PROPOSED FORMAL INFRASTRUCTURE DEVELOPMENT FOR HIGHLANDS ESTATE, PHILIPPI, CITY OF CAPE TOWN, WESTERN CAPE.

The proposed development forms part of the City of Cape Town’s initiative to formalise informal settlements and improve basic service delivery within Highlands Estate, Philippi. The project involves the installation of municipal infrastructure to support future residential and light industrial development, subject to land use and rezoning approvals. The development is located on municipally owned land, historically underserved and characterised by informal structures, unpaved roads, and limited stormwater control. The project scope includes a new waterborne sewerage system, stormwater management infrastructure, and an internal road network.

Sewer Reticulation Infrastructure
The proposed development includes the implementation of a gravity-fed waterborne sewer reticulation network for Highlands Estate, which will ultimately discharge into the upgraded Philippi Collector Sewer located approximately 1 km north of the site. The current sanitation system in the area comprises conservancy and septic tanks, which are inadequate due to the high water table and seasonal flooding, posing significant health risks and groundwater contamination concerns.

Internal Sewer Network:
The internal sewer system has been designed to serve the 264 erven and includes 160 mm diameter uPVC pipes for mains and 110 mm diameter uPVC pipes for erf connections. The hydraulic design was based on an instantaneous peak wet weather flow (IPWWF) of 5.14 ℓ/s. Pipe slopes and velocities were calculated, ensuring compliance with the City of Cape Town’s sewer design guidelines, except at the final outflow pipe, which marginally falls below minimum velocity thresholds.

Pump Station Design:
Due to the flat topography and the need to transport wastewater to the outfall sewer, a new pump station will be constructed. The preferred site for the pump station is Erf 67, which is a vacant, municipally owned erf with access from George Smith Street and Leek Street. Erf 67 will be formally transferred between departments within the City of Cape Town to facilitate the pump station’s development.
Key pump station features include:
A 2m diameter pump sump, 7.5 m deep, with a 6.5 m storage depth.
A 2m diameter sand trap manhole, 6 m deep with a 5.5 m storage depth.
Total storage capacity of approximately 25 m³.
A 1x duty and 1x standby configuration of portable vortex impeller pumps to ensure 100% redundancy.
A flooded suction wet well/dry well system designed to meet a 10-year flow demand.
The rising main will use a 110 mm uPVC Class 12 pipe along Papkuilsvleiweg.

Hydraulic Performance:
At a flow rate of 5.8 ℓ/s, the pump is expected to yield a total dynamic head of +14.3 m, accounting for friction losses (1.96 m) and elevation differences (4.6 m). The pump operates at 90% of its output capacity (2.2 kW of 2.4 kW), maintaining high energy efficiency (81.5% input utilization). Electrical requirements have a total demand of 4.8 kW (3.8 kVA).

Design Considerations:
The design accounts for the site's shallow groundwater conditions, flat terrain, and the need for deep sewer trenches in some sections (>4 m depth). A transition manhole and rising main will bridge the internal network with the upgraded Philippi Collector Sewer.

Internal Road Network
The proposed internal road layout will ensure mobility within the development and facilitate municipal service access. Roads have been designed to follow the natural topography where possible, with levels adjusted to manage local drainage. Due to the site’s overall flatness and varying cadastral constraints, roads have been aligned to the lower tolerance limits of vertical geometry. Existing cadastral splays are absent at many intersections, requiring reduced bell mouth radii (5 m) and possible sidewalk encroachments. Earthworks will be confined to road reserves, and driveway grades to individual properties remain within acceptable limits. The encroachment of informal dwellings into road reserves may necessitate relocation. Proposed road widths are 8 m, 10 m, and 12 m, each with corresponding sidewalks ranging from 1.5 m to 1.8 m, in accordance with the City of Cape Town’s design guidelines

Stormwater Reticulation and Retention
Stormwater management is a key design consideration due to the site’s low gradient (average slope between 0.5% and 1%) and existing runoff challenges. The stormwater network will include kerb inlets and catch pits linked to underground pipes integrated with the road system. Runoff will be conveyed to a retention pond designed for quantity attenuation and water quality treatment, under the City’s Management of Urban Stormwater Impacts Policy (Version 1.1). An existing pond within the site has been earmarked for retention, but current assessments show that it lacks the required capacity and structural suitability. As such, the pond will need to be upgraded, potentially deepened and expanded, to comply with Best Management Practice (BMP) standards.
The pond’s zoning may also need to be amended through the town planning process to allow for formal stormwater use. It will be fenced and access-controlled. Due to the flat terrain and road levels, three inlet structures will be required to convey runoff into the pond. Additional coordination with adjacent landowners and affected communities will be necessary to establish servitudes or consent use agreements to facilitate downstream stormwater outflow.

Bulk Earthworks
The area features medium to soft subterranean conditions with no shallow bedrock, allowing for conventional excavation methods. Earthworks will primarily focus on grading for roads and stormwater infrastructure. A geotechnical investigation confirmed no significant excavation challenges.

VEGETATION
According to Cape Farm Mapper, the site is mapped as falling within Cape Flats Dune Strandveld and a portion within Cape Flats Sand Fynbos, both of which are classified as Critically Endangered vegetation types in terms of Section 52 of the National Environmental Management: Biodiversity Act (NEMBA, 2022). However, much of the site has been historically disturbed by urban encroachment and no longer supports intact indigenous vegetation.

FRESHWATER
During a site visit conducted by GNEC there was pond in the northeast corner of the estate. A Freshwater Impact Assessment is being undertaken to verify the presence of watercourses or wetlands, as these features are not indicated on Cape Farm Mapper. Preliminary indications suggest the possible presence of ephemeral drainage features, but the extent, classification, and risk level will be confirmed through a site-specific assessment.

GEOLOGY
The geological classification of the entire site is mapped to consist of the Sandveld Group (Cape Farm Mapper, 2025).

TOPOGRAPHY
A detailed topographical and contour survey was conducted in October 2023. The site is generally flat with slight undulations, sloping predominantly toward the northeast. An overland drainage path exists, but several localised depressions act as trapped low points.

GROUND CONDITIONS AND GEOTECHNICAL
Shallow groundwater seepage is expected in low-lying areas and along informal drainage lines. The water table is typically shallow, often less than 1 metre below existing ground level, particularly during or after rainfall events. As such, subsurface drainage is strongly recommended in the stormwater management design to address the perched water table conditions.