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RIVER BANK INSTABILITY, CHANNEL FORMATION ANDRIVER BANK INSTABILITY, CHANNEL FORMATION ANDRATES OF INCISION IN MICRORATES OF INCISION IN MICRO--CANYONSCANYONS
OF THE EXPOSED DEAD SEAOF THE EXPOSED DEAD SEA
Itamar Shapira, Shlomo DaboraItamar Shapira, Shlomo DaboraDan Bowman, Tal Svoray and Jonathan B. LaronneDan Bowman, Tal Svoray and Jonathan B. Laronne
Dept. of Geography and Environmental DevelopmentDept. of Geography and Environmental DevelopmentBen Ben GurionGurion University of the NegevUniversity of the Negev
- 4 2 0
- 4 1 5
- 4 1 0
- 4 0 5
- 4 0 0
- 3 9 5
- 3 9 0
- 3 8 51 8 0 0 1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0 2 0 5 0
y e a r
altit
ude,
m
2 0 0 3- 4 1 6 . 4
1 9 4 5- 3 9 2 . 4
recession recession of the of the
Dead SeaDead Sea
Ein-feshca
OutlineOutline
11rate of entrenchmentrate of entrenchment--widening widening WadiWadi ArugotArugot
22bank instability & channel bank instability & channel formation in the formation in the springspring--fed fed EinEin FeschaFescha &&
33flash flood flash flood WadiWadi ZeelimZeelim
the the ArugotArugot Fan near Fan near EinEin GediGedi
basin area 232 kmbasin area 232 km22
entrenchment initiated 1963/64entrenchment initiated 1963/64deltaic fan surface slope 1.2deltaic fan surface slope 1.2oo
11.811.8o o on delta front, channel longitudinal slope: 1.1on delta front, channel longitudinal slope: 1.1--3.73.7oo
max entrenchment 16 mmax entrenchment 16 m
measurement of entrenchment and wideningmeasurement of entrenchment and widening
based on EDM, GPS & digital elevation based on EDM, GPS & digital elevation models using the models using the ErdasErdas Imagine Imagine orthobaseorthobase
on stereo aerial photoson stereo aerial photos
photo year
pixel size
control points
pixel RMSE
vertical error*
m xy m 2002 0.16 16 1.05 0.46 1999 0.16 10 1.20 0.65 1995 0.25 10 1.10 0.78 1990 0.25 6 1.10 0.77
Pixel RMSE is given in pixel units Compared to total station; separately also known for GPS
5 x5 x--sectional locations, exemplified by sectional locations, exemplified by
near shore near shore
near bridgenear bridge
change detection maps change detection maps
19901990--1995 1995
19991999--2002 2002
thus:thus:magnitudes of entrenchment and widening are magnitudes of entrenchment and widening are
related not only to flood peaks and volumes, related not only to flood peaks and volumes, but also to their number and timingbut also to their number and timing
period period
length*
peak flow
flow volume
flow duration
vertical incision
widening sea drop*
yr m3/s 106 m3 hr m/yr m/yr m 1990-95 7.7 160 12.2 700 0.59 2.6 3.9 1995-99 2.4 137 4.6 458 1999-02 3.1 418 3.5 179 1995-02 5.5 418 8.1 637 0.65 2.3 5.6 * between flow events
Summary of Summary of WadiWadi ArugotArugot measurements:measurements:
rates of incision are excessively high, rates of incision are excessively high, almost as those of the receding Dead Seaalmost as those of the receding Dead Sea
rates of widening are also very highrates of widening are also very high
these are fundamentally fast rates at this these are fundamentally fast rates at this particular narrow location with respect to particular narrow location with respect to stability of a future bridge. A safe bridge stability of a future bridge. A safe bridge is apparently prohibitively unfeasible.is apparently prohibitively unfeasible.
500m
Ein Fescha – Zukim Nature Reserve
Spring fed constant discharge ~ 75 106 m3/yr
- using total station & stability tables
N S1
2
3
45
the exposed areathe exposed arealongitudinal profile
0
4
8
12
0 100 200 300 400 500
horizontal distance, m
heig
ht. m
014.1
longitudinal profiles oflongitudinal profiles ofexposed area exposed area && streamstream
0
4
8
12
0 100 200 300 400 500
horizontal distance, m
heig
ht, m
stream
exposed area
014.1
052.0
area 1: incision near the shorearea 1: incision near the shore
0
1
20 1 2 3 4
distance, m
heig
ht, m
0
1
2
3
40 2 4 6 8 10 12 14
distance, m
heig
ht, m
area 2: inception of bank failuresarea 2: inception of bank failures
0
2
4
60 5 10 15 20 25 30
distance, m
heig
ht, m
area 3: massive bank failuresarea 3: massive bank failures
0
2
4
60 10 20 30 40
distance, m
heig
ht, marea 4: meandersarea 4: meanders
area 5: vegetation & cementationarea 5: vegetation & cementation
0
2
4
60 2 4 6 8 10 12 14
distance, m
heig
ht, m
types of failurestypes of failures
types of failurestypes of failures
frequency of failuresfrequency of failuresbased on 12 measured xbased on 12 measured x--sectionssections
rotaional slide 41%
slides46%
m.r.s 41%
translation 18%
flow 12%
fall 42%
fall flow translation rotaional slide m.r.s
y = 1.5337 l(x) - 4.9315R2 = 0.93
0
1
2
3
4
5
0 100 200 300 400 500 600horizontal distance, m
entre
nchm
ent,
mmagnitude of entrenchmentmagnitude of entrenchment
with distance from shorewith distance from shore
number of slides vs bank height
0
2
4
6
8
10
0 1 2 3 4 5bank height, m
num
ber o
f slid
es
number of slides vs bank height
0
2
4
6
8
0 1 2 3 4 5
bank height, m
num
ber o
f slid
es
width of deflation zone vs distance from shore
0
10
20
30
40
0 100 200 300 400 500 600
horizontal distance, m
wid
th, m
width of deflation zone vs distance from shore
0
10
20
30
40
0 100 200 300 400 500 600horizontal distance,m
wid
th, m
EinEin FeschaFescha -- conclusionsconclusions!! Failure development is unrelated to direct shear stress of Failure development is unrelated to direct shear stress of
the flowing stream. It is influenced by the lack of the flowing stream. It is influenced by the lack of flushing of most of the failed material in wider sections.flushing of most of the failed material in wider sections.
!! The number of failures depends on bank height and the The number of failures depends on bank height and the width of the deflation zone.width of the deflation zone.
!! Depth of entrenchment increases with distance from the Depth of entrenchment increases with distance from the receding base level; but decreases in proximity to the receding base level; but decreases in proximity to the reserve due to stability, in part regained by vegetation reserve due to stability, in part regained by vegetation and cementation at this point in time.and cementation at this point in time.
!! The question is not whether the nature reserve will be The question is not whether the nature reserve will be entrenched, but when.entrenched, but when.
03≈
Zeelim fan - flash flood regimeZeelim Fan - flash flood regime
- based on a series of cartoons
first mechanism of lateral widening: undercutting
1st stage:
exposure of the sea bed and divergent flow in channels
2nd stage:
entrenchment with widening by preference
3rd stage:
continued entrenchment
4th stage:
initial mechanism of lateral widening, tension cracks occur, continued vertical entrenchment and initial undercutting
5th stage:
advanced undercutting, widening of tensile cracks
and formation of overhanging cliffs
6th stage:
block failure and inclination
second mechanism of lateral widening: sliding
1st stage:
entrenchment and appearance of tensile cracks
2nd stage:
deep entrenchment and widening of tensile cracks
3rd stage:
development of planar failure planes and sliding
third mechanism of lateral widening: toppling
1st stage:
develoment of tensile cracks in high banks
2nd stage:
collapse of bank
toppling
toppling
10.5.2005
11.2.2004
6.1.2004flushing of failedflushing of failedbank materialbank material
6.1.2004
31.3.2005
flushing of failedflushing of failedbank materialbank material
Ze-elim entrenchment takes place on an identical lacustrine deposit to that in Ein Fescha, though the Ze-elim bed is covered by a thin veneer of coarse alluvium that limits faster incision rates
ZeZe--elimelim -- conclusionsconclusions!! Failure development is related to shear stress of the Failure development is related to shear stress of the
flowing stream: undercutting and transport of failed flowing stream: undercutting and transport of failed material. Rotational slides are infrequent material. Rotational slides are infrequent ––unlike at unlike at EinEin FeschaFescha..
!! Bank height at Bank height at ZeZe--elimelim is more than 2is more than 2--fold compared to fold compared to EinEin FeschaFescha, due to large discharges and undercutting , due to large discharges and undercutting availed by flushing of failed material.availed by flushing of failed material.
!! Depth of entrenchment increases with distance from the Depth of entrenchment increases with distance from the receding base level; but decreases in proximity to the receding base level; but decreases in proximity to the upper fan area due to large input of coarse sediment.upper fan area due to large input of coarse sediment.
03≈
width of flow width of flow vsvs distance between banksdistance between banks
R2 = 0.90
R2 = 0.070
20
40
60
80
100
0 20 40 60 80 100 120
distance between banks, m
wid
th o
f flo
w, m
Ein Fescha Ze'elim
distance between banks distance between banks vsvs distance from shoredistance from shore
0
20
40
60
80
100
0 100 200 300 400 500 600
distance from shore line, m
dist
ance
bet
wee
n ba
nks,
m
Ze'elimEin Fescha
bank stability* bank stability* vsvs distance from shoredistance from shore
* Based on the Thorne* Based on the Thorne--SimonSimon--RinaldiRinaldi stability criteriastability criteria
0 100 200 300 400 500 600
distance from shore line, m
stab
ility
con
ditio
n Ze'elimEin Fescha
stable
unstable
Wadi Ogflash flood regime supplemented by
treated sewage base flow
thank you