Floods - How Much is Too Much Water

Identifying and Adjusting for Effects of Urbanization on Peak Streamflows

  • Thomas Over (USGS)
  • Riki Saito (USGS)
  • David Soong (USGS)
  • T-Y Su (USACE-Chicago District)


Trends in streamflow records are often seen as a potential signature of climate change, but land-use change may be the dominant driver of trends in some settings. Analyzing temporal trends with respect to precipitation and urbanization allows their relative effects to be estimated. In this study, the annual peak flow data series during the period from 1945-2009 from 143 USGS streamgaging stations in the Northeastern Illinois (Chicago metropolitan) region with drainage areas less than 200 sq. mi. were analyzed by multiple linear regression to jointly estimate the effects of urbanization and precipitation on their trends. Urbanization was expressed as the urbanized fraction of each basin and was estimated by using an adjusted decadal Census-based measure of housing density. Precipitation was estimated as the maximum daily rainfall during the period three days before and through one day after the date of the peak, distributed by using Thiessen polygons. It was found that changes in the logarithm of peak flows can be modeled as directly proportional to changes in urbanization and precipitation, with proportionality constants of about 0.51 and 0.085, respectively. The precipitation coefficient may be under-estimated as a result of uncertainty in the precipitation estimates, but it was retained in the regression model to improve the accuracy of the estimated urbanization effect. Without precipitation in the regression, the urbanization coefficient increased to about 0.53, indicating that without precipitation in the analysis, the small increasing trend in precipitation is assigned erroneously to the effects of urbanization. No strong evidence was found region-wide that urbanization in later decades of the analysis period had a smaller impact on peaks than in the earlier decades, despite institution of stormwater detention requirements at varying times beginning in 1972 throughout the region. Using these results, the peak flow data series will be adjusted to present (2010) urbanization conditions to create data that are stationary with respect to urbanization (though not precipitation changes) for use in updating regional regression equations for estimating flood peak quantiles in urbanized areas of northeastern Illinois.

How to Cite:

Over, T. & Saito, R. & Soong, D. & Su, T., (2014) “Identifying and Adjusting for Effects of Urbanization on Peak Streamflows”, National Hydraulic Engineering Conference 2014 1(2014).

Rights: Copyright © 2014, Thomas Over, Riki Saito, David Soong and T-Y Su

Publisher Notes

  • Panel moderated by Steve Sisson, DDOT.
  • About the Presenters: Dr. Over has been with the USGS at the Illinois Water Science Center (IL WSC) since 2001 on a part-time basis and full-time since 2012. He works in areas of prediction of peak and continuous streamflow in ungauged basins by statistical regionalization, hydrologic simulation modeling, disaggregation and scaling of precipitation and streamflow, streamflow measurement uncertainty, hydrometeorological data analysis (evaluation of gage and radar-based precipitation observations and forecasts, development of homogeneous weather databases), and effects of land-use change on streamflow. Prior to his full-time appointment with the USGS he was an assistant research professor at Eastern Illinois University (EIU) in the Geology/Geography Department, a visiting assistant professor at University of Illinois at Urbana-Champaign in the Civil and Environmental Engineering Department, and an assistant professor at Texas A&M University in the Civil Engineering Department, where he taught courses in water resources engineering, engineering hydrology, and stochastic hydrology. His research at EIU was in the area of controls of soil moisture and soil hydrophobicity on wind erosion. His Ph.D. is from University of Colorado - Boulder, Geophysics Program - Hydrology Option, where his dissertation was on multifractal modeling of space-time precipitation fields. Prior to Ph.D. studies, he worked as a consulting civil engineer. He is registered as a professional engineer in the State of Illinois.

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Published on
22 Aug 2014
Peer Reviewed