Kuliah Analisis Geomorfologi :

Analisis Morfometri DASBy : Irvan Sophian

Morphometry ?..............

Morphometry [geomorph] (mor-phom'-e-try)

The measurement and mathematical analysis of the configuration of the Earths surface and of the shape and dimensions of its landforms. The main aspects examined are the area, altitude, volume, slope, profile, and texture of the land as well as the varied characteristics of rivers and drainage basins (Clarke, 1966, p.235).

Dictionary of Earth Science

Terrain Analysis

Regional and local rock types and structural features are identified through terrain analysis.

Rock masses have characteristic features, as deposited, which result in characteristic landforms that become modified by differential weathering.

Deformation and rupture change the rock mass, which subsequently develops new landforms. Some relationships between morphological expression, structure, and lithology are given in Figure.

Diagrams showing effect of varying geologic structure and lithology on morphology of landscapes. (From A. N.

Strahler, Physical Geology, Wiley, Inc.; from Thornbury, W. D., Principles of Geomorphology, Wiley, New York, 1969.)

Stream Forms and Patterns

Rainfall runoff causes erosion, which attacks rock masses most intensely along weakness planes, resulting in stream forms and patterns that are strongly related to rock conditions.

Stream Forms

Stream channels are classified with respect to shape as straight, crooked, braided, or meandering (also classified as young, mature, old age, or rejuvenated).

Drainage Patterns

Catchment Areacatchment area [grd wat]

(a) The recharge area and all areas that contribute water to it.

(b) An area paved or otherwise waterproofed to provide a water supply for a storage reservoir. Syn: collecting area.

Delineation of a watershed boundary

Stream Channels Stream channels carry runoff flows from precipitation in the watershed. The channel is carved by the flowing water . Bankful is defined as the typical flow that forms the shape of the existing channel. Most rivers reach bankful stage, at approximately a two-year reoccurrence interval. If the sediment load in a stream is greater than the streams capacity to move sediment, it becomes deposited in the stream channel, causing it to fill or aggrade. Too little sediment, compared to what the stream was historically carrying, can cause the channel to downcut or degrade in elevation. When either of these conditions happens, the stream channel must adjust upstream and downstream. Streambank erosion, channel widening, and headcut erosion are some of the symptoms of this readjustment.

Stream crossings on roads, particularly bridges, can be seriously impacted by the changes in stream

channel depth and width.

Stream Order

Stream channels connect like the veins on a leaf. This network of smaller tributaries flowing into increasingly larger streams, has several numbering systems. The stream order system refers to numbering tributaries starting in the headwaters.

1. First-order streams have no tributaries;

2. Second-order streams have only first order channels as tributaries, or they occur where two firstorder streams come together;

3. A third-order stream is formed by the joining of two second-order streams, and so on.

Orde sungai (Ratnayake2004)

Stream Categories

Streams are often identified by their flow condition:

perennial those streams which carry water the year round, except for infrequent and extended periods of severe drought.

ephemeral streams consisting of a dry channel throughout most of the year, bearing water only during or immediately after a rain..

intermittent stream channels which carry water only part of the year and are dry the other part, but which receive flow from the groundwater table when it is high enough.

Morphometric Analysis :

Linier Morphometry

Areal Morphometry

Relief Morphometry

Linier Morphometry

Bifurcation Ratio (Rb)

Rb < 3 Alur sungai tersebut mempunyai kenaikan air banjir dengan cepat, sedangkan penurunannyaberjalan lambat

Rb> 5 Alur sungai tersebut mempunyai kenaikan mukaair banjir dengan cepat, demikian pula penurunannyaakan berjalan dengan cepat.

Rb 3 5 Alur sungai tersebut mempunyai kenaikandan penurunan muka air banjir yang tidak terlalu cepatatau tidak terlalu lambat

Areal Morphometry

Drainage Density (Dd)

Adapun klasifikasi indeks kerapatan sungai tersebut (Siwi, S.E. et al, 2008) adalah :

* Dd :< 0,25 km/km2 : rendah

* Dd : 0,25 10 km/km2 : sedang

* Dd : 10 25 km/km2 : tinggi

* Dd :> 25 km/km2 : sangat tinggi

Relief Morphometry

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