Eroding beaches are a challenge for many coastal regions across the globe. Particularly so when we add in all manner of coastal obstructions and generally screw with traditional sediment dynamics anyway we can.
Waikiki is no exception. Indeed, as late as the 1970s the local beach stewards here were importing sand from Manhattan Beach, California to nourish the beaches for tourists. Never mind the cost, then-unimagined carbon footprint, logistical issues, or fact our Manhattan Beach sediment derives from eroding rock and not calcium cardonate organismal skeletons (as most Hawaiian sand does). Their most recent beach nourishment in 2012-2013 pumped sediments up from offshore shoals to return beach width (temporarily) to the extent last seen in the 1980s.
As our experience with Ventura and Los Angeles County beaches illustrates, such nourishment efforts at best buy you a few years. Nature (and hydrology) bats last. Every time.