Beach Renourishment through Spoil Disposal Downdrift of a Dredged Entrance Channel

The offset configuration of Tauranga tidal inlet delta system, in combination with the dredged entrance channel, hinders sediment supply to the down-drift beaches. Maintenance dredging of the entrance channel provides suitable sediment to be deposited as a nearshore berm, downdrift of the entrance channel, as a means to artificially bypass the tidal inlet and renourish the beaches of Mt Maunganui. During April and May of 2004, ~112,000 m³ of dredged medium sand was deposited between two nearshore dump grounds (Sites B and C), under the assumption that onshore transport would occur and act to renourish the beaches shoreward of these sites. Bathymetric and side-scan sonar monitoring showed erosion of the mounds at both sites and significant onshore dispersal at Site B clearly evident after disposal. Sub-aerial beach profile monitoring from 1999 to 2005 shows continued accretion of the sub-aerial beach from 2001 to 2005, partially in response to ongoing beach nourishment. This suggests that any reduction in sediment supply to the down-drift beaches is being successfully alleviated.