Faculty Mentor(s)

Dr. Brian Bodenbender

Document Type

Poster

Event Date

4-10-2015

Abstract

We measured sand movement in open-sand environments exposed on the interiors of parabolic dunes at two sites along Lake Michigan: Saugatuck Harbor Natural Area (SHNA) and the Kitchel Lindquist Hartger Dunes (KLH). The SHNA site is a blowout at the nose of a stabilized, dissected, 11.5 m high parabolic dune 360 m from the beach with an axis bearing of 75 degrees. The KLH site is a 14 m high parabolic dune 400 m from the beach with an axis bearing 70 of degrees. We used web-hosted gigapixel panoramas of digital photographs to record and measure sand surface elevations relative to dune pins designed for photographic measurement (photopins). Error analysis based on geometric principles demonstrates that parallax errors can be non-trivial when measuring photopins photographed at close range, but maximum error drops to less than 5 percent for photos taken at 5 or more meters. SHNA saw average sand loss of 6.76 cm from 2012-2014, but sand movement was variable, with an average net loss of 13.46 cm in 2012-13 partially offset by a net gain of 6.83 cm in 2013-14, recorded at 103 photopins. In contrast, from 2013-2014 KLH saw a net sand loss of 18.80 cm measured at 39 photopins. The sites are 40 km apart so they see similar large-scale storm patterns but different smaller-scale fluctuations in wind direction and strength. Even within a single site, sand movement is patchy, with accumulation and erosion occurring within a few meters. The observation during 2013-14 of net sand accumulation at SHNA, contemporaneous with sand erosion at KLH, shows that sand movement at similar dune sites likely responds to highly localized events and conditions, particularly vegetation on the upper parts of SHNA that promotes sand accumulation. Time-averaging of localized responses produces the observed broad regional similarities in dune morphology.

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