(PESIA) Weg naar Zee 2D Seismic - Staatsolie

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P-all consultants Staatsolie Maatschappij Suriname N.V. PESIA Weg naar Zee 2D Seismic 2012 The wetland access routes are found predominantly within unit 5, the half ripe clays with nearly unripe clay subsoil. The topsoil of these clay soils is fresh and the subsoil brackish. The thickness of the peat layer will vary between 0 and 60 cm depending upon average water depth, vegetation type and frequency of grass and peat fires. Access to the dry land trails will, as much as possible, follow existing roads on ridges of unit 1 and 2 and dams and canals that already exist. Soil properties The clay soils of the Young Coastal Plain (soil units 4, 5, 6, 7, 11 and 18) have a high fertility, due to their high mineral (clay soils) and organic (peat) reserve, they have a high Cat-ion Exchange Capacity (CEC) and they are normally acid to very acid. Soils of units 6 and 7 are brackish to saline and they have a neutral ph. The physical properties of the clay soils are moderate to poor. Permeability and aeration are usually moderate to low and workability with machines is difficult. The bearing capacity will be a problem on less ripe clay soils (4, 5, 6 and 7), especially where a peat layer is present. Drainage is a major problem in all these soils. The ridge soils (soil units 1, 2, 8 and 9) are in general less fertile and they have a lower CEC, but they have more favorable physical properties. Mineral reserve and CEC within the ridge soils is highest in the loamy soils and lowest in the sandy soils. pH ranges from acid (sandy soils) to neutral (shell soils), (Noordam/Teunissen 2008). Soil physical properties of ridge soils are usually good, but natural drainage of the lower ridge soils may be imperfect to poor. Soil suitability Most of the affected soils in the Dry land Area are already cleared for some type of land use. Therefore only the soil suitability of the involved soils in the Wetland Area is briefly discussed. According to Noordam and Teunissen, 2007 the fresh clay soils of the Comowine phase (units 4 and 5) are suitable for wetland rice cultivation and cattle grazing, once polders have been established. However, wetland rice cultivation is not possible in the study area, because no adequate supply of irrigation water is present. The suitability of the soils of units 4 and 5 for dry land crops is limited, given the brackish subsoil that limits deep rooting and that poses the risk of salinization of the topsoil under conditions of artificial drainage and evaporation. The ridge soils within the Wetland Area are suitable for horticulture, but most of the ridges are small, isolated units within the swamps. Therefore the overall suitability of the units 1 and 2 in the Wetland Area is marginal at most. 42
P-all consultants Staatsolie Maatschappij Suriname N.V. PESIA Weg naar Zee 2D Seismic 2012 4.2.7 HYDROLOGY As indicated above, the study area can be divided in a “Wetland Area” and a “Dry land Area”. These two areas are therefore discussed separately. Wetland Area The Surinamese coastal region has about 2,000 km² of brackish wetlands with mangrove forest, salt water lagoons and brackish herbaceous swamps, and 12,000 km² of freshwater wetlands (Teunissen, 1988). In the Eastern Wayambo Swamp about 110 km² of coastal wetland is found, of which less than 15% is mangrove forest. All projected seismic trails are found crossing the well-drained dry land area and the freshwater swamps with poorly to very poorly drained soils, which are inundated either permanently or at least during the greater part of the year (Teunissen, 1993). The higher parts of the ridges, found as small and narrow islands surrounded by the swamps, remain dry throughout the year. Swamps are formed because the low-lying clay flats have a very slow drainage, due to: • the small hydraulic gradient • the very low permeability of the soil • the dense layer of vegetation and peat on top of the soil But although the flow through peat and vegetation is very slow, a considerable amount of water will be discharged due to the large areas over which the process takes place. Creeks, to either a local river or to the Atlantic Ocean, are usually only found along the edges of these swamps where both water velocity and discharge may be high. The Wayambo Swamp drains towards the Atlantic Ocean in the north and towards the Saramacca River in the west. The flow to the north is thought to account for the majority of the drainage of the Eastern Wayambo Swamp. The latter is supported by the generally northern direction of watercourses (shallow swamp gullies) in the Wetland Area. Natural drainage from this swamp towards the south and east is not easily possible because ridges and roads block the flow in these directions. During the rainy season the water level in the Eastern Wayambo Swamp is high (up to 80 cm above the mineral surface) and water is permanently being discharged towards the Atlantic Ocean. With diminishing rainfall at the end of the rainy season, with gradually lowering swamp water levels, the amount of drainage also decreases. At a certain water level the drainage from the swamp will virtually stop and water will mostly be depleted by evapotranspiration. However, in most years a shallow layer water remains present in the swamp and the peat does not completely dry up, (Noordam and Teunissen 2007/2008). But in years with an extremely long dry period, the swamps, including peat, will completely dry up. Starting at the Garnizoenspad, a number of S-N running canals has been excavated. These canals are intended to collect swamp fish in the Dry season, when water level becomes low. Therefore these canals are referred to as “fish holes”. Most of these canals are rather short and none reach the Atlantic Ocean. From satellite imagery it appears that part of these canals is no longer being used. 43
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(PESIA) Weg naar Zee 2D Seismic - Staatsolie

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