Mortimer Spit - North Side Facing Port Browning,
South Pender Island
|Port Browning Area,
North Pender Island
Pebble/sand shoreline are dynamic sediment beaches, with large
supply of smaller sediments. The form of the beach is determined by
the surrounding coastal processes, and beaches can be stable,
accreting or eroding depending on wave energy and currents.
Finer sediments are usually also present in these beaches,
ranging from coarse to fine sands.
Beaches with larger portions of pebbles are typically more
stable than sand beaches due to their larger size but also because
the permeability of pebbles absorbs energy in breaking waves and
reduces the offshore transport.
The pebble/ sand shore type is less than 9% of the total
shoreline in the Islands Trust area based on the twelve major
islands that had shoreline mapping completed. Denman Island
has the most at 18%, while Lasqueti Island has the least at
3%. 17% of South Pender Island's shoreline has been
mapped as the pebble/ sand shore type.
Pebble/sand shorelines are a common sediment shore types in the
Gulf Islands and have a significant supply of easily erodible
materials that can be transported by wave and current
Pebble/sand shorelines can have large sediment transport rates
along the shore. Interruption of the sediments feeding longshore
transport can starve downstream beaches, spits and coastal lagoons
of material leading to increased erosion.
In the Gulf Islands most pebble/sand shores are small pocket
beaches; however some large beaches such as Tribune Bay on Hornby
Island or Walker Hook on Salt Spring Island occur. Many pocket
beaches are composed entirely of bleached white shell
Pebble/sand shorelines are very dynamic on a human time
Pebble/sand shore types are usually bare of attached algae and
invertebrates in the intertidal zone, however clams, worms and
other burrowing species can be common. Mobile invertebrates such as
crabs, sea stars and other shellfish are also
In the lower intertidal zone and nearshore of the protected
pebble/sand shore type, eelgrass meadows are often established.
These habitats are highly productive as well as vulnerable to
disturbance, and are important nursery areas for many species of
nearshore fish including herring and juvenile rockfish.
Upper intertidal zones of the pebble/sand shore types are
potential spawning habitat for sand lance and surf smelt. These
small forage fish are important foundation species in the marine
food chain as they are prey for many other larger species including
salmon and seabirds. Beach spawning sites are particularly
sensitive to disturbances from shoreline changes so potential
suitable spawning beaches need to be identified when modifications
to pebble/sand beaches are proposed.
The backshore vegetation and coastal riparian fringing trees and
shrubs often overhang the uppermost intertidal zone. Not only does
this vegetation help to stabilize the high water line, but it also
contributes to shading and nutrients to the upper beach used by
beach spawning fish (sand lance and smelt).
Protected bays with shallow nearshore beaches are important
forage areas of diving sea ducks and other waterfowl.