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The forest expansion has a pattern following stream where sediments are consentrated. The change to land cover can be seen on Figure 5.15 :
Figure 5.12 Land Cover 2000-2010
The expansion of exposed surface area and the expansion of sedimentation area related closely to erosion rate. The area and the rate of erosion on Buper Watershed will be
studied further in soil erosion analysis.
5.4 Geological Analysis
Geological analysis has purpose to get useful geological information by geological map intrepetation and study site observation. Geological analysis that would be done include
identication of rock formation, identification of soil type and identification of non-groundwater basin.
5.4.1 Identification of Rock Formation
Identification of rock formation is achieved with overlay from watershed boundary with rock formation map. Input data is processed using ArcView 3.3 to get data and layout of
rock formation on Buper Watershed. Geologic formation of Buper watershed consist of ultramafic rock, mafik rock, and
makats formation. Figure 5.13 is geological formation map of Buper Watershed as resulted from ArcView 3.3 processing :
Exposed Surface Expansion
Forest Expansion
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Figure 5.13 Geologycal Formation Map at Buper Watershed
Igneous rocks form from magmas, and most magmas are associated with plate tectonics. Mafic basaltic and ultramafic magmas formalong the divergent mid oceanic
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ridges and are major components of new oceanic crust. More felsic magmas, such as andesites and rhyo -lites, are associated with the edges of continental crust at subduction
zones along converging plate boundaries. Whether a magma are intermediate or felsic may depend on the relative amounts of oceanic crustand continental crust in the subduction zone
that melt to form the magma. The great abundance of granitic intrusions in continental crust is thought to be related to the partial melting of the lower continental crust Crawford, 1998,
p. 21. Mafic rock is an igneous rock containing approximately 50 percent silica and relatively high percentages of iron, magnesium, and calcium. Ultramafic rock rock consisting almost
entirely of ferromagnesian minerals and having no feldspars or quartz Crawford, 1998. According to the history and mineral contents, ultramafic and mafic do not contain
stable minerals e.g. quartz and silica that will affect their corrosion, it will tend to be clay. Clay is an impermeable material that water can not seep through percolation. But clay is a
material with high soil moisture, then this layer can be a habitat for some plant species according to the thickness of the soil, while its bedrock is an impermeable rock too
Dirmawan, 2011.
Figure 5.14 Documentation Mafic Rock Figure 5.15 Mafic Rock Observation Position
Figure 5.16 Documentation Ultra Mafic Rock Figure 5.17 Ultramafic Observation Position
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5.4.2 Identification of Soil Type
