Wave Driven Sediment Transport Calculator

Longshore transport is the volume of sand moved parallel to the shore each year by waves breaking at an oblique angle. The CERC formula routes that estimate through the longshore component of wave energy flux at breaking, Pls = rho_w g Hb squared sqrt(g Hb / 0.78) / 16 multiplied by sin(2 alpha_b), then converts immersed weight to bulk volume by dividing by (rho_s - rho_w) g (1 - p). With quartz sand at 2650 kg/m3, seawater at 1025 kg/m3 and a porosity of 0.40, that denominator is close to 9,570 N/m3. Transport scales with breaking height to the 2.5 power, so doubling Hb increases drift roughly 5.7 times, and it peaks at a breaking angle of 45 degrees because of the sin(2 alpha_b) term, falling to zero for shore-normal approach. Typical exposed ocean coasts move 100,000 to over 1,000,000 m3 per year. Supporting parameters classify beach behaviour rather than feeding the transport equation. The breaking depth follows the saturated surf-zone ratio Hb / 0.78. The cross-shore parameter Hb / (T squared times slope) separates accretionary berm building from erosive bar formation near a threshold of 0.0032, and the Dean dimensionless fall parameter separates reflective beaches below 1.5 from dissipative beaches above 3.2. The main caveat is that the empirical coefficient K = 0.39, calibrated for significant wave height, absorbs everything the equation omits: grain size, beach slope, wave period, and the influence of tidal or wind-driven currents. Field comparisons routinely differ from CERC predictions by factors of two to five, so estimates are checked against dredging records and shoreline surveys.

Quantitative littoral drift estimates grew out of wartime and post-war beach studies in the United States. The Beach Erosion Board, established by Congress in 1930, sponsored laboratory and field work that linked measured sand accumulation against jetties and groynes to incident wave conditions. Per Bruun, Paul Savage and others in the 1950s established the basic proportionality between drift rate and the alongshore component of wave energy flux. The pivotal field evidence came from Douglas Inman and Robert Bagnold, whose measurements and energetics reasoning in the 1960s expressed transport as an immersed weight rate proportional to the longshore energy flux factor, giving the relation its physical footing. The Beach Erosion Board became the Coastal Engineering Research Center in 1963, and its Shore Protection Manual, first published in 1973 and revised in 1977 and 1984, printed the resulting equation with a recommended coefficient; the expression has been known as the CERC formula ever since. The value K = 0.39 corresponds to the manual convention of significant wave height, whereas earlier root-mean-square formulations used about 0.77. Alternatives followed as the limitations became clear, notably the grain-size and slope-dependent Kamphuis formula of 1991 and the Bayram transport relation of 2007. The US Army Corps of Engineers superseded the Shore Protection Manual with the Coastal Engineering Manual from 2002, which retains CERC as a first-order screening method while recommending calibration to local data.