1.5 km from tidal river, no deep flooding. | Easily manageable areas, open canals for water supply and drainage. These areas are usually occupied by local farmers, who settled first. |
| 2.1.2. Areas with a canal distance <1.5 km from tidal river, deep flooding | Dike for flood protection required. Control structures in dike required. | |
|
2.1.3. Areas
with a canal distance >1.5 km from tidal river. Tidal irrigation depends here on the combined effect of rainfall, relatively small canals, high tides and the low position of the land. |
Great care should be taken for “Over-Drainage” when enlarging canals, or when making short-cuts to rivers. Control structures to control water levels are in this case always essential. l | |
| 2.2 Surface flows from nearby peat forest/upland | 2.2. Areas subject to wetting by surface flows. | Hazard of “Over-Drainage” when enlarging canals or after disappearance of the peat dome. Controlled flow required by construction of dikes and structures. |
|
2.3 No-Tidal Irrigation.
Tidal Flooding type C/D
|
2.3. Areas not subject to wetting by surface flows. Also there is no tidal irigation. |
Usually intense leaching in On-Farm water management system required for muck/pyrite soils.No dead-ended canals and one-way flow in major canals are important in places at more than 1.5 km canal distance from river. |
Drainability Land Qualities for developed Tidal Lowlands
| Drainability | Canal distance effect | Recommendations and Potential Use |
|
3.1 Lands without sufficient drainage potential Effective drainage depth <30 cm.(after peat has disappeared) |
3.1.1. Canal
distance less than 1.5 km from tidal river.
These areas can usually still be drained during low tide. |
Rice can be usually cultivated. Multiple connections to nearby river required to increase the drainage potential. Tree crops can grow only on raised beds. |
|
3.1.2. Canal
distance more than 1.5 km from tidal river.
In this case the time available for drainage at low tide is too short for proper drainage. |
No crops recommended here for agricultural development. These areas include major parts of the peat soils. Sustainable forestry with minor drainage inputs may be an option | |
|
3.2. Lands with sufficient drainage potential Effective drainage depth >30 cm (after peat has disappeared)
|
3.2.1. Effective drainage depth 30-60 cm. Canal distance less than 1.5 km from
tidal
river. During low tide more time is available for drainage and drainage potential compares with land quality 3.2.3. |
Tree crops and rice crops can be recommended here. |
|
3.2.2. Effective drainage depth 30-60 cm. Canal distance more than 1.5 km from
tidal river. During low tide less time is available for drainage |
Rice crops are mainly recommended here. Tree crops can grow only on raised beds. | |
|
3.2.3. Effective drainage depth >60 cm In these areas there is never a drainage problem. |
In most cases tree crops might be preferred, but in old, poorly drained, marine deposits usually there is a preference for rice crops. |
Effective drainage depth is the difference in average land level and the average water level in the adjoining Secondary canal with tidal influence. After rehabilitation of the canals the Effective Drainage depth might improve, so it also a dynamic land quality.
Soil Types Land Qualities for developed Tidal Lowlands
| 4.1 Muck/pyrite soils | 4.1.1. Lahan Potensial (Indonesian classification) | Under the present conditions there is a balance between oxidation and leaching to keep the soil non-acid. It is essential that unripe soils in lahan potensial, characterized by a low bulk density, should be made more mature by a shallow on-farm water management system. These soils will become more mature by promoting, during the dry season, a drop of the groundwater tables to 60 cm below the surface.. Ripe soils will make pump irrigation possible in combination with tractor use and by creation of plough-layer. (Unripe soils can not maintain water layers on the field.) |
| 4.1.2. Lahan Sulfat Asam (Indonesian classification) | There is in the present conditions Insufficient potential for leaching and flushing. By introducing an improved on-farm water management system combined with mechanized land preparation, double connected canals and one-way flow flushing in the canals, these lands will return to lahan potensial. | |
| 4.2. Non-Pyrite soils | 4.2.1. Recent Marine/Riverine Sediments | Most of these lands have a potential for rice or deep fish ponds |
| 4.2.2. Old Marine/Riverine Sediments | These lands are mainly used as rice lands. No deep plowing recommended because of hazard of mixing topsoil with toxic (Aluminium) subsoil. | |
| 4.3. Peat soils |
4.3.Lahan Gambut (Indonesian classification) With
sustainable drainage potential Effective drainage depth (>30 cm) after subsidence |
Can be used for tree crop plantations |
|
4.4. Lahan Gambut (Indonesian classification) With no
sustainable drainage potential. Effective drainage depth (<30 cm) after subsidence |
No agricultural use possible at present. Sustainable use only possible when groundwater tables can me maintained above 30-40 cm below surface. Ramin trees might be an option in these conditions. | |
| 4.4 Whitish Low Fertility soils | 4.5 Hydrological conditions may vary | Very low agricultural potentials. Improved drainage might provide potential for Melaleuca Forestry. |
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