Transcript Physical modeling of tidal creek networks

Experimental physical modeling
of tidal creek networks
Brigitte Vlaswinkel
August 2004
Marine Geology and Geophysics Division
Rosenstiel School of Marine and Atmospheric Science
University of Miami
This week’s goal…
Build a tidal drainage network from scratch:


Bidirectional flow
Very low gradient (6.10-4)
Conform to the Reality??
Study Locations
Miami
South Florida
Andros
Island
Tidal Creek Networks


Digitized on IKONOS data and orthophoto
quads
Analyzed in GIS
2000 m
B
© SpaceImaging
500 m
Andros
South Florida
2 km
• muddy carbonates
• microtidal, low energy
• shallow creeks
• juvenile mangrove
5 km
• mixed carbonate / organics
• mesotidal
• deep creeks (3-6 m), more straight
• mature mangrove forests
Andros Island
Bahamas
Big Sable Creek
Southwest Florida
1 km
1
Active
networks
2
3
4
Stabilized
networks
Horton (1945) stream numbering – fluvial
channel segments
Order 1
1
1
2
Order 32
3
Order 2
Tidal Creek Segments
Segment length by network – geographic context
Andros
Exponential distribution
Segment length by network – geographic context
South Florida
1.000
Exceedance Probability
Exceedance Probability
1.000
0.100
(North)
0.010
0
200
0.100
(South)
0.010
400
600
Length (m)
800
1000
0
200
400
600
Length (m)
Exponential distributions
800
1000
Tidal Creek Segments–Interpretation
Exponential distribution: consistent with stochastic processes
Inflection: change in probability distribution structure,
change in processes??
Greater length of inflection = more shorter creeks
• Geographical influence..
length of inflection (m)
600
• Change systematically
from north to south
500
southward
400
300
• more abundant short
creeks to south
200
100
(probabilistically)
0
1
Andros
3
2
network
4
• more later….
Tidal Creek Network Structure
Entropy: measure of network disorder
E    r * log(r )
sys
n
n
i 1
j 1
ij
ij
rij = probability of transition from a stream of order i
into one of order j.
E = 0 indicates a perfectly ordered system (streams
of order i flow only into streams of order i+1).
E=0
E>0
E = 0 means perfectly ordered system
E > 0 means disorder!
1.4
southward
System Entropy
1.15
Creek networks are
less ordered towards
the south…
0.9
0.65
0.4
1
Andros
3
2
Network
4
Network Structure & Segment Length
1.3
1.2
system
entropy
1.1
1
Less order
1.4
Entropy (disorder)
correlates with
0.9
R2 = 0.94
0.8
Abundance of short
creeks
0.7
0.6
0.5
More shorter streams
0.4
200
Andros
400
600
inflection in E.P.
Composition
Configuration
Conclusions

Different settings, but many statistical similarities
exist between two tidal networks in terms of scaling,
patterns and the exponential length-frequency
distributions

Creek network metrics are consistent among
networks within each area

Bottom line: both composition and configuration of
creek networks are predictable (stochastically)
Objectives

Create a tidal creek network with exponential length frequency
distributions similar to drainage systems found along
carbonate dominated shorelines

Observe and quantify (composition & configuration) the spatial
and temporal development of the tidal creek networks

Observe and quantify the similarities and differences that
occur during network elaboration using different scenarios of a
tidal regime (e.g. tidal range, asymmetry)

Compare and contrast the results with morphometric studies
carried out in South Florida and Bahamas
Tidal networks evolve differently though time than river networks…
Hypotheses
Glock,
1931
Hypotheses

Tidal range
Rel. # of 1st order creeks

Vegetation density
Width/depth ratio
Max. channel depth
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A break in the probability distribution structure of creek lengths reflects
an abrupt change in processes

Similar morphometric patterns, even with different hydrology, substrate
and vegetation density, suggest the influence of more universal
processes and responses in the formation and evolution of tidal creek
networks.
References
Rankey, E.C., 2002. Spatial patterns of sediment accumulation on a
Holocene carbonate tidal flat, northwest Andros Island, Bahamas.
Journal of Sedimentary Research, 51, p. 591-601.
Rankey, E and Vlaswinkel, B., 2002. Morphometrics of carbonate tidal
creek systems, Bahamas and Florida: Implications for tidal flat
response to sea-level rise. Abstract and presentation at Geological
Society of America Conference, Denver, Co, October 2002.
My question to you
With limited
and
what would be the most useful dataset to collect ?
 Width/depth
Hydrology
 Gradients
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