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

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 the development of plans to mitigate the effects of anthropogenic changes on watershed processes. This study focused on quantifying the potential 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 have increased by more than 300% in the last 15. years (1992-2006). Differences in the frequency distributions of the flow variables under each scenario were quantified using a Smirnov test. Results indicated 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. An 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.