Table 1.

Example of a landsystems classification for a proposed highway in Papua New Guinea based on aerial photograph interpretation (Griffiths 1994)

LandsystemsDescription of the landscapeGeologyDrainageVegetationEngineering problems
(1) Musa Coastal PlainVery flat low-lying swampland with isolated hillsQuaternary and recent alluvial soils of sands, silts and clays up to 500 m thick. Some coarser material closer to boundaries with higher groundTypical swamp conditions; continuously high water tables; some areas with open water following rains; whole area subject to flooding from riversPrimarily tree swamp with some areas of grassland; areas of mangrove on the coast. Mainly immature alluvial soilsVery difficult construction conditions: very low bearing capacities; subject to flooding; high water table; probably aggressive acid groundwater; former channels with granular materials buried by recent deposits
(2) Dissected Managalase PlateauDissected and eroded volcanic landforms with angular steep ridges and cliffs enclosing alluvial valleys. Relief generally up to 600 mTertiary and Quaternary basalts, basalt agglomerates, lavas and tuffs with shoshonitic affinitiesDense dendritic drainage in steep gullies and river valleysPredominantly rainforest but with some savannah and grassland; possibly some relict ferricretesLikely to be deeply weathered, subject to high rates of erosion through mass movement, hillwash and gullying. Increased erosion wherever forest cover is removed
(3) Korala River FloodplainFlat low-lying swampy areaQuaternary and recent alluviumTypical swamp conditions with continuously high water tables and whole area subject to floodingPrimarily tree swamp; likely to be acid sulphate soilsVery low bearing capacities; subject to flooding; high water table; probably aggressive acid groundwater
(4) Sibium, Didna and Kenam RangesA youthful and rugged mountainous zone with elevations reaching over 700 m; hills developed on the ultramafic rocks such as Ajaura tend to be more rounded, although generally the terrain has fewer steep-sided gullies than Terrain Unit 2Arcuate block-faulted mountain belt comprising Cretaceous granular gabbros (overlain by the Lokanu Volcanics basaltic and pillow lavas, which form Terrain Unit 2)Hillslope drainage down gullies and river channels mainly with a dendritic pattern but becoming rectangular in places. Deep Musa River gorge just outside study area indicative of antecedenceMedium forest cover, which has been cleared in places causing rapid soil erosion; possibly some relict ferricretesLikely to be deeply weathered, subject to high rates of erosion through mass movement, hillwash and gullying. Weathering likely to be deeper around joints and faults. Increased erosion wherever forest cover is removed
(5) Musa River Inland BasinFlat low-lying inland basin developed at the confluences of the Domara, Moni, Ukuma and Foasi rivers. River terraces, meander cut-offs and point bars visible in the aerial photographsQuaternary and recent alluviumFloodplain area adjacent to rivers subject to flooding but terrace will be above flood levels. Generally high groundwater levels. Main rivers meander across the floodplain and will be subject to changes in channel location through meander cutoffs and migrationA partially cleared area now predominantly savannah with some secondary regrowth of forest and areas of medium forestRelatively low bearing capacities; areas adjacent to rivers subject to flooding
(6) Undulating terrain of the Domara ConglomeratesLow-lying hills and strike ridges, incised valleys around rivers producing a generally undulating terrainPliocene conglomerates, sandstones, siltstones, claystones and some volcanic agglomerates. Intramontane basin deposition in a graben developed between the Sibium, Didna and Keman block-faulted mountain rangesMain rivers and channels are located within incised channelsSavannah and medium forest adjacent to river with primary rainforest on surrounding slopesThe comparatively weak and poorly consolidated materials will be deeply weathered and subject to erosion by both running water and mass movement
(7) Owen Stanley Range MountainsMountainous area of high relief reaching an elevation of 1832 m at Mount Clarence, just outside the study area. Maximum height of range is 3445 m at Mount Kenivi. The mountains are deeply incised and characterized by irregularly branching steep ridges with sharp crestsPart of the Suckling–Dayman massif developed in the Upper Cretaceous to Eocene Kutu Volcanics (thought to be former oceanic crust). Thickness of this sequence believed to be 3000 – 4000 m. These comprise basalt and pillow lavas with dykes Edge of belt on the north side has a narrow metamorphic belt of fine-grained schistsGenerally a dendritic pattern with some structural control giving rectangular elementsRainforestHighly variable weathering depths; rapid rates of erosion; subject to landsliding; deep gullying and river undercutting of slopes throughout region; oversteepened slopes of marginal stability; dykes may form harder rock ridges
(8) Cloudy Bay Lowland PlateauPart of the Owen Stanley foothills, the tuffs have produced a relatively flat plateau around 120 m high, which has been eroded by the drainage system. Slopes are relatively gentlePliocene tuffs and tuffaceous sandstonesA fairly open dendritic drainage pattern. Materials are likely to be relatively free drainingRainforest, cleared in placesLikely to be deeply weathered
(9) Mori River FloodplainFlat low-lying ground adjacent to the river, with some indication of a river terrace occupied by rubber plantationsQuaternary and recent alluviumFloodplain area adjacent to rivers subject to flooding but terrace will be above flood levels. Generally high groundwater levels. Main rivers meander across the floodplain and will be subject to changes in channel location through meander cutoffs and migrationPrimarily rainforest with grassland around the river. Large part of area has been cleared for rubber plantationsRelatively low bearing capacities; areas adjacent to rivers subject to flooding