Historical Analysis of the Relationship of Streamflow Flashiness with Population Density, Imperviousness, and Percent Urban Land Cover in the Mid-Atlantic Region

Historical US Census population data was used to estimate population density for 1930–2000 and satellite imagery from circa 1973, 1992, and 2001 was used to estimate the degree of urban development and the percent imperviousness (for 1992 and 2001) for a set of 150 small (< 130 km²) watersheds with long-term (> 20 years) USGS NWIS historical daily mean streamflow datasets in the mid-Atlantic, USA. The Richards-Baker Flashiness Index was used to calculate annual flashiness values and a seven-year-window mean stream flashiness value was calculated for each population/development estimation date. Streamflow stations that showed significant changes in historical flashiness had a higher mean population density than those that showed no change. The strength of the population-flashiness correlation increased as the spatial scale of the population estimator was reduced. Urban development and imperviousness estimators were equally effective at exploring the relationship between stream flashiness and watershed development. Watersheds with less than 10% imperviousness and less than 20% `urban development' displayed background levels of stream flashiness and mean flashiness increased with increasing imperviousness and urban development density thereafter.