Impervious surface regulation and urban sprawl as its unintended consequence
Highlights
► We examined the effect of impervious surface regulation on spatial development pattern. ► We quantified spatial development pattern using lacunarity analysis. ► After adopting the impervious surface regulation, forest patches were fragmented. ► The impervious surface regulation aggravated urban sprawl in urban fringe.
Introduction
Urbanization has detrimental impacts on water resources. Impervious surface generates more stormwater runoff and increases floods in urban streams (Rose and Peters, 2001, Burns et al., 2005). The increased stormwater runoff also degrades water quality by washing off pollutants from an urban watershed (Brezonik and Stadelmann, 2002, Li et al., 2008). These impacts further alter aquatic and riparian ecosystems, such as the change in population and species composition of fish (Sutherland et al., 2002) and vegetation communities (Sung et al., 2011).
To mitigate the negative impacts of urbanization on water resources, a growing number of local governments have adopted impervious surface regulations that limit the ratio of impervious surface to the total site area (Arnold and Gibbons, 1996, Moglen and Kim, 2007). Such regulations, usually in a form of zoning code, intend to maintain relatively high watershed permeability by forcing developers to pave less surface area. In reality, however, developers may simply purchase more land instead of reducing impervious surface area (Jones et al., 2005). This is particularly so in urban fringe where purchasing more land does not significantly raise development cost. For instance, Glaeser and Ward (2009) investigated the cost of housing development in the Greater Boston, USA, and found that cost for purchasing extra square meter of land would be only 39.5 US dollars (USD) in 2000–2005, which is not much expensive compared with the average home sales price of 450,000 USD in the same time period. Results of a housing survey also indicated that most suburban residents who wanted large lot houses were willing to bear cost for large lot houses (Thorsnes, 2000). Combining the low land price and the preference for large lot houses suggests that the cost for extra land seems not to affect residents’ decisions on spending million dollars to build houses in the regulated areas (Esparza and Carruthers, 2000, Talen, 2001). The consequence is the aggravation of urban sprawl, or dispersed urban development that consumes vast land in the United States or elsewhere around the world (Pendall, 1999, Pendall, 2000). Some argued that urban sprawl is a desirable urban form because it improves neighborhood satisfaction and decreases commuting distance in a polycentric city where both job and houses were located in suburban areas (e.g., Gordon and Richardson, 1997), but many others claimed that urban sprawl triggers various social and environmental problems: it requires longer road and utility lines per capita (Carruthers and Ulfarsson, 2003); longer automobile travel distance consumes more energy and ultimately contributes to climate change (Ewing, 1997, Johnson, 2001); it increases habitat fragmentation that threatens local and regional biodiversity (Hawbaker et al., 2006, Sung, 2012).
Previous studies showed that similar land use regulations intended to control the density of urban development, such as minimum lot size regulation and urban growth boundary (UGB), encouraged urban sprawl. For instance, Cho et al. (2008) found that, in Knoxville, new housing construction decreased within the UGB but increased outside of it, which suggests that UGB fueled more dispersed development. Levine (1999) and Landis (2006) independently studied local land use regulations in California, USA, and found that those regulations were unable to suppress urban development but simply displace development to neighboring areas without such regulations.
Although many studies addressed the effect of land use regulations on urban sprawl, only few directly examined spatial development patterns in regulated areas (e.g., Munroe et al., 2005, Robinson et al., 2005). Quantifying spatial development pattern is critical in understanding the effect of land use regulations because urban sprawl, perhaps an outcome of those regulations, has many dimensions that cannot be captured by a aspatial measure alone (Tsai, 2005). Also, to our knowledge, no study has examined how impervious surface regulation affects spatial development pattern. We believe that an empirical study on an impervious surface regulation is still needed because it has a similar but different regulatory mechanism than other land use regulations.
This paper fills the gap in the literature by investigating the change in spatial development patterns before and after the City of Austin adopted the Save Our Springs (SOS) ordinance that regulates impervious surface area at a maximum 15–25% of the total site area. We compared one subwatershed with the SOS ordinance to five control subwatersheds with less stringent impervious surface regulation. Impervious surface was derived from Landsat TM images before and sixteen years after the SOS ordinance, and the spatial patterns of urban development were quantified using the lacunarity index. We hypothesized that the SOS ordinance would have led to a more dispersed development pattern than other subwatersheds with less stringent impervious surface regulation.
Section snippets
Study sites selection
The study area is the City of Austin, Texas, USA, that is located over the Edwards Aquifer, a karst aquifer that is susceptible to surface water contamination (Sung and Li, 2010). The study area has been developed since the early nineteenth century when Austin was established as the capital city of the state of Texas, but the major suburban development began in 1980s when high technology industries settled in this region (Wiggins and Gibson, 2003). Now, Austin is one of the most rapid growing
Results
Fig. 2 illustrates impervious surface maps of all study subwatersheds derived from the Landsat TM images. Impervious surface significantly increased in all of the study subwatersheds during the study period. On the WC subwatershed, impervious surface increased from 25.3% to 52.1% during the two study periods (Table 2). Average impervious surfaces of the five control subwatersheds were 30.4% and 55.6% in 1991 and 2008, respectively. Land uses (data available at //ftp.ci.austin.tx.us/GIS-Data/Regional/coa-gis.html
Discussion
Lacunarity analysis shows that the WC subwatershed where the SOS ordinance regulated impervious surface at 15% of the total site area were more dispersedly developed than the five control subwatersheds. In the WC subwatershed, large forests disappeared and landscape became fragmented to small patches of developed areas and remnant forests after the enactment of the SOS ordinance. This change was not observed in the five control subwatersheds located in other watershed protection zones with less
Conclusion
In this paper, we showed that an impervious surface regulation aggravated urban sprawl by encouraging more dispersed suburban developments in urban fringe. In urban fringe where land price is relatively low, developers can easily meet the requirement of the impervious surface regulation by purchasing more lands. As a result, development occurred in a low density dispersed pattern, and forests were more finely fragmented and evenly distributed throughout landscape. A more rapidly declining
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