The Effects of Waves on Sand Buildup

Dissipative Beaches

• In areas with waves above six feet, no outcroppings and fine sand, two or three underwater bars will form parallel to the shore. These long, featureless beaches may be up to 550 yards long. The outermost bar may be several hundred yards away from the shore. The waves break when they encounter each bar. The waves tend to remove sand from the beach and, unless it is restored, the beach may be bare of sand during prolonged high-wave action.

Longshore Bar and Trough Beaches

• When the waves are between four and six feet high, and the beach is composed of fine or medium sand, the waves will a create a long sandbar running parallel to the beach 110 to 165 yards out to sea. A trough six-to-nine feet deep stretching for 55-to-110 yards will form between the sandbar and the beach. Longshore bar and trough beaches are hazardous to swimmers due to breaks in the sand bar which generate rip tides where water collects behind the bar and rushes through the opening going out to sea.

Rhythmic Bar and Beach

• The rhythmic bar and beach configuration is a complicated version of the longshore bar and trough. It occurs along coastlines that are irregular. The waves form a sandbar, but it varies in depth and width because of the physical irregularities of the beach. The variations create different wave formations, producing strong rip currents and rip current feeder systems running parallel to the shore.

Transverse Bar and Rip Beaches

• The waves on some beaches will form sandbars extending perpendicular to the beach rather than parallel. Wave action responds to the presence of the sandbars and produces stronger waves next to the sandbar and smaller waves in the area between the sandbars.

Reflective Beaches

• Waves less than two feet high produce steep, smooth, featureless beaches in which the waves come into shore and retreat without any difference in wave pattern. Sometimes, the waves will form a flat terrace which is exposed at low tide, extending out from a steeper main beach. Wave action is a simple advance and retreat along the beach with occasional small rip currents.