Assessment of Urbanization Impacts on Surface Runoff and Effects of Green Infrastructure on Hydrology and Water Quality

Jingqiu Chen, Purdue University

Abstract

Urbanization is one of the most important anthropogenic modifications of the global environment. It has significant impacts on hydrologic processes and water quantity and quality. Research related to urbanization impacts on surface runoff has focused on changes up to the watershed scale. However, quantitative assessment at a national scale is scarce. Parallel to urbanization impacts, climate is also one of the greatest challenges facing humanity today and its effects are already being felt from strengthened storms and rising sea levels to changing temperature and weather patterns. The adverse impacts of urbanization and climate can converge in synergistic ways, which may render hundreds of millions of urban residents increasingly vulnerable to floods, landslides and other natural disasters. The challenge is in finding mitigating solutions. The specific objectives of this study were to: 1) assess urbanization impacts on surface runoff of the contiguous United States using the Long-Term Hydrologic Impact Assessment (L-THIA) model based on the 2001, 2006, and 2011 National Land Cover Databases; 2) assess simulated precipitation based on an updated CLIGEN database and associated impacts on the surface runoff using the L-THIA Tabular Tool in the five states of the Great Lakes Region; and 3) evaluate the effectiveness of green infrastructure practices on hydrology and water quality in a Combined Sewer Overflows (CSO) community. National analysis results showed that: 1) urbanization occurred non-uniformly across the nation from 2001 to 2011; 2) urban expansion and intensification were the main driving forces altering surface runoff; 3) the majority of counties had long-term normalized average annual runoff depth (NAARD) from urban land less than 17.8 mm; 4) the states with the largest NAARD values had both high precipitation and increases in urban land, while the ten states with the largest NAARD change percentages were mainly in the western U.S. with low precipitation and the NAARD values were mainly influenced by large increases in urban land; 5) nationally, average annual runoff increased by 10% due to urbanization from 2001 to 2011. Weather generators rely on historical meteorological records to simulate time series of synthetic weather inputs, the quality of which has direct influence on model applications. The weather generator CLIGEN’s database has recently been updated to comprise consistent historical records from 1974 to 2013 compared to the current database in which records are of different lengths. In the second objective, CLIGEN’s performance in estimating precipitation using UCD and the subsequent impact on urban runoff simulations were evaluated. Generally, UCD-based precipitation could replicate observed daily precipitation up to the 99.5th percentile, but maximum precipitation was underestimated. Results from the Long-Term Hydrologic Impact Assessment model using UCD-based precipitation showed about 0.57 billion cubic meters more (14.9%) average annual runoff being simulated compared with simulations based on the current CLIGEN database. Overall, CLIGEN with the updated database was found suitable for providing precipitation estimates and for use with modeling urban runoff or urbanization effects. From Objective 3, the enhanced L-THIA-LID 2.2 model was able to simulate more detailed impervious surfaces including sidewalks, roads, driveways, and parking lots, to conduct cost calculations for these more detailed impervious surfaces, and to consider the actual suitable area for bioretention in the study area. The effectiveness of green infrastructure (GI) practices on hydrology and water quality at a combined sewer overflow urban watershed was examined in 10 simulation scenarios using 8 practices including rain barrels/cisterns, green roofs, green roofs plus rain barrels/cisterns, bioretention, porous roads, porous parking lots, porous sidewalks, and porous driveways. The annual cost and the cost effectiveness for each scenario considering a 20-year GI practices lifetime were examined. Main findings included: (1) combined implementation of GI practices performed better than applying individual practices alone; (2) the various adoption levels and combinations of GI practices could potentially reduce runoff volume by 0.2-23.5%, TSS by 0.18-30.8%, TN by 0.2-27.9%, and TP by 0.20 to 28.1%; (3) based on site characteristics, adding more GI practices did not necessarily mean that substantial runoff and pollutant reduction would be achieved; (4) the most cost-effective scenario had an associated cost of $9.21 to achieve 1 m3 runoff reduction per year and $119 to achieve 1 kg TSS reduction per year. This, however, assumes cooperation from the general public in implementing GI practices on their properties; and, (5) adoption of GI practices on all possible areas could potentially achieve the greatest runoff and pollutant load reduction, but would not be the most cost-effective option. The enhanced model from this research can be applied to various locations to support assessing the beneficial uses of GI practices. (Abstract shortened by ProQuest.)

Degree

Ph.D.

Advisors

Engel, Purdue University.

Subject Area

Hydrologic sciences|Agricultural engineering|Water Resource Management

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