APPENDIX G
SPECIALIST REPORT
Prepared by:
Dean Justin Ollis Pr.Sci.Nat
The Freshwater Consulting Group
Email: [email protected]
Cell: 072 377 7006
August 2014
FRESHWATER ECOSYSTEMS IMPACT ASSESSMENT REPORT:
Proposed completion of bank stabilisation activities along the Newlands Stream at Erf 48509, Newlands
[report completed using the Department of Water Affairs’ Supplementary Water Use Information template
for Section 21(c) and (i) “water uses” in terms of the National Water Act (Act No. 36 of 1998)]
1.
Watercourse Attributes
1.1
Locality
1.1.1. Description of the location of the watercourse
The activities forming the focus of this application and the potentially affected watercourse are located on and adjacent
to Erf 48509, in the built-up residential suburb of Newlands, within the City of Cape Town, Western Cape Province.
The affected watercourse is a tributary of the Liesbeek River, which arises on the eastern slopes of Table Mountain
above the Kirstenbosch National Botanical Garden. The Liesbeek River flows into the Black River, which ultimately
discharges into Table Bay near to Cape Town Harbour.
The study area is located within the Southern Folded Mountains Ecoregion (after Kleynhans et al. 2005). According to
geology maps of the study area (incl. the 1:250,000 scale map 3318 Cape Town), the geology of the area is dominated
by alluvium and/or scree overlying Malmesbury Group shales. The natural vegetation type in the vicinity of the site
would have been Cape Winelands Shale Fynbos (after Mucina & Rutherford 2006), which is listed as a Vulnerable
terrestrial vegetation type on the 2011 National List of Threatened Ecosystems published in terms of the National
Environmental Management: Biodiversity Act (Act No. 10 of 2004).
1.1.2. Locality map indicating relevant catchment, surrounding land use, towns, infrastructure etc.
Newlands
Avenue
Figure 1: Locality map for the site and the potentially affected watercourse/s (1:50,000 scale topographical map reference: 3318CD),
with inset showing location in relation to the boundaries of the Western Cape Province and the City of Cape Town
1.1.3. Catchment reference number:
Quaternary Catchment G22C, which has the following hydrological statistics (estimates from WRC 2008):
Mean Annual Precipitation (MAP) = 654 mm
Mean Annual Evaporation (MAE) = 1 400 mm
Mean Annual Runoff (MAR) = 31.1 x 106 m3
1
1.
Watercourse Attributes
1.2
Description
1.2.1. Name and/or description of the affected watercourse
The affected watercourse is a portion of the Newlands Stream that flows through and adjacent to Erf 48509, Newlands.
As stated above, this river ecosystem is a tributary of the Liesbeek River that flows through a built-up residential area.
Historically, prior to the urbanisation of the Rondebosch-Newlands area, the Newlands Stream presumably originated
within or above the Newlands Forest on the eastern slopes of Table Mountain and flowed in a south-easterly direction
towards the Liesbeek River. Today, the stream course is different to what it would have been under natural conditions.
The upper reaches of the stream appear to have been largely disconnected from the middle to lower reaches, as a result
of diversion of the flow from the upper reaches into canals and underground stormwater pipes associated with the roads
and urban land-uses in the catchment area of the stream.
The remaining section of the Newlands Stream that is still clearly identifiable as a river is approximately 1 km in length,
flowing from Newlands Avenue to the confluence with the Liesbeek River (see map in Figure 1). The main sources of
water input to the stream appear to be (1) a wetland seepage area on a vacant piece of land along Newlands Avenue
(immediately to the north-east of Forresters Arms Restaurant/Pub), near the present-day source of the stream; (2) a
perennial spring that enters the river from Springs Way road (see photos in Figure 2); and (3) stormwater input from
surrounding roads and residential areas (via inlet pipes/culverts and overland runoff).
Figure 2: Photograph of spring water from Springs Way entering the Newlands Stream (inset shows the outlet pipe from the spring)
Below the point where the Springs Way spring enters the Newlands Stream (which is 200 m or so upstream Erf 48509,
Newlands), the river has a perennial flow regime (pers. comm., Mr D. Evans, owner and resident of Erf 48509). Above
this point, the river does not flow the whole year round but has more of a seasonal flow regime linked to the winter
rainfall pattern.
The affected section of the Newlands Stream has a longitudinal gradient (approximately 0.035) that places it in the
Transitional Zone (following the geomorphological river zonation scheme of Rowntree & Wadeson 2000). The
substratum of the stream is dominated by boulders and large cobbles (e.g. see Photo 1 in Figure 3), with the dominant
biotopes upstream of Erf 48509 consisting of a combination of steps, pools, rapids and cobble-bed runs (e.g. see Photo 2
in Figure 3). Approximately 100 m downstream of the site, the Newlands Stream enters a box culvert that goes under
Main Street (see Photo 3 in Figure 3) shortly before the stream joins the Liesbeek River.
The physical instream habitat within the Newlands Stream appears to be relatively intact, relative to the presumed
natural state of the channel. The riparian habitat along the river, on the other hand, has clearly been extensively
modified. Urban development has encroached into the riparian zone, all along the remaining length of the stream, with
virtually the entire river (both the channel and riparian zone) falling within private properties. As a result of this
encroachment, and the associated establishment of residential properties with gardens and/or building platforms that go
right up to or into the active channel of the river, the riparian zone of the river has been constricted. This constriction of
the riparian zone has been compounded by the construction of flood alleviation and river-bank stabilisation measures
along much of the length of the river (see photos in Section 1.2.2). The riparian zone of the Newlands Stream is thus a
lot narrower now than it would have been in its natural state. Further to this, the natural vegetation in what remains of
2
Watercourse Attributes
the riparian zone of the river has been largely replaced by alien trees (such as weeping willows, Salix babylonica) and
exotic garden plants (including alien invasive lawn grass such Kikuyu, Pennisetum clandestinum), or by physical
structures such as pathways, stairways, decks and walls.
1.
Photo 1
(14/03/2014)
Photo 2
(01/04/2014)
Photo 3
(01/04/2014)
Figure 3: Photographs of the instream habitat within the Newlands Stream – Photo 1 shows the substratum immediately upstream of
the site, which is dominated by large cobbles and boulders; Photo 2 shows a sequence of steps, pools, rapids and runs in the section of
the river upstream of the site; Photo 3 shows the culvert under Main Street, downstream of the site
1.2.2. Map with accompanying photographs (dated) showing the affected reach/es of the watercourse, and
indicating/delineating the extent of the riparian habitat and the 1:100 year flood line
The copy of the survey diagram in Figure 4 shows the affected reach of the Newlands Stream in relation to the
boundaries of Erf 48509, Newlands. The diagram shows the 1:50 and 1:100 year floodlines for this reach of the river, as
determined and mapped by the engineering company, Storey Eng (Pty) Ltd. On the diagram, the edges of the active
channel of the river are also indicated (by dotted black lines). The proposed bank stabilisation activities for the section
of river flowing through and adjacent to Erf 48509 would all be undertaken along the edges of the active channel (i.e.
along the bottom edges of the river banks) and would thus clearly fall within the 1:100 and 1:50 year flood zones. It is
presumed that, in its natural state, the riparian zone of the Newlands Stream would have extended from the edge of the
active channel to at least where the 1:100 year floodline currently lies. At present, however, only very small patches of
relatively natural river bank remain along the stream and, where these occur, the extent of the riparian zone is restricted
to a very narrow strip along the edge of the active channel (e.g. see photos in Figure 5). Most of the river bank, on both
sides of the river, consists instead of vertical or near-vertical structures that have been built to prevent flooding and
erosion of properties (e.g. see photos in Figure 6). This implies that there is effectively no riparian zone to speak of
along most of the affected river reach because the riparian zone of a river, by definition, is the strip of land on the bank
of a river.
3
1.
Watercourse Attributes
Erf 48509
EDGE OF ACTIVE CHANNEL
Figure 4: Survey diagram showing 1:100 and 1:50 year floodlines in relation to Erf 48509
Figure 5: Photographs of less modified (topographically intact) patches of river bank along the Newlands Stream, upstream of Erf
48509 (both photos taken on 01/04/2014)
4
1.
Watercourse Attributes
Figure 6: Photographs of sections of the Newlands Stream (upstream and downstream of Erf 48509) where the river banks have been
transformed into hardened, vertical structures (all photos taken on 01/04/2014)
At the site where proposed bank stabilisation activities are proposed, the existing left bank is a vertical wall (see lefthand photo in Figure 7) and the existing right bank is a relatively low (approximately 1 m high), stepped bank made
from cement planting blocks (see right-hand photo in Figure 7). There is thus no riparian zone along the left bank of the
river at the site, but there is a riparian zone of planted vegetation on top of the platform previously created along the
right bank.
Figure 7: Photographs of the river banks at the site (left photo taken on 14/03/2013, looking downstream; right photo taken on
01/04/2014, looking upstream)
5
1.
Watercourse Attributes
1.2.3. Description of the Present Ecological State (PES) of the affected reach/es of the watercourse with respect to flow
(and sediment) regimes, water quality, habitat (instream and riparian), and biota
The Present Ecological State (PES) of the potentially affected section of the Newlands Stream was determined using
DWAF’s (1999) Habitat Integrity assessment method, also known as the Index of Habitat Integrity (IHI, after Kleynhans
1996). This PES assessment method involves the assignment of impact scores to a number of specified abiotic and biotic
criteria, for both the instream and riparian components of a river ecosystem. Impact scores range from zero (no impact)
to 21-25 (critical impact). The prescribed criteria that must be evaluated are water abstraction, extent of inundation,
water quality, flow modification, bed modification, channel modification, presence of exotic aquatic fauna, presence of
exotic macrophytes, solid waste disposal, decrease of indigenous vegetation from the riparian zone, exotic vegetation
encroachment, and bank erosion. For each criterion, an assessor must assign a confidence level (high, medium or low) to
the score given, based on their knowledge of the site and catchment. The impact score for each criterion is weighted,
according to prescribed weightings (ranging from 6 to 14) devised by Kleynhans (1996) based on the perceived relative
threat of the various impacts to the habitat integrity of a riverine ecosystem. The estimated impacts of all criteria
calculated in this way are summed, expressed as a percentage and subtracted from 100 to arrive at a PES (or IHI) score
for the instream and riparian components, respectively. The respective PES % scores are then used to place the instream
and riparian components into a specific PES (or Ecological) Category, according to Table 1.
Table 1: Present Ecological State (PES) Categories for riverine ecosystems (after DWAF 1999)
PES Category
PES % Score
Description
A
90-100%
Unmodified, natural.
B
80-90%
Largely natural with few modifications. A small change in natural habitats and biota may
have taken place but the ecosystem functions are essentially unchanged.
C
60-80%
Moderately modified. Loss and change of natural habitat and biota have occurred, but the
basic ecosystem functions are still predominantly unchanged.
D
40-60%
Largely modified. A large loss of natural habitat, biota and basic ecosystem functions has
occurred.
E
20-40%
Seriously modified. The loss of natural habitat, biota and basic ecosystem functions is
extensive.
F
0-20%
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.
The PES assessment for the Newlands Stream was based on two site visits, undertaken on 14 March and 1 April 2014
(i.e. in autumn), at times when there was a low to moderate flow of water in the river. The information obtained during
the site visits was supplemented by information obtained through an analysis of relevant maps and aerial imagery of the
study area, and through working knowledge of the Liesbeek River and its catchment (into which the Newlands Stream
falls) . The overall results (see Table 2) were that the instream condition of the potentially affected section of river is
moderately modified (Ecological Category C) and that the riparian zone is in a seriously to critically modified ecological
condition (Ecological Category E/F). Although the IHI method assigned the riparian zone a PES% score (~40%) in
Ecological Category D/E, using the default weightings, a score of <20% (i.e. in Ecological Category E/F) was
considered to be more reflective of the true situation (described in Sections 1.2.1 and 1.2.2, above). The higher PES
score (and better Ecological Category) generated by using the default scoring system of the IHI method is largely due to
high relative weightings (of 13) being given to the ‘water abstraction’ and ‘water quality’ riparian zone criteria, both of
which were assigned low impact scores (of <10 out of 25) in the assessment of the Newlands Stream. This high
weighting of criteria that are not of particular relevance to the current assessment generated what are considered to be
biased results. As such, an adjusted PES score (and Ecological Category) was assigned to the riparian zone component
in this case, based on professional judgement and observations made of the situation on the ground.
The main impacts on the present ecological condition of the potentially affected section of the Newlands Stream were
identified to be flow modification (as a result of increased flood peaks due to catchment hardening, and decreased
overbank flooding due to the disconnection of most of the riparian zone from the active channel); channel modification,
especially along the banks of the river; bank erosion; some bed modification (gabion structures across the river channel,
culverts at road crossings, etc); a substantial decrease in the extent of inundation of the riparian zone (through the
creation of artificial, vertical banks along most of the length of the stream), and an extensive decrease of indigenous
vegetation and encroachment of exotic vegetation into riparian zone (mostly through the establishment of residential
gardens along the river). Most of these impacts stem from historical residential urban development along both sides of
6
Watercourse Attributes
the river, which has resulted in the need for the establishment of flood protection measures to protect properties.
1.
Table 2: PES results for Newlands Stream
CRITERIA
INSTREAM
Water abstraction
Extent of inundation
Water quality
Flow modifications
Bed modification
Channel modification
Presence of exotic macrophytes
Presence of exotic fauna
Presence of solid waste
RIPARIAN
Water abstraction
Extent of inundation
Water quality
Flow modifications
Channel modification
Decrease of indigenous vegetation
Exotic vegetation encroachment
Bank erosion
Newlands Stream
(Palmboom Rd reach)
Score
Confidence
8
3
5
10
10
10
3
0
4
M
H
M
M
M
M
H
M
M
8
20
5
20
24
22
15
15
M
M
M
M
M
H
H
H
FINAL IHI SCORES:
Instream IHI
Riparian IHI
Adjusted riparian IHI
76.3%
Eco-Category C
40.3%
Eco-Category D/E
<20%
Eco-Category E/F
Although evidence of small-scale abstraction of water from the river was observed (e.g. pipes in the river connected to
pumps on adjacent properties), the amount of water abstraction appears to be very small. The perennial flow of water in
the river, at least below the spring that enters from Springs Way, supports this observation. No water quality analyses
were conducted for the current investigation, but the water quality of the river is considered to be relatively good most of
the time with the occasional spike of poor water quality when pollutants enter via stormwater runoff. This is because the
primary water sources for the stream are understood to be a seepage wetland and spring water, both of which would
have relatively good water quality (especially the spring water).
1.2.4. Description of the Ecological Importance & Sensitivity (EIS) and the Socio-cultural Importance of the affected
reach/es of the watercourse
The Ecological Importance & Sensitivity (EIS) of a watercourse is an expression of its importance to the maintenance of
ecological diversity and functioning on local and wider scales, taking into account both biotic and abiotic components of
the system. For the current assessment, the EIS of the potentially affected section of the Newlands Stream was
determined using the EIS method for river ecosystems developed by DWAF (1999). Application of this method involves
the rating of a number of prescribed biotic and habitat determinants, using a scoring system that ranges from zero (none /
not applicable) to 4 (very high importance/sensitivity), together with an indication of the confidence level in the rating
given. The median scores of all the biotic and habitat determinants are then separately calculated, and the overall median
score is calculated. The median scores are used to assign EIS Categories for biotic and habitat criteria, and for the river
ecosystem as a whole, based on Table 3.
7
1.
Watercourse Attributes
Table 3: Description of EIS Categories and range of median scores for each category
Ecological Importance & Sensitivity (EIS) Category
Very high
Rivers that are considered unique on a national or even international level based on unique
biodiversity (habitat diversity, species diversity, unique species, rare and endangered species).
These rivers (in terms of biota and habitat) are usually very sensitive to flow modifications and
have no or only a small capacity for use.
High
Rivers that are considered to be unique on a national scale due to biodiversity (habitat diversity,
species diversity, unique species, rare and endangered species). These rivers (in terms of biota
and habitat) may be sensitive to flow modifications but may have a substantial capacity for use.
Moderate
Rivers that are considered to be unique on a provincial or local scale due to biodiversity (habitat
diversity, species diversity, unique species, rare and endangered species). These rivers (in terms
of biota and habitat) are usually not very sensitive to flow modifications and often have a
substantial capacity for use.
Low/marginal
Rivers that are not unique at any scale. These rivers (in terms of biota and habitat) are generally
not very sensitive to flow modifications and usually have a substantial capacity for use.
Range of Median
>3 and <4
>2 and <3
>1 and <2
>0 and <1
The EIS results for the Newlands Stream (see Table 4, below) were that the potentially affected section of the river is of
moderate importance in terms of biotic criteria and of moderate to high importance in terms of habitat criteria. Overall,
the river was rated to be of moderate importance and sensitivity. The biotic criteria/determinants that were given the
highest ratings were ‘unique biota’ and ‘intolerant biota’, due to the probable presence of endemic Cape Galaxius
(Galaxius zebratus) fish species in the river and the presumed intolerance of most of the biota in the river to changes in
the water quality and/or flow regime of the river. Habitat criteria given moderate to high ratings were the ‘diversity of
aquatic habitat types’ (due to a range of instream biotopes being present), ‘sensitivity of habitat to flow and water
quality changes’, and ‘migration route/corridor’ (based on the assumption that the river is an important corridor between
the seepage wetland near the present-day source of the river along Newlands Avenue and the Liesbeek River, in an
increasingly urbanised landscape with very few intact ecological corridors).
Table 4: EIS results for Newlands Stream
Ecological Importance & Sensitivity (EIS)
criteria
Score
Confidence
Rare & endangered biota
0
Medium
Unique biota
3
Medium
2.5
Medium
BIOTIC criteria
Intolerant biota
Species/taxon richness
1
Medium
1.8
(moderate)
Median score (biotic criteria)
HABITAT criteria
Diversity of aquatic habitat types
2
High
1.5
Medium
Sensitivity of habitat to flow changes
2
Medium
Sensitivity of habitat to WQ changes
3
Medium
Migration route/corridor
2
Medium
Protected/natural areas
0
High
Refuge value of habitat types
Median score (habitat criteria)
OVERALL EIS SCORE and CATEGORY
2.0
(moderate to high)
1.9
(MODERATE)
Socio-cultural importance reflects the dependency of people on a healthy functioning watercourse, and also to its
cultural and tourism potential. No formal assessment of the socio-cultural importance of the potentially affected section
of the Newlands River was undertaken. Such as assessment is deemed to be unnecessary in this case, due to the highly
urbanised and ecologically modified setting of the river. It is, however, worth noting that the spring in Springs Way (see
photos in Figure 2), which enters the river upstream of the site, is of relatively high socio-cultural importance, as
8
Watercourse Attributes
evidenced by the observation of a number of people collecting water from the spring when it was visited on 1 April
2014. The proposed activities (described in Section 2, below) will not in any way affect the spring because they will be
conducted in the Newlands Stream itself, at a point some distance downstream of where the spring enters the river.
1.
1.2.5. Description of existing land and water use impacts (and threats) on the characteristics of the watercourse
The dominant existing land-use along both sides of the Newlands Stream is urban residential development. The main
existing impacts (and threats) to the characteristics of the river are those relating to the encroachment of urban
development into the riparian zone of the river. As described in Sections 1.2.1 to 1.2.3, this encroachment has lead to the
need for the construction of extensive flood protection measures to protect properties located alongside the river. The
flood protection measures are mostly in the form of vertical or near-vertical embankments, which have effectively
disconnected large sections of the riparian zone from the active channel of the river. This, coupled with the replacement
of most of the natural riparian vegetation with largely exotic garden plants, has resulted in the near-complete elimination
of the riparian zone that would presumably have occurred in the flood zone of the Newlands Stream under natural
conditions.
1.2.6. Sensitive environments in close proximity to the project locality
The closest protected area to the site is the Newlands Forest, located approximately 1.5 km to the north-west (upstream
of the site, and upstream of the present-day source of the Newlands Stream).
The National Freshwater Ecosystem Priority Areas (NFEPA) project identified the Liesbeek River and its catchment,
which incorporates the Newlands Stream and its catchment, as a Fish Support Area (FSA). This was because the
Liesbeek River was identified as a sanctuary for threatened or near-threatened freshwater fish species, presumably Cape
Galaxius (Galaxius zebratus species complex), but it is not in good condition (Ecological Category A or B) [rivers in
good condition that are fish sanctuaries for threatened fish species were categorised as a Freshwater Ecosystem Priority
Area, or FEPA]. Fish sanctuaries are rivers that are essential for protecting threatened and near-threatened indigenous
freshwater fish species, and there should be no further deterioration in the condition of any river identified to be a fish
sanctuary (Driver et al. 2011). FSAs should be managed to support the conservation of the threatened or near threatened
fish populations they contain (Nel et al. 2011). This implies that all activities in and adjacent to the Newlands Stream
should be managed in such a way as to minimise the disturbance to populations of Cape Galaxius and other potentially
threatened fish species that may occur in the river or in the section of the Liebeek River into which this stream flows.
No wetlands were identified in close proximity to the Newlands Stream by the NFEPA project. The City of Cape
Town’s Wetlands Map (September 2013 revision) also does not show any wetlands along the Newlands Stream (this
largely desktop-based initiative missed the tree-covered wetland area near the present-day source of the river). None of
the land adjacent to the Newlands Stream was identified to be part of the City’s Biodiversity Network, which is not
surprising because this area consists of a built-up residential suburb where there is no natural vegetation remaining. The
Newlands Stream is, however, a natural (albeit modified) river system and rivers are generally treated as “Ecological
Support Areas (ESAs)”, at the very least, in systematic conservation plans. The river itself, including both the active
channel and what remains of the riparian zone, should thus be regarded as a sensitive natural environment.
9
2.
Water Use Information
2.1
Description of Proposed Activities
2.1.1. Description of the activities associated with the water use/s
The objective of the proposed intervention is to stabilise the left and right banks of a section of the Newlands Stream
that runs through and adjacent to Erf 48509, so as to repair existing erosion along the base of the left bank and prevent
further erosion of both banks of the river. According to information provided by the project engineers (Meny-Gibert &
Associates Structural & Civil Engineering Consultants), the proposed means of achieving this is to undertake the
following activities (on both banks of the river):
Excavation of existing rocks and other material from the base of the river bank, to allow for the placement of a
foundation structure;
Placement of reno mattresses (filled with sandstone rocks of size in the range 75-100 mm) as a foundation structure
at the base of the existing, artificially-created river bank (consisting of a vertical concrete wall along the left bank
and of a relatively low, stepped wall of “terraforce” planting blocks along the right bank);
Placement of gabion baskets (filled with sandstone rocks in the size range 100-250 mm) on top of the reno
mattresses, to form a retaining wall;
Along the left bank (where a 2 to 3 m high, near-vertical concrete wall currently exists), the rock-filled gabion
basket retaining wall will be taken to a height of approximately 2 m above the river bed so that it tops out above the
1:100 year floodline, extending along the full frontage of Erf 48509;
Along the right bank (where a relatively low, stepped “terraforce” embankment currently exists), only one or two
rows of gabion baskets will be placed along the toe of the bank; and
Construction of terrace walls on top of the gabion baskets but set back, to be built using conventional soil-filled
“terraforce” rockface blocks, which will be planted up with appropriate vegetation (these terrace walls will extend
well above the 1:100 year floodline along the left bank, where there is already a relatively high near-vertical wall,
but will only extend to the height of the high-water level along the lower right bank so as to allow flooding of the
small riparian platform that still exists on that side of the river).
This form of intervention was selected as the most suitable for the situation because gabion baskets have a high
resistance to displacement by virtue of their mass, assuming the rocks have been securely bound within the wire baskets,
and they have the ability to deform to an extent but still remain as a unit. The proposed gabion basket embankments
should, therefore, be more resistant to erosion than the existing concrete walls. Furthermore, the high porosity of this
form of construction should allows for better dissipation of flows and a rapid release of pore water pressures behind the
wall (see letters from the Engineers in Appendix 2).
2.1.2. Description of the project phases for each activity (i.e. planning, construction, operation and maintenance,
decommissioning) including, but not limited to, the programme for and duration of the various phases
Planning phase – completed (approximately 3 months in duration, from March to June 2014).
Construction phase – estimated timeframe of 3-4 months from commencement (start date dependent on
authorisations, but probably late 2013 or early 2014). The sequence of activities during this phase would be: (1)
excavation of base of river bank; (2) placement of reno mattresses; (3) placement of gabion baskets; (4)
construction of “terraforce” walls on top of gabion baskets; and (5) planting of “terraforce” blocks.
Operational phase – to commence immediately after construction of the proposed bank stabilisation infrastructure is
complete (regular maintenance of the infrastructure will form part of the operational phase).
Decommissioning phase – no decommissioning anticipated in the foreseeable future, as the proposed structures
have been designed as a long-term solution to erosion problems.
2.1.3. Site lay-out plan/s (master plan) indicating the various activities and existing and proposed infrastructure in
relation to the 1:100 flood line and edge of the watercourse, etc.
A site layout plan is provided in Appendix 1, which shows the proposed activities in relation to the edges of the right
and left banks of the river (corresponding to the edges of the active channel). The 1:50 and1:100 year floodlines are
shown in relation to the edges of the active channel on the diagram in Figure 4. These floodlines were delineated by
Storey Eng (Pty) Ltd Consulting Engineers, based on a survey undertaken during 2013 by David Hellig & Abrahamse
with contour intervals of 0.5 m. The floodlines were determined using a Mean Annual Precipitation (MAP) of 1314 mm
(as measured at Claremont Paradise Estate rain-gauging station), a catchment area of 202.1 ha, and discharge estimates
of Q50 = 16.3 m3/s and Q100 = 21.3 m3/s.
2.1.4. Work method statements for the various water use activities
No detailed method statements have been compiled at this stage. The EMP for the proposed project does, however, call
specifically for the contractors to compile a method statement for the proposed sediment-control measures that are to be
put in place during construction. This method statement is to be submitted to the ECO for approval before
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Water Use Information
commencement of the initial excavation work in the river.
2.
Although no detailed method statements have been compiled, the proposed methods for undertaking the proposed
construction activities have been formulated. The proposed approach is as follows:
A low wall of sandbags will be used to temporarily isolate the section of the river where the works are to be carried
out from the rest of the stream (and water may need to be pumped out of this work area);
Instream sediment control measures will be put in place, as per the method statement to be approved by the ECO;
Manual labour will be used to excavate a shallow trench along the base of the existing river embankments;
Excavated material will be stockpiled on the property (Erf 48509) for re-instatement as required once the gabions
are in place;
Reno mattresses will be placed in the excavated trench, using manual labour;
Gabion baskets will be placed on top of the reno mattresses, using manual labour;
The rock for the reno mattresses and gabion baskets will be stockpiled in the garden of Erf 48509;
The wire frames will be constructed on site and placed where required along the river bank;
Rocks will be handed down manually to fill the wire baskets, once they are in place;
After the gabion baskets have been set in place, any material removed from the river will be replaced (as far as
possible) and excess material will be removed from site or used elsewhere on the property;
“Terraforce” planting blocks will be laid on top of the gabion baskets, using cement to bind them together, and the
blocks will be filled with soil and planted with appropriate vegetation; and
The sandbags and other sediment-control measures will be removed from the river after the work has been
completed.
2.1.5. Engineer design drawing(s) for construction activities within the watercourse
See drawing in Appendix 1, as prepared by Meny-Gibert & Associates Consulting Structural and Civil Engineers.
2.1.6. Description and a map/s indicating any Storm Water Management Practices (SWMPs) specifically addressing
‘end of pipe’ practices
Not applicable to the proposed activities.
2.1.7. Information on all existing lawful water uses
No existing lawful water uses on the subject property, except for the use of piped municipal water for domestic purposes
(including watering of a garden) and those uses permissible under Schedule 1 of the National Water Act (Act No. 36 of
1998).
2.1.8. Information on investments already made and to be made by the water user in respect of the proposed water
use/s
It is estimated that the total investment for the proposed activities will be at least R300 000. Of this, approximately
R100 000 will be spent on materials, R100 000 on labour, and R100 000 on professional fees.
2.1.9. Probable duration of any undertaking for which the water use/s should be authorised
The proposed bank stabilisation infrastructure that is to be built is intended to be a long-term solution, which will
presumably be in place for at least 25 years.
2.2
Motivation
2.2.1. Information on the need/intention/objective of the water use/s
As stated previously, the objective of the proposed intervention is to stabilise the left and right banks of a section of the
Newlands Stream that runs through and adjacent to Erf 48509. This intervention is needed to repair existing erosion
along the base of the left bank and to prevent further erosion of both banks of the river.
2.2.2. Information on contributions to rectify the results of past racial and gender discrimination
Not applicable – the proposed project is to stabilise river banks on private residential properties so as to prevent ongoing
erosion.
2.2.3. Information to support efficient and beneficial use of water in the public interest
The proposed activities do not entail the consumptive use of water. The proposed activities are, however, considered to
be in the public interest because they aim to address existing erosion problems along a section of the Newlands Stream.
11
2.
Water Use Information
2.2.4. Information on relevant catchment management strategies and local government planning frameworks that
support the proposed water use
The proposed bank stabilisation activities are in line with the provisions of the City of Cape Town’s (2009) Floodplain
and River Corridor Management Policy. This policy supports the Roads and Stormwater Department objectives
incorporated in the Integrated Development Plan for the City of Cape Town, namely to: (1) Reduce the impact of
flooding on community livelihoods and regional economies; and (2) Safeguard human health, protect natural aquatic
environments, and improve and maintain recreational water quality.
In particular, the Floodplain and River Corridor Management Policy (City of Cape Town 2009) stipulates that bank
protection works (revetments, training walls, levees) below a 1:50 year floodline are conditionally permitted activities.
For these activities, it is a requirement that a registered Engineering Professional must be engaged by the developer to
satisfactorily demonstrate and certify that:
The activity / development will not materially increase flood hazards for other property owners or adversely affect
flood behaviour or the stability of river channels.
Any structure can withstand the forces and effects of flowing floodwaters, including scour of foundations, debris
forces and buoyancy forces.
The engineers for the proposed intervention (Meny-Gibert & Associates) are registered Engineering Professionals and
have indicated that the proposed activities comply with the above requirements (see letters in Appendix 2).
2.2.5. Information on the strategic importance of the water use to be authorised
Not applicable – the proposed project is to stabilise river banks on private residential properties so as to prevent ongoing
erosion.
12
3.
Impact Assessment and Management
3.1
Impact Prediction and Assessment
3.1.1. Prediction and assessment of the likely environmental and socio-economic impacts or effects associated with the
water use/s for the different project phases
A description and assessment of the potential impacts of the proposed activities on the Newlands Stream are provided
below. The methods that were used to assess the significance of the potential impacts are described in Section 3.1.2.
3.1.1.1. Impacts on the watercourse and its characteristics
The potential impacts on the biophysical characteristics of the Newlands Stream have been listed and assessed
separately for the construction and operational phases of the proposed project (in sub-sections (a) and (b), below,
respectively). A discussion of the potential cumulative impacts on the river is also included (in sub-section (c)).
(a) Construction phase impacts on biophysical aspects relating to the river:
The following potentially negative construction-phase impacts on the river ecosystem were identified:
Sedimentation of the river and knock-on effects to aquatic biota, especially when the initial excavation work is
carried out along the base of the river banks.
Disruption of spawning by Cape Galaxius in the Newlands Stream and/or the Liesbeek River downstream of the
construction site (the spawning period for this fish species complex is typically from spring to mid-summer).
Localised alteration of flows and sediment loads in the Newlands Stream at and immediately downstream of the
construction site, due to the presumed temporary isolation of an instream work area within the river when the initial
work in the river is conducted and the pumping of water from this area back into the river.
Physical disturbance to instream and riparian habitat, as a result of construction activities taking place in the river.
Physical damage to river embankments and riparian vegetation through the storage of construction materials
(including rocks) and/or equipment in these areas, especially on the southern side of the river where there is still a
functional riparian zone.
Damage to the riparian areas, especially on the southern side of the river, through the dumping of excavated
material and spoil.
Pollution of the river through leakage of fuels, oils, etc. from construction machinery, or through the runoff of
cement and cement slurry from the construction area.
Generation of litter and other waste material (e.g. wire off-cuts from the construction of the proposed gabion
baskets) in the river channel itself and along the river banks.
Increased disturbance of aquatic and semi-aquatic fauna, due to noise and the presence of a construction team with
their machinery in and adjacent to the river.
The following mitigation measures, which should be included in the EMP for the project, are recommended to reduce
the severity of the above-mentioned construction-phase impacts on the river ecosystem:
When the initial work is undertaken (i.e. excavation of the river bed and bank, and placement of the reno
mattresses), the work area should be isolated from the rest of the stream for the duration of this phase of work (e.g.
using sandbags) and the isolated work area should be kept as dry as possible by pumping water out of this area. The
sediment-laden water that is pumped from the isolated work area must not be discharged directly back into the river,
but rather over land adjacent to the river where there can be some infiltration and settlement (e.g. onto the lawn on
Erf 48509 or into the vegetated riparian area on the southern side of the river). This will reduce the sediment load in
the water and the velocity at which the water enters the river. In addition, as a final line of defence against
sedimentation of downstream areas, a temporary permeable barrier to trap sediments should be placed across the
river immediately downstream of the work area (and downstream of the point at which the water that is pumped
from the work area re-enters the river). This temporary barrier can be constructed using sand bags and/or gabion
baskets, wrapped with geotextile fabric.
The initial work (i.e. excavation of the river bed and bank, and placement of reno mattresses) should be carried out
on one river bank at a time, to provide more space for the stream to still flow through when the work area is isolated
from the rest of the stream. This should also reduce the quantity of sediment generated at any one time during the
initial stage of work.
The work that is to be carried out in the river itself (e.g. the installation of the reno mattresses) should be undertaken
between the beginning of January and the end of March, during the low-flow season and when the spawning period
for the Cape Galaxius fish species (spring to mid-summer) should be over. If any work is to be carried out in the
river during spring or early summer, when Cape Galaxius are potentially spawning downstream of the site, then
more stringent sediment control measures and more frequent monitoring by an ECO will be required.
No construction material (e.g. rocks) or excavated spoil material should be stockpiled in the river channel, on the
river banks or in the riparian zone of the river (especially on the southern side of the river).
No fuel storage, refuelling or maintenance of machinery should be allowed within 10 m of the edge of the river
channel.
No discharge of effluents or polluted water should be allowed into the Newlands Stream.
13
3.
Impact Assessment and Management
All litter and other waste generated during construction (including wire off-cuts from the construction of the gabion
baskets) should be immediately removed from the river channel and banks, and placed in waste bins with lids.
Avoid the use of noisy machinery (as far as possible), minimise the amount of time spent working in the river, and
only allow workers into the river when they need to be in there to complete specific tasks.
The construction area and the section of the stream adjacent to and downstream of this should be inspected on a
regular (at least weekly) basis by the ECO for signs of disturbance, sedimentation and pollution when any work is
being undertaken in the river. 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.
If the ECO observes any incident during the construction phase that results in a visually significant negative impact
on the ecological condition of the Newlands Stream (or is informed of such an incident), a stop-works instruction
should be issued, and the incident should be immediately reported to the Department of Water Affairs (DWA)
(Compliance and Enforcement Unit) and to the City of Cape Town (Environmental Compliance Unit,
Environmental Resource Management Department).
The results of the assessments of potential construction-phase impacts (as completed using the method described in
Section 3.1.2) are summarised in Table 5 (A to G), considering the situation without (prior to) mitigation in comparison
to the situation with (after) implementation of the recommended mitigation measures (as outlined above). All the
potential construction-phase impacts were evaluated to be of low to very low significance with the recommended
mitigation measures assumed to be in place. Without mitigation, however, it was predicated that two of the
potential impacts that could occur during the construction phase would be of medium to high significance. These
are the sedimentation of the river during the initial excavation work (medium significance without mitigation) and the
related impact of possibly disrupting the spawning of Cape Galaxius fish species downstream of the construction site
(high significance without mitigation) largely as a result of the potential smothering of spawning habitat by
sedimentation of the river. The most important recommended mitigation measures for these impacts are to
conduct the proposed activities in the low-flow season and outside of the typical spawning period for Cape
Galaxius – this would be from early January to late March – and to create an isolated instream work area that is
kept as dry as possible while the initial excavation activities are being carried out.
Table 5 (A-F): Results of assessments of potential construction-phase impacts on the river ecosystem
A. Sedimentation of the river, especially during initial excavation work along the base of the river banks:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Local
Site-specific
Magnitude of impact:
Medium to High
Low to Medium
Duration of impact:
Construction period
Construction period
Probability of occurrence:
High
High
Degree to which the impact can be reversed:
Moderate
Degree to which the impact may cause irreplaceable loss of
Low to moderate
resources:
Significance rating of impact prior to mitigation
Medium
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
Moderate
See list of recommended construction-phase mitigation measures for
Proposed mitigation:
protection of the riverine ecosystem
Significance rating of impact after mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
Medium to High
14
3.
Impact Assessment and Management
B. Disruption of spawning by Cape Galaxius fish species in the Newlands Stream and/or the Liesbeek River
downstream of the construction site:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Regional
Regional
Magnitude of impact:
High
Low to Medium
Duration of impact:
Construction period
Construction period
Probability of occurrence:
Moderate
Low
Degree to which the impact can be reversed:
Low
Degree to which the impact may cause irreplaceable loss of
Moderate
resources:
Significance rating of impact prior to mitigation
High
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
High
See list of recommended construction-phase mitigation measures for
protection of the riverine ecosystem. The most important mitigation
Proposed mitigation:
measure for this impact is to avoid construction activities in the river
during the spawning period of Cape Galaxius (i.e. spring to midsummer)
Significance rating of impact after mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Low (not certain whether Cape Galaxius use the river reaches that
Confidence in assessment:
could be affected by the proposed activities for spawning)
C. Localised alteration of flows and sediment loads due to temporary isolation of an instream work area within the river
and the pumping of water from this area back into the river:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Site-specific
Site-specific
Magnitude of impact:
High
Low to Medium
Duration of impact:
Construction period
Construction period
Probability of occurrence:
High
Moderate
Degree to which the impact can be reversed:
Moderate
Degree to which the impact may cause irreplaceable loss of
Low
resources:
Significance rating of impact prior to mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
Moderate to high
See list of recommended construction-phase mitigation measures for
Proposed mitigation:
protection of the riverine ecosystem.
Significance rating of impact after mitigation
Very low
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
Moderate
D. Physical disturbance and/or damage to instream habitat, river banks and riparian areas
through construction-related activities:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Site-specific
Site-specific
Magnitude of impact:
Medium to High
Low to Medium
Duration of impact:
Construction period
Construction period
Probability of occurrence:
High
High
Degree to which the impact can be reversed:
High
Degree to which the impact may cause irreplaceable loss of
Low
resources:
Significance rating of impact prior to mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
Moderate to high
See list of recommended construction-phase mitigation measures for
Proposed mitigation:
protection of the riverine ecosystem
Significance rating of impact after mitigation
Very low
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
High
15
3.
Impact Assessment and Management
E. Pollution of the river through construction-related activities:
Status of impact:
Extent of impact:
Magnitude of impact:
Duration of impact:
Probability of occurrence:
Degree to which the impact can be reversed:
Degree to which the impact may cause irreplaceable loss of
resources:
Significance rating of impact prior to mitigation
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
Proposed mitigation:
Significance rating of impact after mitigation
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
Without (prior to) mitigation
Negative
Local
Medium
Construction period
Moderate
With (after) mitigation
Negative
Local
Low
Construction period
Low
Low
Low
Low
Moderate to high
See list of recommended construction-phase mitigation measures for
protection of the riverine ecosystem
Very low
High
F. Generation of litter and other waste in and alongside the river through construction-related activities:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Site-specific
Site-specific
Magnitude of impact:
Medium
Low
Duration of impact:
Construction period
Construction period
Probability of occurrence:
Moderate
Low
Degree to which the impact can be reversed:
High
Degree to which the impact may cause irreplaceable loss of
Low
resources:
Significance rating of impact prior to mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
High
See list of recommended construction-phase mitigation measures for
Proposed mitigation:
protection of the riverine ecosystem
Significance rating of impact after mitigation
Very low
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
High
G. Increased disturbance of aquatic and semi-aquatic fauna:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Negative
Extent of impact:
Site-specific
Site-specific
Magnitude of impact:
Low to Medium
Low
Duration of impact:
Construction period
Construction period
Probability of occurrence:
High
High
Degree to which the impact can be reversed:
Moderate
Degree to which the impact may cause irreplaceable loss of
Low
resources:
Significance rating of impact prior to mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
Low to moderate
See list of recommended construction-phase mitigation measures for
Proposed mitigation:
protection of the riverine ecosystem
Significance rating of impact after mitigation
Very low
(Low, Medium, Medium-High, High, or Very-High)
Confidence in assessment:
Moderate to high
16
3.
Impact Assessment and Management
(b) Operational phase impacts on biophysical aspects relating to the river:
Once the proposed bank stabilisation activities have been completed, it is predicted that they will have a largely positive
impact on the biophysical characteristics and functioning of the river ecosystem during the operational phase. In
particular, the stabilised bank will reduce ongoing erosion of the river bank, and will allow for better dissipation and
absorption of high flows. The improved dissipation and absorption of high flows would result from the permeable nature
of the reno mattress and gabion baskets that are to be installed along the toe of the river bank, in place of the impervious
concrete structures that currently exist (these concrete structures would deflect high flows and exacerbate erosion
elsewhere). It is predicted that this positive impact on the river ecosystem would be of medium significance, as
summarised in Table 6 (below). No mitigation would be necessary because it is a POSITIVE impact.
A potentially negative impact that could occur during the operational phase is localised destabilisation of the river bank
and a concomitant deterioration in the ecological integrity of the river ecosystem, due to a loss of stones from the reno
mattress and/or gabion baskets. This impact was observed to be prevalent in the section of the Newlands Stream
upstream of Erf 48509 when the site visits were undertaken in March/April 2014. The main reasons for a loss of stones
from some of the gabion baskets that have been placed along portions of the river banks upstream of the site appear to
be the use of baskets with a mesh size that is too big relative to the size of stones in the basket, a lack of quality control
in the construction of the baskets, and/or a lack of maintenance of the baskets. In some cases, the impact is also possibly
related to the improper placement of gabion baskets. The significance of this potential impact was rated to be low
without mitigation, due to the localised nature of the impact. With mitigation (as recommended in Table 6B), it is
predicted that there would be no impact (i.e. it would have a neutral status).
Table 6 (A & B): Results of assessment of potential operational-phase impacts on the river ecosystem
A. Improvement in dissipation and absorption of high flows, and reduced erosion of river banks:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
POSITIVE
n/a
Extent of impact:
Local
n/a
Magnitude of impact:
Low
n/a
Duration of impact:
Long term
n/a
Probability of occurrence:
High
n/a
Degree to which the impact can be reversed:
n/a
Degree to which the impact may cause irreplaceable loss of
n/a
resources:
Significance rating of impact prior to mitigation
Medium (positive)
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
n/a
Proposed mitigation:
n/a
Significance rating of impact after mitigation
n/a
Confidence in assessment:
Moderate to high
B. Localised bank destabilisation and deterioration of ecological integrity of river ecosystem, due to loss of stones from reno
mattress and/or gabion baskets:
Without (prior to) mitigation
With (after) mitigation
Status of impact:
Negative
Neutral
Extent of impact:
Site-specific
n/a
Magnitude of impact:
Low
n/a
Duration of impact:
Long term
n/a
Probability of occurrence:
Moderate
n/a
Degree to which the impact can be reversed:
High
Degree to which the impact may cause irreplaceable loss of
Low
resources:
Significance rating of impact prior to mitigation
Low
(Low, Medium, Medium-High, High, or Very-High)
Degree to which the impact can be mitigated:
High
- Use of small enough mesh size for reno mattress and gabion basket
frames;
- Good supervision and quality control during construction, to ensure
Proposed mitigation:
that the wire frames are put together properly;
- Regular inspection and maintenance of reno mattress and gabion
baskets.
Significance rating of impact after mitigation
n/a
Confidence in assessment:
Moderate to high
17
3.
Impact Assessment and Management
(c) Cumulative impacts on biophysical aspects relating to the river:
No cumulative impacts on the biophysical characteristics of the Newlands Stream are anticipated to result from the
proposed activities.
3.1.1.2. Impacts on other water users
The proposed activities are likely to result in long-term positive impacts on other water users because the scouring of the
eroded river bank will be halted and there will be a reduced risk of ongoing erosion in the section of river that flows
through and adjacent to Erf 48509, and in the section of river immediately downstream of the site. The reduced
incidence of erosion should result in an improvement in the ecological condition and water quality of the affected
portion of the river, which would be of benefit to any water users downstream.
During the construction phase, there would be some negative impacts to other water users (e.g. intermittent siltation of
the section of river in the immediate vicinity of the site). It is anticipated, however, that these impacts would be shortlived and reversible.
3.1.1.3. Impacts on the broader public and property
The proposed bank stabilisation activities are likely to result in positive impacts on the properties where the work is to
be undertaken, and on neighbouring properties immediately upstream and downstream of the site. This is because the
existing erosion problem in the affected section of the river will be stemmed by the proposed intervention. The broader
public is unlikely to be affected by the proposed activities because the affected section of river flows through private
properties. Further downstream, in the vicinity of the confluence of the Newlands Stream with the Liesbeek River, the
broader public may benefit to some degree from the proposed activities due to the localised improvement in the
ecological condition of the river reach that is likely to result from the intervention. During the construction phase, the
broader public may be negatively impacted to a very minor degree by a short-lived deterioration in the water quality
downstream of the site (mainly as a result of siltation).
3.1.1.4. Anticipated consequences if the water use/s is not authorised
If the proposed bank stabilisation activities are not authorised, there will be ongoing erosion of the river bank on Erf
48509. In time, this would lead to undercutting of the river bank and possible slope failure. Should slope failure occur
along the river bank, there would be damage to property, severe localised degradation of the ecological integrity of the
river, and possible endangerment of human lives. The cost of repair to the eroded river bank will also increase
substantially if it is left to continue eroding further.
3.1.2. Description of the methods employed to undertake impact prediction and assessment
The potential impacts of the proposed activities on the affected section of the Newlands Stream were assessed with
regard to their nature, extent, magnitude, duration and probability, using a rating scale recommended by Amathemba
Environmental Management Consulting cc (Table 7). This rating scale is compatible with the rating guidelines outlined
in DEA&DP’s Guideline for Biodiversity Specialist Studies (Brownlie 2005).
Table 7: Categories used to rate the extent, magnitude and duration of potential impacts
CRITERIA
Extent or spatial influence of impact
Magnitude of impact (at the indicated
spatial scale)
Duration of impact
CATEGORY
DESCRIPTION
Regional
Beyond 5 km from the point of impact
Local
Within 5 km from the point of impact
Site specific
On site or within 100 m of the site boundary
High
Natural and/ or social functions and/ or processes are severely altered
Medium
Natural and/ or social functions and/ or processes are notably altered
Low
Natural and/ or social functions and/ or processes are slightly altered
Very Low
Natural and/ or social functions and/ or processes are negligibly altered
Zero
Natural and/ or social functions and/ or processes remain unaltered
Construction period
Up to 2 years
Short Term
0 – 5 years (after construction)
Medium Term
10-15 years (after construction)
Long Term
More than 15 years (after construction)
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3.
Impact Assessment and Management
The potential impacts of the proposed activities on the affected watercourse were assessed both with and without
additional mitigation measures assumed to be in place. Separate assessments were completed for the construction and
operational phases, with consideration given to both positive and negative impacts. The “no-go alternative” was not
separately assessed; rather, in accordance with the DEA&DP (2010) Guideline on Alternatives, it was taken as the
baseline or reference point against which to evaluate the potential impacts associated with the proposed activities.
Significance ratings were derived by taking into account the magnitude/intensity, extent and duration of the potential
impacts, using a protocol developed by the Freshwater Consulting Group for rating the significance of impacts on
aquatic environments (Table 8).
Table 8: Protocol used to assign significance ratings of the basis of impact intensity (magnitude), extent and duration
Rating
Description (i.t.o. intensity, extent and duration)
VERY HIGH
Impacts could be EITHER:
of high intensity at a local level and endure in the long term;
OR
of high intensity at a regional level in the medium term;
OR
of medium intensity at a regional level in the long term.
Impacts could be EITHER:
of high intensity at a local level and endure in the medium term;
OR
of high intensity at a regional level in the short term;
OR
of medium intensity at a regional level in the medium term;
OR
of low intensity at a regional level in the long term;
OR
of high intensity at a site-specific level in the long term;
OR
of medium intensity at a local level in the long term.
Impacts could be EITHER:
of high intensity at a site-specific level and endure in the medium term;
OR
of medium intensity at a local level in the medium term;
OR
of high intensity at a local level in the short term;
OR
of medium intensity at a regional level in the short term;
OR
of medium intensity at a site-specific level in the long term;
OR
of low intensity at a regional level in the medium term;
OR
of low intensity at a local level in the long term.
Impacts could be EITHER:
of low intensity at a local level and endure in the medium term;
OR
of low intensity at a regional level in the short term;
OR
of high intensity at a site-specific level and endure in the short term;
OR
of medium intensity at a local level in the short term;
OR
of low intensity at a site-specific level in the long term;
OR
of medium intensity at a site-specific level and endure in the medium term.
Impacts could be EITHER:
of low intensity at a site-specific level and endure in the medium term;
OR
of low intensity at a local level and endure in the short term;
OR
of low to medium intensity at a site-specific level and endure in the short term.
Impacts with:
Zero intensity with any combination of extent and duration.
In certain cases it may not be possible to determine the significance of an impact.
HIGH
MEDIUM
LOW
VERY LOW
NOT APPLICABLE
UNKNOWN
3.2
Risk Assessment
3.2.1. Assessment of the risks associated with the water use/s and related activities
If the recommended mitigation measures are effectively implemented (as outlined in Section 3.1), there should be a
negligible risk of significant negative impacts on the affected watercourse.
3.3
Alternatives
3.3.1. Description of the alternatives considered
The original proposal to stabilise the eroded sections of the river banks along the Newlands Stream at Erf 48509 was to
reinforce the banks with a combination of retainer blocks, cement and mountain rock, and then to plant vegetation over
the top of the structure to provide additional binding. This alternative was discarded, however, after input was obtained
from an environmental assessment practitioner, a freshwater ecologist and relevant government officials. Reasons for
19
Impact Assessment and Management
discarding this previous alternative were that the construction of a hard surface on the river bank (such as that initially
proposed) would divert and speed up the natural passage of water, especially during high flows, and that the structure
would more than likely be undermined over time by the continually flowing water.
3.
The general consensus from those who provided input was that a better approach would be to use a more permeable
structure, such as gabion baskets, to stabilise the banks and prevent further erosion and possible slope failure. This is
because the high porosity of the stone-filled baskets would allow for the absorption and dissipation of flows, thus
reducing the force of running water and flood waters on the structure. At the same time, gabion baskets are very heavy,
once filled with rocks, and it is highly unlikely that they would be washed away during high flows. The revised proposal
is, therefore, considered to be a more permanent and ecologically appropriate solution than the original proposal. For
this reason, only the revised alternative was considered in the detailed assessment of potential impacts.
3.4
Mitigation and Management Measures
3.4.1. Recommended mitigation measures to prevent, reduce, remediate or compensate the pre-determined impacts
All the recommended mitigation measures for the (a) construction and (b) operational phases of the proposed project are
outlined in Section 3.1.1.1. These mitigation measures should be incorporated into the Environmental Management
Programme (EMP) for the proposed project.
3.4.2. Site map/s marking the limits of disturbance to the watercourse and indicates the erosion and sediment controls
Figure 8: Map showing the anticipated limits of disturbance to the watercourse (red arrow). It is recommended that a sediment
control device be installed at the end of the red arrow or upstream of this point (i.e. downstream of the site, just before the Newlands
Stream flows under Main Street).
3.4.3. Programme for hand over to the successor-in-title including a brief management/maintenance plan for
infrastructure along with allocation of responsibilities (to be provided if the developer/applicant of water use
related infrastructure is not the end user/beneficiary and will not be responsible for long term maintenance of the
infrastructure)
Not applicable. The applicant, Mr David Evans, will be responsible for long-term maintenance and management of the
infrastructure.
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3.
Impact Assessment and Management
3.5
Changes to the Watercourse
3.5.1. Assessment as to what extent the impacts after mitigation will bring about changes in respect of the PES and
functionality of the watercourse; as well as the socio-economic environment (including redress considerations as
well impacts on other water users)
As explained in Section 3.1.1.1(a), it is anticipated that all the potentially negative construction-phase impacts would be
of low to very low significance with the recommended mitigation measures assumed to be in place. In the long-term, the
proposed activities are likely to result in a net positive impact on the watercourse itself and on the surrounding socioeconomic environment, as explained in Section 3.1.1.1(b). In particular, the proposed stabilisation activities will reduce
ongoing erosion of the river bank, and will allow for better dissipation and absorption of high flows. This would result in
a marginal improvement in the PES of the affected section of the Newlands Stream. The proposed activities will only
directly affect approximately 20 m of the length of the river and will, therefore, only have a limited positive impact on
the ecological condition and functionality of the river. To prevent possible negative impacts to the ecological integrity of
the Newlands Stream, which could result in a localised deterioration in the PES of the affected river reach, the
recommended operational-phase mitigation measures to prevent the displacement of rocks from the gabion baskets
should be implemented.
The socio-economic environment is also likely to experience positive impacts as a result of the proposed activities.
Besides the short-term creation of a limited number of jobs during the construction phase, the proposed bank
stabilisation project will address an existing erosion problem that affects a few landowners in the affected section of the
river. The neighbouring landowners and residents are also likely to benefit from an aesthetic improvement in the
relevant section of the stream and possibly from marginally increased property values.
3.6
Monitoring and Compliance
3.6.1. Monitoring programme and description of the auditing, compliance and reporting mechanisms to ensure
execution of the mitigation measures and for informing DWA of incidents
As this application forms part of a NEMA Section 24 G process, the applicant will be required to implement the
recommended mitigation measurements in accordance with the EMP for the project. An Environmental Control Officer
(ECO) should be appointed to monitor the implementation of the project and the provisions of the EMP. One of the
recommended construction-phase mitigation measures relating to incident-reporting for inclusion in the EMP (as listed
in Section 3.1.1.1(a)) is as follows: “If the ECO observes any incident during the construction phase that results in a
visually significant negative impact on the ecological condition of the Newlands Stream (or is informed of such an
incident), a stop-works instruction should be issued, and the incident should be immediately reported to the Department
of Water Affairs (DWA) (Compliance and Enforcement Unit) and to the City of Cape Town (Environmental
Compliance Unit, Environmental Resource Management Department)”.
List of References
Brownlie S (2005). Guideline for Involving Biodiversity Specialists in EIA Processes: Edition 1. CSIR Report No. ENV-S-C 2005
053 C. Department of Environmental Affairs & Development Planning, Provincial Government of the Western Cape.
City of Cape Town (2009). Floodplain and River Corridor Management Policy, Version 2.1, May 2009. Roads & Stormwater
Department: Catchment, Stormwater and River Management Branch.
DEA&DP (2010). EIA Guideline and Information Document Series: Guideline on Alternatives, August 2010. Department of
Environmental Affairs & Development Planning (DEA&DP), Provincial Government of the Western Cape.
Driver A, Nel JL, Snaddon K, Murray K, Roux DJ, Hill L, Swartz ER, Manuel J and Funke N (2011). Implementation Manual for
Freshwater Ecosystem Priority Areas. WRC Report No. 1801/1/11. Water Research Commission, Pretoria
DWAF (1999). Resource Directed Measures for Protection of Water Resources: River Ecosystems. Version 1.0. Department of
Water Affairs and Forestry (DWAF), 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.
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.
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, Murray KM, Maherry AM, Petersen CP, Roux DJ, Driver A, Hill L, Van Deventer H, Funke N, Swartz ER, Smith-Adao LB,
Mbona N, Downsborough L and Nienaber S (2011). Technical Report for the Freshwater Ecosystem Priority Areas Project. WRC
Report No. 1801/2/11. 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.
WRC (2008). Water Resources of South Africa, 2005 (WR2005). WRC Project No. K5/1491. Water Research Commission (WRC),
Pretoria.
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APPENDICES
Appendix 1: Plan for the proposed bank stabilisation intervention
Appendix 2: Letters from the Engineering Consultants (Meny-Gibert & Associates)
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