1.4 - Coastal fieldwork: analysing sediment and profiles
Use 1.4 to analyse beach measurements and coastal sources together. Learn to separate a measured pattern from its possible causes, then judge how confidently the investigation answers its question.
Comparing sediment and beach form
Process each site's evidence using consistent units, categories and definitions. For sediment size, calculate an appropriate mean/median and spread; for shape categories, tally frequencies and calculate shares. A similar mean can conceal a very different range. A compound bar can show shape composition, while a beach-profile graph shows changes in height with cross-shore distance. Locate both in GIS so the pattern can be compared with geology or management.
These original simulated observations concern three sites along one bay. Each sediment sample contains 20 pebbles; “rounded” uses the same classification at each site.
| Site, north to south | Mean pebble diameter (mm) | Rounded pebbles | Beach width at stated tide (m) | Upper-beach gradient |
|---|---|---|---|---|
| N | 50 | 8 | 30 | 6° |
| M | 40 | 12 | 40 | 5° |
| S | 30 | 16 | 50 | 4° |
The rounded shares are 40%, 60% and 80%. Mean size falls by 20 mm, or 40% of N's 50 mm baseline. A paired scatter graph can show decreasing mean size with alongshore position; it does not identify the actual journey of an individual pebble. Check the sample distributions before treating each mean as typical.
What a geology map adds
A supplied local geology map can locate rock types, boundaries and structures. In this simulated enquiry it shows resistant rock near N and unconsolidated deposits behind M/S. A separate historic map comparison records that a beach-replenishment project added material near S two years before the survey. An annotated field sketch at S also records a groyne and a wide upper beach.
Together, these sources complicate a simple transport explanation. Smaller, rounder material towards S could fit movement and abrasion, but replenishment may have introduced a different sediment population. The geology map helps identify possible sources and controls; it does not directly measure pebble size, current wave approach or net transport direction. A hard rock label also does not guarantee that every stretch has the same landforms: structure, wave energy and time matter.
Check the map's date, scale and shoreline definition. Historic maps may differ in survey precision or depict different tidal boundaries. A present-day field sketch provides local detail but cannot establish a past erosion rate. Ask which claim each source actually supports, then identify a needed observation where the evidence stops.
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