IRRIGATIE UIT EEN MOERAS Een hydrologische studie van de ...

however, supplementary information is necessary. After completion of the Stondansie
project in the upper Nickerie river, and the water supply from both reservoirs is joined,
the possibility exists that the Nanni swamp will no longer be used at times of low water.
In this case its drying out to the mineral subsoil is unlikely. Accumulation of peat,
which will increase flow resistance, may limit the irrigation possibilities of the swamp
(Chapter 9).
Conclusions
- By reason of its adaption to the existing water level, the vegetation in a swamp
provides an important indication on aerial photographs of the hydrology.
- The boundary between the Nanni basin and that of the adjoining rivers is not fixed,
but depends on the swamp level.
- About 55 percent of the basin of the Nanni creek does not contribute to the filling
of the Nanni swamp.
- In Suriname and elsewhere stretches of water overgrown with swamp vegetation generally
have a lower rate of evaporation than open water.
- An important factor in the filling of the swamp is the ratio of wet to dry areas at
various water levels. In the Nanni swamp this ratio appears to vary from 1 : 6 to
SO : 1 where the level rise is 1.20 m.
- The level of the Nanni swamp can be calculated with the aid of the noted water balance
to a standard deviation of 4.5 cm between calculated and measured levels.
- The flow of the water from the swamp to the water inlets can be compared to the flow
from a large reservoir to a small one at a rate proportional to the difference in head.
- The possibilities of using the swamp as a reservoir are limited by: (a) the storage
capacity. Above a certain level the leakage into the adjoining rivers increases sharply,
(b) At low levels the flow resistance in the swamp increases greatly so that the available
quantity is less than required, (c) Because of the poor surface/depth ratio there is a
great evaporation loss.
- Despite these poor irrigation reservoir qualities, highly productive rice cultivation
has developed in Nickerie, 15 000 hectare of which is entirely dependent on the swamp
for irrigation. This success is due chiefly to two factors: the rainfall is relatively
evenly spread throughout the year, so that there are only short periods when the supply
in the reservoir drops, and widespread crop failure has been eliminated among the small
scale farmers by reason of flexible water use.
- If the water level is high for too long, peat formation goes on unhindered, therefore
the usefulness of the swamp as an irrigation reservoir will be reduced. This should be
taken into account by those controlling its use as a reservoir.
- In the water balance (supply = drainage + evaporation + changes in storage capacity),
evaporation plays a major part in swamp areas. When partial reclamation is carried out
in these areas and the drainage plus part of the evaporation are made available for
irrigation purposes, an intensive agricultural system can be developed simply and
cheaply. Especially in large coastal plains where the rivers are brackish until far
upstream, fresh water from swamps can play an important part.
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