Coarse sediment storage and connectivity and off-highway vehicle use, Board Camp Creek, Arkansas

Upper Board Camp Creek (BCC) in western Arkansas drains the Wolf Pen Gap (WPG) Trail Complex, a designated Off-Highway Vehicle (OHV) area in use since the 1990s. The mixed bedrock-alluvial channel is quite active, with extensive bars and eroding banks present within the higher-order, main-valley channels. This study was conducted to determine the relative magnitudes of sediment storage and production within the channel, and whether geomorphic changes are synchronous with establishment and increasing OHV use levels on the trail system. Fourteen geomorphically active reaches within the main-valley channels, representing the range of conditions of BCC within the WPG complex, were examined in detail. All sites had significant alluvial storage in the form of point, lateral, or mid-channel bars dominated by cobble and gravel. Sediment storage volumes ranged from 140 to nearly 10,000 m3 per kilometer of channel, with a mean of about 3400. Eleven of 14 reaches also had actively eroding banks. Ten reaches (71%) exhibited net sediment storage. Two are possible net sources, and two may be in approximate steady state (storage ≈ erosion). The imbalance between local bank erosion sources and in-channel storage, and the evidence of activity and mobility of most of the bars indicates a connected system, with coarse sediment mobile during banktop flow events, and no evidence of sediment starvation. Finer (<8 mm) sediment from the trail system does not seem to be accumulating in the stream, suggesting that most is either sequestered before reaching BCC Creek, transported downstream, or deposited on floodplains during overbank flow. Many of the channel bars predate the trail complex, and most are active. This suggests that these features constitute mainly transient storage and are an inherent feature of the channel. At only two reaches could geomorphic changes be confidently attributed to the trail system. Like many streams, BCC has an active channel, independent of the WPG trail system. These results highlight the difficulty of attributing fluvial change to specific causes or forcings in active fluvial systems.