A beach profile is the shore-normal profile of a beach. A beach profile records the occurrence, location, and distribution of features defining the overall beach morphology. In order to fully understand the processes affecting a beach profiles should be made often, and should include the entire shore zone including the shoreface. However, this is beyond the scope of the our field work. We will be profiling the shore weekly.Although a beach profile changes daily there is a general modal morphology that reflects the conditions discussed below.

Waves and related currents

• Waves: Waves move sediment either on or off shore
  • Steep waves typically move sand off shore and shallow waves move sand on shore
• Wave generated currents: Although wave generated currents move sediment on and offshore, the net movement they produce is typically along shore. The strength of the current is related to the wave height and angle of wave approach.
  • Shore normal currents
    • wave current - mass transport
    • swash and backwash
    • rip currents
  • Longshore current
• Tides:
• Tides determine the length of time waves will act on a particular level of the beach
• Tides also influence sediment grain size and variability

• The morphology of a particular beach profile is largely governed by the amount and distribution of wave energy and the ability of the available sediment to dissipate it. (This concept is discussed in more detail later in Morphodynamics lecture)

Beach slope and gradient: slope is the angle of the beach; gradient is h/l or tan(slope). The average slope or gradient of the foreshore (MLW to MHW) is used to define whether a beach is either steep (11° or .2) or shallow (.5° or .01).

Steepness of the beachface is greatly influenced by the relative volume and strength of backwash and swash. Backwash moves sediment offshore resulting in a flatter beachface. Swash on the other hand carries sediment up the beach and will deposit it if allowed to percolate into the sediments. However, backwash can more efficiently move sediment because it works with gravity in the downslope direction. Swash on the other hand must move sediment up slope against gravity.

• Grain size
  • The larger pores between coarse clasts results in greater percolation and less backwash. Also coarser material has a higher angle of repose. Therefore coarse beaches tend to be steeper.
  • Backwash volume is greater along less permeable fine grain beaches resulting in flatter profiles.
• Sorting
  • Well sorted beaches are more permeable. Backwash is minimal and sediment is deposited. 
• Saturation
  • Saturation reduces permeability and increased backwash and porewater pressure promoting a flatter beach.   Groundwater discharge and large short period waves increase saturation and decrease percolation.
    • Changes in permeability are related to wave steepness (H/L). As wave steepness increases beaches become flatter.
      • Wave period (T), height (H), and length (L) determine the volume of water reaching the beach at any one time.
      • When wave heights increase , as during a storm the beach face becomes saturated reducing the infliltration capacity of sediment. As a result backwash increases and more sediment is carried seaward. The beach becomes flatter.
    • Location of water table and volume of gw discharge at the beach face
      • Groundwater adds to backwash which carries sedment seaward.

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Lindley Hanson/email /Gls214

Department of Geological Sciences, Salem State College, Salem, MA