Introduction
The purpose of this experiment was to record baseline values for pebble sizes in different sections of Broad Cove and to get an accurate baseline profile of the cove itself. It was noted that storm waves came into the cove from the northeast which lead to the assumption that the stones in the southwest side of the cove will be the largest, carried by the largest waves. Also, we assumed that the western, low tide side of the cove would have the most uniform sized stones due to the fact that the ocean waves are constantly hitting these stones.
Materials & Methods
Setup
A laser level was set up at a height that would reach the entire cove. The backsight was established from a known pin at an elevation of 13.5 feet above mean low tide. The height of the laser level was then established. The beginning and end of each transect was established and recorded using painted dots on the bedrock of the north and south walls of the cove. Cross sectional transects were established running north and south at the east and west ends of the cove. Longitudinal transects running from the top to the bottom of the intertidal running east and west were established on the north and south sides of the cove.
North & South Transect Protocol
On the north side of the cove was a benchmark pin (13.5 ft). The height of the laser level instrument was calculated by adding the elevation of the benchmark and the back site of the benchmark together. The northern transect was selected by picking a sight most representative of the cove's north side. These characteristics included an absence of boulders on the western side of the transect and the prevalence of four observed zones: upland (mustard plant present; little or no detritus), dry super tidal (large white boulders), wet super tidal (large brown boulders), and intertidal. In the running of these transects measurements directly in front or behind of boulders were not taken in order to avoid what was considered anomalous data due to the buildup of rock and sand in these specific locations. Also, measurements taken on the transects were converted into tenths of feet. Data points along the transects were taken to accurately reflect the slope, not at regular intervals.
North Longitudinal Axis Protocol
The starting point for the northern transect was 47.2 meters from the benchmark at an angle of 250degrees. and 6.7 meters from orange spray painted dots at 210 degrees and 230 degrees. These dots are the first and second dots on the north wall. The endpoint of the this transect was 29.06 meters from the benchmark at an angle of 285 degrees and 16.83 meters from an orange spray painted dot on the bedrock directly north. The length of the stated transect was approximately 238'4''.
South Longitudinal Axis Protocol
The starting point for the southern transect was 10.8 meters from an orange spray painted dot on the southern wall at 294 degrees. This orange dot is located near a water drainage pipe. Near the point just reached with the directions above, there is a large orange arrow. From this measure .6 meters due east. This is the transects starting point. The endpoint for this transect was 11.97 meters directly north from an orange spray painted dot on the southern wall on the eastern side, and 15.26 meters from another dot at 50 degrees. The length of this transect was approximately 170'
West Latitudinal Axis Protocol
The starting point for the western transect was marked with an orange dot on the north wall. Going from west to east, the dot is the 3rd along the wall. The endpoint is also marked by a dot on the south wall. Going west to east, this is the 2nd dot along the wall. During the running of this transect, notes were taken whenever the transect ran over bedrock, and when it crossed the north and south transects.
East Latitudinal Axis Protocol
The starting point for the for the eastern transect was marked with an orange dot on the north wall. Going west to east, this is the 4th dot along the wall. The endpoint for this transect was also marked by an orange dot on the south wall. Going west to east, this is the 3rd dot along the wall. During the running of this transect, notes were taken when this transect crossed north and the south transects.
Pebble Count Protocol
The pebble count area was done along the 4 transects that were previously laid out. The north and south transects were divided into the four previously mentioned zones, upland, dry super tidal, wet super tidal, and intertidal. Each zone was measured in feet. Zones for future experiments could vary, as the tides could be different. For the northern transect, the zones measured as follows: (From starting point of the transect) 0'-51'9''=Upland, 51'9''-108''=Dry super tidal, 108'-133'=Wet super tidal, 133'-200'=Intertidal. For this transect, a total of 190 pebbles were measured in millimeters around the median axis. To find the pebbles to be measured, a team member was given a meter stick. This person would walk two steps to the left of the transect, stop and point the yard stick to the ground without looking. The stone that the end of the stick fell upon was then measured. Then this person would take two steps back toward the transect, and again pointing the stick in a random direction. Then this person would take two steps to the right of the transect, and point the stick once more. This method was repeated along the transect until 190 stones had been measured. The number of pebbles measured in each zone was determined by a number proportional to the zone's total percentage of the entire transect length. For the southern transect, the zones measured as follows: (From the starting point of the transect) 0’-44'=Upland, 44'-88'=Dry super tidal, 88'-105'=Wet super tidal, 105'-165'=Intertidal. For this transect the number of pebbles measured depended on the number of feet in a zone. (The upland had 44', so 44 pebbles were measured). Pebbles were measured on the right and left of the transect line in no particular fashion, only randomly. Again, as in the northern transect, pebbles were measured by the median axis in millimeters. For both the eastern and western transects, no zones were used. The western transect was divided into two sections, and in each section 64 pebbles were measured. The northern zone on the transect was from 0'-59' and the other zone was 59'-the end of the transect. As for the eastern transect, the two zones measured from start-64', and from 64'-the end of the transect. 60 pebbles were measured from each of these two sides.
Gerry Palmer
page last updated 9 August 2006
Banner Photo by Mathew J. Wilson