EARTHSC 1G03 Lecture Notes - Drainage Basin, Laminar Flow, Stream Gradient
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The hydrologic cycle is the interchange of water among sea, air and land. Water flows
through streams on the surface to reach lakes and run off into the sea.
Body of running water moving downhill b/c gravity
Head water: upper part of a stream (i.e. near mountain source)
Stream channel: long narrow depression eroded by the stream into rock or
o Stream bed: bottom of channel
o Stream banks: to the side
Long profile – cross section along channel showing all gradients from source to
Base level- Limiting level below which stream can erode. This is the change from
an erosive environment to a depositional environment.
o Faults can change base level
o Dams can change base level to upstream; sediments need to be dredged
Drainage basin: the particular area that water falls in and drains into the ocean via a
stream and its tributaries. Focus on watersheds in drainage basic – the upstream area
from which the surface water flows towards the channel
Tributary: small stream flowing into large one
Divide: boundary or topographic line seperating one draining basin from another – i.e.
North American continental divide (f/ Yukon Territory to Mexico).
Drainage pattern: the arrangement in a map of a river and its tributaries
Dendritic: resembles branches of a tree; uniformly erodible rock or regolith; most
Radial: diverge outward; high conical mountains
Rectangular: frequent 90 degree bends; regularly fractured rock –
metamorphic/igneous; fractures meeting at 90 degrees form pathway
Trellis: parallel main stream with short tributaries at right angle; tiled resistant
Laminar and turbulent flow both occur
Laminar flow: along the length of the tube; very linear and docile fashion; rare
Turbulent flow: water particles move in a highly unpredictable, high energy
fashion; turbulent flow occurs as velocity increases; it leads to erosion
Volume of water moving past a given point per unit time
(cross sectional area – product of stream width and depth)*(stream
velocity)=discharge in m3/s
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