Site Suitability Analysis of Green Infrastructure in ... · Site Suitability Analysis of Green Infrastructure in Austin, TX Droughts have plagued Texas as far back as the first written

Andy Peterson 12/3/2014

Site Suitability Analysis of Green Infrastructure in Austin, TX

Droughts have plagued Texas as far back as the first written meteorological records. Currently in

Fall of 2014 we are in stage 2 water restrictions despite the fact that the heat of summer is behind

us, and despite the substantial rain in the recent weeks. When drought comes around in this

region it stays, often for years. The problem is compounded by the fact that cities in Texas are

booming, with three of the top ten fastest growing cities in the nation. Number one on that list is

Austin (Dallas, 4 and Houston, 10) which strains important aquatic resources like aquifers,

rivers, lakes, and streams. With increased population comes increase demand, as well as

decreased water quality from pollution. Green infrastructure describes vegetation being

incorporated into the design of urban areas. This can be as simple as city trees being planted next

to sidewalks, to green walls, which add a growing surface to the sides of buildings so that plants

may root vertically. Green infrastructure affixed to buildings will be the investigation of this

project, which is to find out what kind of effect widespread application of this technology would

have here in Austin, Texas, as well as site suitability analysis.

Benefits to investing in Green infrastructure:

Reduced and delayed storm water run off

Water purification

Reduction in the urban heat island effect

Electricity savings through insulation

Habitat; increased urban biodiversity

Improves air quality

Therapeutic (aesthetically pleasing, and absorbs noise)

The first two bullets effects would be most profound if they occurred in urban areas nearest to

creeks. For this reason the first element of a suitable building for a green wall will be proximity

to a creek. The third, fifth, and seventh bullets will be maximized in areas where there is no other

green space, so the second suitability element is distance away from park. With this in mind I

compiled four shapefiles for the city of Austin, creeks, building footprints, parks, and urban

Austin (Figure 1).


Figure 1 Urban Roads Polygon (purple) Building footprints (orange) Parks (green) and Creeks (blue)

The judicial boundaries of the city of Austin were not a good basis for what is “urban” so I used

a shapefile that is based on roads (2222, Loop 1, Hwy 71, 183, etc.) I think that it does a good

job of separating dense, and sparsely populated areas to the east and west. The boundary between

urban and suburban is harder to define to the north and south, but I felt these roads were as good

a definition as any. With this decided I used the clip tool three times with creeks, parks, and


building footprints as the input feature and urban Austin as the clip feature.

Figure 2 Building, Park, and Creek polygons clipped to urban Austin boundaries

Many buildings are not well suited for green walls; curtain wall structures, where the outermost

shell is not load bearing would not likely be able to bear the weight of a substrate layer. A façade

wall made up of climbers and vine plants could work, but may not be desired over the view that

glass provides. Historic buildings could be damaged by plant roots, or failures in the irrigation

system, not to mention it usually isn’t appropriate to cover a historic building. I decided to

differentiate between downtown buildings, and all other urban buildings. Downtown buildings

are on average much taller, and are assumed to have flat roofs, and contain a higher

concentration of buildings not suited for a green wall. I used Lamar St, Town Lake, I-35, and

15th

St. as the boundaries for Downtown. By digitizing the urban Austin polygon, and then using

the intersect tool to create a new Downtown buildings polygon from the newly digitized


boundary polygon, and the buildings footprint polygon. I also buffered the parks and creeks

shapefiles at 150m so they would be ready for the next step.

Figure 3 Downtown buildings polygon created (in red) as well as polygons for creek buffer (teal) and park buffer (lavender).

My map was starting to get a little bit cluttered so I set out to clean things up. First I used erase

to remove the Downtown buildings from the buildings footprints polygon, finally making them

completely separate. Then I used the intersect tool again, this time to create a polygon for

buildings that were within the 150 m creek buffer. I did this twice, once for the Downtown


buildings, and once for non-Downtown buildings.

Figure 4 Both Downtown and Neighborhood shapefiles clipped to only include polygons within 150 meters of creek

The next step was to erase the buildings that met the criteria of being close to a creek, but were

also close to a park. Using erase twice the input feature was by buildings near creek file, and the

erase feature was the park buffer.


The result highlights downtown in red, and non-downtown buildings in orange that are well

positioned for green infrastructure.

Figure 5 Completed site suitability analysis with non-suitable buildings in black, suitable downtown buildings in red, and suitable neighborhood buildings in orange.


Zoomed in to Downtown

Figure 6 Zoomed in completed site suitability map of downtown Austin.

I then set about quantifying all this data. I wanted to find out what the differences in building

height were between neighborhood buildings and downtown buildings, area of the footprints (for

green roofs) and the perimeters of the buildings. The attribute table from the original building

footprint 2013 polygon had fields for length area and height in feet which I was able to find


averages and sums of by right clicking the field header and clicking statistics.

The results were converted to stories, km and km^2

Downtown Buildings Neighborhood Buildings

Average Height 6.7 Story 1.7 Story

Total Length 64.5 km 2544.1 km

Total Area (roof) 0.65 km^2 10.6 km^2

Total Area (four walls)* 1.32 km^2 13.18 km^2

* Assuming all polygon edges represent building walls, and that all buildings are the average

height

These calculations represent 100% coverage of roofs, and over 100% coverage of walls, since

some of the polygon edges were buffered into the middle of a building. Green walls can be

planted on the north, south, east, and west sides of a building, but each side would need to be

designed differently, especially in regards to plant species as they receive a different amount of

light throughout the day and year.

Downtown buildings generally have a flat roof, and only some buildings can handle a green wall.

To make our calculations more realistic I will assume that downtown building walls suitable for

green walls make up 40% and those buildings can only have two of their four walls planted (20%

of original). Since some roof space is needed for air conditioning and other equipment we will

adjust downtown roof space to 75% of the original total.

Neighborhood buildings made of brick and wood are more accepting of green walls, and their

shorter height makes them more manageable. We will assume 80% neighborhood walls are

accepting with half of them receiving adequate sunlight. Neighborhood roofs are generally

sloped so we will assume only 5% can be made into green roofs.


Realistic roof space 0.49 km^2 5.3 km^2

Realistic wall space 0.26 km^2 5.27 km^2

Cost can be as much as $65 per square foot (Hohenadel, n.d.) for intensive green walls (left) that

boarder on works of art, to $10 for extensive walls like the façade made of ivy (right)


Green roofs are on average between $15 and $20 per square foot (K, 2001). Using the intensive

walls for downtown buildings (since they are installed on already expensive buildings and are

highly visible) and extensive walls for neighborhoods, my cost estimate is:


Cost to plant realistic roof

space

105.5 million dollars 1.14 billion

Cost to plant realistic wall

space

181.9 million dollars 567.3 million dollars

Further Considerations:

A better site suitability assessment should be done before targeting which buildings are the best

candidates. A computer model of the urban hydrology of Austin would be most beneficial to find

out where the largest volumes of storm water runoff are coming from. Thermal imaging of

Austin should also be incorporated into the analysis since combating the urban heat island,

through containing and rereleasing storm water is the most important aspect of green

infrastructure here in Austin. I want to note that my analysis has simply taken to account the best

places for green infrastructure, but it would certainly not hurt to install this in areas far from

creeks and close to parks, as they would be beneficial outside of my definition of urban Austin.

The cost may seem high at first, but consider that proposed renovations to McCombs School and

Welch Hall here on campus are over 100 million dollars each—with that money spent on

intensive green walls, the scenery Downtown would change drastically and make Austin the

world leader in green walls.

Site Suitability Analysis of Green Infrastructure in ... · Site Suitability Analysis of Green Infrastructure in Austin, TX Droughts have plagued Texas as far back as the first written

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