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The Role of Water Management in Peat Land Fire Prevention

By Dedi Kusnadi Kalsim

Land and Water Sustainable Development – Retired Lecturer of IPB

HP: 08128132821, email: dedikalsim@yahoo.com

rev 2-4/10/2015

In Metro TV news 24/9/2015, President Joko Widodo said, “The key to reduce peatland fire is by

making a canal in order to keep the peatland constantly wet “. The President commands to build canal

blocking. Kompas daily 26/9/2015, Corner of Science and Technology and Environment, wrote that

Walhi (the Indonesian Forum for Environment) highlighted the statement of President Joko Widodo

in a press release published on the home page of Cabinet Secretary of RI, titled “To overcome fire in

Central Kalimantan, President Joko Widodo asks for canalization”. The President’s statement instead

can be contra-productive toward the efforts of handling land and forest fire.

The statement by President Joko Widodo need to be straightened, this writing is aimed to straighten it.

In the development of peatland cultivation area for agriculture, plantation as well as industrial forest

plantation/HTI, the function of canals are: (a) as a controlled drainage channels to drain excess water

(flood) in the rainy season (RS) and to keep the water elevation at a certain height so there will be no

drought in the dry season (DS), (b) as means of transportation for production facilities and harvest

results. The function of drainage and the function of transportation require two different things; the

drainage needs relatively low water level elevation, while the transportation needs relatively high

water level elevation. Generally there are no irrigation channels in peatland, water supply depend on

rainfall only (rainfed).

A good design of water management is by making transportation channels and drainage separately,

but it will cause higher construction cost than unite them. In Indonesia, these drainage channels are

commonly combined with transportation, so that the construction cost will be less expensive, but as a

result the operational cost become more complicated and more expensive, sometimes one of those

functions has to be sacrificed.

Channels of controlled drainage are different from channels of common drainage. Operational water

level elevation in RS should be determined in channels of controlled drainage, which has to be low

enough so that there will be no flood in concession land and water table depth has to be optimum for

plants to grow. For Industrial Forest Plantation/HTI, the optimum water table depth is around 60-80

cm, palm oil usually 40-60 cm, vegetable plants around 30-40 cm. Therefore, water level elevation for

HTI in drainage channels during the RS is around 70-90 cm below the land. During the DS water

deficit occurs because of much higher evapotranspiration compared to rain, as a result water table

depth will drop around 50-100 cm from the condition of water table depth at the end of RS or at the

beginning of DS (it is local specific depend on how long dryspell occured). Research results in Riau

in DS 2015 (July-August) shown that average water table depletion is 1.19 cm/day. If 30 days

dryspell accurs the water table drop could be 36 cm, if 90 days it could be 107 cm. Without

“controlled drainage” or only with “common drainage”, if water table depth at the beginning of DS is

80 cm, then at the end of DS it will drop to 130-180 cm. In this condition, surface of the peat land will

dry and will be prone to burning. Based on physical characteristic research of peatland conducted

by the writer, a safe condition in DS is at a maximum water table depth of around 120 cm, of where in

this condition soil moisture in the surface of peatland is still higher than irreversible drying (soil

moisture content around 230% w/w), peat land is still moist enough to reduce the burning risk.

How is the way to keep the water table depth no more than 120 cm at the end of DS?

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The way is by making peat dam on every different land elevation of 50 cm along the trace of drainage

channel (canal blocking), equipped with side channel spillway structure. Size of the width and the

number of spillway depend on the designed flood discharge. Elevation of crest spillway in RS is

installed on 80-90 cm below the land. In this condition then the water table depth in land is around 60-

80 below the land (optimum condition). If flood occurs, then the water level will rise and overflow

above crest spillway into the segment of drainage channels at the down-stream side. Thus in RS, the

excess water will be disposed only as needed.

At the beginning of DS or at the end of RS (May-June-July), elevation of crest spillway is increased

into 30-70 cm below land, therefore the water table depth become around 30-60 cm below land. At

the end of DS (August-September-October), the water table depth will be droped gradually at a

maximum 80-120 cm. This condition is still safe against land fire. Some field experiences show that

peat land fire occurs if the water table depth is more than 150 cm.

Peat dam and side channel spillway should be constructed for every controlled points of drainage

channel. One controlled point is served for one Water Management Zone.

How to raise the elevation of crest spillway? The side channel spillway is generally made from

georeinfox materials (thick plastic resistant to acid water and heat) and the crest spillway is made of

piles of georeinfox sandbags. By adding piles of sandbags then the water elevation of crest spillway

will raise. On the contrary, reduction of sandbag pile will decrease water elevation of crest spillway.

The operational is quite simple only conducted twice a year, that is at the beginning and at the end of

RS.

Arranging water elevation in crest spillway cannot be conducted on common drainage system

(uncontrollable) so in DS the water table depth will drop to more than 150 cm and the peat surface

will be prone to burning. Sometimes the drainage channels become empty and dry without water.

How about the canal that already built in peat protected area? The arrangement of water table depth is

not necessary in peat protected area because natural forest plants are water inundation tolerant. So the

already built canal needs to be totally closed (canal blocking) without the need to have any water level

arrangement in the spillway structure. Where is the location of the canal’s blocking? In order to be

able to hold water in that area and not too dry in DS, then the blocking is needed in every different

elevation of 0.3-0.5 m along the canal’s trace. The number of canal blocking locations depends on the

slope of trace of drainage channel. Thus the water will be retained the land and the canal will remain

to fill with water in DS which can be used to extinguish fire if it occurs.

How to maintain the sustainability of the peat cultivation area? Once again, the key is the water

management. Can we able to manage water in RS and DS properly as described above? Peat dome

area must be preserved for peat protected area which function is to hold water in RS and release it

slowly in DS to supply water deficit of underneath cultivation area. The current fact is that most of

these peat domes have been opened for cultivation, so that drier condition is the impact in DS. The

government must be able to redesign the spatial peat land planning so that the peat protected area can

return back to its initial function.

May with this writing the comprehension of “making canal” and “canal blocking” can be easier to

understand and what more important is its implementation in field.