LAB 4 Beach Profiles and Sediment Characteristics
Coastlines:Beach zones Sediment characteristics, hard stabilization Quantification using sieves, scales, and graphical representation of results Introduction This lab examines sediments in one environment, the beach, which is the important interface between land and sea The beach is only one of many different environments in which sediments are deposited The beach is part of a coastline. These slides try to give some perspective as well as more background on the particular barrier beach environment. Coastlines Coasts classified as being erosional or depositional (i.e., lose or gain sediment) Most eastern USA (passive, trailing) coasts are depositional Includes the Gulf coast of Texas Most western USA (active, collision) coasts are erosional (California) Beach dynamics Dynamic processes maintain and destroy the beach
Summer waves deposit, winter waves erode Waves in surf zone produce currents, particles suspended - moved on or offshore Waves crest approaching coast at angle promote a longshore current (drift) Because of this, West and East coasts of USA sediments are slowly moving southwards Summer vs Winter Profiles
5 Sediment classification
Texture Size, sorting, roundness Composition Neritic- coastal sediments Coarser sands and muds Pelagic sediments - open ocean Fine-grained clays and biogenic oozes Origin Terrigenous (land) Biogenous (living organisms) Hydrogenous (water) Cosmogenous (space origin) Poorly sorted Well sorted One size dominates Wide variety of size ranges in ~ equal amounts Sediments are classified in a variety of ways, by texture, composition and origin Padre Island beach shells describe the sediment characteristics and classify these particles based on texture, composition and possible origin. Well sorted or poorly sorted?? Central Padre Island how does this sand compare to the Padre beach shells?
Well sorted or poorly sorted?? Little dune vegetation Wind blown sand over island Hard Stabilization Man-made objects such as groins, jetties, seawalls, and breakwaters affect sediment movement. Look at pictures of hard stabilization and determine the resulting changes to the beach/shoreline. 10 13 Seasonal beach profiles
Notice the difference in winter and summer/spring beach profiles Compare this to the chart you produce from Table 4 in todays lab. Beaches: A River of Sand - Video Class Exercise Compare beach environments
Sediments you will examine today through visual examination and separating and sorting techniques: Texas coastal samples Malaquite Beach northern Padre Island area Little Shell 30 km down Padre Island California coastal sample Huntington Beach Compare beach zones using data from two Texas beach samples: Malaquite Beach Little Shell Beach Hard stabilization- observe the effects of man-made objects on the beach and shoreline Observe seasonal effects on beach systems Dry sieving technique Used to sort and separate particles by size
Standard Sieve # Screen Mesh Size Descriptive Name Numeric (mm) Log2 (mm) 5 4 22 fine gravel, shell fragments 10 2 21 very fine gravel, granules 18 1 20 very coarse sand 35 0.5 2-1 coarse sand 60 0.25 2-2 medium sand 120 0.125 2-3 fine sand 230 0.063 2-4 very fine sand Mud Particle Sizes 0.0039 2-5 silt