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Elizabeth Thornton
Chapter Four
Results
This chapter provides the results of the field and analytical work described in Chapter
Three. Firstly, the scale of each study site is presented in the context of the entire stream
network. Having established the various scales of the reaches, the calculated channel
hydraulic and morphologic variables are presented in the form of downstream hydraulic
geometry trends. The spatial characteristics of local channel morphology are then described
and the results of statistical analyses based on these characteristics are given. Finally, the
spatial patterns of sediment characteristics for the Kangaroo Valley are presented.
4.1 Stream network
The stream network of the Kangaroo River was analysed using a map digitized from
the NSW 1:25000 topographic series in ArcGIS (Figure 4.1). For each study site, stream
order, catchment area and stream length were calculated using this map (Table 4.1). The
drainage density of each individual catchment was then calculated as stream length divided by
catchment area. The values in Table 4.1 indicate a strong positive relationship between stream
order, catchment area and stream length. The relationship between stream length and
catchment area is portrayed in Figure 4.2.
Table 4.1: Stream orders, catchment areas, stream lengths and drainage density for the five study sites.
Site
Stream
Order
Catchment Area
(km2)
Stream Length
(km)
Drainage Density
(km km-2)
DGC
SC1
SC2
KV1
KV2
2
4
4
5
6
5
11
23
120
210
13
26
50
227
573
2.35
2.13
2.17
1.89
2.73
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Figure 4.1: Sub catchments of the Kangaroo Valley and study sites.
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Elizabeth Thornton
800
700
Stream length(km)
600
500
400
300
200
y = 21.006e 0.0169x
100
r2 = 0.9228
0
0
50
100
150
200
250
Catchm ent area km 2
Figure 4. 2: The relationship between stream length and
catchment area.
4.2 Channel morphology
Analyses of the spatial variability of channel form were divided into two sections:
Firstly, calculated channel variables that were used to compute downstream trends at the
network scale are presented. Secondly, the spatial characteristics of channel morphology at
the local (reach) scale are described with reference to the statistical differenced between the
channel forms of pools and riffles. The reach averaged hydraulic geometry and channel
morphology variables presented in Table 4.2. Values in this table were used to examine the
spatial variation of channel morphology at both the network and local (reach) scales.
4.2.1 Downstream hydraulic geometry
Analyses of variables at each site were undertaken to examine downstream trends
between reaches to allow for a greater understanding of stream network evolution. The
coefficients, exponents and p values for the downstream hydraulic geometry relationships are
reported in Table 4.3. Using a probability of greater than 0.1 to indicate significance, it was
established that a significant relationship exists between w and Q and d and Q at both low and
bankfull flow levels. However, a strong relationship between v and Q exists only at the
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Elizabeth Thornton
lowflow level. For the Qbf relationships the exponents add approximately to 1 and the
coefficients multiply approximately to 1. This correlation is consistent with the continuity
equation (4) which requires that f+b+m = 1.
The majority of hydraulic geometry relationships are significant. The exceptions are
between vbf and Q, vbf and A, and s and Q*. Indicating that there is not a strong downstream
relationship between velocity and discharge at bankfull flow, nor is there a strong downstream
trend between bankfull velocity and catchment area. In general, for the Kangaroo Valley
network, reach slope decreases as catchment area increases. One exception is that the slope
value for DGC is smaller than that for SC1 despite DGC having the smaller catchment area.
Despite the fact that there is a general decrease in reach slope as stream order increases, this
relationship was not proven to be significant when related to the scaling variable Q*.
Table 4. 2: Coefficients, exponents and p values for downstream hydraulic relationships.
Low flow
Bankfull
Dimensionless
Catchment area
Equation
Coefficient
Exponent
p value
w=aQb
d=cQf
v=kQm
w=aQb
d=cQf
vbf=kQm
B*=aQ*b
H*=cQ*f
s=kQ*m
w=aAb
d=cAf
vlf=kAm
vbf=kAm
69.90
3.18
0.06
4.51
0.26
0.90
3.94
2.10
0.26
4.87
0.33
0.01
2.01
0.39
0.33
0.35
0.46
0.45
0.06
0.44
0.27
-0.32
0.48
0.41
0.53
-0.17
0.01
0.02
0.002
2.45E-07
2.65E-20
0.77
2.39E-13
3.28E-23
0.57
0.0008
0.03
0.06
0.35
4.2.2 Local morphologic variation
Local characteristics of channel morphology have been sub-divided into channel
bedform morphology and channel cross-section morphology. Firstly, the number of pools and
riffles identified at each site is given, followed by a description of the spatial variation of
bedforms and their morphologies. Secondly, the results of statistical analyses of crosssectional form and asymmetry values for the bedform features are presented.
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Table 4. 3: Reach averaged hydraulic geometry and channel morphology variables for (a) Whole reach (b) Pools (c) Riffles.
(a)
Reach
w
d
F
s
v lf
Q lf
v bf
Q bf
H*
B*
Q*
Abf
A*
D50
DGC
8.85
0.51
18.28
0.01
0.02
0.01
0.91
4.83
25.50
442.47
66421.8
4.79
0.22
0.02
SC1
21.38
1.23
18.30
0.02
0.07
0.02
2.32
54.30
19.34
336.73
41601
22.82
0.18
0.06
SC2
21.47
1.26
18.61
0.009
0.02
0.04
1.37
47.18
125.91
2147.42
3673343
30.43
0.17
0.01
KR1
48.87
2.43
20.77
0.0007
0.13
0.50
0.62
90.84
243.36
4887.19
7220989
141.26
0.13
0.01
KR2
59.15
2.60
24.83
0.002
0.13
0.65
0.88
145.75
33.53
763.24
67859.7
163.76
0.15
0.08
(b)
Reach
w
d
F
v lf
Q lf
v bf
Q bf
H*
B*
Q*
Abf
A*
DGC
8.44
0.61
13.06
0.01
0.01
1.01
6.34
30.27
421.93
87273
5.75
0.17
SC1
20.62
1.44
14.41
0.05
0.02
2.56
63.07
22.61
324.71
48320
24.41
0.18
SC2
17.35
1.53
11.96
0.003
0.05
1.52
53.27
152.52
1734.74
4147335
32.17
0.29
KR1
43.56
2.69
16.28
0.05
0.19
0.66
106.65
269.26
4355.99
8302835
159.71
0.13
2
48.19
3.20
17.55
0.01
0.27
0.97
200.71
41.35
621.75
93449
196.71
0.28
(c)
Reach
w
d
F
v lf
Q lf
v bf
Q bf
H*
B*
Q*
Abf
A*
DGC
9.26
0.41
23.50
0.02
0.01
0.82
3.31
20.72
463.00
45571
3.83
0.28
SC1
22.15
1.02
22.19
0.07
0.02
2.08
45.53
16.07
348.76
34883
21.22
0.17
SC2
23.54
1.13
21.93
0.02
0.03
1.30
44.14
112.60
2353.76
3436347
29.55
0.11
KR1
52.86
2.24
24.14
0.13
0.81
0.60
78.97
223.93
5285.59
6148152
127.43
0.13
KR2
59.85
2.68
24.70
0.13
1.03
0.90
152.19
34.60
772.26
70857
168.01
0.15
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4.2.2a Bedform morphology
Fitting a regression line to the longitudinal profile for each study reach allowed pools
and riffles to be objectively identified (Figure 4.2). At DGC three pools and three riffles were
identified, at SC1 three pools and four riffles were identified, at SC2 there were three pools
and four riffles, at KR1 three pools and four riffles and at KR2 four pools and four riffles
were identified. From these delineations individual cross-sections were designated as either
“pool” or “riffle”.
The longitudinal profile was also used to examine the characteristics of bedform
morphology. In this study these were bedform length, differences in elevation between
adjacent bedforms and bedform spacing. For the majority of reaches, mean riffle length is
greater than mean pool length. The exception to this was KR2, where mean pool length is
greater than mean riffle length (Table 4.4). For all three of the morphological aspects of
bedforms studied there was a general increase in size from the smaller to the larger reaches.
Table 4.4: Characteristics of bedform morphologies as measured at each site.
Site
DGC
SC1
SC2
KR1
KR2
Bedform
Length
(m)
Pool
Riffle
Pool
Riffle
Pool
Riffle
Pool
Riffle
Pool
Riffle
13.9
23.9
11.2
12.1
24.8
27.6
50.6
54.6
46.6
42.7
Chapter Four
Reach Averaged
Bedform Length
(m)
Reach Averaged
Bedform
Elevation (m)
Reach Averaged
Bedform
Spacing (m)
17.9
0.40
37.7
11.7
0.43
22.6
26.4
0.94
74
52.9
1.13
119.7
44.4
0.95
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Elizabeth Thornton
0
0
-0.5
Elevation (m)
Elevation (m)
-0.5
-1
-1
-1.5
-1.5
-2
-2
-2.5
0
20
40
60
80
Distance (m)
(a)
0
100
200
300
400
Distance (m)
(d)
SC1
0.5
100
KR2
0.0
0.0
-0.5
Elevation (m)
Elevation (m)
-0.5
-1.0
-1.5
-1.0
-1.5
-2.0
-2.0
-2.5
-2.5
-3.0
0
20
40
60
80
100
120
Distance (m)
(b)
0.5
0
140
(e)
100
200
300
400
Distance (m)
SC2
0
Elevation (m)
-0.5
-1
-1.5
-2
0
(c)
50
100
150
200
Distance (m)
Figure 4.3: Longitudinal profiles for each of the study reaches with a regression line fitted to denote pools
from riffles. (a) Devil’s Glen Creek, (b) Sawyer’s Creek 1, (c) Sawyer’s Creek 2, (d) Kangaroo River 1, (e)
Kangaroo River 2.
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Reach averaged bedform lengths and elevations were related to the scale variables of
Qbf, catchment area, reach averaged d and reach averaged w to determine whether bedform
morphology scales up with the network. The p values indicate that there is a stronger
relationship between reach averaged bedform length and scale variables than reach averaged
bedform elevation and scale variables (Table 4.5). Indeed, mean bedform length showed a
statistically significant relationship at the 0.10 level with all of the scale parameters where as
mean bedform elevation was statistically related to only reach averaged w at the 0.10
significance level. However, mean bedform length and elevation are not constant proportions
of reach averaged bankfull width and depth (Table 4.6). In addition, the spacing of bedforms
are not constant proportions of bankfull width and depth, suggesting that, using these
longitudinal profiles as a reference, it is evident that at the reach scale pool and riffle spacing
in the Kangaroo River system is irregular.
Table 4.5: Coefficients, exponents and significance values for power relationships
between reach averaged bedform variables and independent scale variables.
Independent
variable
Dependent
variable
Coefficient
Exponent
p value
Elevation
Length
Elevation
Length
Elevation
Length
Elevation
Length
0.25
9.77
0.28
7.90
0.13
3.45
0.58
21.16
0.27
0.26
0.27
0.35
0.52
0.63
0.61
0.69
0.22
0.08
0.22
0.08
0.14
0.05
0.10
0.05
Qbf
Catchment area
Reach average d
Reach average w
Table 4. 6: Bedform elevation and length as a proportion of reach averaged bankfull width and depth
Site
Bedform
Length/Width
Bedform
Elevation/
Width
Bedform
Spacing/
Width
Bedform
Length/Depth
Bedform
Elevation/
Depth
Bedform
Spacing/
Depth
DGC
SC1
SC2
KR1
KR2
2.02
0.55
1.23
1.08
0.75
0.05
0.02
0.04
0.02
0.02
4.26
1.06
3.45
2.45
1.52
35.10
9.51
20.95
21.77
17.08
0.78
0.35
0.75
0.47
0.37
73.87
18.40
58.77
49.17
34.63
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4.2.2a Cross-section morphology
In order to determine significant differences in channel shape, both within and
between reaches, cross-sectional form and absolute asymmetry values were calculated for
each cross-section (Table 4.2 above). A Mann-Whitney U test was used to ascertain whether
there was a statistically significant difference between the form and absolute asymmetry
values of pools and riffles within each study site. With respect to form, this test revealed a
significant difference between pools and riffles for all sites, except KR2. In terms of poolriffle absolute asymmetry, no significant difference was demonstrated within reaches for sites
DGC, KR1 and KR2. However, at both SC1 and SC2 a significant difference between pools
and riffles for absolute A* was shown. When pools and riffles were grouped for the whole
catchment there was a significant difference between the forms of the two populations.
However, when pool and riffle asymmetry values were grouped over all sites there was not a
significant difference.
A trend analysis was preformed using a Mann- Kendall test to identify trends between
sites for F and A*. No trend was shown between sites for F (Figure 4.3) or absolute A*,
indicating that there is no relationship between increasing scale and channel shape.
30
45
40
25
35
Reach averaged F
30
F
25
20
15
20
15
10
10
5
y = 15.537x0.0669
y = 17.402x0.0143
5
2
2
r = 0.445
r = 0.0029
0
(a)
0
0.0
50.0
100.0
150.0
200.0
Qbf (m 3/s)
250.0
300.0
350.0
0.0
(b)
50.0
100.0
150.0
200.0
Qbf (m 3/s)
Figure 4. 4: Relationship between (a) F and Qbf and relationship between reached averaged (b) F and Qbf.
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4.2.3 Velocity
Velocity measurements were taken at each site and used to compute discharge. The mean
velocities for each bedform feature at each site are plotted in Figure 4.5. Mean velocity is
higher across riffles than pools at all sites under low flow conditions. There does not appear to
be a strong downstream trend for pool velocity. Riffle velocity on the other hand shows a
stronger positive relationship between increasing velocity and increasing stream size. When
vbf values are plotted, the reverse is shown, as velocities are higher across pools than riffles.
Lowflow velocity measurements were also used to compute lowflow discharge values for
each reach which are located in Table 4.2 above. Reach average lowflow discharge values
were used in hydraulic geometry relationships, as presented above.
0.14
3.00
0.12
2.50
0.10
v (m/s)
v (m/s)
2.00
0.08
0.06
1.50
1.00
0.04
0.50
0.02
0.00
0.00
Pool
Rif f le
DGC
Pool
Rif f le
Pool
SC1
(a)
Rif f le
SC2
Site
Pool
Rif f le
KR1
Pool
Rif f le
Pool
KR2
Rif f le
DGC
(b)
Pool
Rif f le
SC1
Pool
Rif f le
SC2
Pool
Rif f le
KR1
Pool
Rif f le
KR2
Site
Figure 4.5: Comparison of velocity between pools and riffles at each site. (a) Mean lowflow velocity, (b)
Bankfull velocity.
4.3 Sediment Analysis
4.3.1 Bed sediment
A Wolman analysis was conducted to assess differences in sediment particle sizes for
pools and riffles within a reach and any overall downstream trend between reaches. It was not
possible to conduct a Wolman analysis in the pool of KR2 as water depth was too great to
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Elizabeth Thornton
retrieve a sample and thus it was not possible to compare features within the site KR2. The
results of the Wolman analyses are presented as box and whisker plots in. The upper and
lower lines of the box are the 75th and 25th percentiles of the sediment samples, respectively,
and the centerline represents the median. The lowermost horizontal line (whisker) is drawn
from the lower quartile to the smallest point within 15 interquartile ranges from the lower
quartile. The top whisker is drawn from the upper quartile to the largest point within 15
interquartile ranges from the upper quartile. Values that fall beyond the whiskers, but within
three interquartile ranges are plotted as individual points (outliers). At DGC, SC2 and KR1
the median and mean of particle sizes are higher for the riffle features than for the pool
features. At SC1 both the mean and the median of sediment particle sizes are higher in the
pool feature than the riffle feature (Figure ###). This result indicates that there is no
discernable downstream trend in sediment particle size. However, Figure ### indicates that
there are observable differences between bedform features at all of the sites.
80
Particle B axis Length (cm)
60
40
20
0
DGC_R DGC_P SC1_R SC1_P SC2_R SC2_P KR1_R KR1_P KR2_R
Sites
Figure 4.6: Box plot of B axis measurements of sediment particles for all sites.
Series: 1: DGC, 2: SC1, 3: SC2, 4: KR1, KR2. P: Pool, R: Riffle.
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80
80
Frequency (%)
100
Frequency (%)
100
60
40
20
(a)
0
0
100
200
300
60
40
20
(d)
0
0
Particle Size (mm)
Riffle
200
300
Particle Size (mm)
Pool
Riffle
Pool
Riffle
100
80
100
Frequency (%)
Frequency (%)
100
60
80
(e) 60
(b) 40
20
0
40
20
0
0
100
200
300
Particle Size (mm)
Riffle
0
100
200
300
Particle Size (mm)
Pool
Riffle
100
Frequency (%)
(c)
80
60
40
20
0
0
100
200
300
Particle Size (mm)
Riffle
Pool
Figure 4. 7: Cummulative frequency graphs for sediment sizes in pools and riffles for each site. (a) Devil’s
Glen Creek, (b) Sawyer’s Creek 1, (c) Sawyer’s Creek 2, (d) Kangaroo River 1, (e) Kangaroo River 2.
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4.3.2 Bank sediment
The results of the bank sediment analyses were used to classify the soil in the channel
banks at each site. All sites were classified as Sandy Loam, except SC1 which was a Loamy
Sand (Table 4.7). The silt and clay percentages for each site (Figure 4.8) were used to
compute Schumm’s (1963) M value which was subsequently used to determine relationships
in the Kangaroo River system between form and the silt-clay content of the soil. The p value
indicates that there is not a significant relationship between F and M. To enable comparison
between Schumm’s (1963) relationship for F and M for the Great Plains and the relationship
between F and M for the Kangaroo Valley, both relationships have been plotted in Figure 4.6.
Table 4.7: Soil classification based on percentage of
sand, silt, and clay from bank material samples.
Site
Schumm’s M
Soil
Classification
DGC
0.057
Loamy Sand
SC1
0.055
Loamy Sand
SC2
0.253
Sandy Loam
KV1
0.023
Loamy Sand
KV2
0.014
Loamy Sand
100%
80%
60%
Clay
Silt
Sand
40%
20%
0%
DGC
SC1
SC2
KV1
KV2
Figure 4.8: Percentage of sand, silt and clay for
bank material at each site.
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Figure 4.9: Comparison between the relationship of F and M for the Great Plains (Schumm
1963) and Kangaroo Valley.
4.4 Summary
The network analysis defined a clear difference in scale, based on catchment area, for
each of the sites. With regard to the up scaling of channel form within the network, the
majority of hydraulic relationships were found to be significant, the notable exceptions were
between vbf and Q, vbf and A, and s and Q*. The p values indicate that there is a stronger
relationship between reach averaged bedform length and scale variables than reach averaged
bedform elevation and scale variables (Table 4.5). However, mean bedform length and
elevation are not constant proportions of reach averaged bankfull width and depth (Table 4.6).
In addition, the spacing of bedforms is not constant proportions of bankfull width and depth.
At the local scale a difference in velocity patterns was demonstrated between low flow
discharge and high flow discharge. The data for bed sediment exhibits no strong up scale
trend in sediment particle size, but does exhibit some evidence of sorting within reaches. All
of the sites have similar bank soil types and there is not a significant trend between form and
M for this network.
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