Transcript NEW METHODS FOR DETERMINING ENVIRONMENTAL FLOWS …

HYDROLOGY AND
ECOLOGY
HYDROLOGY
HYDRAULICS
WATER QUALITY
GEOMORPHOLOGY
ECOLOGY
SOCIO/ECONOMICS
RESEARCH
TEACHING
CONSULTANCY
HORIZONTAL INTEGRATION
POLICY
CATCHMENT PROCESSES:
rainfall, evaporation, runoff
infiltration, erosion
production, decomposition
etc.
Hydrology
Water quality
Geomorphology
Hydraulics
Instream biota
Instream habitats
The process used for assessing the water quantity aspects of the
ecological Reserve for rivers
Relating Biota to Hydrology
THE FLOW STRESSOR
RESPONSE METHOD
A Generic Stress Index
• An index of 0 to 10 where 0 indicates no stress,
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and 10 the highest level of stress
Stressors: Flow-related hydraulics and habitat
Biological responses: Reduced abundance (1 to 3),
increasing risk to critical life stages (4 to 6), and
disappearance of populations (7 to 10)
Flow-related hydraulics: Velocity, depth and
wetted perimeter
Habitat: Quantity and quality (the diversity and
connectivity of habitat types)
Assessing increased and decreased stress
S
t
r
e
s
s
Decreased
Flow (C)
Natural (A)
Inc. Flow (C)
% Duration
The process for applying the
FS/R method
• Select a site, survey and model hydraulic
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characteristics
Specialists apply the stress index to the site, in relation
to selected species/groups, to develop stress curves
The hydrologist converts the resulting critical stress
curve to stress time series for flow scenarios
Analyse the stress profile of each scenario in terms of
the magnitude, frequency and duration of different
stresses
Assess the severity of each stress profile in relation to
the natural stress profile
AN EXAMPLE OF A SITE SPECIFIC STRESS
INDEX FOR INVERTEBRATES
Flow
rate
(m33/s)
Stress
Res ponse
4
0
Average velocities > 0.6 m/s, and average depth > 0.4m provides abundant fast
deep and fas t shallow habitat for rheophilic species (such as s imuliids and
hydropsydhids.
3.8
1
Average velocity 0.61 m/s, average depth still > 0.4m. Abundance of critical
habitats is s lightly reduced, but all species are still abundant.
0.3
3
Average velocity 0.2 m/s (therefore ma ximum velocity approximately 0.4 to 0.5
m/s ). Average depth 0.17m, maximum 0.4m. Still some critical habitat, but
rheophilic species abundance much reduced.
0.13
5
Average velocity 0.12 m/s (therefore maximum velocity 0.2 to 0.3 m/s). Average
depth 0.14m, maximum 0.34m. Wetted perimeter 9m - marginal vegetation
habitats only just in the water. Rheophilic species confined to very small areas,
egg and early larval stage probably non-viable.
0.03
7
Average velocity 0.05 m/s (maximum approximately 0.1 m/s ). Average depth
0.12m, ma ximum depth 0.28m. Wetted perimeter 6.4m, no longer in marginal
habitats. Loss of all critical flowing habitat, only remnant areas for short-term
survival of hardy rheophilic species .
0.01
8
Average velocity 0.01 m/s, only s low trickles and s tanding water habitats remain.
All rheophilic species will disappear if this flow condition pers ists.
0
9
Standing water only
Note:
Stresses of 2, 4 and 6 have not been specifically motivated, and are simply extrapolations of the
adjacent stress motivations.
Blyde River
100
10
1
0.1
0.01
0.001
0
Barbus
2
Cpre
4
6
Stress
Inv
8
Rip Veg
10
Total
Black = Natural, Red = Recommended, Blue = Present day
Blyde River spell analysis (Stress = 1.5)
White = natural, Red = recommended, Blue = Present day
EXAMPLE OBJECTIVES
(e.g. to maintain Category B)
• Maintain perennial flow
• Summer flows > winter flows
• Av. velocity > 0.1 m/s at all times for target fish (stress
never > 6)
• Sufficient depth (30 cm) to allow target fish to feed and
breed 85% of time in summer (stress < 1 for 42.5% of time)
• Av. velocity > 0.3 m/sec for 80% of time, to ensure
Trichoptera habitat (stress < 3 for 80% of time)
• Wetted perimeter in reeds for 60% of summer to provide
marginal habitats (stress < 0.8 for 30% of time)
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Inverts:
Stress <3
80% time
8
Fish:
Stress <1
42.5 % time
6
Riparian veg:
Stress <0.8
30% time
4
2
0
0
10
20
30
40
50
60
70
% Time Exceeded
80
90
100
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Inverts:
Stress <3
80% time
8
Fish:
Stress <1
42.5 % time
6
Riparian veg:
Stress <0.8
30% time
4
2
B
0
0
10
20
30
40
50
60
70
% Time Exceeded
80
90
100
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Fish:
Stress <1
42.5 % time
Inverts:
Stress <3
80% time
8
6
Riparian veg:
Stress <0.8
30% time
4
2
D
B
0
0
10
20
30
C
40
50
60
70
% Time Exceeded
80
90
100
Thukela IFR4 Based on dry season flows
B
B/C
Ecological Reserve procedures
Reference
conditions
Present
Ecological
State
Ecological
Importance
and
Sensitivity
Classification and
objectives
DRIFT
DRIFT
Database
Flow Stressor
Response
PHABSIM