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Title: Impacts of urbanization on river flow frequency: A controlled experimental modeling-based evaluation approach

Author
item CHU, MA. - St Louis University
item KNOUFT, JASON - St Louis University
item GHULAM, ABDUWASIT - St Louis University
item Guzman Jaimes, Jorge
item PAN, ZAITAO - St Louis University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2013
Publication Date: 5/13/2013
Citation: Chu, M.L., Knouft, J., Ghulam, A., Guzman, J.A., Pan, Z. 2013. Impacts of urbanization on river flow frequency: A controlled experimental modeling-based evaluation approach. Journal of Hydrology. 495:1-12.

Interpretive Summary: Hydrologic response at the watershed scale results from coupled processes occurring at local and global systems in the atmosphere, surface and subsurface. Identifying changes in hydrological response due to changes in the atmosphere or surface systems is not simple due to cross-interaction processes but fundamental to assessing and mitigating the impacts of urbanization in watershed ecosystems. This study focused on quantifying the effects of varying degrees of urban expansion on the frequency of discharge, velocity, and water depth using modeling approaches. Five land cover scenarios corresponding to varying degrees of urban expansion were used to determine the sensitivity of these flow variables (e.g., streamflow discharge, velocity and water depth) in the Big River watershed located in east central Missouri, where urban areas have increased by more than 300% between 1992 and 2006. The study results indicated that expansion of urban areas in the Big River may result in a significant frequency decrease of more than 100% when evaluating low flow events and an increase of more than 140% in high flow events under long-term steady rainfall scenarios. Increase in frequency of high-flow events is expected to impact the safety of structures, increase transport of sediment load, impair water quality, and increase stresses in the riparian ecosystem. The next phase of this research will be to determine cost-effective mitigation strategies to protect the ecosystem, infrastructure, and livelihood in this and other watersheds where urban development is inevitable.

Technical Abstract: Changes in land use are likely to cause a non-linear response in watershed hydrology. Specifically, small increases in urban expansion may greatly increase surface runoff while decreasing infiltration, impacting aquifer recharge and changing streamflow regimes. Quantifying the effects of urbanization on streamflow is crucial to mitigate the effects of anthropogenic changes in a watershed’s ecosystem. This study focused on quantifying the effects of varying degrees of urban expansion on the frequency of discharge, velocity, and water depth using the physically-based watershed model, MIKE-SHE, and the 1D hydrodynamic river model, MIKE-11. Five land cover scenarios corresponding to varying degrees of urban expansion were used to determine the sensitivity of these flow variables in the Big River watershed located in east central Missouri, in which urban areas increased by more than 300% between 1992 and 2006. Differences in frequency distribution of the flow variables under each scenario were quantified by the Smirnov test. Results showed a potential increase in the frequency of high flow events to more than 140% while decreasing the frequency of low flow events by up to 100% if the current rate of urbanization continues. In general, the frequency of low flow events decreased as urban expansion increased while the frequency of average and high-flow events increased as urbanization increased. Increase in frequency of high-flow events is expected to impact the safety of structures, sediment load, water quality, and the riparian ecosystem. This research will be valuable to assess mitigation strategies in order to protect the ecosystem, infrastructure, and livelihood in the watershed where urban development is inevitable.