Reduced sediment export to the Pennsylvania Lake Erie littoral zone during an era of average lake levels

Abstract

This paper analyzes high-resolution lidar data to estimate sediment export to the Pennsylvania Lake Erie littoral zone from lakefront bluff retreat under relatively unique lake-level conditions: approximately a decade of average lake level transitioning into a mild transgression. Analysis identifies bluff-failure patterns important to coastal hazard planning, possible feeder-bluff conservation areas to preserve sediment supply, and data pertinent to sand management in the western Erie County littoral cell (WECLC) and at Presque Isle State Park in the next-downdrift cell.Based on 2007–2015 bluff-face mapping, there were net losses of 318,250 m3 of total-sediment and 105,700 m3 of sand+ (sand-boulders) to the littoral zone. On an average annual basis, bluffs thus exported 39,800 m3 of total-sediment and 13,300 m3 of sand+ to the WECLC. Exports of sand+ by six HUC-12 watersheds ranged from ~0 to 4600 m3/yr, with ~ 30% supplied by Crooked Creek watershed bluffs that occupy only 18% of the coast. Sand+ export volumes reported here were ~65% lower than prior research covering different lake-level phases. Understanding sediment export during periods of average lake level is important because such lake-level phases occur in the record and will likely recur. Incorporating a decade-scale low sediment-supply scenario for sand management in the Presque Isle littoral cell would permit fine-tuning of estimates of sand nourishment needed to mitigate ongoing beach erosion. Uncertainty in bluff-face change can be minimized by expanding data-comparison windows; future tracking of sediment export from Pennsylvania bluffs may not need lidar surveys any more frequently than once every 10–15 years.