FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT:
PROPOSED AIRCRAFT LANDING STRIP AND ASSOCIATED
INFRASTRUCTURE ON PORTION 4 OF FARM 27, MODDERFONTEIN
Prepared for:
Guillaume Nel Environmental Consultants
Prepared by:
Dean Ollis Pr. Sci. Nat.
9 Orca Close
Kommetjie 7975
Cell: 072 377 7006
Email: [email protected]
Freshwater
Consulting cc
--- Draft Final Report ---
March 2015
FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
TABLE OF CONTENTS
1.
INTRODUCTION ................................................................................................................................. 3
1.1.
1.2.
2.
Background .................................................................................................................................. 3
Terms of Reference ...................................................................................................................... 3
APPROACH TO THE STUDY AND LIMITATIONS .................................................................................. 4
2.1. Approach...................................................................................................................................... 4
2.2. Limitations ................................................................................................................................... 6
3.
BIOPHYSICAL OVERVIEW OF STUDY AREA AND LOCATION OF PROPOSED SITE IN RELATION TO
RELEVANT BIODIVERSITY/CONSERVATION PLANS ...................................................................................... 7
4.
DESCRIPTION OF PROPOSED DEVELOPMENT .................................................................................... 8
5.
DESCRIPTION OF SITE AND POTENTIALLY AFFECTED FRESHWATER ECOSYSTEMS ............................10
5.1. Site description............................................................................................................................10
5.2.
5.3.
5.4.
Freshwater ecosystems on and adjacent to the site .....................................................................10
Present Ecological State (PES) of potentially affected freshwater ecosystems ..............................12
Conservation importance of potentially affected freshwater ecosystems ....................................13
6.
IDENTIFICATION OF DEVELOPMENT CONSTRAINTS RELATING TO FRESHWATER ECOSYSTEMS AND
RECOMMENDED MITIGATION MEASURES .................................................................................................15
7.
CONCLUSIONS AND RECOMMENDATIONS .......................................................................................18
8.
REFERENCES .....................................................................................................................................18
APPENDICES
Appendix 1: Description of WET-Health “Level 1” wetland PES assessment method
Appendix 2: Detailed results of WET-Health assessment for wetlands in SE portion of site
FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
1. INTRODUCTION
1.1.
Background
The establishment of an aircraft landing strip and associated infrastructure is proposed for part of Portion 4
of Farm 27, Modderfontein. The subject property is situated near to Atlantis and Kalbaskraal in the Western
Cape, within the City of Cape Town (see Locality Map in Figure 1). It is located between the N7 freeway
(~600 m to the west of the site) and the Diep River (~2 km to the east of the site).
Figure 1: Locality Map for Portion 4 of Farm 27 Modderfontein [site boundary overlaid on relevant 1:50,000 scale map
obtained from Chief Directorate: National Geo-spatial Information (CD:NGI)]
Guillaume Nel Environmental Consultants (GNEC) were appointed by the applicant to coordinate the
environmental assessment process to be followed to obtain environmental authorisation for the proposed
development in terms of the Environmental Impact Assessment (EIA) Regulations of the National
Environmental Management Act (Act No. 107 of 1998) (NEMA). Due to concerns raised by officials from the
City of Cape Town regarding the possible presence of a stream in the south-eastern portion of the property,
which crosses the proposed landing strip, GNEC appointed Dean Ollis of the Freshwater Consulting Group
(FCG) to provide freshwater ecological input into the environmental assessment.
1.2.
Terms of Reference
The specific Terms of Reference for FCG’s input into the environmental assessment process for the
proposed establishment of an aircraft landing strip and associated infrastructure on Portion 4 of the Farm
27 Modderfontein were to compile an Aquatic Constraints Analysis for the section of the property on which
the landing strip is proposed to be constructed, and to provide recommended mitigation measures for the
protection of any freshwater ecosystems that are confirmed to be present in the affected area.
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2. APPROACH TO THE STUDY AND LIMITATIONS
2.1.
Approach
The approach that was taken to meeting the above-mentioned Terms of Reference was as follows:
1) Relevant conservation and biodiversity plans were examined, to determine whether any wetlands or
other aquatic ecosystems have been mapped on or in close proximity to the site and to note the
conservation status assigned to any mapped aquatic ecosystems. Such plans included the National
Freshwater Ecosystem Priority Areas (NFEPA) project (Nel et al. 2011), and the City of Cape Town’s
Wetlands Map and associated Biodiversity Network.
2) Reports that were compiled for a previous development proposal for the property were reviewed,
including an aquatic constraints analysis by DH Environmental Consultants (Harding 2012), a botanical
assessment by Bergwind (Emms 2012) and a brief palaeontological assessment (Pether 2012). The
botanical assessment report for the currently proposed development (Nicolson 2014) was also
reviewed.
3) Freshwater ecosystems on and adjacent to the proposed site were identified on the basis of an analysis
of maps, aerial photographs and Google Earth imagery, and visual observations made during a site visit
conducted on 9 February 2013. Reference was also made to the wetlands and other freshwater
ecosystems previously mapped on the subject property by DHEC (Harding 2012).
4) Identified freshwater ecosystems were classified (i.e. typed) according to SANBI’s classification system
for wetlands and other inland aquatic ecosystems in South Africa (Ollis et al. 2013). This classification
system distinguishes between seven “hydrogeomorphic (HGM) types” occurring within four landscape
settings, and it makes a distinction between naturally-occurring and artificial systems. The four
landscape settings are ‘valley floor’, ‘slope’, ‘plain’, and ‘bench’. The seven possible HGM types are as
follows:
River;
Channelled valley-bottom wetland;
Unchannelled valley-bottom wetland;
Floodplain wetland;
Seep;
Depression; and
Wetland flat.
The approximate extent of wetland areas (see Box 1) on the site was determined on the basis of field
observations of soil and vegetation characteristics, following the guidelines of DWAF (2005) and Job
(2009) for the identification and delineation of wetlands.
BOX 1: WETLAND DEFINITION
The definition of “wetland” that has been adopted for this investigation is that of the National Water Act (Act
No. 36 of 1998), whereby a wetland is defined as “land which is transitional between terrestrial and aquatic
systems, where the water table is usually at, or near the surface, or the land is periodically covered with shallow
water and which land in normal circumstances supports, or would support, vegetation adapted to life in saturated
soil.”
The prolonged presence of water is a fundamental feature of wetlands because of its driving influence on the
soil characteristics and the plant and animal species composition associated with these areas. Any part of the
landscape where water accumulates for long enough and often enough to influence the plants, animals and soils
occurring in that area is thus considered to be a wetland according to the National Water Act definition (DWAF
2005).
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
4) The Present Ecological State (PES) of the potentially affected wetlands was assessed using the WETHealth “Level 1” assessment technique (after Macfarlane et al. 2009), as described in Appendix 1, with
final results presented according to the PES categories (A to F) commonly used for the assessment of
aquatic ecosystems in South Africa (see Table 1). As the WET-Health assessment method does not
include a module for the assessment of water quality PES, this component of wetland condition was
assessed using an Excel model for the tentative categorisation of the PES of water quality within a
wetland, as presented in the Manual for the Rapid Ecological Reserve Determination of Inland
Wetlands (Rountree et al. 2013), which is based primarily on the estimation of the extent of different
land-uses in the catchment of a wetland.
Table 1: Present Ecological Status (PES) categories for freshwater ecosystems (after Kleynhans 1996)
PES
Category
PES
Score
A
90-100%
B
80-90%
C
60-80%
D
40-60%
E
20-40%
F
0-20%
%
Description
Unmodified, natural.
Largely natural with few modifications. A small change in natural habitats
and biota may have taken place but the ecosystem functions are essentially
unchanged.
Moderately modified. Loss and change of natural habitat and biota have
occurred, but the basic ecosystem functions are still predominantly
unchanged.
Largely modified. A large loss of natural habitat, biota and basic ecosystem
functions has occurred.
Seriously modified. The loss of natural habitat, biota and basic ecosystem
functions is extensive.
Critically / Extremely modified. Modifications have reached a critical level
and the system has been modified completely with an almost complete loss
of natural habitat and biota. In the worst instances the basic ecosystem
functions have been destroyed and the changes are irreversible.
5) The conservation importance of the freshwater ecosystems on the site was categorised on the basis of
a range of criteria developed by the Freshwater Consulting cc for such purposes (after Ewart-Smith &
Ractliffe 2002), as summarised in Table 2 (below).
To provide additional information for the assignment of a conservation importance category to the
freshwater ecosystems on the proposed site, a list of frog species that could occur in the area was
compiled by determining which species have an estimated distribution range (after IUCN 2009) that
overlaps the site. For those species with distribution ranges overlapping the site, the current IUCN Red
List status was recorded (from http://www.iucnredlist.org/initiatives/amphibians) and information on
the preferred habitat of each species was obtained (from Du Preez & Caruthers 2009 and Measey 2011)
to determine the likelihood of occurrence on the proposed site.
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Table 2: Criteria used to assign low, moderate or high conservation importance to freshwater ecosystems
identified on the site (note that the highest category applicable to any freshwater ecosystem, based on any one
criteria, is the one accorded the ecosystem as a whole) [adapted from Ewart-Smith & Ractliffe (2002)]
Low importance:
does not provide ecologically or functionally significant aquatic habitat because of extremely small size or relatively
high degree of degradation; and/or
of extremely limited importance as a corridor between systems that are themselves of low conservation
importance.
Moderate importance:
provides ecologically significant aquatic habitat (e.g. locally important aquatic ecosystem habitat types); and/or
fulfils some functional roles within the catchment; and/or
acts as a corridor for fauna and/or flora between other aquatic ecosystems or ecologically important habitat types;
and/or
supports (or is likely to support) fauna or flora that are characteristic of the region and/or provides habitat to
indigenous flora and fauna; and/or
is a degraded but threatened habitat type (e.g. seasonal wetlands); and/or
is degraded but has high potential for rehabilitation; and/or
has been identified as a Freshwater Ecosystem Priority Area (FEPA) in terms of the National Freshwater
Ecosystem Priority Areas (NFEPA) project or as an aquatic Critical Biodiversity Area (CBA) in terms of a regional
biodiversity conservation plan, but is in relatively poor present ecological condition; and/or
has been identified as an aquatic Critical Ecosystem Support Area (CESA) in terms of a regional biodiversity
conservation plan; and/or
functions as a buffer area between terrestrial systems and more ecologically important aquatic ecosystems; and/or
is upstream of aquatic ecosystems that are of high conservation importance.
High importance:
supports a high diversity of indigenous plant / animal species; and/or
supports, or is likely to support, red data species; and/or;
supports relatively undisturbed aquatic communities; and/or
forms an integral part of the habitat mosaic within a landscape; and/or
is representative of a regionally threatened / restricted habitat type; and/or
has been identified as a FEPA in terms of the NFEPA project or as an aquatic CBA in terms of a regional
biodiversity conservation plan, and is in fair to good present ecological condition; and/or
has a high functional importance (e.g. nutrient filtration; flood attenuation) in the catchment; and/or
is of a significant size (and therefore provides significant aquatic habitat, albeit degraded or of low diversity).
7) Recommended mitigation measures were formulated for the protection of freshwater ecosystems that
could be affected by the proposed development activities.
8) The current report was compiled, which provides a summary of the findings.
2.2.
Limitations
The following limitations apply to the freshwater ecology study that was undertaken:
The focus of the field assessment was the south-eastern portion of the subject property, with reliance
on previous studies (particularly that of Harding 2012) for information on the freshwater ecosystems
on the other portions of the property;
No water quality data were collected for the freshwater ecosystems on the site, but it is unlikely that
the collection of such data would have changed any of the findings; and
No fauna were collected from the freshwater ecosystems, and the list of possible frog species that was
compiled for the site was not field-verified by a frog specialist; and
This study provides an assessment of the constraints relating to freshwater ecosystems, and not a
comprehensive assessment of the potential impacts on freshwater ecosystems that are likely to result
from the proposed development activities.
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
3. BIOPHYSICAL OVERVIEW OF STUDY AREA AND LOCATION OF PROPOSED SITE IN
RELATION TO RELEVANT BIODIVERSITY/CONSERVATION PLANS
The surface geology of the study area is dominated by Quaternary-age, non-calcareous sands of the
Springfontyn Formation, underlain by deeply-weathered bedrock and clays of the Populierbos Formation
(Klipheuwel Group) (Pether 2012). It is the pink-hued clays of these underlying sediments that were
exploited for brick-making on the subject property.
According to the most recent national vegetation map (Mucina & Rutherford 2006), the proposed site is
located in an area that would have naturally consisted of Atlantis Sand Fynbos, with Swartland Shale
Renosterveld and a band of Swartland Alluvium Renosterveld (along a portion of the Diep River) to the east.
Atlantis Sand Fynbos is categorised as a Critically Endangered terrestrial vegetation type on the National
List of Threatened Ecosystems published in terms of the National Environmental Management: Biodiversity
Act (Act No. 10 of 2004) (Government Notice 1002 of 9 December 2011), due the exceptionally high
number of threatened plant species associated with this vegetation type. This Fynbos vegetation type is
characteristically associated with acidic tertiary sands that are usually white or yellow in colour (Rebelo et
al. 2006).
The proposed site is situated within the South Western Coastal Belt Ecoregion (after Kleynhans et al. 2005).
The topography of this ecoregion is dominated by plains with a moderate to low relief, and there is a
predominance of slopes with a gradient of <5%. The most dominant vegetation type in the ecoregion is
Renosterveld, although significant areas of Fynbos, Succulent Karoo and Thicket are also present. One of
the more significant rivers that flow through this ecoregion is the Diep River. Portion 4 of Farm No. 27,
Modderfontein is situated in DWS Quaternary Catchment G21D. The modelled hydrological characteristics
of this Quaternary Catchment are as follows (after WRC 2008):
Mean Annual Precipitation (MAP) = 384 mm [strongly seasonal, mostly in winter]
Mean Annual Evaporation (MAE) = 1490 mm
Mean Annual Runoff (MAR) = 12 X 106 m3
The MAP and MAE of the quaternary catchment (as listed above) are similar to the MAP and MAE figures
given by Rebelo et al. (2006) for the entire area of occurrence of the Atlantis Sand Fynbos (at 438 mm and
2149 mm, respectively).
The portion of the Diep River that flows in a southward direction approximately 2 km to the east of the site,
which forms part of the Lower Foothills Zone of the river (after Rowntree & Wadeson 2000), was mapped
by the National Freshwater Ecosystem Priority Areas (NFEPA) project (Nel et al. 2011) and was categorised
as a “Fish Sanctuary Area” (FSA) due to the presence of threatened indigenous fish species in the relevant
reach of the river. The NFEPA sub-catchment that the site falls into was categorised as an “Upstream
catchment” (i.e. upstream of a FSA) because the area was mapped as draining into the Swart River to the
north, which flows into the FSA section of the Diep River. The location of the subject property within a
catchment that drains into a river system that forms a tributary of a FSA implies that no land-use and
development activities should be undertaken that could compromise the ecological integrity of the
downstream rivers.
No naturally-occurring wetlands were mapped on or adjacent to the proposed site by the NFEPA project,
but several artificial systems (dams, as taken from the relevant 1:50 000 scale topographical maps) were
captured on the site and in the surrounding area. Similarly, the City of Cape Town’s Wetlands Map
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
(September 2013 version) did not map any naturally-occurring wetlands on or in the vicinity of the subject
property but did include a number of artificial systems (dams).
A significant portion of the subject property (south-eastern section), and adjacent land to the east and
south-east, falls within the City of Cape Town’s Biodiversity Network and has been designated as a Critical
Biodiversity Area (CBA) for the conservation of terrestrial vegetation. More specifically, the relevant area
has been categorised as CBA 1b (i.e. “Irreplaceable High and Medium Condition Site”), which is reserved for
patches of Critically Endangered vegetation of high or medium quality that are needed for national targets.
Any loss of natural habitat within these areas is considered permanent and irrevocable, and the
recommendations are that natural ecosystems within these areas should be maintained and degraded land
restored to natural condition. The management objective for CBA 1b should be to ensure no further
degradation of the vegetation. No hard infrastructure should not be located in relatively intact CBAs, but
rather outside and adjacent to these areas or in already highly degraded patches of vegetation within a
designated CBA. The preferred land-uses for CBAs are conservation, low impact recreation and
environmental education.
4. DESCRIPTION OF PROPOSED DEVELOPMENT
The proposed development is to establish an aircraft landing strip and associated infrastructure on Portion
4 of Farm 27, Modderfontein. The associated infrastructure would include aircraft taxi-ways connected to
the landing strip, a service road, and access road from the N7, and a number of hangars and workshops
(see proposed Site Development Plan in Figure 2). The total area to be occupied by the proposed
development is approximately 21 ha (Du Toit 2014), with the remainder of the subject property
(approximately 40 ha in extent) not to be affected by the currently proposed development.
In terms of services for the proposed development, water supply (and storage) is to be obtained from the
existing quarry dam on the site and rainwater harvesting, sewage is to be piped into an on-site conservancy
tank that will be cleared out by the Municipality, and stormwater is to be managed primarily through the
provision of underground pipes and a centralised bioretention area (Du Toit 2014). According to the Civil
Services Report for the proposed development (Du Toit 2014), the proposed stormwater management
measures will comply with the City of Cape Town’s (2009) policy on the management of urban stormwater
impacts.
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
Figure 2: Site Development Plan for the proposed aircraft landing strip and associated infrastructure
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
5. DESCRIPTION OF SITE AND POTENTIALLY AFFECTED FRESHWATER ECOSYSTEMS
5.1.
Site description
The proposed site lies along the eastern side of the N7 freeway, approximately 3 km south-west of the
town of Kalbaskraal and 40 km north of Cape Town CBD (see Locality Map in Figure 1). The Diep River flows
in a southerly direction approximately 2 km to the east of the site, while the Swart River (a tributary of the
Diep) flows in an easterly direction approximately 1 km to the north-east of the site.
The topography of the site is relatively flat, with the highest point in the south-eastern corner (at at altitude
of approximately 80 m), sloping gently towards the Swart River to the north and the Diep River to the east.
The upper soils of the southern third of the site consist of acidic white, regic sands – typical acid sand flats –
underlain by clay at varying depths from the surface, but the upper soils in the northern two-thirds of the
site have been significantly disturbed through past vegetation removal and brick manufacturing activities,
now consisting of clay at the surface (Emms 2012; Nicolson 2014). The southern portion of the site, where
the soils are less disturbed and sand is still present at the surface, comprises degraded, previously
ploughed, abandoned farmland that is dominated by grasses and herbaceous weed species (Emms 2012).
The vegetation of this portion of the site was described by Nicolson (2014) as “Disturbed Sand Fynbos” (as
opposed to “Transformed Vegetation” on the northern portion of the site). Despite the southern portion
being degraded, the area may harbour threatened geophyte (bulb) species, which can only be confirmed
through the completion of a botanical survey during spring (Emms 2012; Nicolson 2014).
5.2.
Freshwater ecosystems on and adjacent to the site
There is an existing quarry near the south-eastern corner of the site, where clays of the Populierbos
Formation were excavated for the brick works that used to operate on the site. The central portion of this
quarry has filled with water, forming a relatively large dam (this is the dam from which water would be
abstracted for water supply for the currently proposed development). Near the centre of the site is a
relatively major berm, as previously mapped by DHEC (Harding 2012). To the north of this berm are
another two dams in excavated areas. To the south of the berm, several wetlands were delineated by DHEC
(Harding 2012) during a previous aquatic constraints analysis of the subject property (as shown on the map
in Figure 3). These wetlands occur on a portion of the site that historically formed part of a natural drainage
line that flowed towards the Swart River, as indicated on the relevant 1:50 000 topographical map (see
Figure 1). The drainage line is no longer evident as surface flow in a discernable channel across the site, but
there are still seasonally wet remnant wetlands in this area (Harding 2012).
During the site visit undertaken for the currently proposed development, the wetlands in the southwestern portion of the site were not delineated or assessed in detail because the focus of the investigation
was the south-eastern portion of the site, where direct impacts associated with the proposed landing strip
are more likely. The dry conditions at the time of the site visit (undertaken in February 2015, i.e. late
summer) were, in any event, not conducive to accurate mapping of wetlands, whereas the site visit by
DHEC (Harding 2012) was undertaken in October 2012 (i.e. during spring, when it would presumably have
been relatively wet). As such, the prior mapping of wetlands in the south-western portion of the site by
DHEC has been used in the current report. It should be noted that, while the main wetland areas in the
south-western portion of the site were mapped by DHEC, they did indicate that the entire south-western
quadrant is considered to be of importance in terms of aquatic environments (Harding 2012).
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During the site visit by FCG in February 2015, a seep wetland was identified along the alignment shown as a
non-perennial drainage line on the relevant 1:50 000 scale topographical map (see location of mapped
drainage line in Figure 1, and location and extent of seep wetland mapped by FCG in Figure 3). This wetland
occurs in a localised low-point in the landscape, situated upstream and downstream of an existing dam on
the neighbouring property to the south (see map in Figure 3).
Figure 3: Map of freshwater ecosystems on and adjacent to Portion 4 of Farm 27, Modderfontein
At the time of the site visit, the sandy surface soils in the south-eastern wetland area were dry but lowchroma (greyish) colours and feint reddish-orange mottles were observed within 50 cm of the surface in
places, while in some locations damp yellow-coloured sandy soils were encountered within 50 to 80 cm of
the surface. An impermeable clay subsoil layer was encountered below the sandy upper soils at some
sampling points, close to a metre below the surface. Towards the eastern site boundary, clay soils (with no
or very little overlying sand) were observed at or close to the surface, together with visible signs of the
temporary pooling of water in these areas. All of these soil characteristics suggest that seasonally to
intermittently saturated conditions are present, with intermittent inundation of the surface in places. At
the same time, plant species that tend to occur in wetland areas were observed within the area delineated
by FCG as a seep wetland, including Ornithogalum thyrsoides (chincherinchee), Micranthus sp., Cyperus
sphaerospermus, and the exotic rye grass (Lolium multiflorum). A number of other indigenous and exotic
plant species were identified by Nicolson (2014) within the seasonally damp wetland areas in the southeastern portion of the site.
To the east of the site boundary, the seep wetland narrows into a more channelised, seasonally or
intermittently flowing drainage line that flows under an existing gravel road (via a pipe culvert). The
drainage line flows through a forest of alien invasive Port Jackson (Acacia saligna) and pine (Pinus sp.) trees
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before opening up into a flatter, grass-dominated area. Where the drainage line disperses out onto the
flatter area, it becomes a seep wetland dominated by Cyperus c.f. sphaerospermus and Juncus effusus.
Further to the east, the wetland area once again narrows into a more confined and highly modified
drainage line, which ultimately flows into the Diep River.
To the east and the north of the site, in areas that are unlikely to be affected by the proposed
development, desktop-based mapping (including analysis of historical Google Earth imagery) and visual
observations made during the site visit revealed that relatively large patches of wetland are present (as
shown on the map in Figure 3), occurring as a mosaic with terrestrial areas. The wetlands in these areas
were not carefully delineated or assessed as part of the current investigation but it was noted that there
has been significant ecological degradation of these areas as a result of historical and current-day farming
activities, including cultivation and grazing.
Due to the presence of a clay subsoil layer, occurring within a metre or so of the ground surface in places,
most of the wetlands that occur on and adjacent to the subject property are assumed to be “perched”
systems. This implies that the wetlands are dominantly fed by rainfall and localised (surface and
subsurface) runoff, and are characterised by a “perched water table”, instead of being fed by true
groundwater associated with the regional water table. The presence of such a impervious subsoil layer (and
so-called “duplex soils”) also means that topographical alteration of the land, especially the excavation of
upper soils and subsequent lowering of the depth to the impervious subsoil layer, can lead to the formation
of wetlands in areas where wetlands did not occur naturally.
5.3.
Present Ecological State (PES) of potentially affected freshwater ecosystems
A summary of the overall results of the PES assessment that was completed for the seep wetland area
identified in the south-eastern portion of the site are presented in Table 3, below. The detailed results of
the assessment for each PES component are given in Appendix 2.
Table 3: Overall PES assessment results for seep wetland in SE portion of site
PES component
PES% Score
PES Category
Description
Moderately to
Hydrology
60 %
C/D
largely modified
Largely natural with
Geomorphology
86 %
B
few modifications
Largely natural with
Water quality
85 %
B
few modifications
Vegetation
45 %
D
Largely modified
The hydrology, and to some extent the geomorphology, of the wetland area in the south-eastern portion of
the site has been significantly affected by the presence of a drainage ditch through the natural flow-path
and a dam near the head (source) of the wetland (see location of drainage ditch and dam on the map in
Figure 3). It is presumed that, due to the presence of the dam and as a result of agricultural land-use
activities in the broader catchment of the wetland, there has been an overall reduction in the inflows to the
wetland and a slight deterioration in the water quality, relative to the presumed natural state. This,
together with historical ploughing and other agricultural activities within and around the wetland, has lead
to a reduction in the diversity of indigenous plant species within the wetland. Although there are still
indigenous wetland plant species within the wetland, as observed during the site visit by FCG, the wetland
is in its present state dominated by alien grass species such as Lolium multiflorum (ryegrass), Avena fatua
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(wild oats), Bromus diandrus (ripgut brome), and indigenous but invasive Cynodon dactylon (kweekgras) (as
confirmed in the botanical assessment by Nicolson 2014).
No formalised or detailed assessments of the PES of the wetlands in the south-western portion of the site
(as delineated by DHEC) or of the off-site wetlands to the north and east of the subject property were
completed as part of the current study, largely because these wetland areas are not likely to be directly
affected by the proposed landing strip or associated infrastructure. It is however noted, on the basis of
visual observations of these areas made during the site visit by FCG, that these wetlands are more highly
modified, relative to the perceived natural reference state, than the wetland area identified in the southeastern portion of the site.
No formal or detailed PES assessments were completed for the river channels downstream of the subject
property either because, again, these freshwater ecosystems are unlikely to be directly affected by the
currently proposed development. On the basis of visual observations made during the site visit by FCG,
however, the river channel is clearly a highly modified system that is unlikely to be in better condition than
PES Category D/E. The section of the Diep River that flows to the east of the site, and into which most
runoff from the site ultimately drains, was assigned a desktop-based rating of PES Category D (largely
modified) by the NFEPA project, using the broad-scale PES categories generated for the main-stem rivers in
each Quaternary Catchment by DWS in 1999. Although the relevant section of the Diep River was not
visited or assessed for the current study, based on observations of land-use in the catchment, the PES of
the relevant river reach is unlikely to be in a better state than this desktop-based rating (if anything, it is
likely to be more degraded than PES Category D).
5.4.
Conservation importance of potentially affected freshwater ecosystems
A summary of the conservation importance ratings assigned to the freshwater ecosystems identified on
and adjacent to the proposed site is presented in Table 4, including both natural and artificial systems. The
assignment of conservation importance ratings was done according to the criteria outlined in Table 2.
Table 4: Conservation importance of potentially affected freshwater ecosystems
Freshwater ecosystem type
Dams
(artificial, permanent open waterbodies)
Wetlands in SW portion of site
(as identified and delineated by DHEC)
Seep wetland in SE portion of site
(as identified and delineated by FCG)
Off-site wetlands to N and E of site
(not accurately delineated or assessed)
River channels to N and E of site
(tributaries of the Diep and Swart Rivers)
Diep River
(section of river E of the site)
Conservation importance
LOW
MODERATE
MODERATE
LOW TO MODERATE
MODERATE
MODERATE TO HIGH
The list of frog species with distribution ranges that overlap the proposed site and nearby surrounds (see
Table 5) indicates that there are 7 species with relevant broad distribution ranges. Only one of these
species is, however, of conservation concern and that is the Cape Caco (Cacosternum capense). The Cape
Caco is endemic to the South Western Cape and is listed as Near Threatened. This frog species tends to
occur in low-lying flat or gently undulating areas with poorly drained clay or loamy soils, and it typically
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
breeds in shallow, temporary rain-filled depressions (Du Preez & Caruthers 2009). As such, it is possible that
Cape Caco are present on the site and that they breed in the wetlands in the southern portion of the site.
Table 5: List of frog species with a broad distribution range (at quarter-degree-square scale) that overlaps Farm 27/4
Modderfontein
Family
BUFONIDAE
PIPIDAE
PYXICEPHALIDAE
PYXICEPHALIDAE
PYXICEPHALIDAE
PYXICEPHALIDAE
PYXICEPHALIDAE
Species
Vandijkophrynus angusticeps
Xenopus laevis
Amietia fuscigula
Cacosternum capense
Cacosternum platys
Strongylopus grayii
Tomopterna delalandii
Common name
IUCN status*
Endemism
Cape Sand Toad
LC
SW Cape
Common Platanna
LC
no
Cape River Frog
LC
SA & Namibia
Cape Caco
NT
SW Cape
Flat Caco
LC
SW Cape
Clicking Stream Frog
LC
SA (near)
Cape Sand Frog
LC
SA (W-Cape, N-Cape, E-Cape)
* LC = Least Concern; NT = Near Threatened; VU = Vulnerable; EN = Endangered; CR = Critically Endangered
The artificially created dams on the subject property, including the quarry that is to be used for water
supply to the proposed development, were rated to be of low conservation importance because of the
limited aquatic habitat that that these freshwater systems are providing and because of the prevalence of
such systems in the broader study area.
The wetlands in the south-western and south-eastern portions of the site, as delineated by DHEC (Harding
2012) and FCG, respectively, were rated to be of moderate conservation importance. This rating was
assigned because these wetlands are located within a terrestrial CBA, according to the City of Cape Town’s
Biodiversity Network and, if they had been included on the City’s Wetlands Map they would most likely
have been categorised as Aquatic CBAs (according to Snaddon & Day 2009, most of the Aquatic CBAs within
the City are situated within terrestrial CBAs). In addition, these wetlands are thought to meet the following
criteria for being of moderate conservation importance (as per Table 2):
They provide ecologically significant aquatic habitat in that they represent (albeit degraded) locally to
regionally important aquatic ecosystem habitat types (i.e. relatively intact wetlands within Critically
Endangered Atlantic Sand Fynbos vegetation);
They fulfil some functional roles within the catchment, including flood attenuation and streamflow
regulation for downstream river systems;
They potentially act as corridors for the movement of fauna and/or flora within a largely disturbed
agricultural landscape;
They provides habitat to indigenous flora and fauna;
They represent remnants of a degraded but threatened habitat type (i.e. seasonal wetlands within a
critically endangered vegetation type);
They are degraded but have high potential for rehabilitation; and
They function as a buffer area between surrounding terrestrial systems and the ecologically important
Diep River system further downstream.
If the wetlands in the south-western and/or south-eastern portions of the site were in a more pristine
present ecological condition (e.g. with a greater diversity of indigenous wetland plant species) and/or if
they were confirmed to be important breeding sites for the Near Threatened Cape Caco frog species, their
conservation importance rating would be elevated to at least moderate to high.
The off-site wetlands to the north and east of the subject property, which were not accurately delineated
or properly assessed as part of the current investigation, were rated (with a relatively low level of
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confidence) to be of low to moderate conservation importance. This is because these wetlands appear to
be more degraded than the wetlands identified in the south-western and south-eastern portions of the
site, thus providing less valuable habitat for aquatic and semi-aquatic flora and fauna, and they are likely to
be providing a lower level of ecosystem service provision within the catchment. The off-site wetlands are
also not located within a terrestrial CBA. If the present ecological condition of these wetlands were to be
improved (especially in terms of vegetation) or if they were confirmed to be important breeding habitats
for Cape Caco frog species, they would be rated to be of higher conservation importance.
The section of the Diep River to the east of the subject property was rated to be of at least moderate to
high conservation importance, partly because this is a regionally significant river and the relevant reach has
been categorised by the NFEPA project as a Fish Sanctuary Area (FSA). In addition, this river system forms a
very important ecological corridor through a highly disturbed agricultural landscape and is likely to be
providing a number of important ecosystem services (i.e. it is of relatively high functional importance). The
river systems to the north and east of the site, which flow into the Diep River, were rated to be of
moderate conservation importance because they are upstream of a freshwater ecosystem that is of at least
moderate to high conservation importance.
6. IDENTIFICATION OF DEVELOPMENT CONSTRAINTS RELATING TO FRESHWATER
ECOSYSTEMS AND RECOMMENDED MITIGATION MEASURES
From an ecological perspective, development within the area to the south of the berm and to the west of
the existing quarry on Farm 27/4 Modderfontein should be avoided and, ideally, this area should be
rehabilitated. This is because there are remnant wetlands within this degraded, but not transformed, area
that has been categorised as a CBA. Furthermore, it was previously recommended by both a botanical
specialist (Emms 2012) and a freshwater specialist (Harding 2012) that there should be no development in
this area (i.e. it was highlighted as a “no-go” area for ecological reasons).
The identification of wetland seeps to the south and south-east of the quarry during the current
investigation, within the terrestrial CBA that encompasses the south-western portion of Farm 27/4, has
highlighted another area within which there should, ideally, be no development to ensure the protection of
wetlands that have been rated to be of at least moderate conservation importance. This area (to the south
and the south-east of the quarry) was not, however, rated to be particularly sensitive from a botanical
perspective, despite being located within a terrestrial CBA on the City’s Biodiversity Network, according to
the recent botanical assessment of the proposed landing strip by Nicolson (2014). As such, it may be
acceptable from an ecological perspective, to locate infrastructure within the terrestrial CBA to the south
and south-east of the quarry, provided the wetlands (and, ideally, a buffer around the wetlands) are
avoided.
According to the most recent layout plan for the currently proposed landing strip and associated
infrastructure, the proposed landing strip itself would cross a portion of the seep wetland mapped in the
south-eastern portion of the site, and one of the proposed service roads would cross through the CBA to
the west of the quarry (passing close to one of the wetlands in this area that was delineated by DHEC) and
over a portion of the seep wetland mapped by FCG to the south of the quarry (as highlighted on the map in
Figure 4).
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
Figure 4: Map highlighting (with pink circles) where the proposed landing strip (shown in dark grey) and service road
(shown in orange) would cross the seep wetland (shown in green) mapped by FCG to the south and south-east of the
quarry [pink shading shows the terrestrial CBA on the City’s Biodiversity Network, while the wetlands mapped within
this area by DHEC are shown in greenish-yellow]
Without any mitigation, the implementation of the currently proposed layout plan would result in the
direct loss of relatively important wetlands (through infilling), and there would be a number of negative
impacts on the wetlands during both the construction and operational phases. The implementation of
mitigation measures is thus going to be essential for the protection of the potentially affected wetlands. It
is also important to note that, if any wetlands are to be filled in to allow for the crossing of a landing strip or
a road through these areas, this would trigger the need to obtain a “water use” licence from the
Department of Water & Sanitation in terms of the National Water Act (Act No. 36 of 1998).
Ideally, the wetlands that have been mapped in the southern portion of the site should be avoided
altogether. It is thus recommended that, if possible, the length of the proposed landing strip and the
routing of the service road should be reconsidered. More specifically, consideration should be given to
shortening the landing strip so that it ends to the north of the mapped wetland, and the service road
should be re-routed to avoid the crossing of any wetlands and (if possible) the traversing of the CBA (e.g.
consideration could be given to routing the road around the disturbed edge of the quarry).
If the crossing of the mapped wetland by the proposed landing strip is unavoidable, then properly sized
culverts should be built under the landing strip to allow for the unimpeded and unconfined flow of water
through the wetland. It should be possible to avoid the crossing of the wetland by the proposed service
road but, if this is not the case, then a routing must be found for the road where it can cross the wetland in
a perpendicular direction and sufficiently sized culverts must be placed under the road at that point.
Ideally, in addition to these mitigation measures to minimise the loss of wetland, the seep wetland should
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
be rehabilitated as part of the proposed development to improve its present ecological condition. This
could be done by removing the dam and the drainage ditch, which currently affect the flow of water into
and through the wetland.
The following construction-phase mitigation measures, which should be included in the Environmental
Management Programme (EMP) for the project and implemented under the guidance of an Environmental
Control Officer (ECO), are recommended to reduce the severity of potential construction-phase impacts on
the on-site wetlands and downstream freshwater ecosystems:
The site office, construction camp, all toilets, fuel/material storage areas, refuelling areas, parking areas
and vehicle/machinery washing areas must be located at least 20 m from the edge of any wetland or
river channel;
All wetlands and river channels, together with a 10 m wide buffer area along the edges of these
features, must be treated as “no-go” areas and appropriately demarcated as such. No vehicles,
machinery, personnel, construction material, fuel, oil, bitumen or waste should be allowed into these
areas without the express permission of and supervision by the ECO;
Refuelling and fuel storage areas, and areas used for the servicing or parking of vehicles and machinery,
should be located on impervious bases and should have adequately sized bunds around them to
prevent the runoff of pollutants such as fuel and oil from these areas;
No discharge of effluents or polluted water must be allowed into any wetland, dam or river channel;
No spoil material, including stripped topsoil, should be temporarily stockpiled within 20 m of the edge
of any wetland or river channel;
If construction areas are to be pumped of water (e.g. after rains), this water must be pumped into an
appropriate settlement area, and not allowed to flow into any wetland or river channel;
Freshwater ecosystems located on and in close proximity to the site should be inspected on a regular
basis by the ECO for signs of disturbance, sedimentation and pollution – these inspections should form
part of every site inspection carried out by the ECO. If signs of disturbance, sedimentation or pollution
are noted, immediate action should be taken to remedy the situation and, if necessary, a freshwater
ecologist should be consulted for advice on the most suitable remediation measures.
During the operational phase of the proposed landing strip and associated infrastructure, the biggest
potential impacts on freshwater ecosystems are those relating to the runoff of polluted stormwater from
the hardened surfaces that are to be created, and the possible mowing/clearing of wetland areas adjacent
to the landing strip. To mitigate against stormwater-related impacts, it is important to ensure that no
stormwater runoff is allowed to flow from the proposed landing strip, roads or parking areas into any
wetlands or river channels without prior attenuation and treatment. To mitigate against the possible
maintenance-related damage to wetland vegetation during the operational phase, it is important that the
clearing or mowing of the vegetation in wetlands is not to be permitted (even adjacent to the landing strip)
– this highlights another reason why it is preferable to avoid the crossing of wetlands by the landing strip.
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FRESHWATER ECOSYSTEMS CONSTRAINTS ASSESSMENT: LANDING STRIP ON FARM 27/4, MODDERFONTEIN
7. CONCLUSIONS AND RECOMMENDATIONS
The main conclusion of the freshwater ecosystems constraints assessment that was undertaken by FCG is
that there are wetlands on Farm 27/4 Modderfontein that pose a constraint for the proposed development
of an aircraft landing strip and associated infrastructure on the property. In particular, there are wetlands
on the southern portion of the property, within an area categorised as a CBA in the Biodiversity Network of
the City, that should be protected. These wetlands, although somewhat degraded in terms of their present
ecological condition, were rated to be of at least moderate conservation importance.
It is recommended that encroachment into the wetlands on the southern portion of Farm 27/4 by a landing
strip, taxi-way, roads or any other infrastructure should be avoided, if possible. If encroachment into these
wetlands is unavoidable, then, as a minimum, sufficiently large culverts should be placed under the landing
strip and/or roads where they cross the wetlands. In addition, the affected wetlands should be
rehabilitated to improve their present ecological condition, as part of the proposed development.
The recommended construction-phase mitigation measures to minimise negative impacts to wetlands and
other freshwater ecosystems (as outlined in Section 6 of the current report) should be written into the EMP
for the proposed development.
To mitigate against possible stormwater-related impacts during the operational phase, no stormwater
runoff should be allowed to flow from the proposed landing strip, roads or parking areas into any wetlands
or river channels without prior attenuation and treatment. Finally, to mitigate against the possible
maintenance-related damage to wetland vegetation during the operational phase, it is recommended that
no clearing or mowing of the vegetation in wetlands should be permitted (including the vegetation within
the wetlands immediately adjacent to the landing strip).
8. REFERENCES
City of Cape Town (2009). Management of Urban Stormwater Impacts Policy, Version 1.1, May 2009. Roads &
Stormwater Department: Catchment, Stormwater and River Management Branch.
Department of Water Affairs and Forestry [DWAF] (2005). A Practical Field Procedure for Identification and
Delineation of Wetlands and Riparian Areas. Department of Water Affairs and Forestry, Pretoria.
Du Preez L and Caruthers V (2009). A Complete Guide to the Frogs of Southern Africa. Struik Nature, Cape Town.
Du Toit J (2014). Aircraft Landing, Hangers and Workshops on a portion of Farm 27/4 Modderfontein, Kalbaskraal. Civil
Services Report (Revision 1). Prepared for WIC by STAC Consulting Engineers, June 2014.
Emms P (2012). Botanical Assessment for proposed Solar Alfa PV Site, Modderfontein 27 Portion 4, near Atlantis, City
of Cape Town. Report prepared for Guillaume Environmental Consultants by Bergwind Botanical Surveys &
Tours, February 2012.
Ewart-Smith JL and Ractliffe SG (2002). Assessment of the Potential Impacts of the Proposed N1 / N2 Winelands Toll
Highway Project on Aquatic Ecosystems. Specialist EIA Report to Crowther Campbell & Associates, on behalf of
the National Roads Agency.
Harding WR (2012). Aquatics Constraints Analysis: Solar Alfa PV Site, Farm Modderfontein 27, Portion 4, Kalbaskraal,
Western Province. Report to Guillaume Nel Environmental Consulting, on behalf of Western Investment
Company (Pty) Ltd by DH Environmental Consulting, October 2012.
IUCN (2009). IUCN Red List of Threatened Species: Anura distribution ranges. Version 2009.1.
http://www.iucnredlist.org/technical-documents/spatial-data#amphibians.
Job N (2009). Report on the Application of the Department of Water Affairs and Forestry (DWAF) Wetland Delineation
Method to Wetland Soils of the Western Cape. WRC Report No. K8-718. Water Research Commission, Pretoria.
Kleynhans CJ (1996). A qualitative procedure for the assessment of the habitat integrity status of the Luvuvhu River.
Journal of Aquatic Ecosystem Health 5: 41–54.
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Kleynhans CJ, Thirion C and Moolman J (2005). A Level I River Ecoregion classification System for South Africa, Lesotho
and Swaziland. Report No. N/0000/00/REQ0104. Resource Quality Services, Department of Water Affairs and
Forestry, Pretoria.
Macfarlane D, Kotze D, Ellery W, Walters D, Koopman V, Goodman P and Goge C (2009). WET-Health: A technique for
rapidly assessing wetland health. WRC Report No. TT 340/08. Water Research Commission, Pretoria.
Measey GJ (2011). A workshop to reassess the IUCN Red List status of South African amphibians. Appendix 1 in:
Measey GJ (ed). Ensuring a Future for South Africa’s Frogs: A Strategy for Conservation Research. SANBI
Biodiversity Series 19. South African National Biodiversity Institute, Pretoria.
Mucina L and Rutherford MC (eds) (2006). The Vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South
African National Biodiversity Institute, Pretoria.
Nel JL, Driver A, Strydom WF, Maherry A, Petersen C, Hill L, Roux DJ, Nienaber S, Van Deventer H, Swartz E and SmithAdao LB (2011). Atlas of Freshwater Ecosystem Priority Areas in South Africa: Maps to support sustainable
development of water resources. WRC Report No. TT 500/11. Water Research Commission, Pretoria.
Nicolson G (2014). Botanical Impact Assessment, Modderfontein Airfield, Portion 4 of Farm 25, Kalbaskraal, City of
Cape Town, Western Cape Province. Report prepared for Guillaume Environmental Consultants by Bergwind
Botanical Surveys & Tours, December 2014.
Ollis DJ, Snaddon CD, Job NM and Mbona N (2013). Classification System for Wetlands and other Aquatic Ecosystems
in South Africa. User Manual: Inland Systems. SANBI Biodiversity Series 22. South African National Biodiversity
Institute, Pretoria.
Pether J (2012). Brief Palaeontological Impact Assessment. Proposed PV Solar Alfa Photovoltaic Solar Energy Facility
on Farm Modderfontein 27, Portion 4, near Atlantis, City Of Cape Town, Western Cape. Consulting report
Prepared at the request of Guillaume Nel Environmental Management Consultants for Integrated Renewable
Energy Development (Pty) Ltd, 27 August 2012.
Rebelo AG, Boucher C, Helme N, Mucina L and Rutherford MC (2006). Fynbos Biome. In: Mucina L and Rutherford MC
(eds.) The Vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity
Institute, Pretoria.
Rountree M, Malan H and Weston B (2013). Manual for the Rapid Ecological Reserve Determination of Inland
Wetlands (Version 2.0). Joint Department of Water Affairs and Water Research Commission report. Water
Research Commission, Pretoria.
Rowntree KM and Wadeson RA (2000). Field manual for channel classification and condition assessment. National
Aquatic Ecosystem Biomonitoring Programme Report Series No. 13. Institute for Water Quality Studies,
Department of Water Affairs and Forestry, Pretoria, South Africa.
Snaddon K and Day E (2009). Prioritisation of City Wetlands. Report prepared by the Freshwater Consulting Group for
the Department of Environmental Resource Management, City of Cape Town.
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K5/1491. Water Research Commission, Pretoria.
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APPENDICES
Appendix 1: Description of WET-Health “Level 1” wetland PES assessment method
Appendix 2: Detailed results of WET-Health assessment for wetlands in SE portion of site