Transcript lecture-12 Drainage

TERRAIN CHARACTERIZATION AND
EVALUATION
From a utilitarian view point - why do we need to
characterize terrains?
Direct relation between the terrain type and
- nature/competency/strength/structure of the bed rocks
- soil type, and
- vegetation.
Geographers
Soil scientists
Civil engineers
Geologists
Urban planners
Landscape architects
Land-use managers
Agriculture scientists, foresters, botanists, ecologists
Terrain characteristics that can be studied using
remote sensing data:
• Landforms and topography
• Drainage pattern and texture
LANDFORMS AND TOPOGRAPHY
• Landform is a geomorphologic unit
largely defined by its surface form
• Includes seascape and oceanic waterbody interface features such as bays,
peninsulas, seas etc
• Also include sub-aqueous terrain
features such as submersed mountain
ranges, volcanoes, and the great ocean
basins.
Categorised by physical attributes such
as elevation, slope, orientation
(Topography)
JPL, Pasadena
TOPOGRAPHY
• Elevation of a landform
DRAINAGE PATTERN
A drainage system is the pattern formed by the streams, rivers, and lakes in a particular
drainage basin.
Governed by:
•Topography of the land
•Nature of underlying rocks (compatibility, permeability and porosity), and
• Gradient of the land.
A drainage basin is the topographic region from which a stream receives runoff, throughflow, and groundwater flow.
Drainage basins are divided from each other by topographic barriers called a watershed.
A watershed represents all of the stream tributaries that flow to some location along the
stream channel. The number, size, and shape of the drainage basins found in an area
varies and the larger the topographic map, the more information on the drainage basin is
available.
Drainage basin = catchment, catchment area, catchment basin, drainage
area, river basin, water basin and watershed
DRAINAGE PATTERN
Drainage pattern
1 1
2
3
4
Drainage basin
Watershed
Why study drainage?
Fundamental input in many applications:
- Civil engineering
- Agriculture
- Hydrology
- Disaster management
- Geology
DRAINAGE PATTERN
A dendritic drainage pattern is the most common form and looks like the
branching pattern of tree roots.
Develops in regions underlain by homogeneous material. That is, the
subsurface rocks have similar resistance to weathering so there is no apparent
control over the direction the tributaries take.
Tributaries joining larger streams at acute angle (less than 90 degrees).
DRAINAGE PATTERN
Parallel drainage patterns form where there is a pronounced slope to the
surface
Tributary streams tend to stretch out in a parallel-like fashion following the
slope of the surface.
DRAINAGE PATTERN
Trellis drainage patterns look similar common garden trellis.
Trellis drainage develops in folded topography
Down-turned folds called synclines form valleys in which resides the main
channel of the stream. Short tributary streams enter the main channel at sharp
angles as they run down sides of parallel ridges called anticlines.
Tributaries join the main stream at nearly right angles
DRAINAGE PATTERN
Rectangular drainage develops on rocks that are of approximately uniform
resistance to erosion, but which have two directions of jointing at approximately
right angles.
The joints are usually less resistant to erosion than the bulk rock so erosion
tends to preferentially open the joints and streams eventually develop along the
joints.
The result is a stream system in which streams consist mainly of straight line
segments with right angle bends, and tributaries join larger streams at right
angles.
DRAINAGE PATTERN
The radial drainage pattern develops around a central elevated point.
Commonly found around dome shaped features as volcanoes. The tributary
streams extend the head-ward reaches upslope toward the top of the volcano.
DRAINAGE PATTERN
The centripetal drainage pattern is the reverse of radial drainage pattern,
where streams from all directions flow towards a central depression.
Common to basin shaped features as volcanic/meteoric craters, sink holes,
structural basins.
DRAINAGE PATTERN
Deranged or contorted patterns develop from the disruption of a pre-existing
drainage pattern.
DRAINAGE PATTERN
DRAINAGE PATTERN
DRAINAGE PATTERN
DRAINAGE PATTERN
DRAINAGE PATTERN
DRAINAGE TEXTURE
Refers to the relative spacing of streams in a
drainage system
Drainage density: Total length of the streams
in a drainage system/Total area of the
drainage system
Drainage frequency: Total number of
individual streams channels/Total area of the
drainage system
Coarse-texture – Little surface runoff, good
internal drainage, hard permeable rocks
such granite;
Fine grained – Poor internal drainage, high
surface runoff, soft, impermeable and
incompetent rocks such as shale.