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Storm Hydrographs - Coggle Diagram
Storm Hydrographs
What are they?
graphs used to show how a rivers
changing discharge levels over the
course of a storm event
Annual Hydrographs
(regimes)
graphs used to show a
rivers changing discharge
levels over the course of a year
Simple
-
only 1 period of high discharge a year
E.g. Murray - Australia
Blue Nile - Sudan
Complex
-
two or more periods of high discharge
a year - E.g. Rhine - Netherlands
Terms
Peak Discharge
point of highest discharge
Peak Rainfall
point of highest precipitation
Lag Time
time difference between peak
rainfall and peak discharge
Rising Limb
period of increasing discharge
levels following rainfall event
Falling Limb
period of decreasing discharge
levels from peak discharge to baseflow
Storm Flow
storm hydrograph higher level
of discharge experienced following
rainfall event
Base Flow
steady continuous background
discharge level
Flashy Response
Characteristics
short lag time
high peak discharge
GRADIENT
steep slopes
precipitation in contact with land
less perpendicular so no infiltration
higher gravitational pull force
larger volume and speed of transfer
to channel - SURFACE RUNOFF
SOIL TYPE
CLAY
small pore spaces
reduced infiltration + increased
surface runoff
as soil more saturated quickly
water get to channel quickly
GEOLOGY
impermeable - BASALT
reduced infiltration + increased
surface runoff
water get to channel quickly
BASIN SIZE
smaller basins
few square km
water get to channel quickly
less distance to travel
shorter period of storm flow
lag time very short
BASIN SHAPE
short, circular basin
all points on watershed equal
distance from gauging station
all rainfall reach river at same time
short lag time and high peak discharge
LAND USE
towns and cities (urbanisation)
increased amount of impermeable
surfaces
increases surface runoff
no infiltration/percolation
water reaches channel very fast
DRAINAGE DENSITY
higher drainage density
lots of surface streams
greater chance of flooding
through increased surface runoff
PRECIPITATION
long and intense period of
precipitation
soil becomes saturated and
exceeds infiltration capacity
result in increased overland flow
Lag (Normal)
Response
Characteristics
long lag time
low peak discharge
GRADIENT
gentle slopes
precipitation in contact with land
more perpendicular so long time infiltration
lower gravitational pull force
smaller volume + speed of transfer to channel
through surface runoff
SOIL TYPE
SAND
larger pore spaces
increased infiltration + decreased
surface runoff
as saturation less likely to occur
water take longer to get to channel
GEOLOGY
permeable
porous rocks - CHALK
pervious - CARBONIFEROUS LIMESTONE
increase infiltration + decrease surface runoff
water get to channel slowly
BASIN SIZE
large basin - Nile/Congo
water get to channel less quickly
to large distance to travel over
long lag time
BASIN SHAPE
long, thin (elongated)
rainfall reaches river channel at different times
points on watershed different distances
from gauging point
lag time long and lower peak discharge
LAND USE
forests - lots of vegetation
increased interception and
vegetation storage
roots take up water from soil
storage
fallen debris cause mini dams to
be created and trap water to allow
time for infiltration
water takes longer to get to channel
DRAINAGE DENSITY
low density
small amount of surface
streams
water infiltrates and percolates
PRECIPITATION
short + less intense period of
precipitation
infiltration capacity of soil not be
exceeded = decreased overland flow
SNOW
holds water in storage