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rrain analysis
ITC, The
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
YANGON RIVER GEOMORPHOLOGY IDENTIFICATION AND ITS ENVIROMENTAL
IMAPACTS ANALSYSI BY OPTICAL AND RADAR SENSING TECHNIQUES
Aung Lwin®, Myint Myint Khaing®
"Remote Sensing Department, Mandalay Technological University, Myanmar - aung.al2006@ gmail.com
"Remote Sensing Department, Mandalay Technological University, Myanmar - drmmkhaing@gmail.com
Working Group VIII/4: Water
KEY WORDS: Fluvial, Sedimentology, LULC, Hydrologic process, Environmental impacts
ABSTRACT:
The Yangon river, also known as the Rangoon river, is about 40 km long (25miles), and flows from southern Myanmar as an outlet
of the Irrawaddy (Ayeyarwady) river into the Ayeyarwady delta. The Yangon river drains the Pegu Mountains; both the Yangon and
the Pathein rivers enter the Ayeyarwady at the delta. Fluvial geomorphology is based primarily on rivers of manageable dimensions.
The emphasis is on geomorphology, sedimentology of Yangon river and techniques for their identification and management. Present
techniques such as remote sensing have made it easier to investigate and interpret in details analysis of river geomorphology. In this
paper, attempt has been made the complicated issues of geomorphology, sedimentation patterns and management of river system and
evolution studied. The analysis was carried out for the impact of land use/ land cover (LULC) changes on stream flow patterns. The
hydrologic response to intense, flood producing rainfall events bears the signatures of the geomorphic structure of the channel
network and of the characteristic slope lengths defining the drainage density of the basin. The interpretation of the hydrologic
response as the travel time distribution of a water particle randomly injected in a distributed manner across the landscape inspired
many geomorphic insights. In 2008, Cyclone Nargis was seriously damaged to mangrove area and its biodiversity system in and
around of Yangon river terraces. A combination of digital image processing techniques was employed for enhancement and
classification process. It is observed from the study that middle infra red band (0.77mm - 0.86mm) is highly suitable for mapping
mangroves. Two major classes of mangroves, dense and open mangroves were delineated from the digital data.
1. INTRODUCTION
1.1 Landforms formed by rivers
Running water in fixed channels is the most widespread agent
of land sculpturing working on earth's surface. Therefore, the
landforms created are more important than those formed by
other agents. Flow of water takes place in rivers under the
influence of gravitation. The type of flow can be laminar or
turbulent. ‘Laminar’ flow is a flow in which the streamlines
remain parallel to the axis of the flow. In a ‘turbulent’ flowing
river, a mixing of water by turbulent eddies takes place.
A river can erode when it transports material. The transport can
take place in different ways:
- in solution
- in suspension - these are the small particles carried in
suspension.
- in saltation - sand grains hop over the bottom, the
sand grain reaching the bottom gives an impulse to
another sand particle.
- shoving: coarse material rolls over the river bed.
Coarse material is often deposited as riffles and bars in the
riverbed, these bars are placed alternating in the left and right
side of the river and form bank bars. In braided channels with
criss crossing waterways, channel-bars and islands develop
between the water courses. Laboratory experiments have shown
that the cross section of a channel transporting the same volume
of water is dependent on the type of bed material. Fine material
gives a deeper bed, coarse material a flatter, broader river bed.
A river can have a straight, a sinuous, meandering, or
a braiding channel. A meandering river flows in sinuous curves.
Meanders are arbitrarily confined to a ratio of channel length
to valley length. The water in the meander moves as a
corkscrew, the so called helicoidal flow, that means that the
flow is downstream, but besides that a movement in
perpendicular direction occurs, formed by the centrifugal force
on the water in the bend. This type of flow causes erosion in the
outer(concave) side of the meander and deposition in the
inner(convex) side. The strongest erosion takes place a short
distance after the central part of the bend. This causes "point
bars" to develop on the inner side, and the meander to migrate
downstream. A meander tries to broaden and to move
downstream. When meanders attain extreme looping, a cutting
of the meander can be formed during avulsions. In the cut-off
part an oxbow-lake is formed. In aerial photographs old cut-off
meanders, meander scrolls or point bars etc. can be easily
distinguished.
The zone where the meanders are formed is called
"meander-belt". Sometimes a relation between the width of the
channel and the width of the meander belt exists, according to
different authors the relation varies between 1:12 and 1:18. A
'braiding' river is characterised by different criss-crossing
channel ways around alluvial islands. The growth of an island
begins as the deposition of a central bar starts. The bar grows
downstream and in height and forces the water to pass through
the flowing water channels.
1.2 Remote sensing techniques for landform Analysis
Remote sensing techniques have opened new vistas for
landform analysis (both static and dynamic aspects), coupled
with field verification surveys. Landforms can be directly and
best viewed using remotely sensed data, since relief forms are
well expressed on the surface of the earth and recorded in
