17.3 Environmental Flow Assessment and Water Resources…
383
1,343
1,289
474
300
146
128
96
82
0
5
10
15
20
25
0
50
100
150
200
250
Chainage (m)
Elevation (m)
cease to flow
Numbers indicate discharge in m
3 s
-1
I = Bench 1
II = Bench 2
III = Bench 3
BF = Bankfull level
I
II
III
BF
Fig. 17.5 Cross section in Reach 3. Source WET (2007). Permission granted by WET project
subject to proper citation
Bankfull Flow
Like Zhu Creek, Yong’an Creek is a typical gravel-bed river in which many of
the natural channel features (pools, riffles, bars) are maintained by bankfull flows
mobilizing bed material and scouring encroaching terrestrial vegetation. Such flows
should occur on average 1.3 times per year (or four events every three years) based
on the natural frequency of occurrence.
Overbank Flow
Overbank flows were not recommended for this reach due to the presence of extensive
levee banks that limit the potential benefits of overbank flows.
(4) Reach 4 recommendations
The recommended environmental flows for Reach 4 are provided in Table 17.9. In
this section of the Ling River, flows will reflect overall levels of water extraction
from the entire upstream catchment rather than solely diversions from Zhu Creek.
Low Flow
Due to marked seasonal variation in natural low flows over the dry season, separate low flow components have been specified for October–January (16 m
3 /s) and
February–March (31.8 m
3 /s). It is expected that this will maintain the flow of lowsalinity water on the ebb tide in the upper part of the reach, helping to maintain the
position of the fresh/brackish/saline interface.
383
1,343
1,289
474
300
146
128
96
82
0
5
10
15
20
25
0
50
100
150
200
250
Chainage (m)
Elevation (m)
cease to flow
Numbers indicate discharge in m
3 s
-1
I = Bench 1
II = Bench 2
III = Bench 3
BF = Bankfull level
I
II
III
BF
Fig. 17.5 Cross section in Reach 3. Source WET (2007). Permission granted by WET project
subject to proper citation
Bankfull Flow
Like Zhu Creek, Yong’an Creek is a typical gravel-bed river in which many of
the natural channel features (pools, riffles, bars) are maintained by bankfull flows
mobilizing bed material and scouring encroaching terrestrial vegetation. Such flows
should occur on average 1.3 times per year (or four events every three years) based
on the natural frequency of occurrence.
Overbank Flow
Overbank flows were not recommended for this reach due to the presence of extensive
levee banks that limit the potential benefits of overbank flows.
(4) Reach 4 recommendations
The recommended environmental flows for Reach 4 are provided in Table 17.9. In
this section of the Ling River, flows will reflect overall levels of water extraction
from the entire upstream catchment rather than solely diversions from Zhu Creek.
Low Flow
Due to marked seasonal variation in natural low flows over the dry season, separate low flow components have been specified for October–January (16 m
3 /s) and
February–March (31.8 m
3 /s). It is expected that this will maintain the flow of lowsalinity water on the ebb tide in the upper part of the reach, helping to maintain the
position of the fresh/brackish/saline interface.