Study area concentrated was analysis in some catchments area in relation with geological setting. Based on Strahler’s river ordering system, there were 6 six catchments consisting of 1
one of five order catchment and 5 five of fore order catchmentsfigure 4.
Figure 4. Distribution of Catchments as Concentrated Study Area in relation with Geological Setting
V. Result of Study
5.1. Catchment Areal Morphometry and lineaments
The first step of study was identifying and delineating catchments area, from the smallest or the first order river to the largest based on Strahler’s river order system Chorley R.J, 1969.
Delineation generate as much as 391 first order, 69 second order, and 24 third order catchments. Figure 5,6 and 7 shows from the left to the right: delineated first, second, and third order
catchments spreaded five in order fore catchments and one in order five catchment, lineaments based on direction tendency of catchments order one, and the dominant lineaments direction.
Circularity is the index value of roundness. 1 is the maximum index value which means catchments have a round shape, the smaller the value means that the catchments have more
elongated shape.
Circularity are usually written two digits after the decimal. Circularity index might be clasifyed as very elongated 0.2-0.3; elongngated 0.40-0.50; somewhat elongated
0.50-0.60; slightly rounded 0.60-0.70; rounded 0.70. Relatively elongated shape 0.60 provide ease of making lineament directions. In the case of rounded catchment, lineament
direction was made depend on its location of river flow.
Figure 5. Delineated first order Catchments on the left, lineaments of first orde catchments in the middle, and dominance of lineaments directions on the right.
Figure 6. Delineated second order Catchments on the left, lineaments of second order in the middle, and dominance of lineaments directions of second order on the right .
Figure 7. Delineated third orde Catchments on the left, lineaments of thirdorder in the middle, and dominance of lineaments directions of third orde on the right.
5.2. Regional Tectonic Analysis
Bandung Basin is inter-mountane basin because of its location lies between the volcanoes, a structural formations such as depression, surrounded by a height of Quaternary
volcanoes. Tectonic background that controls the formation of the basin, initiated by compressional tectonic structures that produce fold thrust belt at the Tertiary sedimentary rocks
are now the position covered by quarternary volcanic materialsHaryanto, 2014. This tectonic activity peaked in the Late Tertiary Martodjojo, 1984. As a result of these events, Bandung and
surrounding areas become the top of the Java geantiklin zone. After the compression forces on the island of Java gradually diminish, as the equilibrium compensation formation of a number of
normal faults or depression occurred. In the geometry of the structural formations named as antiklinal collapse basin, under the influence of extensional tectonics. In line with the on going
extensional tectonic, volcanic activities also takes place that happens on a large scale, so that by the time it generated a lot of volcanic material and most of Tertiary sedimentary rocks covered
by these volvanic materials.
In Bandung and the surrounding area, some of the existence of an ancient volcanic eruption centers form one lane lineaments with the northeast-southwest direction, so that the
inferred its presence controlled by fault structures Figure 8. Straightness of the structure in this region, also occurs in the vocanic material. This shows tectonic activity continued until the
End of Pleistocene, even supposedly still active until now.
In general, based on regional geological structure, the Bandung area is surrounded by a regional fault, which is in the northern part traversed by Cimandiri and Lembang Fault, in the
east by Citanduy Fault and in the south by Jampang Fault figure 8. Throughout the regional fault, indirectly affect the geological conditions in Bandung and the surrounding area. From the
analysis of DEM and field trips, the structural lineaments is not only known caused by a fault structure. Some lineament structures in the study area cut young volcanic rocks field data figure
9, thus affecting the shape of the topography and drainage patterns. Theoretically joints structure can reach hundreds of meters, and can affect the landform.
Drainage pattern and catchments direction can be used as guidance existence of fault structures and joints structures, because both the geological structure is weak zone destroyed
that easily weathered and eroded by flowing water. In a relatively long time, the crack area as a forerunner to the formation of river channel. On the basis of this concept, the determination of
local structural lineaments can be done based on interpretation of river catchments pattern or catchments direction, as depicted in above figure 5,6,and 7 .
Drainage pattern in the area of young volcanic are generaly radier, this indicates the drainage pattern is not only controlled by the structure of the cracks, but is also influenced by the
geometry of a volvano that is conical shaped.
Figure 8. Lane lineaments that form ancient volcanic eruption centers in Bandung and the surrounding area Katili and Sudradjat, 1984, modified.
Figure 9 . Rosette Diagam based on field measurements
5.3. Discussion
