Acknowledgements

I would like to thank my family, Michael, Elsa and Emil for their unwavering support and trust in me. Giving me the time and space to explore a new terrain or better a new horizon. Thank you to my parents Birgit and Heinz for bringing me up in the believe, that anything is possible and their continued support throughout my life.

Thank you Tina, Sabina, Eva and Marion for your inspiration, the important talks, your understanding and believing in me.

The person who taught me to find treasure in drawing, if you interpret things while drawing them and at the same time make them accessible for everybody else, thank you Tarna.

A big thank you to Willem Hutten from the Cape Town Heritage and Environmental resources department for finding all these beautiful maps for me.

Thank you to my two supervisors Roy Holzey and Dr. Kevin Winter for agreeing on the topic and supporting me.

Urban estuaries are under threat all over the world, they are drained, cut off or piped. Open water bodies especially close to the sea are seen as a flood risk to properties and human life’s. The role of estuaries as transition zones between land and sea is undermined. Extreme flood events and sea level rise give estuaries a new importance of buffering floods. Urban rivers and streams in South African are often piped or canalized. The Salt River canal in Cape Town, a former lagoon, is currently concrete lined with no lateral or interstitial connection.

The hypothesis of this study is, that a reinstated estuary can protect from tidal and fluvial flooding, improve water quality, and be a biodiversity asset for the city. The historical analysis of the evolvement from an estuary to a canal, which is presented as a graphical analysis with historical maps and aerials, sets the scene in understanding the current system.

Research of methodologies of river and estuary restoration methods are discussed together with a review of international best practice projects. City of Cape Town strategies towards climate change on the case of rivers are reviewed.

Further a analysis of the catchment and the study area and findings from site visits, describe the status quo of the Salt River canal. This was constrained by the fact that critical information could not be collected due to Covid-19 restrictions, which also affected and closed CoCT operations.

Different approaches exist to describe the methods of returning an engineered system to a close to natural system. Three of these terminologies were used to develop and discuss scenarios for the canal. Detailing and evaluation of the rehabilitation and reclaimation scenarios gives a informed feed back of the restoration options and their limits for the study area..

1. Introduction

1.1 Problem area and objective

In response to a changing climate, the restoration of urban rivers plays a vital role in the protection and improvement of the urban environment. The Salt River is a man made canal in Cape Town, that drains the Salt River catchment into the Table Bay. Its short reach is situated between industrial areas, railway yards, container depots and mixeduse areas. It is crossed by several rail, highway and road bridges, that feed the Cape Town city centre. More than 300 years ago the estuary was destroyed to gain agricultural land. Today the Salt River is Cape Town’s river with the poorest water quality and is out of sight in the “backyard of the city”. With its place so close to the city, a restored river could have a positive effect on the urban micro climate in the immediate surrounding areas, the water quality in the Table Bay, the recharge of the groundwater, the fish population of the Liesbeek and Black River and the bird population of the Raapenberg and Zoarvlei wetlands. Currently the sole function of the canal comprises of directing the flood water from the catchment as fast as possible into the sea. It is understood that a restored river has a much greater environmental and hydrological potential.

1.2 Investigation framework

The Hypothesis of this study is, that a reinstated estuary can protect from tidal and fluvial flooding, improve water quality and be a biodiversity asset for the city.

A great part of the study focuses on the historical evolve- ment of the canal from an estuary. For that research historical maps and books discussing the history of the Cape Town rivers were used and compared.

Due to the Covid-19 pandemic it was not possible to receive any current flow or water quality data, latest aerials or recent survey data for the study area and the catchments. The research requests were done on time, but were delayed and in the end fell through because of the lock down of all administrations. Initially it was planned to model scenarios for the study, but without the necessary data input the modelling was not possible. In preparation for that a student licence for the program PSWMM used by the CoCT was acquired. As a response to that the study is based on available old reports and site visits before lock down.

The main research method was to collect, combine, overlay and simplify information in a graphical way to highlight major problems. It emphasizes the current situation of a once fluvial systems now in an urban context. Water bodies are negated and regarded as flood risks only.

The scenario method was used to discuss different techniques and evaluate them. Three scenarios were developed. In case of the Salt River canal the interchange of river, sea and urban environment comes into focus. In times of protecting our cities from the effects of climate change, a balance needs to be found for natural processes to happen within the urban context and the protection of land, lives and goods.

1.3 Structure of the study

The analysis of the current situation starts with a research of the historical evolvement from an estuary to a canal, which is represented as a graphical analysis with historical maps and aerials. Some of the findings in this research are contradictory to the commonly known history of the Salt River, found in books and articles. The gradual degradation of the salt marsh and the Salt River is summarized in a juxtaposition of all the diagrams traced from the historical maps.

A review of contemporary methodologies of river and estuary restoration methods was done and completed with a discussion of international best practice projects. City of Cape Town strategies towards climate change on the case of rivers are reviewed as a way forward from current conservation thinking to a pro active restoration.

A catchment and study area analysis investigates the system and its influences correlating information from site visit and publicly available. It was not possible to obtain detailed information on flow data, water quality data, visions and restrictions for the canal, the harbour and the catchment, due to the closure of all administration during lock down.

Different approaches exist to describe the methods of returning an engineered system to a close to natural system. Three of these terminologies were used to develop and discuss scenarios for the canal. Detailing and evaluation of the rehabilitation and reclaimation scenarios gives a informed feed back of the restoration options and their limits for the study area..