Exploring The Relationship Between Urban Morphology And

Resilience In A Few Neighbourhoods In

Pretoria

Darren Nel & Karina Landman University of Pretoria

Contents

• Introduction

• Resilience and urban form• Comparison of four neighbourhoods • The evolution of the suburban tree• Conclusion

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Introduction

• Recent studies in urban planning highlighted importance of urban resilience

• Of these – few starting to show relevance of urban morphology for resilience– Attributes & indicators– Also linked to typical structure: tree or leaf– Paving way for new ways to study urban

phenomena

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Urban Resilience

• Amount of change system can experience without collapse or total transformation

• Specific sub-systems more vulnerable to such changes due to disturbances–Maybe because it is still recovering from

disturbances or shocks• Important to understand pattern of

disturbances and ability of urban system to deal with these to strengthen resilience

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Resilience and urban form

• “Urban resilience can be understood as the robustness of urban structures and networks against random failures” (Salat 2012)

• Failures: small scale (disruption in local transport networks or energy supply) or large scale

• Influenced by urban form

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Lattice (tree) or semi-lattice

• Alexander (1965): Cities may reflect lattice (no overlaps) or semi-lattice (overlaps)

City should not be a tree

– Need to allow

for social & spatial

overlaps

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Tree or a leaf

• Salat (2011): 2 paradigms– TREE: Disconnected and

closed (travel far)– LEAF: Connected on

intermediate scales

More resilient: Fractal structureMulti-connected

Complex on all scales

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Resilience and urban form

• Histories of cities have evolved from leaf-like structures to tree-like structures with consequent loss of efficiency and resilience

(Salat 2011)8

Change over time

(Salat 2011)9

Indicators

COMPLEXITY INTENSITY

DIVERSITY PROXIMITY

CONNECTIVITY

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Complexity

• Quality environments: complex, diverse & with overlap

• Due to incremental change and adaptation over time

• Essential for resilient city: – Rich urban fabric through

multiple points of contact, engage & interface

– Link to connectivity & diversity(Salat 2011)

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Connectivity

• In historical city it grew, in Modern City over-simplification reduced connectivity

• Understood through role of streets & intersections

• Need high connectivity, mechanisms to create new connections & low control

• Thus adaptive capacity critical – ability for self-organisation

Le Havre (Salat 2011)

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Diversity

• Complexity & adaptive capacity enhanced through diversity

• Among similar objects at same scale– E.g. population groups, income groups,

housing units• Or objects at different scales– E.g. metropolitan facilities or landmarks in

selective areas• Increased diversity also allows for

greater redundancy and thus ability to cope with disturbances

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Proximity

• Diversity also linked to proximity

• Average distance between two things– E.g. home & leisure /

home & work• Aim – minimum

distance to reduce travel needs and related costs & energy

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Intensity (density)

• Biggest opportunity for generation of urban opportunity through intense interactions & high levels of population support

• Link to complexity & diversity• Concentration of object in given area• -E.g. people or housing

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Indicators

Indicator

ComplexityDiversity

Connectivity

Proximity

Intensity

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MeasurementsIndicator: Diversity Measurement

The number of different uses The number of uses within the area

Number of road hierarchies The number of different road hierarchies within the area

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Measurements (2)Indicator: Proximity Measurement

The mean distance between two destinations

Average distance between two things (nearest shopping centre – straight line distance)

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• Connectivity– Nodes

(Intersections)– Connections– Distance between

intersections – Cyclomatic

complexity

Measurements (3)

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Selected study areas: older areas

Typical older neighbourhood, BUT closed-off

Typical older ‘open’

neighbourhood

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Analysis of two older neighbourhoods

• Typical older neighbourhood in Brooklyn– Grid pattern

• Typical older neighbourhood– Internally: grid

pattern– BUT closed-off

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Case 1: Brooklyn

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Brooklyn: unit of analysis(800 x 800 m blocks)

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Brooklyn; Proximity

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Does not lend itself to large enclosures

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Case 2: Irene

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Irene: unit of analysis (800 x 800 m blocks)

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Irene: Proximity

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Selected area of concentration

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Concentration of different types

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Concentration of different types

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Selected study areas: gated areas

Enclosed Neighbourhood

Security Estate

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Analysis of two types of gated communities

• Enclosed neighbourhood– Existing area

closed off for security purposes

• Security estate– Private

development

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Case 3: Newlands

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Case 3: Newlands (enclosed area)

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Newlands: Unit of analysis

(800 x 800m block)

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Newlands: Proximity

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Most of Pretoria east: suburban layout

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Case 4: Silver Lakes

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Silver Lakes: unit of analysis

(800 x 800 m block)

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Silver Lakes: Proximity

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The evolution of the suburban tree

Indicator What is being calculated Brooklyn Irene NewlandsSilver Lakes

IntensitySurface occupied by road network

(%)9.1 15.4 37.5 24.8

Connectivity

Connectivity of the car grid 31.6 28.1 28.1 12.5Cyclomatic complexity of the car

grid (per 0.64 km²)25 26 14 11

Average distance between intersections car grid (m)

150 152 147 224

External Connectivity (How easy is it to get outside of the area)

34 2 3 2

Proximity

The mean distance between two destinations (nearest major

shopping centre – straight line distance)

> 1 km > 1 km > 1 km 1 - 2 km

DiversityThe number of different uses < 6 < 6 1 2Number of road hierarchies 2 1 2 1

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The evolution of the suburban tree

Salat (2012)

A B C D

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The evolution of the suburban tree

Salat (2012)

A B C D

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The evolution of the suburban tree

Adapted from Salat (2012)

A B C D E

Should a gated community be considered as a new type of urban morphology or just the ultimate manifestation of suburbia?

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The evolution of the suburban tree

Evolution of modernistic planning In Tshwane

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The evolution of the suburban tree

Evolution of modernistic planning In Tshwane

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Conclusion (1)

• Gated communities represent an evolution of modern town planning principles

• Can be considered as the ultimate representation of suburbia with a wall

• In terms of morphology and function – very different from typical Medieval towns that were complex and well connected

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Conclusion (2)

• Suburbia & typical gated communities can be well connected internally but disconnected with the larger urban fabric.

• Therefore it tends to follow a typical tree-like structure

• However, a city is/should not be a tree– As a tree is not resilient– Tree-like structures did not perform well in terms of

indicators for resilience– Therefore, based on morphology, suburbia and the

typical gated community is not likely to be very resilient

• Need a city of leaves to enhance resilience– To accommodate complexity, connectivity,

diversity, proximity & intensity 49

Questions?

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Fragmentation

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Fragmentation

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Fragmentation

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