| 摘要: | Urbanization and climate change are associated with extreme changes to hydrologic processes that alter the amount and timing of runoff delivery in the Anthropocene. This dissertation research examined the degree of urbanization, climate change, and hydrologic responses in Rocky Branch Watershed (RBW), a small, highly urbanized catchment with dense vegetation canopy in Columbia, South Carolina. This dissertation is composed of three parts: (1) an automated algorithm for mapping building impervious areas (BIA) from remote sensing data for estimating percent impervious area (PIA), (2) a paired watershed study contrasting a forested with an urban watershed, and (3) a hydrologic simulation model to compare land-use and climate changes in an urban watershed.
One key cause of hydrologic change, and also a measure of the degree of urbanization, is the PIA. However, mapping PIA under dense vegetation canopy is a challenge. Moreover, hydrologic changes to surface runoff in response to high PIA include an increase in peak flows and a decrease in peak flow arrival times. Although these relationships are general understood, details are missing—especially for small watersheds. This research presents a new building extraction approach that is based on and optimized for estimating building impervious areas (BIA) for hydrologic purposes.
The Building Extraction from LiDAR Last Returns (BELLR) model, uses a non-spatial, local vertical-difference filter on LiDAR point-cloud data to automatically identify and map building footprints under dense vegetation canopy. The BELLR- estimated BIAs were tested using two different types of hydrologic models to compare BELLR results with results using the National Land Cover Database (NLCD) 2011 Percent Developed Imperviousness data. The BELLR BIA values provide more accurate results than the use of the 2011 NLCD PIA data in both models.
Comparisons between RBW and a forested watershed under different land-use conditions utilized field measurements of rainfall and streamflow to characterize storm hydrographs in order to quantify hydrologic responses to anthropogenic changes in small, heavily urbanized watersheds. It contrasts peak discharges, stormflow durations, volumes of storm water, shapes of storm hydrographs, and runoff coefficients generated by a variety of storm events between the two watersheds.
The EPA Storm Water Management Model (SWMM) was used to study the effects of urbanization and climate change on stormwater in RBW. SWMM was applied to a series of scenarios to compare relative effects of projected PIA and climate-change scenarios on runoff for the near term (2035) and far term (2060). This analysis showed that climate change has generated a greater impact on runoff than urbanization. |
