Effects of Urban Infill on Surface Permeability | Denver
At the turn of the millennia, cities throughout North America reversed suburban trends and began up-zoning urban centers to commence a new era of urban infill. There are numerous consequences from these changes - both good and bad. The front range (a corridor of urban settlements stretching I-25 through Pueblo, CO to Cheyenne, WY) lies in a semi-arid temperate desert. This climate is prone to extreme weather events straying from the norm (temperature changes, tornadoes, extreme drought resulting in fires, etc.).
Climate change increases the frequency and severity of extreme weather events. This report tracks changes in permeable surfaces to propose a typology of measurement for cities to consider. The hope is this typology can help cities plan and evaluate development, to prepare for extreme precipitation events.
Images overlays from the same site showing change in development in Lowry neighborhood, Denver, CO
This report compares building morphologies to track changes in permeable surfaces from large scale development in Denver. Building morphologies refers to types of buildings: single family detached, multi-unit complexes, row/townhouse, etc. The study uses the following tools to compare and calculate change: Google Earth to locate/visualize historical development change, ArcGIS to calculate surface areas, and fieldwork to log streetscape and morphology features.
Process
Sites are selected on two principal factors: large-scale development & areas that are more or less 'greenfield' developments. Choosing large-scale areas ensures more calculation accuracy, because morphology measurements can be multiplied and averaged over large areas of change. None of the sites were purely 'greenfield' because each area was once home to large infrastructure development which was either retrofitted or transferred to other locations: Stapleton Airport, Lowry Airfield, and Union Station. However, each of these sites had large swathes of permeable land (grass or wild prairie) which developed into large changes of impermeable surfaces.
The results from the study are not meant to be limited to large-scale or 100% permeable land. Rather, they are meant to be applied to all development. The scale and terrain were held as constants to ensure more reliable measurements, and to set a base for calculations (greenfield sites are assumed 100% permeable). In example, if an area were up-zoning from single family detached to multi-family complexes, single-family detached calculations would be used as the base comparison. If open-space was developed, then greenfield calculations would be set as the base. The base-comparison always uses the calculated permeable surface that was attributed to the area before development/change.
This image is a slide pulled from a presentation to cities in the Denver-Boulder region presenting the permeability study methodology and calculation results.
The Lowry and Stapleton neighborhoods are ideal because of their similar development styles: low-mid density residential, commercial, and mixed use development. The Union Station study stands alone in the report for high-density development. While it would be ideal to have another similar development density to compare, at the very least, the Union Station study helps give a benchmark comparison for the lower-density neighborhoods. Naturally, the reliability of these measurements could be tweaked as more neighborhoods and density types are studied and compared.
The next step is a fieldwork study to confirm the building morphologies and to take notes for the sites' permeable (vegetation and landscaping such as rock/gravel) and impermeable surfaces (structures, sidewalks, streets, etc.). The notes and imagery are then calculated with ArcGIS and compared to the Google Earth historical imagery. Results for each building morphology are added up and averaged at each site. The results from each site can then be compared to similar development averages at other sites to continuously fine-tune the averages.
After subtracting the sum of the public infrastructure area, the same process is repeated for adding up the structures which is again subtracted from the total area.
Total Area — Public Infrastructure — Structural Area = Remaining Permeable Surface
Calculation methods repeated for different building typologies in each neighborhood. Findings from building typologies across neighborhoods are added up and averaged. Averages indicate total change in permeable surface for each building morphology.
Site selection: primarily permeable surfaces - gravel roads and limited structures
Site Selection: large development with various zoning densities to measure (this image reflects single family detached zoning study for Lowry)
Total area of site added up
area of public infrastructure added up and subtracted from the total area
Lowery Single-Family Development | Calculations
