Regional variations in rip density

An extensive dataset combining information obtained from aerial photographs of selected Australian beaches and studies in the literature from a wide v ariety of sites in Europe, the United States, Japan, South Africa and New Z ealand is used to investigate the relationship between rip current spacing on intermediate beaches and regional wave climate. A new parameter termed r ip density (RD) is introduced which defines the number of rips per kilometr e of beach and is defined as the relationship y(r)/L-r, where y(r) is rip s pacing and L-r is a nominal length of beach. The variation in rip density w as examined for five different regional wave environments termed west coast swell (WCS), east coast swell (ECS), fetch-limited wind wave with strong ( SWS) and moderate (MWS) winds, and fetch-limited bays (SWB). Patterns of ri p density were extremely consistent between the grouped wave climate enviro nments with WCS beaches characterised by the lowest RD of 2 rips/km and SWB and MWS beaches having the highest RD with values ranging from 11-13 rips/ km. ECS beaches have a RD of 5 with SWS lying in between the range for WCS and ECS beaches at approximately 3 rips/km. The variation in rip density between environments exhibits distinct scaling relationships with RD on SWB and MWS beaches being approximately 5 times g reater than on WCS beaches and twice as great than on ECS beaches. ECS beac hes also have 2.5 times the number of rips on WCS beaches. Based on measure ments and estimates of np channel and surf zone width, there is evidence to suggest that these scaling factors may also be applied to the variation in two-dimensional planform morphology between the environments. The results of this study also indicate that rip density decreases with increasing wave height, wave period, surf zone width, wave energy, and wave power, thus pr oviding quantitative links between observed rip density and regional wave c limate.