94
7.7 Ecological Planning and Design
The best way to understand McHarg’s ecological method is to reflect upon a formative project worthy
of study, the Potomac River Basin Study (1965–66), recorded in Design with Nature (1992 [1969]).
This study used most of McHarg’s methods and was the first project that combined the physiographic
region and the river basin as the primary organizing context for ecological planning and designing a
framework that links past, present, and the anticipated future in multiple landscape scales, from the
region to the garden (Spirn, 2000, p. 106). The Potomac River Basin Study provides the opportunity
to address all aspects of McHarg’s methods, as the Basin is a single hydraulic unit that transcends a
number of physiographic regions, and as such it could provide opportunities for different and specific
land uses. For McHarg this was the best opportunity to test the ecological planning method – which,
McHarg noted, employed a ‘rationale method’, whereby evidence is derived from the collection of
environmental factors of the site, and the study then identifies merely those areas where certain land
uses could occur with the least costs and greatest savings (McHarg, 1992 [1969], p. 105). This process
of McHarg’s ecological method can be summarised as:
1. Identify the area of study and set the boundaries
2. Compile and map data of the site in the following order:
(a) Climate
(b) Historical geology
(c) Surficial geology
(d) Physiography
(e) Hydrology
(f) Soils
(g) Plant ecology
(h) Wildlife habitats
(i) Land use
3. Analyse data within a value system process
4. Report on the analysis with the best proposed land use based on the value system
Following the step-by-step process above, the mapping of the ‘ecological inventory’ of the Potomac
River Basin recorded maps with longitudinal sections which included the diverse physiographic
regions of the area. It also summarised patterns of topography, hydrology, geology, soils, vegetation,
and current land use. These maps and cross sections made it possible to analyse a comparison of patterns from region to region within the river basin/catchment.
McHarg was very specific about this order, and his students called it ‘the layer cake’ (see Fig. 7.3)
(Spirn, 2000, p. 108). Analysis of sites always follows the same order (climate, geology, hydrology,
soils, vegetation, wildlife), and McHarg described the reasons for this ordering as follows:
Written on the place and upon its inhabitants lies mute all physical, biological and cultural history to be understood by those who can read it. This is the prerequisite for intelligent intervention adaptation. So, let us begin at
the beginning. The place, any place, can only be understood through its physical evolution. Both climate and
geology can be invoked to interpret physiography, the current configuration of the place. If one knows historical
geology, climate, and physiography, then the water regimen becomes comprehensible: the pattern of rivers and
aquifers, their physical properties and relative abundance, oscillation between flood and drought. Knowing the
foregoing and the prior history of plant evolution, we can now comprehend the nature and pattern of soils. By
identifying physiographic, climatic zones and soils, we can perceive order and predictability in the distribution
of constituent plant communities. Animals are fundamentally related so that given the preceding information,
with the addition of the stage of succession of the plant communities and their age, it is possible both to understand and to predict the species, abundance or scarcity of wild animal populations (Spirn, 2000; McHarg, 1992
[1969], pp. 105-7).
7 Design and Planning with Nature
7.7 Ecological Planning and Design
The best way to understand McHarg’s ecological method is to reflect upon a formative project worthy
of study, the Potomac River Basin Study (1965–66), recorded in Design with Nature (1992 [1969]).
This study used most of McHarg’s methods and was the first project that combined the physiographic
region and the river basin as the primary organizing context for ecological planning and designing a
framework that links past, present, and the anticipated future in multiple landscape scales, from the
region to the garden (Spirn, 2000, p. 106). The Potomac River Basin Study provides the opportunity
to address all aspects of McHarg’s methods, as the Basin is a single hydraulic unit that transcends a
number of physiographic regions, and as such it could provide opportunities for different and specific
land uses. For McHarg this was the best opportunity to test the ecological planning method – which,
McHarg noted, employed a ‘rationale method’, whereby evidence is derived from the collection of
environmental factors of the site, and the study then identifies merely those areas where certain land
uses could occur with the least costs and greatest savings (McHarg, 1992 [1969], p. 105). This process
of McHarg’s ecological method can be summarised as:
1. Identify the area of study and set the boundaries
2. Compile and map data of the site in the following order:
(a) Climate
(b) Historical geology
(c) Surficial geology
(d) Physiography
(e) Hydrology
(f) Soils
(g) Plant ecology
(h) Wildlife habitats
(i) Land use
3. Analyse data within a value system process
4. Report on the analysis with the best proposed land use based on the value system
Following the step-by-step process above, the mapping of the ‘ecological inventory’ of the Potomac
River Basin recorded maps with longitudinal sections which included the diverse physiographic
regions of the area. It also summarised patterns of topography, hydrology, geology, soils, vegetation,
and current land use. These maps and cross sections made it possible to analyse a comparison of patterns from region to region within the river basin/catchment.
McHarg was very specific about this order, and his students called it ‘the layer cake’ (see Fig. 7.3)
(Spirn, 2000, p. 108). Analysis of sites always follows the same order (climate, geology, hydrology,
soils, vegetation, wildlife), and McHarg described the reasons for this ordering as follows:
Written on the place and upon its inhabitants lies mute all physical, biological and cultural history to be understood by those who can read it. This is the prerequisite for intelligent intervention adaptation. So, let us begin at
the beginning. The place, any place, can only be understood through its physical evolution. Both climate and
geology can be invoked to interpret physiography, the current configuration of the place. If one knows historical
geology, climate, and physiography, then the water regimen becomes comprehensible: the pattern of rivers and
aquifers, their physical properties and relative abundance, oscillation between flood and drought. Knowing the
foregoing and the prior history of plant evolution, we can now comprehend the nature and pattern of soils. By
identifying physiographic, climatic zones and soils, we can perceive order and predictability in the distribution
of constituent plant communities. Animals are fundamentally related so that given the preceding information,
with the addition of the stage of succession of the plant communities and their age, it is possible both to understand and to predict the species, abundance or scarcity of wild animal populations (Spirn, 2000; McHarg, 1992
[1969], pp. 105-7).
7 Design and Planning with Nature