Historical urban flood management to understand urban ecosystem disturbance: A comparative study
Urban ecology lacks a theory of urban ecosystem disturbance. Such a theory would use the ecological definition of disturbance developed for natural ecosystems as a starting point but must conceptualize the effects of disturbances on the integrated social-ecological system rather than solely on biophysical components. Urban stormwater is an ideal system within which to develop these ideas. Stormwater infrastructure is a major component of the urban hydrologic system, but is explicitly designed, with consequences for human well-being. At large scales, the way that stormwater is managed has changed significantly over time. We ask: What are local patterns of infrastructure change? What is the role of disturbance in driving spatial and temporal patterns of infrastructure use? What are the mechanisms linking disturbance and landscape change in a social-ecological system? We use a multi-method approach to address these questions in three cities from an urbanization gradient along the Wasatch Front in Utah: Salt Lake City, Logan, and Heber City. We describe changes in the use of different stormwater infrastructure (conveyance vs retention) over time and over space in each city. We also constructed flooding and flood management histories (1850-2000) for each city using archival media sources.
Spatial and temporal patterns of stormwater infrastructure design varied across cities. All three cities transitioned from agriculture to urban land use, and legacies are evident in the use of agricultural canals for stormwater in Logan and Heber. Canals were historically used for stormwater in Salt Lake, but this is no longer the case. Use of retentive features spiked in the 1960s in Logan, but not until 1975 in Salt Lake. Meanwhile, the density and size of retentive infrastructure is greater in Salt Lake than in Logan. Our media analysis suggests that local disturbances such as floods and water pollution events drive changes in stormwater infrastructure. However, local constraints, particularly the availability of funding, often limit changes. In Salt Lake, for example, the need for a centralized storm sewer was recognized in the late 1800’s, but the first storm mains were constructed in 1925 after years of agitation by citizens, business owners, and city engineers. In cities, the linkages between disturbances and changes in ecosystem structure involve complex social processes. However, disturbance may be an important driver of heterogeneity within and between cities, with important consequences for ecosystem functioning.