Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
WATER RESOURCE PROTECTION AND ASSESSMENT POLICY IMPLEMENTATION PROCESS
RESOURCE DIRECTED MEASURES FOR PROTECTION OF WATER RESOURCES: ESTUARINE
ECOSYSTEMS COMPONENT
SECTION E: PROCEDURE FOR THE INTERMEDIATE DETERMINATION OF RDM FOR ESTUARINE
ECOSYSTEMS
Senior Authors: Ms Susan Taljaard, Environmentek, CSIR
Dr Jane Turpie, Percy FitzPatrick Institute, University of Cape Town
Dr Janine Adams, University of Port Elizabeth
Editors:
Dr H MacKay, Department of Water Affairs and Forestry,
Ms Barbara Weston, Department of Water Affairs and Forestry,
Ms Lizette Guest, Guest Environmental Management
Version 1.0:
Date:
24 September 1999
M:\f_rdm_october\estuaries\version 1.0\est_sectione_version1.0.doc
Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Section E: Intermediate Determination of RDM for Estuarine
Ecosystems
E.1 Flow chart of the Intermediate RDM Determination Process
A flow chart of events for the Intermediate determination of RDM as it applies to the estuarine component is given in
Figure E.1.
STEPS IN INTERMEDIATE DETERMINATION OF
RESOURCE DIRECTED MEASURES FOR
ESTUARIES
FLOW CHART OF EVENTS IN THE INTEREMEDIATE
DETERMINATION OF RDM FOR ESTUARIES
HUMAN RESOURCES/SKILLS BASE
Confirm that generic definition applies, i.e.:
Downstream: Estuary mouth
Upstream: Extent of tidal influence
Along banks: 5 m above MSL contour
STEP 1: DELINEATE GEOGRAPHICAL
BOUNDARIES
... days
Consultant coordinating RDM
process for Catchment
plus
Consultant coordinating estuarine
section
DWAF (Planning)
Hydrologist
Estuarine hydrologist
... weeks
Simulate run-off scenarios for reference, present
and selected future scenarios
Specialist studies
(including limited field surveys)
Studies need to include:
STEP 3: ASSESS PRESENT STATE
(a & b) AND REFERENCE CONDITION
-
Description of present state
Estimation of reference condition
Assessment of the selected future scenarios
List additional monitoring requirements
Estuarine specialist team with
following expertise, i.e.:
... weeks
STEP 4: DETERMINE PRESENT
(a & b) ECOLOGICAL STATUS
AND IMPORTANCE
Integration workshop
At the workshop the following need to be achieved:
STEP 5: DETERMINE ECOLOGICAL
MANAGEMENT CLASS
-
STEP 6: QUANTIFY RESERVE AND
SET RESOUIRCE QUALITY
OBJECTIVES
STEP 7: DESIGN RESOURCE
MONITORING PROGRAM
-
physical dynamics
water quality
Flora (marophytes, microphytes)
Fauna (invertebrates, fish, birds)
Assess present ecological status (using the EHI)
Assess ecological importance (using the EII)
Determine desired ecological management class
Evaluate ecological implications of the different future
scenarios
- Select acceptable scenario (desired EMC)
- Determine an ecological reserve for water quantity and
quality based on the acceptable scenario
- Design monitoring program
Documentation of Intermediate RDM
The report should include:
Description of reference condition
Description of present ecological status
Evaluation of ecological implications of the future scenarios
Determination of desired EMC
Reserve for water quantity and quality (based on desired EMC)
List of future monitoring requirements (including requirements
for Comprehensive RDM)
... weeks
... weeks
Peer review
Consultant coordinating
estuarine section
Consultants with expertise
in RDM for estuaries
Figure E.1 Flow chart of events for the Determination of Intermediate RDM as it applies to the estuarine
component
NOTE: Estimates on the time requirements and costing of the different components illustrated above will be added
after the pilot study on an estuary has been completed .
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.2 Data Requirements for Intermediate Determination of RDM
Unlike the case for many of South Africa’s rivers, there are very few long-term monitoring programmes conducted on
a national scale on South African estuaries. Programmes that do exist include:




gauging stations (measuring river inflow) installed at some estuaries (managed by DWAF)
continuous water level recorders installed at some estuaries (managed by DWAF)
topographic surveys of estuary mouths (since 1985) and of upstream cross sections (since 1996) conducted every
2-3 years on a selection of Cape estuaries (project of the CSIR, commissioned by DEAT
fish data (species composition in different estuaries based on number and biomass) was collected on numerous
South African estuaries (project of the CSIR (Durban), commissioned by DEAT
For any particular estuary, the extent and availability of data and information therefore depends on:


data available from previous research projects conducted in the estuary
short-term data records collected during, for example EFR studies or EIA studies involving the estuary.
NOTES:



Due to the complex nature of estuarine processes, and the limited availability of detailed data and information, it
would be expected that the time required and the intensity of data collection for a RDM determination could be
greater for estuaries than it is for rivers.
Before any additional data is acquired on a particular system it is necessary to undertake a desktop assessment to
determine the availability and suitability of existing data sets to address the requirements of the Intermediate
determination of RDM as listed in the following sections.
If additional field data are required (refer to Tables E.2.1 – E.2.3) the abiotic and biotic data must be collected
during the same field exercise to enable the linkage of the abiotic characteristics with the biotic responses.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.2.1
Data requirements for Abiotic (or driving) Components
In estuaries, the data requirements for abiotic (or driving) components, i.e. hydrodynamics, sediment dynamics and
water quality, are strongly inter-linked and are addressed in Table E.2.1.
Table E.2.1 Data requirements on abiotic components (physical dynamics and water quality) for the
Intermediate Determination of RDM in estuaries
DATA REQUIRED1
Set of cross section profiles (taken at about 500 m intervals)
representative of the present bathymetry of the estuary
Simulated monthly runoff data (at the head of the estuary) for
present and reference conditions over a 50 to 70 year period 1
Aerial photographs of estuary
Measured river inflow data (gauging stations) at the head of
the estuary over a 5-year period 2
Continuous water level recordings near mouth of the estuary3
Longitudinal salinity and temperature profiles (in situ) taken
on a spring high and low tide at 4:

end of low flow season (i.e. period of maximum
seawater intrusion)

peak of high flow season (i.e. period of maximum
flushing by river water)
Water quality measurements (i.e. system variables, and
nutrients) taken along the length of the estuary (surface and
bottom samples) on a spring high tide at 4,5:

end of low flow season

peak of high flow season
Measurements on organic content and toxic substances (e.g.
trace metals and hydrocarbons) in sediments along length of
the estuary 6
Water quality (e.g. system variables, nutrients and toxic
substances)measurements on river water entering at the head
of the estuary 7
Water quality (e.g. system variables, nutrients and toxic
substances)measurements on near-shore seawater 7
1
PURPOSE
These measurements are required if numerical hydronamic
modelling is to be used in estimating reference conditions
and the implication of future scenarios (typically data older
than 3 years should not be used, as well as data collected
prior to a major flood).
To estimate seasonal variability in river flow patterns (the
accuracy and confidence limits of the simulations must be
indicated). The magnitude of smaller floods, i.e. 1:1 to 1:5
year can be estimated from these tables
To derive the effect of wave action on the mouth dynamics,
in particular, the extent to which the mouth is exposed to
direct wave action and width of the breaker zone (indicative
of the beach slope).
This data is crucial to be able to correlate river flow to the
state of the mouth (as reflected by water level recordings),
particularly in temporarily open/closed estuaries. The
dataset duration required will depend on, for example the
frequency of mouth closure in the particular estuary
To obtain long-term records of variations in tidal levels and
periods of mouth closure
These measurements, together with the river inflow data are
used
to
estimate
the
correlation
between
salinity/temperature distribution patterns along the length of
the estuary and river flow. Where only a limited amount of
field work would be possible, this could best be achieved
by measuring the two ‘extremes’ i.e. end of low flow
season and the peak of high flow season
The water quality field exercise must coincide with the
salinity/temperature profiling. In this way a limited water
quality data set (which is usually very expensive to acquire)
can be used to derive water quality characteristics under
different tidal conditions, using salinity data, expert opinion
or appropriate assessment tools, e.g. numerical models
To establish the spatial distribution and extent of toxic
pollutant distribution in the estuary.
To prevent duplicate sampling, this data must be obtained
from the water resource unit just upstream of the estuary.
At present these parameters are not measured on a routine
basis along the SA coast, as is the case for some rivers.
Because the seawater quality may show strong seasonal
variability, particularly along the SA West coast, a short
term monitoring programme (e.g. 6 week period) may not
necessarily be representative. In the short term, data on
near-shore seawater quality therefore need to be derived
from available data sources, including the South African
Water Quality Guidelines for Coastal Marine Waters.
Volume 1: Natural Environment (DWAF, 1995), until such
time as routine water quality monitoring programmes are
implemented along the SA coast.
Editor’s note: Author to clarify whether WR90 can be used
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
NOTES on Table E.2.1:
NO.
1
2
3
4
5
6
7
DESCRIPTION
It is assumed that the DWAF will not use the Intermediate reserve determination to allocate water to other users
that will affect the larger floods, i.e. 1:5 years and bigger. For this reason the data requirements specified for the
intermediate reserve DO NOT include data to estimate sediment scour/erosion (which usually needs to be
collected over several years). This will however, be specified for the comprehensive reserve (Section F).
Gauging stations are currently not installed at many estuaries. As a result such data will initially have to be
estimated from the simulated run-off data, but with much lower confidence. It is therefore strongly recommended
that gauging stations are installed, even for the intermediate phase, and especially since between 5-15 year of data
is required for the comprehensive determination of RDM.
Continuous water level recordings are currently not available for many estuaries. As a result such information will
have to be based on limited visual observations of tidal variation (i.e. over at least 2 tidal cycles), but with much
lower confidence. It is therefore strongly recommended that water level recorders be installed, even for the
intermediate phase, and especially since between 5-15 year of data is required for the comprehensive
determination of RDM
It is strongly recommended that both the low flow and high flow seasons be covered to obtain the two ‘endpoints’.
This, in turn, will improve confidence in deriving intermediate conditions (i.e. the in between months), using for
example numerical models. If, however, it is only possible to one survey, this should be done at the end of the low
flow season, particularly for permanently open estuaries.
The analytical techniques used in the processing of marine and estuarine water quality samples, may vary greatly
form those used in the analysis of fresh water samples It is therefore crucial that a recognised marine analytical
laboratory conduct the analyses of water quality samples
For once off sampling of toxic substances (e.g. trace metals and hydrocarbons) in highly dynamic systems such as
estuaries, it is considered more appropriate to sample environmental components which tend to integrate or
accumulate change over time, such as sediments. These surveys need, however, not be done in ALL estuaries,
only in systems where river water quality or human activities along the banks of the estuary suggest possible
contamination (e.g. industrial effluents or storm water run-off from large urban developments).
Estuaries receive water from two sources, i.e. the river and sea, each with distinctively different water quality
characteristics, particularly in terms of system variables and nutrients. In turn, the water quality characteristics
along the length of an estuary depend on the extent of each these sources’ influence (governed by hydrodynamic
process), as well as biochemical processes (e.g. organic degradation, eutrophication) taking place at that point
within the estuary. The influence of biochemical processes is particularly evident in parts of an estuary where
residence time of water becomes longer, often observed along the middle reaches of an estuary during the low
flow season.
Therefore, available water quality data from the water sources will be crucial to predict/estimate seasonal
variability in the water quality distribution patterns in estuaries where actual data on such distribution patterns
within the estuary are limited.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.2.2
Data requirements for Biotic (or response) Components
Data requirements for flora (microalgae and macrophytes)
Data requirements on estuarine flora for the Intermediate Determination of RDM are listed in Table E.2.2
Table E.2.2 Data requirements on flora for the Intermediate Determination of RDM in estuaries
DATA REQUIRED3
Aerial photographs of the estuary (ideally 1:1000
scale) reflecting the present status, as well as the
reference condition (if available)
PURPOSE
To map the distribution of the different plant community types
and to calculate the area covered by different plant community
types (habitat types1).
Available orthophoto maps
Aerial photographs can be used to monitor habitat change from
reference to present day, e.g. reed encroachment.
This information is required to determine the regional and
national botanical importance of an estuary, and to set the future
management class of an estuary.
Number of plant community types, identification and
total number of macrophyte species, number of rare or
endangered species or those with limited populations
documented during a field visit.
Permanent transects (a fix monitoring station that can
be used to measure change in vegetation in response to
changes in salinity and inundatiuon patterns)2:
Measurements of percentage plant cover along an
elevation gradient
Measurements of salinity, water level, sediment
moisture content and turbidity
These measurements are used to relate changes in the flora to
changes in salinity, water level, flooding and sedimentation.
From these data the sensitivity of the flora to changes in
freshwater input can be determined and reference conditions can
be estimated. In addition the implications of future run-off
scenarios can be predicted and used to set the Resource Quality
Objectives for water quantity.
Chlorophyll-a measurements taken at 5 stations (at
least) at the surface, 0.5 m and 1 m depth intervals
thereafter. Cell counts of dominant phytoplankton
groups i.e. flagellates, dinoflagellates, diatoms and
blue-green algae.
To determine phytoplankton biomass and dominant
phytoplankton types. Phytoplankton biomass is an index of
eutrophication while changes in the dominant phytoplankton
groups indicate changes in response to water quality and
quantity.
Measurements must be taken coinciding with typically
high and low flow conditions.
A study of this nature is probably only necessary in large
permanently open estuaries where phytoplankton are important
primary producers.
Intertidal and subtidal benthic chlorophyll-a
measurements taken at 5 stations (at least).
Epipelic diatoms need to be collected for identification.
These measurements must to be taken coinciding with
a typical high and low flow condition (in temporarily
closed estuaries measurements must include open as
well as closed mouth conditions).
Simultaneous measurements of flow, light, salinity,
temperature, nutrients and substrate type (for benthic
microalgae) need to be taken at the sampling stations
during both the phytoplankton and benthic microalgae
surveys.
Measurements for different flow conditions are required to
establish natural variability.
To determine benthic microalgal biomass and dominant epipelic
diatom species. Benthic microalgae are important primary
producers in shallow estuaries or those with large intertidal
areas. Epipelic diatoms composition can indicate changes in
water quality.
Measurements for different flow and mouth conditions are
required to establish natural variability.
Measurements of different abiotic parameters are required to
determine their effect on phytoplankton and benthic microalgae.
In turn, this information is used to estimate reference conditions
and predict the implication of future runoff scenarios. Change in
microalgal biomass and composition indicates changes in water
quality that is strongly related to freshwater input. These data
are used to set the Resource Quality Objectives for both water
quality and water quantity
Microalgal field excursion should coincide
hydrodynamic and water quality field exercise.
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NOTES on Table E.2.2:
NO.
DESCRIPTION
Available information on the flora of South African estuaries includes Begg’s (1984) early surveys in KwaZulu-Natal and
the CSIR’s surveys of Cape estuaries. Ward and Steinke (1982) documented the distribution of mangroves. O’Callaghan
(1994) described the salt marsh vegetation of a number of Cape estuaries and more recently Colloty et. al. (1999) have
compiled a database on all available botanical information on South African estuaries. Colloty (1999) completed a survey
of Transkei and Ciskei estuaries and baseline information is now available for approximately 80 % of South African
estuaries
There are nine different habitat types recognised for estuaries, i.e.:
HABITAT TYPE
Open surface water area
Indicates available habitat for phytoplankton
Exposed intertidal sand and mudflats
Supratidal saltmarsh
Indicates available habitat for intertidal benthic
microalgae
Zostera capensis (eelgrass), Ruppia cirrhosa,
Potamogeton pectinatus)
Cladophora spp., Enteromorpha spp., Caulerpa
filiformis
Spartina maritima, Sarcocornia perennis, Triglochin
spp,
Sarcocornia pillansii, Sporobolus virginicus
Reeds and sedges
Phragmites australis, Schoenoplectus littoralis
Mangroves
Avicennia marina, Rhizophora mucronata, Bruguiera
gymnorrhiza
Barringtonia racemosa, Hibiscus tiliaceus
Submerged macrophyte beds
Macroalgae
1
Intertidal saltmarsh
Swamp forest
2
3
INDICATOR SPECIES
These data are currently not available for many estuaries but are required for the comprehensive determination of
RDM so that Resource Quality Objectives can be set for water quantity and quality with some degree of
confidence
Sampling of estuarine flora should coincide with water quality and hydrodynamic field exercises.
Data requirements for fauna (Invertebrates, fish and birds)
From a temporal point of view it must be noted that faunal components should ideally be sampled over at least a one
year period, preferably on a quarterly basis for any meaningful results to be obtained. However, if only two seasons
(e.g. low and high flow season) were going to be sampled some first order estimates would have to be obtained. If
only one season was sampled, then the birds need to be sampled in summer, because the major bird component of
estuaries are the aquatic Palaearctic migrants which arrive in South Africa for our summer
Data requirements on fauna for the Intermediate Determination of RDM are listed in Table E.2.3.
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Table E.2.3 Data requirements on fauna for the Intermediate Determination of RDM in estuaries
DATA REQUIRED3
Derive preliminary sediment map of the estuary.
Obtain a preliminary determination of the extent and distribution
of shallows and tidally exposed substrates.
For six benthic sites, collect sediment samples for analysis of grain
size 1 and organic content 2
Determine the longitudinal distribution of salinity, as well as other
system variables (e.g. temperature, pH and dissolved oxygen and
turbidity) 3 at each of the six benthic sampling sites
During a spring tide (preferably for both low flow and high flow
conditions), collect a set of six benthic samples each consisting of
five grabs. Collect two each from sand, mud and interface
substrates. If possible, spread sites for each between upper and
lower reaches of the estuary. One mud sample should be in an
organically rich area. Species should be identified to the lowest
taxon possible and densities (animal/m2) must also be determined.
During a spring tide (preferably for both low flow and high flow
conditions), collect two sets of beam trawl samples (i.e. mud and
sand). Lay two sets of five, baited prawn/crab traps overnight, one
each in the upper and lower reaches of the estuary. Species should
be identified to the lowest taxon possible and densities
(animal/m2) must also be determined.
Survey as much shoreline for signs of crabs and prawns and record
observations.
During a spring tide, collect three samples, at night, one each from
the upper, middle and lower reaches of the estuary.
During a spring tide, collect three sets of small and large seine and
gill net samples, one each from the lower, middle and upper
reaches of the estuary. Depending on the size and depth of the
estuary, it may be necessary to also undertake cast netting,
particularly in smaller systems.
Information on fish gained during the macrocrustacean beam
trawls should also be used.
During a summer spring tide, undertake one full count of all
water-associated birds, covering as much of the estuarine area as
possible. All birds should be identified to species level and the
total number of each counted.
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PURPOSE
This is required to identify different habitats types,
e.g. sand, mud, detritus distribution and interface
area.
These measurements are required gain understanding
on key links between the abiotic parameters and
biological components
To estimate biomass distribution and key species of
the benthos.
To estimate biomass distribution and key species of
the macrocrustacea.
To estimate biomass distribution and key species of
the zooplankton.
To estimate biomass distribution and key species of
the fish.
To estimate biomass distribution and key species of
the birds.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
NOTES on Table E.2.3
NO.
1
2
3
4
DESCRIPTION
Seven-grain size categories should be used, ranging from mud to very coarse sand. Each category relates to a
particular size diameter in the following manner:
>2 mm: > very coarse sand
2 - 1 mm: very coarse sand
1 - 0.5 mm: coarse sand
0.5 – 0.25 mm: medium sand
0.25 – 0.125 mm: fine sand
0.125 – 0.0625 mm: very fine sand
<0.0625 mm: mud (silt and clay)
The percentage organic content of sediments may be classified as:
<0.5%: Very low
0.5 – 2%: Low
1 – 2%: Moderately low
2 –4%: Medium
> 4%: High
Data on salinity and other water quality parameters along the length of the estuary are measured as part of the
abiotic data acquisition programme (Table E.2.1). Therefore, to ensure that data collection is as cost effective as
possible, benthic surveys should be conducted simultaneously with relevant abiotic data collection exercises.
Sampling of estuarine fauna should coincide with water quality and hydrodynamic field exercises.
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E.3 Procedures for Intermediate Determination of RDM
E.3.1
Delineation of geographical boundaries (Step 1)
For the purposes of the Intermediate Determination of RDM for estuaries, the geographical boundaries of an estuary
are defined as follows:
Downstream boundary: The estuary mouth. However, in systems where the near shore marine ecosystem may be
dependent on river input via the estuary, this should be noted to be addressed during the Comprehensive
Determination of RDM for the system.
Upstream boundary: The extent of tidal influence, i.e. the point up to where tidal variation in water levels can still
be detected.
Lateral boundaries: The 5 m above MSL contour along each bank.
The boundaries should be mapped on aerial photograph or orthophoto map. Should the boundaries of any estuary
need to be defined differently, a motivation must be provided.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.2
Description of present status2 (Step 3a)
The present ecological status of an estuary (defined within specific geographical boundaries) is a quantitative
description of the present abiotic and biotic characteristics and functioning of the system.
The description of the present ecological status, together with the reference conditions, forms the basis for the RDM
Determination Process, for it is here where specialist scientists describe and document their understanding of the
characteristics and functioning of an estuary (backed by appropriate field measurements and scientific expertise).
For the Intermediate Determination of RDM for estuaries, present ecological status needs to be described in terms of
the following components:
Abiotic (or driving components):
 Hydrodynamics (measured in terms of seasonal river inflow patterns, floods, mouth dynamics, water level
variations and water movement patterns)
 Sediment dynamics (measured in terms of changes in cross section profiles and particle size distribution)
 Water quality (measured in terms of system variables, nutrients and toxic substances) (if social and economic
aspects are to be considered in the allocation of the FMC, microbiological contaminants may need to be included).
Biotic (response) components:
 Estuarine flora (microalgae and macrophytes)
 Estuarine fauna (invertebrates, fish and birds)
The following sections provide protocols on the presentation of results on the ecological status for the abiotic and
biotic components, respectively. All assumptions and interpretations of data and results must be fully documented in
appendices to the RDM study report.
The accuracy with which the ecological status of any estuary could be described will largely depend on:
 The extent and detail of available data (i.e. existing data and information)
 Additional data that could be collected within time/budget constraints
 The complexity of processes in a particular estuary.
The description of the present ecological status, in terms of the different abiotic and biotic components, can therefore
vary from a detailed quantitative characterisation based on measured data, to a narrative statement based on expert
opinion. For this reason, confidence in the assessment must be documented.
Results on abiotic components must be presented in a format that would be useful and appropriate for estuarine
biologists to derive biological responses. The format in which information on the present ecological status of abiotic
components need to be presented is as follows:
Editor’s note: The use of both terms “present state” and “present ecological status” is not appropriate. This
terminology must be resolved in Version 1.1
2
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
a.
Seasonal variability in river flows
Tabulate the monthly simulated run-off data for present conditions (flow in m3/s) for 50-70 year period. Plot the
simulated run-off data, indicating the monthly median values.
Year
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1949
1950
1951
1952
1953
1954
1955
…….
…….
Oct
141.00
17.86
137.67
0.20
21.32
33.04
92.96
32.85
13.40
84.16
7.18
1.95
2.35
1.09
13.61
1.06
6.97
6.48
67.10
17.99
8.82
2.70
19.53
415.95
65.27
1.13
16.38
11.16
9.17
11.35
4.16
33.97
Nov
87.44
731.06
267.92
7.07
212.86
42.51
89.15
25.01
12.09
178.57
8.00
4.54
29.17
253.43
150.39
1.93
307.05
7.84
55.52
290.62
53.73
6.37
322.13
458.26
39.51
0.99
94.57
214.33
15.42
73.59
11.34
16.68
Dec
52.61
658.65
237.03
20.13
314.49
23.99
85.54
74.92
53.87
155.97
43.00
8.02
71.45
424.82
507.98
5.56
170.97
169.49
247.10
237.93
295.20
14.90
444.60
249.22
11.22
1.72
56.30
230.17
24.09
169.38
134.17
37.64
Jan
35.73
216.76
230.48
102.67
257.05
181.86
87.09
166.53
80.36
255.38
287.84
29.25
34.24
863.35
231.57
250.52
254.16
182.30
218.10
91.40
229.98
228.96
450.26
148.32
10.80
71.02
20.15
245.50
191.63
89.65
102.94
420.
Feb
167.73
73.02
305.13
122.32
216.14
102.12
189.46
102.81
85.08
157.61
219.55
559.94
68.14
446.71
136.60
428.39
365.34
132.05
697.37
62.51
219.99
325.35
192.82
453.15
29.96
102.68
182.74
155.51
214.72
40.19
63.94
280.64
Mar
235.89
128.25
108.62
95.29
0.03
74.79
211.62
84.80
253.80
146.27
66.36
391.01
53.57
129.41
113.36
240.39
132.08
52.18
388.53
51.07
134.55
247.55
104.58
208.06
341.45
142.35
168.12
169.27
127.68
182.51
45.02
74.55
Apr
96.71
63.89
14.82
40.98
819.13
36.07
80.28
37.07
136.22
73.48
26.75
93.17
21.26
88.36
51.49
71.72
19.31
54.64
65.22
25.66
105.61
108.31
555.46
29.98
176.19
62.57
61.38
93.53
85.76
99.86
29.22
37.22
May
20.83
11.42
3.07
10.19
82.22
9.39
10.58
8.77
19.55
13.20
7.76
34.03
4.39
43.76
19.23
110.13
3.06
26.51
23.01
206.35
43.80
26.27
287.05
5.74
18.00
7.14
13.78
21.54
33.35
29.79
9.50
14.32
Jun
8.27
13.47
0.93
3.07
24.52
12.40
1.85
1.97
22.17
5.34
1.23
22.15
1.14
18.97
14.68
68.44
0.95
17.29
11.37
158.83
10.68
12.67
49.65
16.11
4.59
1.39
16.93
6.58
9.10
12.87
3.99
6.11
Jul
2.58
7.27
2.19
1.11
11.73
7.45
3.28
0.56
31.10
2.08
3.67
9.05
5.26
15.33
6.76
12.42
0.68
25.36
12.56
39.51
2.71
5.41
80.00
11.19
1.26
0.55
10.92
1.61
2.50
4.49
1.39
11.55
Aug
0.83
17.37
1.16
0.87
3.30
2.70
5.04
0.97
15.42
2.11
1.01
2.38
2.53
24.12
2.82
2.11
0.74
17.31
8.97
8.89
0.91
4.03
418.99
4.35
0.57
0.36
3.96
0.63
1.37
5.93
32.89
6.66
Sep
18.09
13.61
0.30
6.52
19.23
40.63
3.32
4.18
79.77
5.14
0.49
1.82
0.86
10.28
1.24
1.77
0.76
6.69
9.74
10.04
1.32
8.13
194.17
54.83
0.25
0.36
2.80
0.68
1.29
2.33
29.22
1.58
Average monthly flows (in m³/s)
Simulated data for present conditions
50
40
Median
95%ile
10%ile
30
20
10
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
b.
Present status of abiotic components
Because the Reserve and RQO for water quality and water quantity need to be specified on a monthly basis (Step 6),
an attempt should be made to document present status information on similar time scales, particularly for the abiotic
components. However, if only the minimum data sets, as listed in Tables E.2.1 – E.2.3, will be available for an
intermediate determination of RDM, it may not be possible to describe the present status in such detail. It will be
more appropriate to provide the required information for typical periods, e.g. low flow season (January – March),
rather than for individual months.
For each month (or selected period) provide the following information, including the confidence in the assessment
(refer to Appendix E5, Table E5.1 for presentation format):






Typical flow pattern (derived from 50-70 year simulation data set), expressed in terms on the 10%ile, median and
95%ile.
Describe the state of the mouth
Describe flood inundation patterns
Describe the amplitude of tidal variation (indicative of the exposure of intertidal habitats during low tide)
Describe the salinity characteristics of the nearshore seawater* and river water**, as well as the distribution
patterns in the estuary.
Describe the characteristics of other system variables (e.g.temperature, pH, dissolved oxygen and SS/turbidity),
nutrients (e.g. nitrate, nitrite, total ammonia, reactive phosphate, reactive silicate) and toxic substances (e.g trace
metals and hydrocarbons) of the nearshore seawater* and river water**, as well as the distribution patterns in the
estuary.
(*) Obtained from the South African Water Quality Guidelines for Coastal Marine Waters. Volume 1: Natural
Environment
(DWAF, 1995) or available data sets
(**) Obtain these from present conditions specified for ‘river section’ just upstream of estuary
c.
Describe how human interference is presently affecting abiotic components. Indicate extent of
impacts caused. These may include:



Structures/activities affecting river inflow volumes (e.g. dams, irrigation abstraction):
Structures affecting water movement patterns in the estuary (e.g. marinas, bridges, mouth stabilisation):
Point source/diffuse sources of contamination affecting the river water quality (extract from information on the
present status of the ‘river section’ just upstream of the estuary)
Point source/diffuse sources of contamination along the estuary’s banks affecting the water quality in the estuary

Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Biotic Components – present status assessment3
a:
Describe the present state for each biotic component. This should attempt to provide assessments for the
following as far as possible on the available data and based on a ‘considered opinion’ and ‘best estimate’
approach:
 Biomass distribution
 Species diversity, richness and rarity (e.g. provide details on endemic and Red Data species)
 Seasonal and inter-annual variability, as well as flood situations and drought conditions
 Assessment of the relationship to other nearby estuarine and marine systems
 Local/regional/national importance of the estuary in terms of the biotic component.
A locality map, showing the spatial distribution of key species and/or habitat types should accompany the
description, where applicable.
If only the minimum data sets (i.e. as listed in Tables E.2.1 – E.2.3) are available for the Intermediate
determination of RDM of a particular estuary, much of the above information will not be available or can
only be provided with low confidence. These gaps need to be identified in the description of the present
status, to ensure that is addressed in future data acquisition exercises, e.g. for the Comprehensive
Determination of RDM (Section F).
b:
Provide a general overview on the influence of the following abiotic (or driving) components, as well as
other biotic processes on a particular biotic component (i.e. identifying key links and also indicate critical
periods of the year). Provide the confidence assessment (refer to Appendix E5, Table E5.2 for presentation
format). :
 State of the mouth, including frequency and duration of closure;
 Flood plain inundation
 Exposure of intertidal area during low tide
 Sediment characteristics (including sedimentation)
 Salinity distribution patterns
 Other water quality constituents(be as specific as possible)
 Other biotic components
c:
Describe the human interferences that have had direct impact on the biotic functioning and Indicate to
what extent these have caused irreversible impact on the biota. These may include:
 Structures (e.g. bridges, marinas)
 Human exploitation of resources (e.g. bait collection)
 Flood plain and catchment development
3
Editor’s note: Review layout and headings in Section E for version 1.1
Department of Water Affairs and Forestry, South Africa
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E/14
Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.3
Estimate reference conditions (Step 3b)
The reference condition, together with the description of the present state are considered to be the most important steps
in the RDM determination process, for it is during these two steps that specialist scientists describe and document their
understanding on the characteristics and functioning of the estuary, backed by appropriate field measurements and
scientific expertise. This forms the basis for:
 allocation of the Ecological Management Class (Step 5)
 determination of the ecological reserve for water quantity and water quality (Step 6)
For the purposes of the determination of RDM, the reference condition of an estuary refers to the ecological status that
it would have had:
 when receiving 100% of the natural MAR
 before any human development in the catchment or within the estuary
 before any mouth manipulation practices (e.g. artificial breaching)
Typically the reference conditions in an estuary thus refer to its ecological status 50 to 100 years ago.
Although the generic definition of the reference condition states that this condition should refer to the natural
unimpacted ecological state of the estuary, it is important to realize that in some estuaries changes have occurred that
may be irreversible. If there is no practical way of restoring the original ecological characteristics of a particular water
resource, then there may be justification for resetting the reference condition to more accurately reflect the new
ecological characteristics of the resource ( See Integrated Manual).
The following sections provide protocols on the presentation of results on the reference condition for the abiotic and
biotic components, respectively. All assumptions and interpretations of data and results must be fully documented in
appendices to the project report.
The description of the reference condition, in terms of the different abiotic and biotic components, can vary from a
detailed quantitative characterisation based on measured data to merely a narrative statement based on expert opinion.
For this reason, confidence limits must be documented along any different statements on the reference conditions.
Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Abiotic (or driving) components – reference conditions
Results related to abiotic components must be presented in a format that would be useful and appropriate for estuarine
biologists to derive expected biological responses. The format in which information on the reference conditions of
abiotic components should be presented is as follows:
a.
Year
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1949
1950
1951
1952
1953
1954
1955
…….
…….
Obtain monthly simulated run-off data for the reference condition (flows in m3/s) for 50-70 year
period. Plot the simulated results, together with the monthly median values.
Oct
141.00
17.86
137.67
0.20
21.32
33.04
92.96
32.85
13.40
84.16
7.18
1.95
2.35
1.09
13.61
1.06
6.97
6.48
67.10
17.99
8.82
2.70
19.53
415.95
65.27
1.13
16.38
11.16
9.17
11.35
4.16
33.97
Nov
87.44
731.06
267.92
7.07
212.86
42.51
89.15
25.01
12.09
178.57
8.00
4.54
29.17
253.43
150.39
1.93
307.05
7.84
55.52
290.62
53.73
6.37
322.13
458.26
39.51
0.99
94.57
214.33
15.42
73.59
11.34
16.68
Dec
52.61
658.65
237.03
20.13
314.49
23.99
85.54
74.92
53.87
155.97
43.00
8.02
71.45
424.82
507.98
5.56
170.97
169.49
247.10
237.93
295.20
14.90
444.60
249.22
11.22
1.72
56.30
230.17
24.09
169.38
134.17
37.64
Jan
35.73
216.76
230.48
102.67
257.05
181.86
87.09
166.53
80.36
255.38
287.84
29.25
34.24
863.35
231.57
250.52
254.16
182.30
218.10
91.40
229.98
228.96
450.26
148.32
10.80
71.02
20.15
245.50
191.63
89.65
102.94
420.
Feb
167.73
73.02
305.13
122.32
216.14
102.12
189.46
102.81
85.08
157.61
219.55
559.94
68.14
446.71
136.60
428.39
365.34
132.05
697.37
62.51
219.99
325.35
192.82
453.15
29.96
102.68
182.74
155.51
214.72
40.19
63.94
280.64
Mar
235.89
128.25
108.62
95.29
0.03
74.79
211.62
84.80
253.80
146.27
66.36
391.01
53.57
129.41
113.36
240.39
132.08
52.18
388.53
51.07
134.55
247.55
104.58
208.06
341.45
142.35
168.12
169.27
127.68
182.51
45.02
74.55
Apr
96.71
63.89
14.82
40.98
819.13
36.07
80.28
37.07
136.22
73.48
26.75
93.17
21.26
88.36
51.49
71.72
19.31
54.64
65.22
25.66
105.61
108.31
555.46
29.98
176.19
62.57
61.38
93.53
85.76
99.86
29.22
37.22
May
20.83
11.42
3.07
10.19
82.22
9.39
10.58
8.77
19.55
13.20
7.76
34.03
4.39
43.76
19.23
110.13
3.06
26.51
23.01
206.35
43.80
26.27
287.05
5.74
18.00
7.14
13.78
21.54
33.35
29.79
9.50
14.32
Jun
8.27
13.47
0.93
3.07
24.52
12.40
1.85
1.97
22.17
5.34
1.23
22.15
1.14
18.97
14.68
68.44
0.95
17.29
11.37
158.83
10.68
12.67
49.65
16.11
4.59
1.39
16.93
6.58
9.10
12.87
3.99
6.11
Jul
2.58
7.27
2.19
1.11
11.73
7.45
3.28
0.56
31.10
2.08
3.67
9.05
5.26
15.33
6.76
12.42
0.68
25.36
12.56
39.51
2.71
5.41
80.00
11.19
1.26
0.55
10.92
1.61
2.50
4.49
1.39
11.55
Aug
0.83
17.37
1.16
0.87
3.30
2.70
5.04
0.97
15.42
2.11
1.01
2.38
2.53
24.12
2.82
2.11
0.74
17.31
8.97
8.89
0.91
4.03
418.99
4.35
0.57
0.36
3.96
0.63
1.37
5.93
32.89
6.66
Sep
18.09
13.61
0.30
6.52
19.23
40.63
3.32
4.18
79.77
5.14
0.49
1.82
0.86
10.28
1.24
1.77
0.76
6.69
9.74
10.04
1.32
8.13
194.17
54.83
0.25
0.36
2.80
0.68
1.29
2.33
29.22
1.58
Average monthly flows (in m³/s)
Simulated data for present conditions
50
40
Median
95%ile
10%ile
30
20
10
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
b.
Use the simulated run-off data for the reference condition, as well as for understanding abiotic processes and
their relationship to flows, to estimate the reference condition for the different abiotic parameters
(where these have not changed markedly from those described for the present state, note “same as present
state”):
Because the Reserve and RQO for water quality and water quantity need to be specified on a monthly basis (Step 6),
an attempt should be made to present information on reference conditions on similar time scales, particularly for the
abiotic components. However, if only the minimum data sets, i.e. as listed in Tables E.2.1 – E.2.3, will be available for
an intermediate determination of RDM, it may not be possible to describe the reference conditions in such detail. It
will then be more appropriate to provide the required information for typical periods, e.g. low flow season (January –
March), rather than for individual months.
For each month (or selected period) provide the following information, including the confidence limits of data (refer to
Appendix E5, Table E5.1 for presentation format):






Typical flow pattern (derived from 50-70 year simulation data set), expressed in terms on the 10%ile, median and
95%ile.
Describe the state of the mouth
Describe flood inundation patterns
Describe the amplitude of tidal variation (indicative of the exposure of intertidal during low tide
Describe the salinity characteristics of the nearshore seawater* and river water**, as well as the distribution
patterns in the estuary.
Describe the characteristics of other system variables (e.g. temperature, pH, dissolved oxygen and SS/turbidity),
nutrients (e.g. nitrate, nitrite, total ammonia, reactive phosphate, reactive silicate) and toxic substances (e.g. trace
metals and hydrocarbons) of the nearshore seawater* and river water**, as well as the distribution patterns in the
estuary.
Obtained from the South African Water Quality Guidelines for Coastal Marine Waters. Volume 1: Natural
Environment (DWAF, 1995) or available data sets. This document contains a chapter containing background
information on constituents in seawater, including a sub-section on natural occurrence, which provides
estimates on the reference condition concentrations for most system variables, nutrients and toxic substances
along the SA coast.
Obtain these from reference conditions specified for ‘river section’ just upstream of estuary.
(*)
(**)
Biotic components- reference conditions
a.
Review the changes that have occurred in abiotic parameters from the reference to present day conditions.
Estimate to what extent these changes would have affected the reference condition for a particular biological
component, (changes in related biotic components must also be assessed). Assess these in terms of the following
abiotic variables (provide confidence limits of the data):







b.
State of the mouth
Flood plain inundation
Exposure of intertidal area during low tide
Sediment characteristics (including sedimentation)
Salinity distribution patterns
Other water quality parameters (be as specific as possible)
Other biotic components
Estimate the biotic functioning of each component without the human interferences identified under the
present state (Section E.3.2), including confidence These may include:



Structures (e.g. bridges, marinas)
Human exploitation of resources (e.g. bait collection)
Flood plain and catchment development
Department of Water Affairs and Forestry, South Africa
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
c.
Use the information in (a) and (c) above to estimate the reference condition for a particular biotic
component, in terms of:



Species diversity, richness and rarity
Biomass distribution
Seasonal variability, taking both of the above into account.
A locality map, showing the spatial distribution of different key species and/or habitat types could accompany the
description of each biotic component, where applicable.
Department of Water Affairs and Forestry, South Africa
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E/18
Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.4
Assessment of the present ecological status (Step 4a)4
Present Ecological Status is a measure of the health of a resource, based on a comparison between the reference
condition (Section E.3.2) and the present state (Section E.3.3). An Ecological Health Index (EHI) is used to assess the
present ecological status for estuaries. On the basis of the EHI, the PES will be assigned a category A to F, as follows
(Table E.3.1)
Table E.3.1.Recommended guidelines for the classification of PES, or present condition, of an estuary
based on an integrity score which indicates present state as a percentage of pristine state.
EHI SCORE
91 – 100
76 – 90
61 – 75
41 – 60
21 – 40
0 – 20
PES CATEGORY
A
B
C
D
E
F
The development and application of the EHI is described in detail in Appendix E3. The structure of the index, its
scoring methods and criteria weightings were refined during two workshop sessions. A brief summary of structure and
criteria weightings of the EHI is provided below. Details regarding the scoring systems are in Appendix E3. The
Index is constructed as follows (Table E. 3.2)
Table E.3.2. Scoring system for the EHI
VARIABLE
WEIGHT
Abiotic (habitat) variables
1
Hydrology
2
Hydrodynamics and mouth condition
3
Water quality
4
Physical habitat
5
Human disturbance
1. Habitat health score = weighted mean
25
20
20
20
15
50
Biotic variables
1
Plants
2
Invertebrates
3
Fish
4
Birds
2. Biological health score = weighted mean
40
20
20
20
50
ESTUARINE HEALTH SCORE = weighted mean of 1 and 2
Hydrology
VARIABLE
WEIGHT
a.
% decrease in period of non-low flows (measure of change in low flow period)
60
b.
% decrease in mean annual frequency of floods
40
Hydrology health score = 100 – (a + b )/2
80
Editor’s note: Author to clarify terminology. Use of “present state” and “present ecological state” is not appropriate
and must be addressed in the Version 1.1 documents.
4
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Hydrodynamics and mouth condition
VARIABLE
A
WEIGHT
Change in mean duration of closure, e.g. over a 5 or 10 year period
Water quality
VARIABLE
1
WEIGHT
Salinity
% change in axial salinity gradient and vertical salinity stratification
2
General water quality
a
Nitrate and phosphate concentrations in estuary
b
Suspended solids in inflowing freshwater
c
Dissolved oxygen (mg/l) of inflowing freshwater
d
Level of toxins
40
General water quality = Min (a to d)
Water quality health score =
60
Weighted mean
Physical habitat alteration
VARIABLE
1
Change in intertidal sediment structure and distribution
1a

1b
% change in sand fraction relative to total sand and mud
WEIGHT
50
% change in intertidal area expose
50
Mean
50
2
Change in subtidal estuary: bed or channel modification, canalisation
30
3
Migration barriers, bridges, weirs, bulkheads, training walls, jetties, marinas
20
Weighted mean
% similarity in physical habitat
Human disturbance of habitats and biota
a
b
VARIABLE
Degree of human non-consumptive activity on estuary, e.g. walking, water-skiing.,
and associated damage of habitats (e.g. by trampling, boats).
Degree of human consumptive activity (fishing and bait collecting) on estuary, and
associated levels of exploitation and damage of habitats (e.g. due to digging by bait
collectors)
WEIGHT
40
60
Weighted mean
Human disturbance score = 100 – weighted mean disturbance
Biotic variables
VARIABLE
MEASUREMENT
1. Species richness
Estimated % of original species remaining
2a. Abundance
Estimated % of total biomass remaining
b. Community composition
Estimated % resemblance to original composition.
Weighted abundance
= b x c%
Plant / Invertebrate / Fish / Bird community health score = weighted mean of 1 and 2
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
WEIGHT
25
75
E/20
Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.5
Assessment of ecological importance (Step 4b)
Ecological importance is an expression of the importance of an estuary to the maintenance of ecological diversity and
functioning on local and wider scales. Some of the variables that can be considered as the basis for the estimation of
ecological importance of estuaries are listed in Table E.3.5.1 These variables were selected and weighted during two
workshops, in order to construct an Ecological Importance Index. The selected variables can each be categorised as
measures of rarity, abundance or ecological function. The rationale for selecting these variables, as well as further
details on the ecological importance index are discussed in detail in Appendix E4.
In the Ecological Importance Index, all scores are presented on a scale of 0 (totally unimportant) to 100 (critically
important). Overall Estuary Importance is calculated as follows:
Table E.3.5.1 Estimation of ecological importance of estuaries 5
CRITERION
Size
Zonal Type Rarity
Habitat Diversity
Biodiversity Importance
Functional Importance
ESTUARY IMPORTANCE SCORE =
WEIGHT
15
10
25
25
25
Weighted Mean
The components of the index are used as summarised in Tables E.3.5.2 to E.3.5.4. Details of the way in which indices
are converted to importance scores are given in Appendix E4.
Notes on Table E.3.5.1
(a)
Size:
Estuary size is defined as the total area (ha) within the geographical boundaries described in section E.3.1.
(b)
Rarity of estuary type wrt to geographic position:
It is proposed that estuary type and geographical position are taken into account in a Zonal Type Rarity Index, as
follows:
ZTR = 100 x 1/Ntz,
where Ntz is the number of estuaries of type t within the same biogeographical zone z. This index yields scores in the
range from 1 to 100, which are then used to allocate importance scores (Table E.3.5.2)
Table E.3.5. 2 Number of estuaries of each physical type in each biogeographical zone, and their ZTR scores
Estuarine Bay
Permanently open
River mouth
Estuarine lake
Temporarily closed
Cool Temperate
Number
Score
0
2
50
1
100
0
10
10
Warm Temperate
Number
Score
1
100
29
3
7
14
4
25
86
1
Subtropical
Number
2
16
4
4
90
Score
50
6
25
25
1
This index can potentially be extended to include the existence of unique physical features which would add to the
reason for desiring a high management class. For example, these could be canyons e.g. Msikaba, ravines or gorges,
small estuaries that remain permanently open e.g. Lupatana. Then the estuary’s ZTR might change from 1/16
permanently open subtropical to 1/1 permanently open subtropical with feature X.
(c)
Habitat diversity:
An estuary can be considered more important if it has a high diversity of habitat types, or on the basis of
representativeness, in terms of the size and rarity of those habitat types that it contains. These parameters are
measured by means of a habitat rarity index, as follows:
HR = 1000 x  ai/Ai
5
Editor’s note: Authors to review table numbering convention for version 1.1
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
where ai is area of the ith habitat in the estuary and Ai is the total area of that habitat in the country. Four abiotic
habitat types (channel area, intertidal sandflats, intertidal mudflats, rock) and six biotic habitat types (supratidal
saltmarsh, intertidal saltmarsh, mangroves, submerged macrophytes, swamp forest , and reeds and sedge) are included
in the index.
(d)
Biodiversity importance:
Biodiversity importance will be determined on the basis of the importance of an estuary for each of the four biotic
groups. A species rarity score is used as a measure of biodiversity importance for each group, as it incorporates
measures of diversity, rarity/endemism and, where data are available, abundance.
The rarity score is a simple addition of a score for each species present in viable quantity in the system:
R = 100 x ri,
where ri is the rarity score of the ith species. The rarity score for each species can be calculated differs depending on
the level of data available. With abundance data:
ri = qi/Qi,
where qi = number or area in estuary and Qi = total number or area in whole country (not in biog zone – this will
confer undue importance to spp which only just occur in that zone). With species presence-absence data only:
ri = 1/Ni.
where Ni = the number of estuaries in which the species occurs in viable populations in SA. Index values are
converted to importance scores using taxon-specific guidelines.
Table E.3.5.3: Proposed calculation of the biodiversity importance score
TAXONOMIC GROUP
Plant importance score
Invertebrate importance score
Fish importance score
Bird importance score
Mean score
Max score
Biodiversity Importance Score
WEIGHT
25
25
25
25
50
50
Biogeographical considerations are taken into account as a modifying determinant.
(e)
Functional importance:
Estuaries provide several ecological services to their surrounding environments, particularly the marine environment.
These have been identified as follows:
Table E.3.5.4: Calculation of the functional importance of etuaries on the basis of services provided to the
surrounding environment.
CRITERIA FOR CONSIDERATION
a. Input of detritus and nutrients to the coastal zone
b. Nursery function for marine-living fish and crustaceans
c. Movement corridor for river invertebrates that breed in the marine environment (e.g. river crab Varuna littoralis)
d. Stop-over function for migratory birds
e. Roosting area for marine or coastal birds
Overall functional importance score = Max (a to e)
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.6
Determination of ecological management class (Step 5)6
The Ecological Management Class (EMC) represents the level of protection assigned to the estuary and will be used in
determining the ecological Reserve. An EMC of lower than class D is not a valid management option. Should the
present status be either an E or F, recommendations must be made as to how the status can be lifted at least to a D
class (Table E.3.6.1).
Table E.3.6.1. Proposed relationships between Ecological Management Classes based on an present ecological
status for a comprehensive Reserve determination
PRESENT ECOLOGICAL STATUS
A
B
C
D
E
F
RECOMMENDED
ECOLOGICAL MANAGEMENT CLASS
A
B or A
C or higher
C/D or higher
D or higher
D or higher
The Ecological Management Class is used as a proxy for the overall Management Class (MC) in an intermediate RDM
determination. In a comprehensive RDM determination, the MC will be set in a consultative process on the basis of
EMC and other socio-economic parameters.
The level to which Ecological Management Class is elevated relative to current status will be motivated on the basis of
its present health status (PES), the importance of the system and modifying determinants. Thus:
Health (PES) + Importance + Modifying determinants  Future status (EMC)
The ecological management class will be allocated on the basis of the ecological importance score (Section E 3.5),
using the ecological health index (Section E.3.4) as a starting point. The rules for allocation need to be calibrated.
That is, it depends on the desired relative frequency of A class, vs B class, etc, estuaries in the country. Thus we
would have to look at a preliminary distribution of scores, in order to set the EMC allocation rules which would result
in the desired distribution of management classes. The EMC’s refer to the same classes of health status as outlined in
Table E.3.1.
The degree to which EMC is set higher than present ecological status category depends on level of importance, level
of protection or desired protection, and the best attainable state. The rules for allocation of the EMC are given in
Table E.3.6.2.
Modifying determinants are protected area status and desired protected area status. A status of “area requiring
high protection” should be assigned to estuaries that are identified as vital for the full and most efficient representation
of estuarine biodiversity. This will be determined on the basis of complementarity and gap analysis (see Appendix
E4). Guidelines for allocation of EMC are given in Table E.3.6.2.
6
Editor’s note: This section E.3.6 must be reviewed for clarity.
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Table E.3.6.2 Guidelines for allocation of EMC on the basis of ecological importance
MODIFYING DETERMINANTS AND
ECOLOGICAL IMPORTANCE SCORE
Protected Area
Area requiring high protection
Estuarine Importance = 80 – 1008
Estuarine Importance = 60 – 80
Estuarine Importance = 40 – 60
Estuarine Importance = 20 – 40
Estuarine Importance = 0 – 20
RECOMMENDED EMC
BAS (Best attainable state)7
BAS
EHC + 2, minimum Class B, or BAS
EHC + 1, minimum Class C, or BAS - 1
EHC, minimum Class D
EHC, mininum Class D
EHC, minimum Class D
Editor’s note: EHC and BAS are note adequately explained, nor is their application clearly explained. Relevant
author to clarify in version 1.1
7
8
Editor’s note: Authors to clarify use of the terms “estuarine importance” and “ecological importance” in version 1.1
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
E.3.7
Quantification of the Reserve and resource quality objectives (Step 6)
Important considerations for estuaries
In estuaries, river inflow patterns (i.e. water quantity) show strong correlation with important hydrodynamic and
sediment characteristics, such as state of the mouth, amplitude of tidal variation, water circulation patterns and
sediment deposition/erosion. However, the relationships between these characteristics and river inflow are generally
complicated to interpret, owing to the influence of the sea, i.e. state of the tide and associated seawater intrusion. The
manner in which these characteristics are influenced by river flows is often not the result of a single flow event, but
rather that of characteristic flow patterns occurring over weeks or months.
Marked differences exist between the chemistry (or water quality) of river water and seawater, particularly in terms of
system variables (e.g. salinity, temperatures, oxygen levels, pH and suspended solids) and nutrients (e.g. nitrate,
ammonium, phosphate). As a result, river inflow patterns (i.e. water quantity) also have a strong influence on water
quality characteristics of estuaries. The water quality characteristics along the length of the estuary, at any point in
time, are dependent on the extent of marine or freshwater influence at that point. This, in turn, is primarily determined
by the quantity of river water entering the estuary during that period, and also by the state of the tide. Longitudinal
salinity distribution profiles are typically used as primary indicators of water quality. The distribution patterns of
other water quality constituents within the estuary can then be derived, provided that the chemical composition of the
marine and freshwater are known, as well as an understanding of biochemical processes which may take place within
the estuary.
In estuaries there is a much larger buffer or delay-effect between river inflow patterns and their effect on abiotic
parameters than in rivers. This, in addition to the complex relationship between river inflow patterns and processes in
estuaries, requires a much more holistic and processed-orientated approach for setting the reserve and RQO for
estuaries.
The following sections provide protocols on the presentation of results on the assessment of future runoff scenarios
and quantification of the Reserve and RQO. All assumptions and interpretations of data and results must be fully
documented in appendices to the study report when a RDM determination is carried out.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Water quantity component of the Reserve
To derive the water quantity component of the Reserve, realistic future river run-off scenarios, together with data for
present status and reference conditions, are used to estimate the extent to which the occurrence and duration of typical
abiotic states within an estuary are likely to change with changes in river run-off. In turn, changes in abiotic
characteristics are then evaluated in terms of their biological significance. Results from these evaluations are then
used to select an acceptable scenario, defined as the future run-off scenario, or a slight modification thereof, that
represents the highest reduction in river inflow that will still protect the aquatic ecosystem of the estuary and to keep it
in the desired EMC.
Procedures in this regard to be followed are:
a.
Decide on realistic future run-off scenarios for the catchment of a particular estuary (i.e. possible
hydrological regimes), taking into account aspects such as planned dam development, future agricultural
abstractions, etc.
Where future water resource developments are planned for a particular catchment, these should be used to
compile run-off scenarios. In the absence of future water resource development scenarios, a series of
hypothetical, but realistic run-off scenarios (e.g. 75%, 50% and 25% of natural MAR) should be simulated, as
a starting point. The confidence in the accuracy of these simulations must be provided since they form the
basis of the quantification of the Reserve.
These simulations should be carried out as a collaborative effort amongst the DWAF planning directorate, a
hydrologist (with experience in generation of such scenarioss) and an estuarine hydrodynamic specialist (to
stipulate specific output requirements).
b.
Tabulate and plot the monthly simulated run-off data for each future scenario, as for the present status
and reference conditions.
c.
Derive typical abiotic states for the estuary. Because river inflow into an estuary, generally shows strong
correlation with certain abiotic parameters, such as state of the mouth and longitudinal salinity distribution
patterns, it is usually possible, for a particular estuary, to link or correlate river inflow ranges to typical
‘abiotic states’.
Based on the above assumption, derive typical ‘abiotic states’ for a particular estuary linking it to typical
river inflow patterns (use the data gathered on the present status and reference conditions to derive these).
For each of the ‘abiotic states’, provide a brief summary as follows (give confidence limits of the
information):






d.
River inflow range
State of the mouth under that state
Flood plain inundation patterns
Amplitude of tidal variation typical of that state
Salinity distribution patterns typical of that state
Other water quality characteristics typical of that state.
Predict effect of different future runoff scenarios on the occurrence and variability of ‘abiotic states’,
using monthly median flows and flow ranges estimated for the different states (this provides a simplified
means of depicting changes in the seasonal variability of abiotic parameters for future runoff scenarios,
relative to reference conditions and present status), for example see Figure E2.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
Natural conditions:
20
State 2
(50 % possibility)
State 4, periodically State
5
State 3
State 3
15
10
5
0
1
Jan
2
Feb
3
Mar
4
Apr
5
May
6
Jun
7
Jul
8
Aug
9
Sept
10
Oct
11
Nov
12
Dec
13
Jan
Present status:
20
State 2
State 4,
periodically
State 5
State 3
State 1 may occur for
short periods
15
State 2
State 3
10
River flow (m³/s)
5
0
1
Jan
2
Feb
3
Mar
4
Apr
5
May
6
Jun
7
Jul
8
Aug
9
Sept
10
Oct
11
Nov
12
Dec
13
Jan
Future runoff scenario 1:
20
State 2
State 4,
periodically
State 5
State 3
State 1 occurring for
short periods
15
State 3
State 2
10
5
0
1
Jan
2
Feb
3
Mar
4
Apr
5
May
6
Jun
7
Jul
8
Aug
9
Sept
10
Oct
11
Nov
12
Dec
13
Jan
Future runoff scenario 2:
20
State 2
(50 % possibility)
State 2
(50 % possibility)
State 3
15
10
5
0
1
Jan
2
Feb
3
Mar
4
Apr
5
May
6
Jun
7
Jul
8
Aug
9
Sept
10
Oct
11
Nov
12
Dec
13
Jan
Months
Figure E2: Occurrence of different abiotic states related to different river flows.
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Resource Directed Measures for Protection of Water Resources: Estuarine Ecosystems
e.
Predict the effect of each of the future scenarios on the biotic components, based on the changes in
occurrence and variability of ‘abiotic states’. Provide the confidence limits of these predictions.
f.
Use Ecological Health Index to assess the implication of each scenario on the overall ecological status of
the estuary (Appendix E3), using the predicted changes in abiotic and biotic components as described in (a)
to (d) above.
g.
Summarize the EHI results in a table (see below). To be able to derive the acceptable scenario, the overall
ecological significance of the different scenarios needs to be evaluated. To provide an overview for the
evaluation process, the following summary table need to be produced:
VARIABLE
% SIMILARITY TO REFERENCE
Present
Scenario 1
Scenario 2
Scenario n
Abiotic (habitat) variables
1
Hydrology
2
Hydrodynamics and mouth condition
3
Water quality
4
Physical habitat
5
Human disturbance
Habitat health score
Biotic variables
1
Plants
2
Invertebrates
3
Fish
4
Birds
Biological health score
ECOLOGICAL HEALTH SCORE
Corresponding EMC
h.
Select the acceptable scenario, defined as the future runoff scenario, or a slight modification thereof, that
represents the highest reduction in river inflow that will still maintain the aquatic ecosystem in the desired
EMC. This evaluation must be done by a group of experts, e.g. at a workshop. Translate the acceptable
scenario into the format required for the water quantity component of the Reserve, i.e.:
Jan
Feb
March
April
May
June
July
Normal seasonal flows (m3/s):
95%ile
….
Median
….
10%ile
….
Droughts: Minimum flows (m3/s)
….
Floods (is assumed that the Reserve specified for water quantity as part of the Intermediate Determination of RDM,
will NOT be used to allocate licenses that will affect the magnitudes of the 1:5 year floods and above. Requirements
for floods are therefore not specified are therefore not specified as part of the Reserve
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Quantification of the water quality component of the Reserve
Superimposed on the influences that river water quantity (i.e. inflow patterns) has on water quality characteristics of
estuaries, there are potential influences from anthropogenic waste inputs through



waste inputs into river water entering the estuary
waste inputs into seawater entering the estuary
waste inputs directly into the estuary.
The aim of setting the water quality component of the Reserve is to set concentration limits for water quality
constituents so as to ensure that the aquatic ecosystem is protected. For rivers these are set in terms of monthly limits,
which can be monitored at a single point within the resource unit. However, in estuarine systems where water quality
along the length of the estuary may change continuously, owing to diurnal tidal variations, it is not sensible for
management purposes to set the requirements for the water quality component of the Reserve as monthly limits to be
measured at points within the estuary itself.
For estuaries it is therefore proposed that the water quality components of the reserve for estuaries be defined as limits
on the concentration and/or loads of water quality constituents which may enter the estuary from the river, from the
sea or from outfalls directly into the estuary.
Of the above, the only source of inflows over which the Department of Water Affairs and Forestry, appears to have
sole administrative control over water quality matters, is the river. For discharges into the sea and estuary, several
other statutes may also apply, including those administered by Department of Environment Affairs and Tourism and
Provincial authorities. In terms of the National Water Act 36 of 1998, it is considered appropriate, for management
purposes to set the water quality component of the Reserve for the estuary as that pertaining to the quality of the river
inflow to the estuary (Table E3.7.1)
Table E3.7.1 Other statutes relevant to management and protection of water quality, particularly at sea and in
estuaries(CSIR, 1991)
STATUTES
Dumping at sea control Act (73 of 1980)
Environmental conservation Act (73 of 1989
National environmental management Act (107 of 1998)
Prevention and combating of pollution of the sea by oil Act (6 of 1981)
International convention for prevention of pollution from Ships Act (2 of 1986)
International convention relating to intervention on the high seas in cases of oil
pollution Act (64 of 1987)
Cape and Kwazulu Natal Conservation Ordinances
Harbour Regulations
ADMINISTRATIVE
AUTHORITY
Department of Environment
Affairs and tourism (DEAT)
Department of Transport
Provincial Nature
Conservation agencies
Portnet
To ensure that the reserve and RQO for the estuary link with those specified for resource units in the river further
upstream, the following approach needs to be followed:
a.
Obtain the water quality component of the Reserve specified for the riverine resource unit just
upstream of the estuary (this would specify the water quality at the end of that resource unit, and would
therefore be representative of the river water entering the estuary).
b.
Compare water quality concentrations and/or loads with those of the present state and reference conditions.
Evaluate the effect which any changes in river water quality may have on the water quality in the
estuary. Describe these in terms of the different water quality components, i.e:



c.
System variables
Nutrients
Toxic substances
Predict the implications of these changes on the biotic component, i.e. flora and fauna.
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d.
Use Ecological Health Index to assess the implication of the above on the overall ecological status of the
estuary (Appendix E3). Assume that unaffected variables listed in the EHI will have the same score as for
the present ecological state.
e.
If the EHI score indicates that the estuary will remain in the desired EMC, accept the Reserve of the
riverine resource as that for the estuary.
E.3.8
Design of Resource Monitoring Programs
The purpose of monitoring programs, in the context of the determination of RDM, would be as follows:



to improve the confidence in the determination of the RDM particularly where rapid or intermediate
determinations of RDM were carried out;
to verify predictions made during the determination of RDM, i.e. likely changes in abitoic and biotic
components associated with changes in the quality and quantity of river inflow.
to audit whether the reserve and RQO are being adhered to once licenses are allocated and, where necessary, to
adapt the Reserve and ROQ.
The extent of monitoring programmes that would be required, as the final step in an Intermediate Determination of
RDM, will be site specific and will largely depend on factors such as:




the amount of data that could be acquired for the RDM determination on a particular estuary, largely affected by
time/budget constraints;
existing data and information which had already been available for a particular estuary and the suitability thereof;
complexity of estuarine processes which had not been foreseen at the onset of the RDM determination, mainly
identified by low confidence levels;
type of longer-term water demands anticipated in the particular catchment (e.g. if dam developments are
considered in the future, then data requirements for a comprehensive determination of RDM will have to be
considered, particularly those that need to be acquired over 5-15 year periods).
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