Laboratory experiments on beach change due to nearshore mound placement

• Published in: Coastal engineering (Amsterdam) Vol. 121; pp. 119 - 128
• Main Authors: Smith, Ernest R., Mohr, Michael C., Chader, Shanon A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2017
• Subjects: Dredged material; Longshore sediment transport; Movable-bed modeling; Nearshore-placed mounds; Physical modeling; Surf zone processes; Physical modeling; Surf zone processes; Movable-bed modeling; Nearshore-placed mounds; Longshore sediment transport; Dredged material
• ISSN: 0378-3839; 1872-7379
• DOI: 10.1016/j.coastaleng.2016.12.010

Movable-bed large-scale laboratory experiments were conducted to examine the fate and quantify the benefits of nearshore placed dredged material. Two tests were performed on a beach classified as eroding [19] for mounds placed in the active zone described by Hands and Allison [12] at two depths. Mound sand was dyed to provide contrast and to differentiate it from the native sand beach. Beach surveys were performed intermittently during each experiment with a laser scanner. In addition to beach change elevations, the scanner provided RGB color components, which permitted tracking of the mound sand. The experiments showed that the mound sand dispersed rapidly and was transported mainly downdrift. Sand accumulation was observed on the beach onshore and adjacent to the mounds mainly due to wave sheltering of the mounds described as the longshore effect by [28]. There was little contribution to onshore accretion from cross-shore migration of the mounds. Beach response was similar to that of an offshore breakwater in which the mounds provided a wave shadow zone to the leeward beach. The results from the experiment will provide validation data for the numerical morphological model C2SHORE [15]. •Physical model tests demonstrated the direct and indirect benefits of nearshore placed mounds to the littoral zone.•Sand from nearshore mounds placed in the surf zone remained in the littoral zone.•Sand from the mounds dispersed quickly and was transported predominately downdrift.•The beach onshore and updrift of the mounds accreted due to the longshore effect, with very little contribution from cross-shore mound migration.•Volume increased on the dry beach for both mounds from sand transported alongshore from updrift, but not directly from the mounds.