Riparian Forest Impacts on Aquatic Habitat Variability

We compared the variability in morphology and physical habitat characteristics between 14 stream reach pairs with forested and non-forested riparian vegetation in the Piedmont Physiographic Provence of southeastern Pennsylvania. Each pair consisted of nearly contiguous forested and non-forested 1^st though 4^th order stream reaches. One-dimensional hydraulic models were developed for the paired reaches using the U.S. Army Corps of Engineers' River Analysis System (HEC-RAS). The models were constructed using stream survey data, orthophotos, and flow estimates. Traditional statistical methods were unable to distinguish a difference in the variance of a habitat parameter (Froude number), while there was a clear difference in spatial correlation. Experimental and theoretical variograms were used to compare the variability of measured widths and predicted Froude number values in one of the forested and non-forested stream reach pair. Initial analyses suggest that there is more spatial correlation of surveyed width and predicted Froude number for the non-forested stream reaches. In our example, under similar flow conditions, a stream reach with forested riparian vegetation has more physical and spatial hydraulic complexity than an adjacent non-forested reach.