Capturing the Downstream Fining Pattern by Stream Orders in the Contiguous U.S.

Abstract

<b><sc>Abstract.</sc></b> Bed materials of stream channels exhibit spatial size variation that is commonly attributed to abrasion and selective sorting. This spatial variation results in a process known as downstream fining, which becomes evident as one traverses from upstream to the downstream section of a river channel. This study attempted to capture the fining phenomenon using a comprehensive dataset that spanned the contiguous U.S. The dataset analyzed includes major hydrological and morphological parameters including discharge, channel slope, stream order, and median grain size for over 2200 data points. The approach adopted a regional framework of five large regions for data analyses and model development. Consistently for all five regions, the channel slope showed a continuous decremental trend with an increase in stream order. The downstream fining process was captured in most regions through a decremental trend in median grain size that is often initiated at a stream order of three or four. For lower stream orders, an increase in median grain size was observed probably due to the high unit stream power that usually resides at low-order headwater streams.