HomeMy WebLinkAbout20260623 Observations of subtidal sediment grain characteristics and cohesiveness along the shore from Bridge St (1)Observations of subtidal sediment grain characteristics and cohesiveness along the shore from
Bridge St. public launch to the Dock at 239 Eel River Road, Osterville. June 19 2026 10-11:20
AM Low tide at 10:08AM
Method of assessment: Chest waders and a 53” metal ski pole with a 3”dia. circular basket 3” above
bottom point. Metal shaft allowed me to estimate sediment composition as silt/clay versus sand
versus cobble as these combinations have characteristic and distinguishable sounds when the
pole was planted into surface sediments. Cohesiveness was evaluated by how deep and with
what force it took to push the basket into and past the surface sediment/water interface. Color of
sediment (black anoxic versus lighter oxic) was visually evaluated from surface sediment stirred
by wader boots and ski pole plume.
1st pier has 3 tied up boats, very large boat deeper than waders but at the stern of western boat
sediment softer @ 2 ½ ft depth. Under dock at same distance from shore it was 2 ft depth
sediment firm. On eastern side of dock boat closest to shore has bow out, engines in toward
land. Sediment soft off transom and 2 ½ ft deep. 15 ft away at same distance from shore depth
is 2 ft and sediment is firm
2nd pier Firm sandy sediment all around dock and float. 30 ft beyond float in depth 40” sediment still
firm and oxic colored.
3rd pier End of float is only 20” deep, firm sediment all around and out to 30 ft beyond float
4th pier (95 Eel River Rd) has a sailboat tied up on north side of float. Depth at end of float is 29”
with firm sediment all around float and sailboat. Walked out to where end of new float would be
(depth 38”) where surface was softer sediment (higher percentage of silt/clay) but sediment firm
below and still has sand in the sediment mixture.
5th pier (117 Eel River Rd) Firm sediment all around float. Where end of new float it’s 33” depth and
sediment has interspersed firm sand&gravel with softer sediments. At 39” depth sediment is
softer, but not black colored.
6th pier has a long 10’x20’ float and on north side of float sediment is firm and sandy mixture. On
south side there are tie off piles (presumably for a motor boat) and just shoreward of the tie-off
rectangle depth it's 6-12” deeper (at same distance from shore as north side). Within the tie-off
area sediment is very soft mud and dangerous to wade into.
Moving to the 7th pier at same distance from shore as the tie-off area sediment is firm pebble/sand
bottom..
7th pier 30” depth at float end with a motorized inflatable craft on the south side of float with bow in
motor out. North side sediment all firm. A 3 to 4” depression in sediment noted just aft of the
inflatable transom. Sediment consisted of larger gravel and pebbles suggesting minor
prop-dredging but without filling in of fine grained silt/clay.
8th pier has a very long length with tie-off piles on north side. Too deep to wade.
9th pier also too long/deep to sample
10th pier (239 Eel River rd) big pier with platform at end. 3 boats (sail, inflatable and large motorcraft).
South tied off boat has twin 300hp engines with bow out and engines landward. Deep black mud
depression even 20ft shoreward of the transom and too dangerous to wade further into. ½ way to
11th pier at same distance from shore as the prop-dredged hole sediment is much firmer, shallower
and has sand mixed in surface sediment.